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  • 1. Aiba, N
    et al.
    Giroud, C
    Honda, M
    Delabie, E
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Saarelma, S
    Hillesheim, J
    Pamela, S
    Wiesen, S
    Maggi, C
    Urano, H
    Drewelow, P
    Leyland, M
    Moulton, D
    Menmuir, S
    Diamagnetic MHD Equations for Plasmas with Fast Flow and its Application to ELM Analysis in JT-60U and JET-ILW2016Inngår i: 26th IAEA Fusion Energy Conference, 17-22 October 2016, 2016Konferansepaper (Fagfellevurdert)
  • 2. Aiba, N
    et al.
    Giroud, C
    Honda, M
    Delabie, E
    Saarelma, S
    Lupelli, I
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Maggi, C
    Impact of rotation and ion diamagnetic drift on ELM stability in JET-ILW2016Inngår i: 33rd Annual meeting of Japan society of plasma science and nuclear fusion research JSPF, Nov 2016. Japan, 2016Konferansepaper (Annet vitenskapelig)
  • 3. Aiba, N.
    et al.
    Pamela, S.
    Honda, M.
    Urano, H.
    Giroud, C.
    Delabie, E.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Lupelli, I.
    Hayashi, N.
    Huijsmans, G.
    Analysis of ELM stability with extended MHD models in JET, JT-60U and future JT-60SA tokamak plasmas2018Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 60, nr 1, artikkel-id 014032Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The stability with respect to a peeling-ballooning mode (PBM) was investigated numerically with extended MHD simulation codes in JET, JT-60U and future JT-60SA plasmas. The MINERVA-DI code was used to analyze the linear stability, including the effects of rotation and ion diamagnetic drift (omega(*i)), in JET-ILW and JT-60SA plasmas, and the JOREK code was used to simulate nonlinear dynamics with rotation, viscosity and resistivity in JT-60U plasmas. It was validated quantitatively that the ELM trigger condition in JET-ILW plasmas can be reasonably explained by taking into account both the rotation and omega(*i) effects in the numerical analysis. When deuterium poloidal rotation is evaluated based on neoclassical theory, an increase in the effective charge of plasma destabilizes the PBM because of an acceleration of rotation and a decrease in omega(*i). The difference in the amount of ELM energy loss in JT-60U plasmas rotating in opposite directions was reproduced qualitatively with JOREK. By comparing the ELM affected areas with linear eigenfunctions, it was confirmed that the difference in the linear stability property, due not to the rotation direction but to the plasma density profile, is thought to be responsible for changing the ELM energy loss just after the ELM crash. A predictive study to determine the pedestal profiles in JT-60SA was performed by updating the EPED1 model to include the rotation and w*i effects in the PBM stability analysis. It was shown that the plasma rotation predicted with the neoclassical toroidal viscosity degrades the pedestal performance by about 10% by destabilizing the PBM, but the pressure pedestal height will be high enough to achieve the target parameters required for the ITER-like shape inductive scenario in JT-60SA.

  • 4. Alfier, A.
    et al.
    Annibaldi, Silvia Valeria
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. Euratom/ENEA Association, Italy.
    Bonomo, F.
    Buratti, P.
    Franz, P.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marrelli, L.
    Pasqualotto, R.
    Piovesan, P.
    Spizzo, G.
    Energy confinement in high current RFX-mod plasmas2007Inngår i: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, 2007, nr 1, s. 415-418Konferansepaper (Fagfellevurdert)
  • 5. Alfier, A.
    et al.
    Pasqualotto, R.
    Spizzo, G.
    Canton, A.
    Fassina, A.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Electron temperature profiles in RFX-mod2008Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 50, nr 3, s. 035013-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electron temperature profiles have been measured by the main Thomson scattering ( TS) diagnostic on the RFX-mod reversed field pinch experiment in Padova, Italy. The increased accuracy and spatial and temporal resolution permits one to measure in detail the improvements in T-e profiles, obtained with the active saddle coil system, which allows one to obtain core temperature 30% higher and scaling stronger with plasma current, steeper gradients in the core (+30%) and at the edge (+60%). 1D power balance calculations show that the active control of MHD modes largely reduces the values of electron heat diffusivity along the whole plasma radius, with similar to 50% reduction at the edge and similar to 30% in the core. The resulting electron energy confinement time is doubled. Further improvements occur during quasi-single helicity (QSH) states: the new TS allows one to study in detail the hot island that develops in the core. A characterization of the island electron thermal profile is presented, in terms of width, temperature increase, gradients and asymmetry; the effect on density profile is also discussed. A 2D transport code has been applied to calculate the heat diffusivity inside the magnetic island corresponding to the QSH state, also considering the correlation between temperature increase and pressure gradient with the chaos level around the island. Finally, electron energy confinement time during QSH states is compared with that in MH states.

  • 6. Arnoux, G.
    et al.
    Loenen, J.
    Bazylev, B.
    Corre, Y.
    Matthews, G. F.
    Balboa, I.
    Clever, M.
    Dejarnac, R.
    Devaux, S.
    Eich, T.
    Gauthier, E.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Horacek, J.
    Jachmich, S.
    Kinna, D.
    Marsen, S.
    Mertens, Ph.
    Pitts, R. A.
    Rack, M.
    Sergienko, G.
    Sieglin, B.
    Stamp, M.
    Thompson, V.
    Thermal analysis of an exposed tungsten edge in the JET divertor2015Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, s. 415-419Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the recent melt experiments with the JET tungsten divertor, we observe that the heat flux impacting on a leading edge is 3-10 times lower than a geometrical projection would predict. The surface temperature, tungsten vaporisation rate and melt motion measured during these experiments is consistent with the simulations using the MEMOS code, only if one applies the heat flux reduction. This unexpected observation is the result of our efforts to demonstrate that the tungsten lamella was melted by ELM induced transient heat loads only. This paper describes in details the measurements and data analysis method that led us to this strong conclusion. The reason for the reduced heat flux are yet to be clearly established and we provide some ideas to explore. Explaining the physics of this heat flux reduction would allow to understand whether it can be extrapolated to ITER.

  • 7.
    Bergsåker, Henric
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Drake, James R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Metal impurity fluxes and plasma-surface interactions in EXTRAP T2R2008Inngår i: PROCEEDINGS OF THE 17TH INTERNATIONAL VACUUM CONGRESS/13TH INTERNATIONAL CONFERENCE ON SURFACE SCIENCE/INTERNATIONAL CONFERENCE ON NANOSCIENCE AND TECHNOLOGY, 2008, Vol. 100Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The EXTRAP T2R is a large aspect ratio Reversed Field Pinch device. The main focus of interest for the experiments is the active feedback control of resistive wall modes [1]. With feedback it has been possible to prolong plasma discharges in T2R from about 20 ms to nearly 100 ms. In a series of experiments in T2R, in H- and D- plasmas with and without feedback, quantitative spectroscopy and passive collector probes have been used to study the flux of metal impurities. Time resolved spectroscopic measurements of Cr and Mo lines showed large metal release towards discharge termination without feedback. Discharge integrated fluxes of Cr, Fe, Ni and Mo were also measured with collector probes at wall position. Reasonable quantitative agreement was found between the spectroscopic and collector probe measurements. The roles of sputtering, thermal evaporation and arcing in impurity production are evaluated based on the composition of the measured impurity flux.

