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  • 1151. Wilder, F. D.
    et al.
    Ergun, R. E.
    Eriksson, S.
    Phan, T. D.
    Burch, J. L.
    Ahmadi, N.
    Goodrich, K. A.
    Newman, D. L.
    Trattner, K. J.
    Torbert, R. B.
    Giles, B. L.
    Strangeway, R. J.
    Magnes, W.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Khotyaintsev, Yu-V.
    Multipoint Measurements of the Electron Jet of Symmetric Magnetic Reconnection with a Moderate Guide Field2017Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 118, nr 26, artikkel-id 265101Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report observations from the Magnetospheric Multiscale (MMS) satellites of the electron jet in a symmetric magnetic reconnection event with moderate guide field. All four spacecraft sampled the ion diffusion region and observed the electron exhaust. The observations suggest that the presence of the guide field leads to an asymmetric Hall field, which results in an electron jet skewed towards the separatrix with a nonzero component along the magnetic field. The jet appears in conjunction with a spatially and temporally persistent parallel electric field ranging from -3 to -5 mV/m, which led to dissipation on the order of 8 nW/m(3). The parallel electric field heats electrons that drift through it, and is associated with a streaming instability and electron phase space holes.

  • 1152. Wilson, H. R.
    et al.
    Bowman, C.
    Cowley, S. C.
    Cziegler, I.
    Dickinson, D.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Gibson, K.
    Ham, C.
    Horvath, L.
    Kirk, A.
    Lipschultz, B.
    Lunniss, A. E. L.
    Maggi, C. F.
    Roach, C. M.
    Saarelma, S.
    Snyder, P. B.
    Thornton, A.
    Wynn, A.
    Inter-ELM pedestal evolution in low triangularity JET-ILW discharges2017Inngår i: 44th EPS Conference on Plasma Physics, EPS 2017, European Physical Society (EPS) , 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Studies of the pedestal stability in low triangularity, d=0.2, JET ITER-Like Wall discharges are presented, following the evolution between ELMs. The pressure gradient tracks the ideal MHD ballooning threshold, only lagging behind it when the threshold rises rapidly as the plasma penetrates the second stability region. This is consistent with a role for the kinetic ballooning mode in the pedestal structure. When the plasma has second stability access, e.g. for low gas puff discharges, the peeling-ballooning mode is marginally stable at ELM onset. In cases where there is no second stability access the discharges are some way short of the peeling-ballooning threshold, so this alone cannot be the trigger for the ELM. A low amplitude sinusoidal oscillation in the Be-II emission is observed that correlates well with the ELMs, and has an associated high frequency magnetic field fluctuation, ~100-250kHz, with modulated amplitude. This might be associated with a new filamentary equilibrium state. 

  • 1153. Wolfrum, E.
    et al.
    Beurskens, M.
    Dunne, M. G.
    Frassinetti, Lorenzo
    Gao, X.
    Giroud, C.
    Hughes, J.
    Lunt, T.
    Maingi, R.
    Osborne, T.
    Reinke, M.
    Urano, H.
    Impact Of Wall Materials And Seeding Gases On The Pedestal And On Core Plasma Performance2017Inngår i: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, s. 18-27Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Plasmas in machines with all metal plasma facing components have a lower Z(eff), less radiation cooling in the scrape-offlayer and divertor regions and are prone to impurity accumulation in the core. Higher gas puff and the seeding of low-Z impurities are applied to prevent impurity accumulation, to increase the frequency of edge localised modes and to cool the divertor. A lower power threshold for the transition from low- confinement mode to high confinement mode has been found in all metal wall machines when compared to carbon wall machines. The application of lithium before or during discharges can lead to ELM free H-modes. The seeding of high-Z impurities increases core radiation, reduces the power flux across the separatrix and, if applied in the right amount, does not lead to deterioration of the confinement. All these effects have in common that they can often be explained by the shape or position of the density profile. Not only the peakedness of the density profile in the core but also the position of the edge pressure gradient influences global confinement. It is shown how (i) ionisation in the pedestal region due to higher reflection of deuterium from high-Z walls, (ii) reduced recycling in consequence of lithium wall conditioning, (iii) the fostering of edge modes with lithium dropping, (iv) increased gas puffand (v) the cooling of the scrape-offlayer by medium-Z impurities such as nitrogen affect the edge density profile. The consequence is a shift in the pressure profile relative to the separatrix, leading to improved pedestal stability of H-mode plasmas when the direction is inwards.