  • 8. Beurskens, M
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. EURATOM-VR.
    Maggi, C
    Calabro, C
    Alper, B
    Bourdelle, C
    Angioni, C
    Brezinsek, S
    Buratti, P
    Challis, C
    Flanagan, J
    Giovannozzi, E
    Giroud, C
    Groth, M
    Hobirk, J
    Joffrin, E
    Leyland, M
    Lomas, P
    de la Luna, E
    Kampenaars, M
    Mantica, P
    Maslov, M
    Matthews, G
    Mayoral, M
    Neu, R
    Snyder, P
    Saarelma, P
    Osborne, T
    de Vries, P
    L-H power Threshold, Pedestal Stability and Confinement in JET with a Metallic Wall2012Inngår i: 24th IAEA Fusion Energy Conference, 8-13 October 2012, 2012, s. EX/P4-23-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    After the change-over from the Carbon-Fibre Composite (CFC) wall to an ITER-like metallic wall (ILW) the baseline type I ELMy H-mode scenario has been re-established in JET with the new plasma-facing materials Be and W. A key finding for ITER is that the power required to enter H-mode has reduced with respect to that in JET with the CFC wall. In JET with the ILW the power threshold to enter H-mode (PL-H) is below the international L-H power threshold scaling P_Martin-08. The minimum threshold is P_L-H=1.8MW compared to P_Martin-08=4MW with a pedestal density of nped=2x10^19m^-3 in plasmas with I_p=2.0 MA, B_t=2.4T. However the threshold depends strongly on density; using slow ion cyclotron heating (ICRH) power ramps P_L-H varies from 1.8 to 4.5MW in a range of lower and upper plasma triangularity (delta_L=0.32-0.4, delta_U =0.19-0.38). Stationary Type I ELMy H-mode operation has been re-established at both low and high triangularity with I_p≤ 2.5MA, q_95=2.8-3.6 and H_98≤1. The achieved plasma collisionality is relatively high, in the range of 1< nu_eff<4 due to the required strong gas dosing. Stability analysis with the linear MHD stability code ELITE show that the pedestal is marginally unstable with respect to the Peeling Ballooning boundary. Due to the stabilising effect of the global pressure Beta_N on the pedestal stability, a strong coupling between core and edge confinement is expected. Indeed in an H-mode profile database comparison with 119 CFC- (0.1< nu_eff<1) and 40 ILW-H-modes a strong coupling of the core versus edge confinement is found, independent of wall material. In addition, the pedestal predictions using the EPED predictive pedestal code coincide with the measured pedestal height over a wide range of normalised pressure 1.5< Beta_N<3.5. Due to the strong core-edge coupling, beneficial effects of core profile peaking on confinement are weak in the database comparison. However, differences in the individual temperature and density profile peaking occur across the database. When collisionality is increased from nu_eff=0.1 to 4, the density peaking decreases from R/L_ne=4 to 0.5 but is compensated by an increase in temperature peaking from R/L_Te = 5-8, offering a challenge for micro turbulence-transport models.

  • 9. Beurskens, M. N. A.
    et al.
    Dunne, M. G.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bernert, M.
    Cavedon, M.
    Fischer, R.
    Järvinen, A.
    Kallenbach, A.
    Laggner, F. M.
    McDermott, R. M.
    Potzel, S.
    Schweinzer, J.
    Tardini, G.
    Viezzer, E.
    Wolfrum, E.
    The role of carbon and nitrogen on the H-mode confinement in ASDEX Upgrade with a metal wall2016Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 56, nr 5, artikkel-id 056014Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Carbon (CD4) and nitrogen (N2) have been seeded in ASDEX Upgrade (AUG) with a tungsten wall and have both led to a 20-30% confinement improvement. The reference plasma is a standard target plasma with I p /B T = 1 MA/2.5 T, total input power P tot ∼ 12 MW and normalized pressure of β N ∼ 1.8. Carbon and nitrogen are almost perfectly exchangeable for the core, pedestal and divertor plasma in this experiment where impurity concentrations of C and N of 2% are achieved and Z eff only mildly increases from ∼1.3 to ∼1.7. As the radiation potentials of C and N are similar and peak well below 100 eV, both impurities act as divertor radiators and radiate well outside the pedestal region. The outer divertor is purposely kept in an attached state when C and N are seeded to avoid confinement degradation by detachment. As reported in earlier publications for nitrogen, carbon is also seen to reduce the high field side high density (the so-called HFSHD) in the scrape off layer above the inner divertor strike point by about 50%. This is accompanied by a confinement improvement for both low (δ ∼ 0.25) and high (δ ∼ 0.4) triangularity configurations for both seeding gases, due to an increase of pedestal temperature and stiff core temperature profiles. The electron density profiles show no apparent change due to the seeding. As an orthogonal effect, increasing the triangularity leads to an additionally increased pedestal density, independent of the impurity seeding. This experiment further closes the gap in understanding the confinement differences observed in carbon and metal wall devices; the absence of carbon can be substituted by nitrogen which leads to a similar confinement benefit. So far, no definite physics explanation for the confinement enhancement has been obtained, but the experimental observations in this paper provide input for further model development.

  • 10. Beurskens, M. N. A.
    et al.
    Dunne, M. G.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bernert, M.
    Cavedon, M.
    Fischer, R.
    Järvinen, A.
    Kallenbach, A.
    Laggner, F. M.
    McDermott, R. M.
    Tardini, G.
    Viezzer, E.
    Wolfrum, E.
    The role of carbon on the H-mode confinement in ASDEX Upgrade with a metal wall2015Inngår i: 42nd European Physical Society Conference on Plasma Physics, EPS 2015, European Physical Society (EPS) , 2015Konferansepaper (Fagfellevurdert)
  • 11. Beurskens, M. N. A.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Challis, C.
    Giroud, C.
    Saarelma, S.
    Alper, B.
    Angioni, C.
    Bilkova, P.
    Bourdelle, C.
    Brezinsek, S.
    Buratti, P.
    Calabro, G.
    Eich, T.
    Flanagan, J.
    Giovannozzi, E.
    Groth, M.
    Hobirk, J.
    Joffrin, E.
    Leyland, M. J.
    Lomas, P.
    de la Luna, E.
    Kempenaars, M.
    Maddison, G.
    Maggi, C.
    Mantica, P.
    Maslov, M.
    Matthews, G.
    Mayoral, M-L
    Neu, R.
    Nunes, I.
    Osborne, T.
    Rimini, F.
    Scannell, R.
    Solano, E. R.
    Snyder, P. B.
    Voitsekhovitch, I.
    de Vries, Peter
    Global and pedestal confinement in JET with a Be/W metallic wall2014Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 54, nr 4, s. 043001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Type I ELMy H-mode operation in JET with the ITER-like Be/W wall (JET-ILW) generally occurs at lower pedestal pressures compared to those with the full carbon wall (JET-C). The pedestal density is similar but the pedestal temperature where type I ELMs occur is reduced and below to the so-called critical type I-type III transition temperature reported in JET-C experiments. Furthermore, the confinement factor H-98(y,H- 2) in type I ELMy H-mode baseline plasmas is generally lower in JET-ILWcompared to JET-C at low power fractions Ploss/P-thr,(08)< 2 (where P-loss is (P-in-dW/dt), and P-thr,(08) the L-H power threshold from Martin et al 2008 (J. Phys. Conf. Ser. 123 012033)). Higher power fractions have thus far not been achieved in the baseline plasmas. At Ploss/P-thr,P- 08 > 2, the confinement in JET-ILW hybrid plasmas is similar to that in JET-C. A reduction in pedestal pressure is the main reason for the reduced confinement in JET-ILW baseline ELMy H-mode plasmas where typically H-98((y, 2)) = 0.8 is obtained, compared to H-98((y, 2)) = 1.0 in JET-C. In JET-ILW hybrid plasmas a similarly reduced pedestal pressure is compensated by an increased peaking of the core pressure profile resulting in H-98((y, 2)) <= 1.25. The pedestal stability has significantly changed in high triangularity baseline plasmas where the confinement loss is also most apparent. Applying the same stability analysis for JET-C and JET-ILW, the measured pedestal in JET-ILW is stable with respect to the calculated peeling-ballooning stability limit and the ELM collapse time has increased to 2ms from typically 200 mu s in JET-C. This indicates that changes in the pedestal stability may have contributed to the reduced pedestal confinement in JET-ILW plasmas. A comparison of EPED1 pedestal pressure prediction with JET-ILW experimental data in over 500 JET-C and JET-ILW baseline and hybrid plasmas shows a good agreement with 0.8 < (measured p(ped))/(predicted p(ped), EPED) < 1.2, but that the role of triangularity is generally weaker in the JET-ILW experimental data than in the model predictions.

  • 12. Beurskens, M. N. A.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Challis, C.
    Osborne, T.
    Snyder, P. B.
    Alper, B.
    Angioni, C.
    Bourdelle, C.
    Buratti, P.
    Crisanti, F.
    Giovannozzi, E.
    Giroud, C.
    Groebner, R.
    Hobirk, J.
    Jenkins, I.
    Joffrin, E.
    Leyland, M. J.
    Lomas, P.
    Mantica, P.
    McDonald, D.
    Nunes, I.
    Rimini, F.
    Saarelma, S.
    Voitsekhovitch, I.
    De Vries, P.
    Zarzoso, D.
    Comparison of hybrid and baseline ELMy H-mode confinement in JET with the carbon wall2013Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, nr 1, s. 013001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The confinement in JET baseline type I ELMy H-mode plasmas is compared to that in so-called hybrid H-modes in a database study of 112 plasmas in JET with the carbon fibre composite (CFC) wall. The baseline plasmas typically have βN ∼ 1.5-2, H98 ∼ 1, whereas the hybrid plasmas have βN ∼ 2.5-3, H98 &lt; 1.5. The database study contains both low- (δ ∼ 0.2-0.25) and high-triangularity (δ ∼ 0.4) hybrid and baseline H-mode plasmas from the last JET operational campaigns in the CFC wall from the period 2008-2009. Based on a detailed confinement study of the global as well as the pedestal and core confinement, there is no evidence that the hybrid and baseline plasmas form separate confinement groups; it emerges that the transition between the two scenarios is of a gradual kind rather than demonstrating a bifurcation in the confinement. The elevated confinement enhancement factor H98 in the hybrid plasmas may possibly be explained by the density dependence in the τ98 scaling as n0.41 and the fact that the hybrid plasmas operate at low plasma density compared to the baseline ELMy H-mode plasmas. A separate regression on the confinement data in this study shows a reduction in the density dependence as n0.09±0.08. Furthermore, inclusion of the plasma toroidal rotation in the confinement regression provides a scaling with the toroidal Alfvén Mach number as and again a reduced density dependence as n0.15±0.08. The differences in pedestal confinement can be explained on the basis of linear MHD stability through a coupling of the total and pedestal poloidal pressure and the pedestal performance can be improved through plasma shaping as well as high β operation. This has been confirmed in a comparison with the EPED1 predictive pedestal code which shows a good agreement between the predicted and measured pedestal pressure within 20-30% for a wide range of βN ∼ 1.5-3.5. The core profiles show a strong degree of pressure profile consistency. No beneficial effect of core density peaking on confinement could be identified for the majority of the plasmas presented here as the density peaking is compensated by a temperature de-peaking resulting in no or only a weak variation in the pressure peaking. The core confinement could only be optimized in case the ions and electrons are decoupled, in which case the ion temperature profile peaking can be enhanced, which benefits confinement. In this study, the latter has only been achieved in the low-triangularity hybrid plasmas, and can be attributed to low-density operation. Plasma rotation has been found to reduce core profile stiffness, and can explain an increase in profile peaking at small radius ρtor = 0.3.

  • 13. Beurskens, M. N. A.
    et al.
    Osborne, T. H.
    Horton, L. D.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Groebner, R.
    Leonard, A.
    Lomas, P.
    Nunes, I.
    Saarelma, S.
    Snyder, P. B.
    Balboa, I.
    Bray, B.
    Crombe, K.
    Flanagan, J.
    Giroud, C.
    Giovannozzi, E.
    Kempenaars, M.
    Kohen, N.
    Loarte, A.
    Lonnroth, J.
    de la Luna, E.
    Maddison, G.
    Maggi, C.
    McDonald, D.
    McKee, G.
    Pasqualotto, R.
    Saibene, G.
    Sartori, R.
    Solano, E.
    Suttrop, W.
    Wolfrum, E.
    Walsh, M.
    Yan, Z.
    Zabeo, L.
    Zarzoso, D.
    Pedestal width and ELM size identity studies in JET and DIII-D; implications for ITER2009Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 51, nr 12, s. 124051-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dependence of the H-mode edge transport barrier width on normalized ion gyroradius (rho* = rho/a) in discharges with type I ELMs was examined in experiments combining data for the JET and DIII-D tokamaks. The plasma configuration as well as the local normalized pressure (beta), collisionality (nu*), Mach number and the ratio of ion and electron temperature at the pedestal top were kept constant, while rho* was varied by a factor of four. The width of the steep gradient region of the electron temperature (T-e) and density (n(e)) pedestals normalized to machine size showed no or only a weak trend with rho*. A rho(1/2) or rho(1) dependence of the pedestal width, given by some theoretical predictions, is not supported by the current experiments. This is encouraging for the pedestal scaling towards ITER as it operates at lower rho* than existing devices. Some differences in pedestal structure and ELM behaviour were, however, found between the devices; in the DIII-D discharges, the n(e) and T-e pedestal were aligned at high rho* but the ne pedestal shifted outwards in radius relative to T-e as rho* decreases, while on JET the profiles remained aligned while rho* was scanned by a factor of two. The energy loss at an ELM normalized to the pedestal energy increased from 10% to 40% as rho* increased by a factor of two in the DIII-D discharges but no such variation was observed in the case of JET. The measured pedestal pressures and widths were found to be consistent with the predictions from modelling based on peeling-ballooning stability theory, and are used to make projections towards ITER

  • 14. Beurskens, M N A
    et al.
    Osborne, T H
    Schneider, P A
    Wolfrum, E
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Groebner, R
    Lomas, P
    Nunes, I
    Saarelma, S
    Scannell, R
    Snyder, P B
    Zarzoso, D
    Balboa, I
    Bray, B
    Brix, M
    Flanagan, J
    Giroud, C
    Giovannozzi, E
    Kempenaars, M
    Loarte, A
    de la Luna, E
    Maddison, G
    Maggi, C F
    McDonald, D
    Pasqualotto, R
    Saibene, G
    Sartori, R
    Solano, E
    Walsh, M
    Zabeo, L
    Team, D I I I-D
    Team, ASDEX Upgrade
    Contributors, J E T-E F D A
    H-mode pedestal scaling in DIII-D, ASDEX Upgrade, and JET2011Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 18, nr 5Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Multidevice pedestal scaling experiments in the DIII-D, ASDEX Upgrade (AUG), and JET tokamaks are presented in order to test two plasma physics pedestal width models. The first model proposes a scaling of the pedestal width Delta/a proportional to rho*(1/2) to rho* based on the radial extent of the pedestal being set by the point where the linear turbulence growth rate exceeds the E x B velocity. In the multidevice experiment where rho* at the pedestal top was varied by a factor of four while other dimensionless parameters where kept fixed, it has been observed that the temperature pedestal width in real space coordinates scales with machine size, and that therefore the gyroradius scaling suggested by the model is not supported by the experiments. The density pedestal width is not invariant with rho* which after comparison with a simple neutral fuelling model may be attributed to variations in the neutral fuelling patterns. The second model, EPED1, is based on kinetic ballooning modes setting the limit of the radial extent of the pedestal region and leads to Delta(psi) proportional to beta p(1/2). All three devices show a scaling of the pedestal width in normalised poloidal flux as Delta(psi) proportional to beta p(1/2), as described by the kinetic ballooning model; however, on JET and AUG, this could not be distinguished from an interpretation where the pedestal is fixed in real space. Pedestal data from all three devices have been compared with the predictive pedestal model EPED1 and the model produces pedestal height values that match the experimental data well.

  • 15. Beurskens, M. N. A.
    et al.
    Schweinzer, J.
    Angioni, C.
    Burckhart, A.
    Challis, C. D.
    Chapman, I.
    Fischer, R.
    Flanagan, J.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Giroud, C.
    Hobirk, J.
    Joffrin, E.
    Kallenbach, A.
    Kempenaars, M.
    Leyland, M.
    Lomas, P.
    Maddison, G.
    Maslov, M.
    McDermott, R.
    Neu, R.
    Nunes, I.
    Osborne, T.
    Ryter, F.
    Saarelma, S.
    Schneider, P. A.
    Snyder, P.
    Tardini, G.
    Viezzer, E.
    Wolfrum, E.
    The effect of a metal wall on confinement in JET and ASDEX Upgrade2013Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 55, nr 12, s. 124043-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In both JET and ASDEX Upgrade (AUG) the plasma energy confinement has been affected by the presence of a metal wall by the requirement of increased gas fuelling to avoid tungsten pollution of the plasma. In JET with a beryllium/tungsten wall the high triangularity baseline H-mode scenario (i.e. similar to the ITER reference scenario) has been the strongest affected and the benefit of high shaping to give good normalized confinement of H-98 similar to 1 at high Greenwald density fraction of f(GW) similar to 0.8 has not been recovered to date. In AUG with a full tungsten wall, a good normalized confinement H-98 similar to 1 could be achieved in the high triangularity baseline plasmas, albeit at elevated normalized pressure beta(N) > 2. The confinement lost with respect to the carbon devices can be largely recovered by the seeding of nitrogen in both JET and AUG. This suggests that the absence of carbon in JET and AUG with a metal wall may have affected the achievable confinement. Three mechanisms have been tested that could explain the effect of carbon or nitrogen (and the absence thereof) on the plasma confinement. First it has been seen in experiments and by means of nonlinear gyrokinetic simulations (with the GENE code), that nitrogen seeding does not significantly change the core temperature profile peaking and does not affect the critical ion temperature gradient. Secondly, the dilution of the edge ion density by the injection of nitrogen is not sufficient to explain the plasma temperature and pressure rise. For this latter mechanism to explain the confinement improvement with nitrogen seeding, strongly hollow Z(eff) profiles would be required which is not supported by experimental observations. The confinement improvement with nitrogen seeding cannot be explained with these two mechanisms. Thirdly, detailed pedestal structure analysis in JET high triangularity baseline plasmas have shown that the fuelling of either deuterium or nitrogen widens the pressure pedestal. However, in JET-ILW this only leads to a confinement benefit in the case of nitrogen seeding where, as the pedestal widens, the obtained pedestal pressure gradient is conserved. In the case of deuterium fuelling in JET-ILW the pressure gradient is strongly degraded in the fuelling scan leading to no net confinement gain due to the pedestal widening. The pedestal code EPED correctly predicts the pedestal pressure of the unseeded plasmas in JET-ILW within +/- 5%, however it does not capture the complex variation of pedestal width and gradient with fuelling and impurity seeding. Also it does not predict the observed increase of pedestal pressure by nitrogen seeding in JET-ILW. Ideal peeling ballooning MHD stability analysis shows that the widening of the pedestal leads to a down shift of the marginal stability boundary by only 10-20%. However, the variations in the pressure gradient observed in the JET-ILW fuelling experiment is much larger and spans a factor of more than two. As a result the experimental points move from deeply unstable to deeply stable on the stability diagram in a deuterium fuelling scan. In AUG-W nitrogen seeded plasmas, a widening of the pedestal has also been observed, consistent with the JET observations. The absence of carbon can thus affect the pedestal structure, and mainly the achieved pedestal gradient, which can be recovered by seeding nitrogen. The underlying physics mechanism is still under investigation and requires further understanding of the role of impurities on the pedestal stability and pedestal structure formation.