  • 1154. Wu, D J
    et al.
    Huang, G L
    Wang, D Y
    Fälthammar, Carl-Gunne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Solitary kinetic Alfven waves in the two-fluid model1996Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 3, s. 2879-2884Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Employing the two-fluid model, a generalized Sagdeev equation governing solitary kinetic Alfven waves (SKAWs) and the criterion for the existence of SKAWs, which are valid for different ranges of plasma pressure parameter beta, are presented. In the limit cases of beta much greater than m(e)/m(i) and beta much less than m(e)/m(i), the present results correspond, respectively, with conclusions obtained by Hasegawa ct al. [Phys. Rev. Lett. 37, 690 (1976)] and by Shukla et al. [J. Plasma Phys. 28, 125 (1982)], that is, SKAWs accompanied by, respectively, hump and dip density solitons for beta much greater than m(e)/m(i) and beta much less than m(e)/m(i). However, for the case of beta similar to m(e)/m(i), the present results show that SKAWs accompanied by both hump and dip density solitons are possible, and lead to KdV solitons in the small amplitude limit. In addition, the possibility for applying these results to electromagnetic spikes observed by the Freja scientific satellite is discussed [detailed information about the Freja satellite experiments can be found in serial papers presented in Space Sci. Rev. 70, Nos. 3/4 (1994)]. (C) 1996 American Institute of Physics.

  • 1155. Wu, D J
    et al.
    Wang, D U
    Fälthammar, Carl-Gunne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Coupling Alfvenic and ion-acoustic solitons1996Inngår i: Chinese Physics Letters, ISSN 0256-307X, E-ISSN 1741-3540, Vol. 13, s. 594-597Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An exact nonlinear equation governing the coupling Alfvenic aad ion-acoustic solitons and criterion for their existence are presented. For the case of low-beta plasmas. the two modes decouple. In the small amplitude limit, the analytical results lead to KdV solitons.

  • 1156. Wu, D.J.
    et al.
    Wang, D.Y.
    Fälthammar, Carl-Gunne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    An analytical solution of finite‐amplitude solitary kinetic Alfvén waves1995Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 2, s. 4476-4481Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An analytical solution of finite-amplitude solitary kinetic Alfven waves (SKAWs) in a low-beta (beta much less than m(e)/m(i) much less than 1) plasma is presented. This solution has been compared with the solution of the Korteweg-de Vries (KdV) equation in the small-amplitude limit. It is found that the KdV soliton solution is valid only for the maximum relative density perturbation N-m<0.1. For the larger N-m, the exact analytical solution shows that the SKAWs have a much wider structure and much stronger perturbed fields than the KdV solitons with the same N-m. Moreover, the relations between the width and the amplitude of SKAWs are also considerably different from that of the KdV solitons. In addition the possibility for applying these results to some events observed from the Freja scientific satellite is discussed. (The Freja is a Swedish-German scientific project for the investigation of ionospheric and magnetospheric plasmas, and the Freja satellite was launched on a Long-March II rocket of China on October 6, 1992.) (C) 1995 American Institute of Physics.

  • 1157. Wurz, Peter
    et al.
    Blomberg, Lars G.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Particle populations in Mercury's magnetosphere2001Inngår i: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 49, nr 14-15, s. 1643-1653Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Observations by Mariner 10 during its first and third flybys showed that Mercury possesses an intrinsic magnetic field resulting in a small magnetosphere that can keep the solar wind from directly interacting with the planet's surface under usual conditions. Since Mercury occupies a large fraction of its magnetosphere, regions of trapped charged particles in the inner magnetosphere, the plasmasphere and the energetic radiation belts, would all be absent. During the first flyby, energetic particle bursts were detected and interpreted as hermean substroms analogous to the terrestrial magnetosphere. Moreover, during this flyby, ULF waves and field-aligned currents were detected in the data. Earth-based observations of Na, K, and Ca populations in the exosphere strongly suggest the existence of dynamic magnetospheric processes at high latitudes interacting with the planet's surface.