  • 16. Beurskens, M.N.A.
    et al.
    Schweinzer, J
    Angioni, C
    Bourdelle, C
    Challis, C
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Giroud, C
    Hobirk, J
    Joffrin, E
    Kallenbach, A
    Maddison, G.
    Neu, R.
    Osborne, T.
    Ryter, F.
    Saarelma, S.
    Schneider, P.
    Snyder, P.
    Wolfrum, E.
    The Effect of a Metal Wall on Confinement in JET and ASDEX-Upgrade2013Inngår i: 40th European Physical Society Conference on Plasma Physics: Espoo, Finland, 1st - 5th July 2013, European Physical Society , 2013Konferansepaper (Fagfellevurdert)
  • 17.
    Blanken, T. C.
    et al.
    Eindhoven Univ Technol, Control Syst Technol Grp, Dept Mech Engn, POB 513, NL-5600 MB Eindhoven, Netherlands.;Eindhoven Univ Technol, POB 513, NL-5600 MB Eindhoven, Netherlands..
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Fridström, Richard
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Garcia-Carrasco, Alvaro
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Jonsson, T.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Vallejos, Pablo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Vignitchouk, Ladislas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Dori, V
    Univ Split, Fac Elect Engn Mech Engn & Naval Architecture, R Boskovica 32, Split 21000, Croatia..
    Real-time plasma state monitoring and supervisory control on TCV2019Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, nr 2, artikkel-id 026017Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In ITER and DEMO, various control objectives related to plasma control must be simultaneously achieved by the plasma control system (PCS), in both normal operation as well as off-normal conditions. The PCS must act on off-normal events and deviations from the target scenario, since certain sequences (chains) of events can precede disruptions. It is important that these decisions are made while maintaining a coherent prioritization between the real-time control tasks to ensure high-performance operation. In this paper, a generic architecture for task-based integrated plasma control is proposed. The architecture is characterized by the separation of state estimation, event detection, decisions and task execution among different algorithms, with standardized signal interfaces. Central to the architecture are a plasma state monitor and supervisory controller. In the plasma state monitor, discrete events in the continuous-valued plasma state arc modeled using finite state machines. This provides a high-level representation of the plasma state. The supervisory controller coordinates the execution of multiple plasma control tasks by assigning task priorities, based on the finite states of the plasma and the pulse schedule. These algorithms were implemented on the TCV digital control system and integrated with actuator resource management and existing state estimation algorithms and controllers. The plasma state monitor on TCV can track a multitude of plasma events, related to plasma current, rotating and locked neoclassical tearing modes, and position displacements. In TCV experiments on simultaneous control of plasma pressure, safety factor profile and NTMs using electron cyclotron heating (ECI I) and current drive (ECCD), the supervisory controller assigns priorities to the relevant control tasks. The tasks are then executed by feedback controllers and actuator allocation management. This work forms a significant step forward in the ongoing integration of control capabilities in experiments on TCV, in support of tokamak reactor operation.

  • 18. Bogomolov, A. V.
    et al.
    Classen, I. G. J.
    Donne, A. J. H.
    Meyer, H.
    Dunne, M.
    Schneider, P. A.
    Wolfrum, E.
    Vanovac, B.
    Fischer, R.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Luhmann, N.C., Jr.
    The effect of nitrogen seeding on ELM filaments2015Inngår i: 42nd European Physical Society Conference on Plasma Physics, EPS 2015, European Physical Society (EPS) , 2015Konferansepaper (Fagfellevurdert)
  • 19. Bohm, P.
    et al.
    Aftanas, M.
    Bilkova, P.
    Stefanikova, E.
    Mikulin, O.
    Melich, R.
    Janky, F.
    Havlicek, J.
    Sestak, D.
    Weinzettl, V.
    Stockel, J.
    Hron, M.
    Panek, R.
    Scannell, R.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Fassina, A.
    Naylor, G.
    Walsh, M. J.
    Edge Thomson scattering diagnostic on COMPASS tokamak: Installation, calibration, operation, improvements2014Inngår i: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 85, nr 11, s. 11E431-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The core Thomson scattering diagnostic (TS) on the COMPASS tokamak was put in operation and reported earlier. Implementation of edge TS, with spatial resolution along the laser beam up to similar to 1/100 of the tokamak minor radius, is presented now. The procedure for spatial calibration and alignment of both core and edge systems is described. Several further upgrades of the TS system, like a triggering unit and piezo motor driven vacuum window shutter, are introduced as well. The edge TS system, together with the core TS, is now in routine operation and provides electron temperature and density profiles.

  • 20. Bohm, P
    et al.
    Bilkova, P
    Aftanas, M
    Stefanikova, E
    Mikulin, O
    Melich, R
    Janky, J
    Havlicek, H
    Sestak, D
    Weinzettl, V
    Stockel, A
    Hron, R
    Panek, R
    Scannell, R
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Fassina, A
    Naylor, N
    Walsh, J
    Thomson Scattering on COMPASS tokamak: Plasma Edge Profile2013Inngår i: 16th International Symposium on Laser Aided Plasma Diagnostics Conference: Madison, Wisconsin, USA, 22-26 September, 2013, 2013Konferansepaper (Annet vitenskapelig)
  • 21. Borodkina, I.
    et al.
    Borodin, D.
    Brezinsek, S.
    Tsvetkov, I. V.
    Kurnaev, V. A.
    Guillemaut, C.
    Maslov, M.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Intra-ELM tungsten sputtering in JET ITER-like wall: analytical studies of Be impurity and ELM type influence2017Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T170, artikkel-id 014065Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The W source strength in JET H-mode discharges depends on the W sputtering in the inter and the intra-ELM phase due to impinging hydrogenic ions (D or H) and impurities (mainly Be). The analytical approach for interpretation of the Langmuir probe measurements is applied to model the ELM ion parallel transport and the W sputtering flux in intra-ELM and inter-ELM conditions in JET-ITER-like wall (ILW) hydrogen and deuterium plasmas. The impact of the Be ion charge and the Be concentration in the impinging ion flux on the W sputtering was estimated. Be2+ concentrations of 0.5% and 1% in the impinging ion flux increases the W sputtering fluence per ELM by 20%-30% and 35%-55% correspondingly with respect to pure deuterium plasma; the charge state of Be ions has no substantial effect on W sputtering in the intra-ELM phase. The analysis of JET ELMy H-mode discharges in hydrogen with different types of ELMs is presented. The W sputtering source under inter-and intra-ELM conditions is estimated using the analytical approach and validated by optical emission spectroscopy in these discharges. The intra-ELM W sputtering flux increases 2-4 times in comparison to the inter-ELM flux.