  • 1158. Xiong, Xiangming
    et al.
    Tao, Jianjun
    Chen, Shiyi
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Turbulent bands in plane-Poiseuille flow at moderate Reynolds numbers2015Inngår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 27, nr 4, artikkel-id 041702Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this letter, we show via numerical simulations that the typical flow structures appearing in transitional channel flows at moderate Reynolds numbers are not spots but isolated turbulent bands, which have much longer lifetimes than the spots. Localized perturbations can evolve into isolated turbulent bands by continuously growing obliquely when the Reynolds number is larger than 660. However, interactions with other bands and local perturbations cause band breaking and decay. The competition between the band extension and breaking does not lead to a sustained turbulence until Re becomes larger than about 1000. Above this critical value, the bands split, providing an effective mechanism for turbulence spreading.

  • 1159.
    Xu, Junjie
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Effect of escaping photoelectrons on the magnetic field of Mercury2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Mercury is the tiniest planet in the solar system and that closest tothe Sun. It has a similar magnetosphere like the Earth, which to firstorder can be described as a magnetic dipole. The center of the dipoleis shifted 0.2 Mercury radii toward north, hence, the magnetic strengthare not equal at same latitude on the north and the south hemisphere.This asymmetric magnetosphere in reference to Mercury's equatorialplan, leads to the consequences that only some of the photoelectronsemitted from the south surface will reach the conjugate surface, andsome of them will mirror, whereas all the photoelectrons from the northwill reach the south surface. This phenomenon induces a potential difference,an electric field, and a current. It is the aim of this project thatto study the structure of Mercury's magnetosphere, the distribution ofthe photoelectrons, the electric field and the photoelectron currents.

  • 1160.
    Xu, Yiwen
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Frequency analysis of low-frequency field fluctuations detected by the Cluster satellites2007Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 1161.
    Yadikin, Dmitriy
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Intelligent shell feedback control of resistive wall modes in EXTRAP T2R2005Inngår i: 32nd EPS Conference on Plasma Physics 2005, EPS 2005, Held with the 8th International Workshop on Fast Ignition of Fusion Targets: Europhysics Conference Abstracts, 2005, s. 1602-1605Konferansepaper (Fagfellevurdert)
  • 1162. Yadykin, D.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Delabie, E.
    Chapman, I. T.
    Gerasimov, S.
    Kempenaars, M.
    Rimini, F. G.
    Studies of the non-axisymmetric plasma boundary displacement in JET in presence of externally applied magnetic field2015Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 57, nr 10, artikkel-id 104003Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Non-axisymmetric plasma boundary displacement is caused by the application of the external magnetic field with low toroidal mode number. Such displacement affects edge stability, power load on the first wall and could affect efficiency of the ICRH coupling in ITER. Studies of the displacement are presented for JET tokamak focusing on the interaction between error field correction coils (EFCCs) and shape control system. First results are shown on the direct measurement of the plasma boundary displacement at different toroidal locations. Both qualitative and quantitative studies of the plasma boundary displacement caused by interaction between EFCCs and shape control system are performed for different toroidal phases of the external field. Axisymmetric plasma boundary displacement caused by the EFCC/shape control system interaction is seen for certain phase values of the external field. The value of axisymmetric plasma boundary displacement caused by interaction can be comparable to the non-axisymmetric plasma boundary displacement value produced by EFCCs.

  • 1163. Yadykin, D.
    et al.
    Gryaznevich, M.
    Frasinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Gerasimov, S.
    Effect of the external helical fields on the plasma boundary shape in JET2014Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 54, nr 1, s. 013016-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Externally applied helical magnetic fields are now often used on tokamaks for various purposes. This paper presents results of studies of the effect of the external fields, produced by the error field correction coils (EFCCs) on JET, on the plasma boundary shape. Significant 3D distortions, predicted in the previous studies, have been confirmed using upgraded magnetic diagnostics and high-resolution Thomson scattering diagnostics. A simple method of estimating the edge distortion using magnetic diagnostics calibrated on the kinetic measurements is proposed and demonstrated.