  • 22. Bowman, C.
    et al.
    Dickinson, D.
    Horvath, L.
    Lunniss, A. E.
    Wilson, H. R.
    Cziegler, I.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Gibson, K.
    Kirk, A.
    Lipschultz, B.
    Maggi, C. F.
    Roach, C. M.
    Saarelma, S.
    Snyder, P. B.
    Thornton, A.
    Wynn, A.
    Pedestal evolution physics in low triangularity JET tokamak discharges with ITER-like wall2018Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, nr 1, artikkel-id 016021Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The pressure gradient of the high confinement pedestal region at the edge of tokamak plasmas rapidly collapses during plasma eruptions called edge localised modes (ELMs), and then re-builds over a longer time scale before the next ELM. The physics that controls the evolution of the JET pedestal between ELMs is analysed for 1.4 MA, 1.7 T, low triangularity, delta = 0.2, discharges with the ITER-like wall, finding that the pressure gradient typically tracks the ideal magneto-hydrodynamic ballooning limit, consistent with a role for the kinetic ballooning mode. Furthermore, the pedestal width is often influenced by the region of plasma that has second stability access to the ballooning mode, which can explain its sometimes complex evolution between ELMs. A local gyrokinetic analysis of a second stable flux surface reveals stability to kinetic ballooning modes; global effects are expected to provide a destabilising mechanism and need to be retained in such second stable situations. As well as an electronscale electron temperature gradient mode, ion scale instabilities associated with this flux surface include an electro-magnetic trapped electron branch and two electrostatic branches propagating in the ion direction, one with high radial wavenumber. In these second stability situations, the ELM is triggered by a peeling-ballooning mode; otherwise the pedestal is somewhat below the peeling-ballooning mode marginal stability boundary at ELM onset. In this latter situation, there is evidence that higher frequency ELMs are paced by an oscillation in the plasma, causing a crash in the pedestal before the peeling-ballooning boundary is reached. A model is proposed in which the oscillation is associated with hot plasma filaments that are pushed out towards the plasma edge by a ballooning mode, draining their free energy into the cooler plasma there, and then relaxing back to repeat the process. The results suggest that avoiding the oscillation and maximising the region of plasma that has second stability access will lead to the highest pedestal heights and, therefore, best confinement-a key result for optimising the fusion performance of JET and future tokamaks, such as ITER.

  • 23.
    Brunsell, Per
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Volpe, Francesco
    Columbia University, New York, NY, USA.
    Olofsson, Erik
    Columbia University, New York, NY, USA.
    Fridström, Rickard
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Setiadi, Agung Chris
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Resistive Wall Mode Studies utilizing External Magnetic Perturbations2014Inngår i: Proceeding of the 25th IAEA Fusion Energy Conference, 2014, artikkel-id Paper EX/P4-20Konferansepaper (Annet vitenskapelig)
  • 24.
    Brunsell, Per
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Volpe, Francesco
    Columbia University, New York, NY, USA.
    Olofsson, Erik
    Columbia University, New York, NY, USA.
    Fridström, Rickard
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Setiadi, Agung Chris
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Resistive Wall Mode Studies utilizing External Magnetic PerturbationsManuskript (preprint) (Annet vitenskapelig)
  • 25.
    Brunsell, Per
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Olofsson, K. Erik J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Cecconello, Marco
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Yadikin, D.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Kuldkepp, Mattias
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabethth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Resistive wall mode feedback control experiments in EXTRAP T2R2007Inngår i: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, 2007, s. 544-547Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Experiments in EXTRAP T2R on RWM stabilization using intelligent shell feedback with a P-controller showed that mode suppression improves with increasing gain up to the system stability limit. A PD-controller gives faster response and allows operation with higher gain. The PI-controller is useful for suppression of modes driven by external resonant field error. Best mode suppression was in the present study achieved with a PID-controller.

  • 26. Brunsell, Per R.
    et al.
    Olofsson, K. E. J.
    Frassinetti, L.
    Drake, James R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Resistive wall mode feedback control in EXTRAP T2R with improved steady-state error and transient response2007Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, nr 10Artikkel i tidsskrift (Fagfellevurdert)
  • 27. Bucalossi, J.
    et al.
    Neu, R.
    Joffrin, E.
    Lomas, P.
    Nunes, I.
    Rimini, F.
    Beurskens, M.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Baruzzo, M.
    Bourdelle, C.
    Challis, C.
    Coenen, J.
    De Vries, P.
    Dux, R.
    Giroud, C.
    Giruzzi, G.
    Maddison, G.
    Mayoral, M.
    Characterization of the ELMy H-mode regime with the ITER-like wall in JET2012Inngår i: 39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics: Volume 1, 2012, 2012, s. 45-48Konferansepaper (Fagfellevurdert)
  • 28.
    Bykov, Igor
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Vignitchouk, Ladislas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Banon, Jean-Philippe
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Transport asymmetry and release mechanisms of metal dust in the reversed-field pinch configuration2014Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 56, nr 3, s. 035014-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Experimental data on dust resident in the EXTRAP T2R reversed-field pinch are reported. Mobile dust grains are captured in situ by silicon collectors, whereas immobile grains are sampled post mortem from the wall by adhesive tape. The simulation of collection asymmetries by the MIGRAINe dust dynamics code in combination with the experimental results is employed to deduce some characteristics of the mechanism of intrinsic dust release. All evidence suggests that re-mobilization is dominant with respect to dust production.

  • 29. Bílková, P.
    et al.
    Böhm, P.
    Komm, M.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Stefániková, Estera
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Peterka, M.
    Šos, M.
    Seidl, J.
    Grover, O.
    Havlíček, J.
    Mitošinková, K.
    Varju, J.
    Vondráček, P.
    Urban, J.
    Imríšek, M.
    Markovič, T.
    Weinzettl, V.
    Hron, M.
    Pánek, R.
    Relative shift in position of temperature and density pedestals at the COMPASS tokamak2017Inngår i: 44th EPS Conference on Plasma Physics, EPS 2017, European Physical Society (EPS) , 2017Konferansepaper (Fagfellevurdert)
  • 30.
    Cecconello, Marco
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Olofsson, Erik
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Khan, Muhammad Waqas Mehmood
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Resistive tearing modes dynamics with plasma control in a reversed field pinch2008Inngår i: 35th EPS Conference on Plasma Physics 2008, EPS 2008 - Europhysics Conference Abstracts: Volume 32, Issue 1, 2008, s. 429-432Konferansepaper (Fagfellevurdert)
  • 31. Challis, C. D.
    et al.
    Garcia, J.
    Beurskens, M.
    Buratti, P.
    Delabie, E.
    Drewelow, P.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Giroud, C.
    Hawkes, N.
    Hobirk, J.
    Joffrin, E.
    Keeling, D.
    King, D. B.
    Maggi, C. F.
    Mailloux, J.
    Marchetto, C.
    McDonald, D.
    Nunes, I.
    Pucella, G.
    Saarelma, S.
    Simpson, J.
    Improved confinement in JET high β plasmas with an ITER-like wall2015Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, nr 5, artikkel-id 053031Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The replacement of the JET carbon wall (C-wall) by a Be/W ITER-like wall (ILW) has affected the plasma energy confinement. To investigate this, experiments have been performed with both the C-wall and ILW to vary the heating power over a wide range for plasmas with different shapes. It was found that the power degradation of thermal energy confinement was weak with the ILW; much weaker than the IPB98(y,2) scaling and resulting in an increase in normalized confinement from H<inf>98</inf> ∼ 0.9 at β<inf>N</inf> ∼ 1.5 to H<inf>98</inf> ∼ 1.2-1.3 at β<inf>N</inf> ∼ 2.5 - 3.0 as the power was increased (where H<inf>98</inf> = τ<inf>E</inf>/τ<inf>IPB98(y,2)</inf> and β<inf>N</inf> = β<inf>T</inf>B<inf>T</inf>/aI<inf>P</inf> in % T/mMA). This reproduces the general trend in JET of higher normalized confinement in the so-called 'hybrid' domain, where normalized β is typically above 2.5, compared with 'baseline' ELMy H-mode plasmas with β<inf>N</inf> ∼ 1.5 - 2.0. This weak power degradation of confinement, which was also seen with the C-wall experiments at low triangularity, is due to both increased edge pedestal pressure and core pressure peaking at high power. By contrast, the high triangularity C-wall plasmas exhibited elevated H<inf>98</inf> over a wide power range with strong, IPB98(y,2)-like, power degradation. This strong power degradation of confinement appears to be linked to an increase in the source of neutral particles from the wall as the power increased, an effect that was not reproduced with the ILW. The reason for the loss of improved confinement domain at low power with the ILW is yet to be clarified, but contributing factors may include changes in the rate of gas injection, wall recycling, plasma composition and radiation. The results presented in this paper show that the choice of wall materials can strongly affect plasma performance, even changing confinement scalings that are relied upon for extrapolation to future devices.