  • 1164. Yagi, Y.
    et al.
    Frassinetti, Lorenzo
    Advanved insittute of Industrial Science and Technology (JAPAN).
    Hirano, Y.
    Koguchi, H.
    Sakakita, H.
    The magnitude of sawtooth crash events in multiple and quasi-single helicity states in a reversed-field-pinch plasma2005Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 12, nr 8, s. 082507-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Factors affecting the magnitude of sawtooth crashes in soft x-ray (SXR) signals (I-SXR) have been studied using data from high-Theta (pinch parameter) discharges in the toroidal pinch experiment TPE-1RM20 reversed-field pinch device [Y. Yagi , J. Plasma Fusion Research 69, 700 (1993)]. In TPE-1RM20, discharges with a high Theta that are free of large sawteeth (improved high-Theta mode discharges), spontaneously appeared [Y. Hirano , Nucl. Fusion 36, 721 (1996)] among typical conventional discharges exhibiting large sawtooth crashes. The reason for the spontaneous appearance of sawtooth-free discharges has been unclear. It is shown that the normalized magnitude of the SXR crashes, [Delta(I-SXR)/I-SXR], is well correlated with the m (poloidal mode number)=0 mode amplitude in the postcrash phase. It is also shown that Delta(I-SXR)/I-SXR is smaller when the quasi-single helicity state precedes the crash rather than when the multiple-helicity state precedes the crash, and Delta(I-SXR)/I-SXR is smaller when E-parallel to (the parallel electric field at the plasma surface) is approximately zero in the precrash phase rather than E-parallel to being negative.

  • 1165. Yagi, Y.
    et al.
    Koguchi, H.
    Hirano, Y.
    Sakakita, H.
    Frassinetti, Lorenzo
    Advanved insittute of Industrial Science and Technology (JAPAN).
    An empirical scaling law for improved confinement in reversed-field pinch plasmas2005Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 45, nr 2, s. 138-142Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A database of the confinement properties of the toroidal pinch experiment (TPE) series reversed-field pinch (RFP) devices was established, and an empirical scaling law for the energy confinement time, tau(E), was deduced for a consistently selected set of the database (Yagi Y. et al 2003 Nucl. Fusion 43 1787). The scaling for tau(E) [TPE-scaling; tau(E) similar to a(1.7)I(p)(0.8) (I-p/N)(0.3)Theta(3)], in particular, is a power law similar to that predicted on the basis of the tearing modes, P as a function of the plasma minor radius (a), plasma current (I-p), and I-p/N, where N is the column density. On the other hand, the TPE-scaling has a strong dependence on the pinch parameter, Theta, namely tau(E) similar to Theta(3). Recently, we have investigated the database of the improved confinement in the pulsed poloidal current drive (PPCD). We show that the TPE-scaling agrees well with the improved tau(E) in the PPCD database, because of its strong Theta dependence. Namely, Theta(3) is a factor of merit for RFP plasmas. We discuss why this agreement is obtained in spite of the general difference between the underlying transport mechanisms of the standard and PPCD discharges. We also show that this improvement, represented by Theta(3), is related to the increase in magnetic shear with Theta.

  • 1166. Yagi, Y
    et al.
    Koguchi, H
    Sakakita, H
    Sekine, S
    Brunsell, P R
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Malmberg, J-A
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Evolution process of the mode wall-locking and phase-locking in a reversed field pinch plasma2001Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 8, nr 5, s. 1625-1635Artikkel i tidsskrift (Fagfellevurdert)
  • 1167. Yamauchi, M.
    et al.
    Andersson, L.
    Lindqvist, Per-Arne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Ohtani, S.
    Clemmons, J.
    Wahlund, J. E.
    Eliasson, L.
    Lundin, R.
    Acceleration signatures in the dayside boundary layer and the cusp2001Inngår i: Physics and Chemistry of the Earth, Part C: Solar, Terrestial & Planetary Science, ISSN 1464-1917, E-ISSN 1873-4685, Vol. 26, nr 03-jan, s. 195-200Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Freja data show various electron acceleration signatures in the cusp and the dayside boundary layer: (1) time dispersive super-Alfvénic electrons followed by strong wave activity which accompanies transient downward super-thermal electron burst in both the boundary layer and the cusp; (2) quasi-stationary bidirectional electron burst coinciding with localized intense field-aligned current in the boundary layer; (3) downgoing electron burst without visible time dispersion in the cusp; and (4) thermal electrons accelerated by electrostatic potential in both the boundary layer and the cusp. The first and last signatures are different between two regions for typical energies and fluxes, and these differences probably reflect the different auroral emission in the cusp proper (red) and the boundary layer (green). Contributions of these electrons to the large-scale field-aligned currents are also different between two regions. The dispersed electron burst is probably accelerated within 1 Re above the ionosphere. From this result we believe that the cusp red aurora is caused mainly by accelerated electrons, but not by the smoothly entering magnetosheath electrons without acceleration. This also requires revisions of flux transfer event models for the structured cusp red aurora.