  • 32. Coda, S.
    et al.
    Ahn, J.
    Albanese, R.
    Alberti, S.
    Alessi, E.
    Allan, S.
    Anand, H.
    Anastassiou, G.
    Andrèbe, Y.
    Angioni, C.
    Ariola, M.
    Bernert, M.
    Beurskens, M.
    Bin, W.
    Blanchard, P.
    Blanken, T. C.
    Boedo, J. A.
    Bolzonella, T.
    Bouquey, F.
    Braunmüller, F. H.
    Bufferand, H.
    Buratti, P.
    Calabró, G.
    Camenen, Y.
    Carnevale, D.
    Carpanese, F.
    Causa, F.
    Cesario, R.
    Chapman, I. T.
    Chellai, O.
    Choi, D.
    Cianfarani, C.
    Ciraolo, G.
    Citrin, J.
    Costea, S.
    Crisanti, F.
    Cruz, N.
    Czarnecka, A.
    Decker, J.
    De Masi, G.
    De Tommasi, G.
    Douai, D.
    Dunne, M.
    Duval, B. P.
    Eich, T.
    Elmore, S.
    Esposito, B.
    Faitsch, M.
    Fasoli, A.
    Fedorczak, N.
    Felici, F.
    Février, O.
    Ficker, O.
    Fietz, S.
    Fontana, M.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Furno, I.
    Galeani, S.
    Gallo, A.
    Galperti, C.
    Garavaglia, S.
    Garrido, I.
    Geiger, B.
    Giovannozzi, E.
    Gobbin, M.
    Goodman, T. P.
    Gorini, G.
    Gospodarczyk, M.
    Granucci, G.
    Graves, J. P.
    Guirlet, R.
    Hakola, A.
    Ham, C.
    Harrison, J.
    Hawke, J.
    Hennequin, P.
    Hnat, B.
    Hogeweij, D.
    Hogge, J. -P
    Honoré, C.
    Hopf, C.
    Horáček, J.
    Huang, Z.
    Igochine, V.
    Innocente, P.
    Ionita Schrittwieser, C.
    Isliker, H.
    Jacquier, R.
    Jardin, A.
    Kamleitner, J.
    Karpushov, A.
    Keeling, D. L.
    Kirneva, N.
    Kong, M.
    Koubiti, M.
    Kovacic, J.
    Krämer-Flecken, A.
    Krawczyk, N.
    Kudlacek, O.
    Labit, B.
    Lazzaro, E.
    Le, H. B.
    Lipschultz, B.
    Llobet, X.
    Lomanowski, B.
    Loschiavo, V. P.
    Lunt, T.
    Maget, P.
    Maljaars, E.
    Malygin, A.
    Maraschek, M.
    Marini, C.
    Martin, P.
    Martin, Y.
    Mastrostefano, S.
    Maurizio, R.
    Mavridis, M.
    Mazon, D.
    McAdams, R.
    McDermott, R.
    Merle, A.
    Meyer, H.
    Militello, F.
    Miron, I. G.
    Molina Cabrera, P. A.
    Moret, J. -M
    Moro, A.
    Moulton, D.
    Naulin, V.
    Nespoli, F.
    Nielsen, A. H.
    Nocente, M.
    Nouailletas, R.
    Nowak, S.
    Odstrčil, T.
    Papp, G.
    Papřok, R.
    Pau, A.
    Pautasso, G.
    Pericoli Ridolfini, V.
    Piovesan, P.
    Piron, C.
    Pisokas, T.
    Porte, L.
    Preynas, M.
    Ramogida, G.
    Rapson, C.
    Juul Rasmussen, J.
    Reich, M.
    Reimerdes, H.
    Reux, C.
    Ricci, P.
    Rittich, D.
    Riva, F.
    Robinson, T.
    Saarelma, S.
    Saint-Laurent, F.
    Sauter, O.
    Scannell, R.
    Schlatter, C.
    Schneider, B.
    Schneider, P.
    Schrittwieser, R.
    Sciortino, F.
    Sertoli, M.
    Sheikh, U.
    Sieglin, B.
    Silva, M.
    Sinha, J.
    Sozzi, C.
    Spolaore, M.
    Stange, T.
    Stoltzfus-Dueck, T.
    Tamain, P.
    Teplukhina, A.
    Testa, D.
    Theiler, C.
    Thornton, A.
    Tophøj, L.
    Tran, M. Q.
    Tsironis, C.
    Tsui, C.
    Uccello, A.
    Vartanian, S.
    Verdoolaege, G.
    Verhaegh, K.
    Vermare, L.
    Vianello, N.
    Vijvers, W. A. J.
    Vlahos, L.
    Vu, N. M. T.
    Walkden, N.
    Wauters, T.
    Weisen, H.
    Wischmeier, M.
    Zestanakis, P.
    Zuin, M.
    Overview of the TCV tokamak program: Scientific progress and facility upgrades2017Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, nr 10, artikkel-id 102011Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The TCV tokamak is augmenting its unique historical capabilities (strong shaping, strong electron heating) with ion heating, additional electron heating compatible with high densities, and variable divertor geometry, in a multifaceted upgrade program designed to broaden its operational range without sacrificing its fundamental flexibility. The TCV program is rooted in a three-pronged approach aimed at ITER support, explorations towards DEMO, and fundamental research. A 1 MW, tangential neutral beam injector (NBI) was recently installed and promptly extended the TCV parameter range, with record ion temperatures and toroidal rotation velocities and measurable neutral-beam current drive. ITER-relevant scenario development has received particular attention, with strategies aimed at maximizing performance through optimized discharge trajectories to avoid MHD instabilities, such as peeling-ballooning and neoclassical tearing modes. Experiments on exhaust physics have focused particularly on detachment, a necessary step to a DEMO reactor, in a comprehensive set of conventional and advanced divertor concepts. The specific theoretical prediction of an enhanced radiation region between the two X-points in the low-field-side snowflake-minus configuration was experimentally confirmed. Fundamental investigations of the power decay length in the scrape-off layer (SOL) are progressing rapidly, again in widely varying configurations and in both D and He plasmas; in particular, the double decay length in L-mode limited plasmas was found to be replaced by a single length at high SOL resistivity. Experiments on disruption mitigation by massive gas injection and electron-cyclotron resonance heating (ECRH) have begun in earnest, in parallel with studies of runaway electron generation and control, in both stable and disruptive conditions; a quiescent runaway beam carrying the entire electrical current appears to develop in some cases. Developments in plasma control have benefited from progress in individual controller design and have evolved steadily towards controller integration, mostly within an environment supervised by a tokamak profile control simulator. TCV has demonstrated effective wall conditioning with ECRH in He in support of the preparations for JT-60SA operation.

  • 33.
    Coda, S.
    et al.
    Ecole Polytech Fed Lausanne, Swiss Plasma Ctr, CH-1015 Lausanne, Switzerland..
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Zuin, M.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    et al.,
    Physics research on the TCV tokamak facility: from conventional to alternative scenarios and beyond2019Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, nr 11, artikkel-id 112023Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The research program of the TCV tokamak ranges from conventional to advanced-tokamak scenarios and alternative divertor configurations, to exploratory plasmas driven by theoretical insight, exploiting the device's unique shaping capabilities. Disruption avoidance by real-time locked mode prevention or unlocking with electron-cyclotron resonance heating (ECRH) was thoroughly documented, using magnetic and radiation triggers. Runaway generation with high-Z noble-gas injection and runaway dissipation by subsequent Ne or Ar injection were studied for model validation. The new 1 MW neutral beam injector has expanded the parameter range, now encompassing ELMy H-modes in an ITER-like shape and nearly noninductive II-mode discharges sustained by electron cyclotron and neutral beam current drive. In the H-mode, the pedestal pressure increases modestly with nitrogen seeding while fueling moves the density pedestal outwards, but the plasma stored energy is largely uncorrelated to either seeding or fueling. High fueling at high triangularity is key to accessing the attractive small edge-localized mode (type-II) regime. Turbulence is reduced in the core at negative triangularity, consistent with increased confinement and in accord with global gyrokinetic simulations. The geodesic acoustic mode, possibly coupled with avalanche events, has been linked with particle flow to the wall in diverted plasmas. Detachment, scrape-off layer transport, and turbulence were studied in L- and H-modes in both standard and alternative configurations (snowflake, super-X, and beyond). The detachment process is caused by power `starvation' reducing the ionization source, with volume recombination playing only a minor role. Partial detachment in the H-mode is obtained with impurity seeding and has shown little dependence on flux expansion in standard single-null geometry. In the attached 1,-mode phase, increasing the outer connection length reduces the in-out heat-flow asymmetry. A doublet plasma, featuring an internal X-point, was achieved successfully, and a transport barrier was observed in the mantle just outside the internal separatrix. In the near future variableconfiguration baffles and possibly divertor ptunping will be introduced to investigate the effect of divertor closure on exhaust and performance, and 3.5 MW ECR and 1 MW neutral beam injection heating will be added.

  • 34. Coenen, J. W.
    et al.
    Arnoux, G.
    Bazylev, B.
    Matthews, G. F.
    Autricque, A.
    Balboa, I.
    Clever, M.
    Dejarnac, R.
    Coffey, I.
    Corre, Y.
    Devaux, S.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Gauthier, E.
    Horacek, J.
    Jachmich, S.
    Komm, M.
    Knaup, M.
    Krieger, K.
    Marsen, S.
    Meigs, A.
    Mertens, Ph.
    Pitts, R. A.
    Puetterich, T.
    Rack, M.
    Stamp, M.
    Sergienko, G.
    Tamain, P.
    Thompson, V.
    ELM-induced transient tungsten melting in the JET divertor2015Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, nr 2, artikkel-id 023010Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The original goals of the JET ITER-like wall included the study of the impact of an all W divertor on plasma operation (Coenen et al 2013 Nucl. Fusion 53 073043) and fuel retention (Brezinsek et al 2013 Nucl. Fusion 53 083023). ITER has recently decided to install a full-tungsten (W) divertor from the start of operations. One of the key inputs required in support of this decision was the study of the possibility of W melting and melt splashing during transients. Damage of this type can lead to modifications of surface topology which could lead to higher disruption frequency or compromise subsequent plasma operation. Although every effort will be made to avoid leading edges, ITER plasma stored energies are sufficient that transients can drive shallow melting on the top surfaces of components. JET is able to produce ELMs large enough to allow access to transient melting in a regime of relevance to ITER. Transient W melt experiments were performed in JET using a dedicated divertor module and a sequence of I-P = 3.0 MA/B-T = 2.9 T H-mode pulses with an input power of P-IN = 23 MW, a stored energy of similar to 6 MJ and regular type I ELMs at Delta W-ELM = 0.3 MJ and f(ELM) similar to 30 Hz. By moving the outer strike point onto a dedicated leading edge in the W divertor the base temperature was raised within similar to 1 s to a level allowing transient, ELM-driven melting during the subsequent 0.5 s. Such ELMs (delta W similar to 300 kJ per ELM) are comparable to mitigated ELMs expected in ITER (Pitts et al 2011 J. Nucl. Mater. 415 (Suppl.) S957-64). Although significant material losses in terms of ejections into the plasma were not observed, there is indirect evidence that some small droplets (similar to 80 mu m) were released. Almost 1 mm (similar to 6 mm(3)) of W was moved by similar to 150 ELMs within 7 subsequent discharges. The impact on the main plasma parameters was minor and no disruptions occurred. The W-melt gradually moved along the leading edge towards the high-field side, driven by j x B forces. The evaporation rate determined from spectroscopy is 100 times less than expected from steady state melting and is thus consistent only with transient melting during the individual ELMs. Analysis of IR data and spectroscopy together with modelling using the MEMOS code Bazylev et al 2009 J. Nucl. Mater. 390-391 810-13 point to transient melting as the main process. 3D MEMOS simulations on the consequences of multiple ELMs on damage of tungsten castellated armour have been performed. These experiments provide the first experimental evidence for the absence of significant melt splashing at transient events resembling mitigated ELMs on ITER and establish a key experimental benchmark for the MEMOS code.

  • 35. Coenen, J. W.
    et al.
    Arnoux, G.
    Bazylev, B.
    Matthews, G. F.
    Jachmich, S.
    Balboa, I.
    Clever, M.
    Dejarnac, R.
    Coffey, I.
    Corre, Y.
    Devaux, S.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Gauthier, E.
    Horacek, J.
    Knaup, M.
    Komm, M.
    Krieger, K.
    Marsen, S.
    Meigs, A.
    Mertens, Ph.
    Pitts, R. A.
    Puetterich, T.
    Rack, M.
    Stamp, M.
    Sergienko, G.
    Tamain, P.
    Thompson, V.
    ELM induced tungsten melting and its impact on tokamak operation2015Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, s. 78-84Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In JET-ILW dedicated melt exposures were performed using a sequence of 3MA/2.9T H-Mode JET pulses with an input power of P-IN = 23 MW, a stored energy of similar to 6 MJ and regular type I ELMs at Delta W-ELM = 0.3 MJ and f(ELM) similar to 30 Hz. In order to assess the risk of starting ITER operations with a full W divertor, one of the task was to measure the consequences of W transients melting due to ELMs. JET is the only tokamak able to produce transients/ ELMs large enough (>300 kJ per ELM) to facilitate melting of tungsten. Such ELMs are comparable to mitigated ELMs expected in ITER. By moving the outer strike point (OSP) onto a dedicated leading edge the base temperature was raised within similar to 1 s to allow transient ELM-driven melting during the subsequent 0.5 s. Almost 1 mm (similar to 6 mm(3)) of W was moved by similar to 150 ELMs within 5 subsequent discharges. Significant material losses in terms of ejections into the plasma were not observed. There is indirect evidence that some small droplets (similar to 80 mu m) were ejected. The impact on the main plasma parameters is minor and no disruptions occurred. The W-melt gradually moved along the lamella edge towards the high field side, driven by j x B forces. The evaporation rate determined is 100 times less than expected from steady state melting and thus only consistent with transient melting during individual ELMs. IR data, spectroscopy, as well as melt modeling point to transient melting. Although the type of damage studied in these JET experiments is unlikely to be experienced in ITER, the results do strongly support the design strategy to avoid exposed edges in the ITER divertor. The JET experiments required a surface at normal incidence and considerable pre-heating to produce tungsten melting. They provide unique experimental evidence for the absence of significant melt splashing at events resembling mitigated ELMs on ITER and establish a unique experimental benchmark for the simulations being used to study transient shallow melting on ITER W divertor PFUs.

  • 36. de la Luna, E
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Lomas, P
    Maggi, C
    Brezinsek, S
    Challis, C
    Nunes, I
    Rimini, F
    Type I ELM characterization in JET with the ITER-like wall2015Inngår i: 15th International Workshop on H-mode Physics and Transport Barriers, 19-21 October 2015. Garching, Germany, 2015Konferansepaper (Annet vitenskapelig)
  • 37. de la Luna, E
    et al.
    Rimini, F
    Lomas, P
    Sips, A
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Amicucci, L
    Drewelow, P
    Flanagan, J
    Nunes, I
    Saarelma, S
    Recent Results on High-Triangularity H-Mode Studies in JET-ILW2016Inngår i: 26th IAEA Fusion Energy Conference, 17-22 October 2016, 2016Konferansepaper (Fagfellevurdert)
  • 38. Dejarnac, R.
    et al.
    Podolnik, A.
    Komm, M.
    Arnoux, G.
    Coenen, J. W.
    Devaux, S.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Gunn, J. P.
    Matthews, G. F.
    Pitts, R. A.
    Numerical evaluation of heat flux and surface temperature on a misaligned JET divertor W lamella during ELMs2014Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 54, nr 12, s. 123011-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A series of experiments has been performed on JET to investigate the dynamics of transient melting due to edge localized modes (ELMs). The experiment employs a deliberately misaligned lamella in one module of the JET bulk tungsten outer divertor, allowing the combination of stationary power flux and ELMs to transiently melt the misaligned edge. During the design of the experiment a number of calculations were performed using 2D particle-in-cell simulations and a heat transfer code to investigate the influence on the deposited power flux of finite Larmor radius effects associated with the energetic ELM ions. This has been performed using parameter scans inside a range of pedestal temperatures and densities to scope different experimentally expected ELM energies. On the one hand, we observe optimistic results, with smoothing of the heat flux due to the Larmor gyration on the protruding side of the lamella which sees the direct parallel flux-the deposited power tends to be lower than the nominal value expected from geometric magnetic field line impact over a distance smaller than 2 Larmor radii, a finding which is always valid during ELMs for such a geometry. On the other hand, the fraction of the flux not reaching the directly wetted side is transferred and spread to the top surface of the lamella. The hottest point of the lamella (corner side/top) does not always benefit from the gain from the Larmor smoothing effect because of an enhanced power deposition from the second contribution.

  • 39.
    Drake, James Robert
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bolzonella, T.
    Olofsson, Erik
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Baruzzo, T. M.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Guo, S. C.
    Igochine, V.
    Liu, Y. Q.
    Marchiori, G.
    Paccagnella, R.
    Rubinacci, G.
    Soppelsa, A.
    Villone, F.
    Yadikin, D.
    Martin, P.
    Zohm, H.
    Reversed-Field Pinch Contributions to Resistive Wall Mode Physics and Control2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Optimal feedback control of resistive-wall modes (RWM) is of common interest for toroidal fusionconcepts that use conducting walls for stabilization of ideal MHD modes. From the RWM control point of view,the RFP situation is in many respects similar to the advanced tokamak situation in the presence of very lowplasma rotation, where the most effective stabilizing mechanism is the feedback action of a set of active coils.Results from EXTRAP T2R (Sweden) and RFX-mod (Italy) RFP experiments have shown that full feedbackcontrol of multiple RWMs is possible and their deleterious effects can be completely suppressed. However it isnow important to optimize the RWM control systems both for the RFP and tokamak configuration for futureimplementation. Important aspects of optimization are effective mode identification and tracking capability,avoidance of the harmful effects of sideband modes (aliasing) in the control spectrum, minimized powerrequirements and robust controller stability. The paper describes collaborative work carried out on the two RFPexperiments. Controller models based on the mode harmonic control concept and on a state-space multipleinputmultiple-output intelligent shell concept are studied. Progress in development of optimal control schemesare presented both through experimental studies and simulations.