  • 1168.
    Yamauchi, M.
    et al.
    Swedish Institute of Space Physics, Kiruna.
    Blomberg, Lars
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Problems on mappings of the convection and on the fluid concept1997Inngår i: Physics and Chemistry of the Earth, ISSN 00791946 (ISSN), Vol. 22, nr 7-8, s. 709-714Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mapping of electric fields and convection under ideal MHD or perfect gyro-trapping from the magnetopause to the ionosphere needs special caution, especially in critical regions such as the cusp and the boundary layer. Besides the existence of parallel electric fields which have been repeatedly pointed out by Alfvén, non-Maxwellian plasma distribution is another important factor that limits such mappings. The non-Maxwellian distribution sometimes destroy even the hydrodynamic concept of the convection. © 1997 Published by Elsevier Science Ltd.

  • 1169. Yamauchi, M
    et al.
    Nilsson, H
    Eliasson, L
    Norberg, O
    Boehm, M
    Clemmons, J H
    Lepping, R P
    Blomberg, Lars
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ohtani, S I
    Yamamoto, T
    Mukai, T
    Terasawa, T
    Kokubun, S
    Dynamic response of the cusp morphology to the solar wind: A case study during passage of the solar wind plasma cloud on February 21, 19941996Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 101, nr A11, s. 24675-24687Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    On February 21, 1994, both Geotail and LMP 8 satellites detected an interplanetary plasma cloud with intense interplanetary magnetic field (IMF>50 nT) and high dynamic pressure (> 50 nPa). During this interval the Freja satellite detected intense cusp-like plasma injections in four out of six dayside traversals. The first two traversals are carefully studied, During the first traversal the overall morphology of the ion injection is characterized by a ''multiple-injection'' signature over a wide magnetic local time (MLT) range, whereas it is characterized by a ''single-injection'' signature with narrow injection region at 8 MLT in the second traversal, The solar wind conditions were also quite different between these two periods: while both dynamic and magnetic pressures stayed high during entire period, the dynamic beta was much higher during the first Freja traversal than during the second traversal. Between these two traversals, the cusp plasma injection is detected by the Sondre Stromfjord radar. The radar signature of the plasma injection is identified using the satellite particle data when the satellite and the radar were conjugate (the satellite's footprint was in the radar's field of view.) The cusp position and dynamics observed by the Sondre Stromfjord radar again show a very good correlation to the solar wind condition, especially to the dynamic pressure. The result indicates the following. (1) During southward IMF the cusp morphology differs for conditions of high or low solar wind dynamic pressure. High dynamic pressure widens the cusp (with multiple injections), whereas high magnetic pressure narrows it (with single injection), The effect of the IMF on the cusp locations and morphology becomes dominant only when the dynamic pressure is not very high, (2) Such a morphological difference reflects dynamic pressure more than dynamic beta during southward IMF at least during times of high solar wind dynamic pressure. (3) The cusp morphology responds very quickly to the changes in the solar wind conditions.