  • 40. Dunne, M
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Poetzel, S
    Reimold, F
    Wischmeier, M
    Wolfrum, E
    Bernerdt, M
    The Role of the Density Profile Location on Pedestal Stability in ASDEX-Upgrade2016Inngår i: 26th IAEA Fusion Energy Conference, 17-22 October 2016, 2016Konferansepaper (Fagfellevurdert)
  • 41. Dunne, M. G.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Beurskens, M.
    Cavedon, M.
    Fischer, R.
    Huijsmans, G. T. A.
    Laggner, F. M.
    McDermott, R. M.
    Tardini, G.
    Viezzer, E.
    Wolfrum, E.
    Impact of nitrogen seeding on the AUG pedestal: Experiments and modelling2015Inngår i: 42nd European Physical Society Conference on Plasma Physics, EPS 2015, European Physical Society (EPS) , 2015Konferansepaper (Fagfellevurdert)
  • 42. Dunne, M. G.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Beurskens, M. N. A.
    Cavedon, M.
    Fietz, S.
    Fischer, R.
    Giannone, L.
    Huijsmans, G. T. A.
    Kurzan, B.
    Laggner, F.
    McCarthy, P. J.
    McDermott, R. M.
    Tardini, G.
    Viezzer, E.
    Willensdorfer, M.
    Wolfrum, E.
    Global performance enhancements via pedestal optimisation on ASDEX Upgrade2017Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 59, nr 2, artikkel-id 025010Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Results of experimental scans of heating power, plasma shape, and nitrogen content are presented, with a focus on global performance and pedestal alteration. In detailed scans at low triangularity, it is shown that the increase in stored energy due to nitrogen seeding stems from the pedestal. It is also shown that the confinement increase is driven through the temperature pedestal at the three heating power levels studied. In a triangularity scan, an orthogonal effect of shaping and seeding is observed, where increased plasma triangularity increases the pedestal density, while impurity seeding (carbon and nitrogen) increases the pedestal temperature in addition to this effect. Modelling of these effects was also undertaken, with interpretive and predictive models being employed. The interpretive analysis shows a general agreement of the experimental pedestals in separate power, shaping, and seeding scans with peeling-ballooning theory. Predictive analysis was used to isolate the individual effects, showing that the trends of additional heating power and increased triangularity can be recoverd. However, a simple change of the effective charge in the plasma cannot explain the observed levels of confinement improvement in the present models.

  • 43. Dunne, M. G.
    et al.
    Potzel, S.
    Reimold, F.
    Wischmeier, M.
    Wolfrum, E.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Beurskens, M.
    Bilkova, P.
    Cavedon, M.
    Fischer, R.
    Kurzan, B.
    Laggner, F. M.
    McDermott, R. M.
    Tardini, G.
    Trier, E.
    Viezzer, E.
    Willensdorfer, M.
    The role of the density profile in the ASDEX-Upgrade pedestal structure2017Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 59, nr 1, artikkel-id 014017Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Experimental evidence for the impact of a region of high density localised in the high-field side scrape-off layer (the HFSHD) on plasma confinement is shown in various dedicated experiments on ASDEX Upgrade (AUG). Increasing main ion fuelling is shown to increase the separatrix density and shift the density profile outwards. Predictive pedestal modelling of this shift indicates a 25% decrease in the attainable pedestal top pressure, which compares well with experimental observations in the gas scan. Since the HFSHD can be mitigated by applying nitrogen seeding, a combined scan in fuelling rate, heating power, and nitrogen seeding is presented. Significant increases in the achievable pedestal top pressure are observed with seeding, in particular at high heating powers, and are correlated with inward shifted density profiles and a reduction of the HFSHD and separatrix density. Interpretive linear stability analysis also confirms the impact of a radially shifted pressure profile on peeling-ballooning stability, with an inward shift allowing access to higher pressure gradients and pedestal widths.

  • 44. Dunne, M
    et al.
    Poetzel, S
    Wischmeier, M
    Wolfrum, E
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Reimold, F
    Predictive  modelling  of  the  impact  of  a  radiative  divertor  on pedestal  con nement  on  ASDEX  Upgrade2015Inngår i: 57rd Meeting of the APS Division of Plasma Physics, November 2015, Savannah, USA, 2015Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    In future devices, tailoring of the edge density profile and radiation profile for power exhaust control via a deuterium gas puff and extrinsic impurity seeding will be necessary. It has been observed on present day machines that high D fuelling can reduce the plasma stored energy while adding impurity seeding can act to improve confinement by up to 40{\%}. This study presents a combination of observations and modelling completed on AUG with the aim of determining the mechanisms behind the confinement degradation with a gas puff and improvement with impurity seeding. In particular, predictive modelling, based on the EPED pedestal model, has been extensively used. Alterations of the temperature and density at the separatrix are found to have large impacts on pedestal stability. Measured changes in divertor properties are used to inform the direction and magnitude of these alterations, with experimentally relevant confinement changes being recovered via pressure profile shifts.

  • 45. Dunne, M
    et al.
    Potzel, S
    Remold, F
    Viezzer, E
    Wischmeier, M
    Wolfrum, E
    Bernerdt, M
    Beurskens, M
    Cavedon, M
    Fischer, R
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Kurzan, B
    The role of the density profile in the ASDEX-Upgrade pedestal structure2016Inngår i: 43th European Physical Society (EPS) Conference on Plasma Physics. July 4 – July 8, 2016, 2016Konferansepaper (Fagfellevurdert)
  • 46. Field, A. R.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Maggi, C.
    Saarelma, S.
    Inter-ELM power losses and their dependence on pedestal parameters in JET C-And ITER-like wall H-mode plasmas2018Inngår i: 45th EPS Conference on Plasma Physics, EPS 2018, European Physical Society (EPS) , 2018, s. 1636-1639Konferansepaper (Fagfellevurdert)
  • 47. Franz, P
    et al.
    Marrelli, L
    Piovesan, P
    Predebon, I
    Bonomo, F
    Frassinetti, Lorenzo
    Consorzio RFX.
    Martin, P
    Spizzo, G
    Chapman, BE
    Craig, D.
    Sarff, J. S.
    Tomographic imaging of resistive mode dynamics in the Madison Symmetric Torus reversed-field pinch2006Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, nr 1, s. 012510-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A detailed study of the dynamics and magnetic topological effects of resistive-tearing modes is presented for different operational regimes in the Madison Symmetric Torus reversed-field pinch [R. N. Dexter , Fusion Technol. 19, 131 (1991)]. Soft-x-ray tomography and magnetic measurements, along with numerical reconstruction of magnetic-field lines with the ORBIT code [R. B. White and M. S. Chance, Phys. Fluids 27, 2455 (1984)], have been employed. Magnetic-mode dynamics has been investigated in standard plasmas during the transition to the quasi-single helicity state, in which a single mode dominates the mode spectrum. Single helical soft-x-ray structures are studied with tomography in these cases. These structures are associated with magnetic islands, indicating that helical flux surfaces appear in the plasma. Mode dynamics has also been examined during auxiliary inductive current drive, the goal of which is to reduce the tearing-mode amplitudes. In this case the phenomenology of the soft-x-ray structures appearing in the plasma is more complex. In fact, when a quasi-single helicity spectrum occurs, a single island bigger than in the standard case is usually found. On the other hand, when all modes decrease, two helical soft-x-ray structures are observed, with the same helicity as the two innermost resonant modes. This constitutes the first direct evidence of magnetic-chaos reduction during auxiliary inductive current drive, which is responsible for the achievement of the best confinement in the reversed-field pinch configuration up to now.

  • 48.
    Frassinetti, L.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Brunsell, Per R.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Drake, James R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, S.
    Cecconello, Marco
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Spontaneous quasi single helicity regimes in EXTRAP T2R reversed-field pinch2007Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, nr 11Artikkel i tidsskrift (Fagfellevurdert)
  • 49.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Inter-ELM evolution of the pedestal structure in JET-ILW2016Inngår i: 24th European Fusion Physics Workshop, 28-30 November 2016, 2016Konferansepaper (Annet vitenskapelig)
  • 50.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Magnetic perturbation and dynamo generation effects on 3-d flows in RFPs2010Inngår i: 18th European Fusion Physics Workshop, December 2010, Mayrhofen, Austria, 2010Konferansepaper (Annet vitenskapelig)
12345 1 - 50 of 235
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