  • 1170. Yambe, Kiyoyuki
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hirano, Yoichi
    Yagi, Yasuyuki
    Koguchi, Haruisa
    Sakakita, Hajime
    Frequency Dependence of Fast Magnetic Fluctuations in TPE-RX plasma2008Inngår i: Journal of Plasma and Fusion Research, ISSN 0918-7928, Vol. 3, s. 060-Artikkel i tidsskrift (Fagfellevurdert)
  • 1171.
    Yao, S. T.
    et al.
    Shandong Univ, Inst Space Sci, Shandong Prov Key Lab Opt Astron & Solar Terr Env, Weihai, Peoples R China.;Chinese Acad Sci, Natl Space Sci Ctr, State Key Lab Space Weather, Beijing, Peoples R China..
    Shi, Q. Q.
    Shandong Univ, Inst Space Sci, Shandong Prov Key Lab Opt Astron & Solar Terr Env, Weihai, Peoples R China..
    Yao, Z. H.
    UCL, Mullard Space Sci Lab, London, England.;Univ Liege, STAR Inst, Lab Phys Atmospher & Planetaire, Liege, Belgium..
    Li, J. X.
    Univ Calif Los Angeles, Dept Atmospher & Ocean Sci, Los Angeles, CA USA..
    Yue, C.
    Univ Calif Los Angeles, Dept Atmospher & Ocean Sci, Los Angeles, CA USA..
    Tao, X.
    Univ Sci & Technol China, Dept Geophys & Planetary Sci, CAS Key Lab Geospace Environm, Hefei, Anhui, Peoples R China..
    Degeling, A. W.
    Shandong Univ, Inst Space Sci, Shandong Prov Key Lab Opt Astron & Solar Terr Env, Weihai, Peoples R China..
    Zong, Q. G.
    Peking Univ, Sch Earth & Space Sci, Beijing, Peoples R China..
    Wang, X. G.
    Harbin Inst Technol, Dept Phys, Harbin, Heilongjiang, Peoples R China..
    Tian, A. M.
    Shandong Univ, Inst Space Sci, Shandong Prov Key Lab Opt Astron & Solar Terr Env, Weihai, Peoples R China..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Zhou, X. Z.
    Peking Univ, Sch Earth & Space Sci, Beijing, Peoples R China..
    Guo, R. L.
    Chinese Acad Sci, Inst Geol & Geophys, Key Lab Earth & Planetary Phys, Beijing, Peoples R China..
    Rae, I. J.
    UCL, Mullard Space Sci Lab, London, England..
    Fu, H. S.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China..
    Zhang, H.
    Univ Alaska Fairbanks, Phys Dept, Fairbanks, AK USA.;Univ Alaska Fairbanks, Geophys Inst, Fairbanks, AK 99775 USA..
    Li, L.
    Harbin Inst Technol, Dept Phys, Harbin, Heilongjiang, Peoples R China..
    Le Contel, O.
    Univ Paris Sud, Sorbonne Univ, Lab Phys Plasmas, Observ Paris,Ecole Polytech,CNRS,UMR7648, Paris, France..
    Torbert, R. B.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Ergun, R. E.
    Univ Colorado, Dept Astrophys & Planetary Sci, Boulder, CO 80309 USA..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Pollock, C. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Waves in Kinetic-Scale Magnetic Dips: MMS Observations in the Magnetosheath2019Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, nr 2, s. 523-533Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Kinetic scale magnetic dips (KSMDs), with a significant depression in magnetic field strength, and scale length close to and less than one proton gyroradius, were reported in the turbulent plasmas both in recent observation and numerical simulation studies. These KSMDs likely play important roles in energy conversion and dissipation. In this study, we present observations of the KSMDs that are labeled whistler mode waves, electrostatic solitary waves, and electron cyclotron waves in the magnetosheath. The observations suggest that electron temperature anisotropy or beams within KSMD structures provide free energy to generate these waves. In addition, the occurrence rates of the waves are higher in the center of the magnetic dips than at their edges, implying that the KSMDs might be the origin of various kinds of waves. We suggest that the KSMDs could provide favorable conditions for the generation of waves and transfer energy to the waves in turbulent magnetosheath plasmas. Plain Language Summary The Earth's magnetosheath is a turbulent plasma environment where energy conversion, particle acceleration, and mass and momentum transport take place. Many of these key processes involve kinetic-scale physics. However, in-depth studies from previous missions are limited by their lower spacecraft data resolution. The recent Magnetospheric Multiscale (MMS) mission provides us with a large amount of high-temporal cadence data for studying kinetic-scale physics in the magnetosheath. In this study, we report whistler mode waves, electrostatic solitary waves and electron cyclotron waves within kinetic-scale magnetic dips (KSMDs) that can be generated in the turbulent magnetosheath. These waves could be excited by electron temperature anisotropy or beams. As is well known, plasma waves are important processes in converting energy, accelerating and scattering electrons and ions, and modifying the distributions of charged particles. If plasma instabilities develop within the KSMDs, the resulting waves could absorb free energy from plasma particles and may propagate out of the KSMDs. Thus, our discoveries could significantly advance the understanding of energy conversion and dissipation for kinetic-scale turbulence. This study provides a new reference not only for observations in space physics but also for related basic plasma theories and numerical simulations.

  • 1172.
    Yaroshenko, V.V.
    et al.
    Max-Planck-Institute für extraterrestriche Physik, Germany.
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Olson, Jonas
    KTH, Skolan för elektro- och systemteknik (EES). KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Brenning, Nils
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Wahlund, J.-E.
    Swedish Instituet of Space Physics, Uppsala.
    Morooka, M.
    Swedish Institute of Space Physics, Uppsala.
    Kurth, W.S.
    Department of Physics and Astronomy, University of Iowa, USA.
    Gurnett, D.A.
    Department of Physics and Astronomy, University of Iowa, USA.
    Morfill, G.E.
    Characteristics of charged dust inferred from the Cassini RPWS measurements in the vicinity of Enceladus2009Inngår i: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 57, nr 14-15, s. 1807-1812Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The data obtained by the Cassini Radio and Plasma Wave Science (RPWS) instrument during the shallow (17.02.2005) and the steep (14.07.2005) crossings of the E-ring revealed a considerable electron depletion in proximity to Enceladus's orbit (the difference between the ion and electron densities can reach similar to 70 cm(-3)). Assuming that this depletion is a signature of the presence of charged dust particles, the main characteristics of dust down to submicron sized particles are derived. The differential size distribution is found to be well described by a power law with an index mu similar to 5.5-6 for the lower size limit a(min) = 0.03 mu m and mu similar to 7.3-8 for a(min) = 0.1 mu m. The calculated average integral dust number density is weakly affected by values of mu and a(min). For a greater than or similar to 0.1 mu m, both flybys gave the maximum dust density about 0.1-0.3 cm(-3) in the vicinity of Enceladus. Our results imply that the dust structure near Enceladus is characterized by approximately the same vertical length scale of 8000 km and reaches a maximum at the same radial distance (displaced outward of the orbit of Enceladus) as found by Kempf et al. [2008. The E-ring in the vicinity of Enceladus. Spatial distribution and properties of the ring particles. Icarus 193, 420-437], from the dust impact data.

  • 1173. Yee, H. C.
    et al.
    Sjögreen, Björn
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Nonlinear filtering in compact high-order schemes2006Inngår i: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 72, s. 833-836Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The adaptive nonlinear filtering approach for shock/turbulence gas dynamics and magnetohydrodynamics (MHD) flows adopted in our previous world is employed in conjunction with compact high-order methods as the spatial base scheme. The objective is to compare the performance of nonlinear filtering in compact high-order schemes with nonlinear filtering in standard central (non-compact) schemes for multiseale problems containing shock waves.

  • 1174. Zaitsev, F. S.
    et al.
    Gondhalekar, A.
    Johnson, Thomas Joe
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Kiptily, V. G.
    Sharapov, S. E.
    Simulations to elucidate suprathermal deuterium ion tail observed in He3 minority ICRF heated JET plasmas2008Inngår i: EPS Conf. Plasma Phys., EPS - Europhys. Conf. Abstr., 2008, nr 1, s. 501-504Konferansepaper (Fagfellevurdert)
  • 1175. Zaitsev, F. S.
    et al.
    Gondhalekar, A.
    Johnson, Thomas Joe
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Sharapov, S. E.
    Testa, D. S.
    Kurbet, I. I.
    Simulation of deuteron tails produced by close collisions with ICRH Accelerated He3 ions in JET2006Inngår i: EPS Conf. Plasma Phys., EPS, 2006, s. 412-415Konferansepaper (Fagfellevurdert)
  • 1176. Zarzoso, D.
    et al.
    Beurskens, M.N.A.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Joffrin, E.
    ELM size scaling in JET advanced tokamak scenarios2010Konferansepaper (Fagfellevurdert)
  • 1177. Zettergren, M. D.
    et al.
    Semeter, J. L.
    Dahlgren, Hanna
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. Space Environment Physics, University of Southampton, Southampton, United Kingdom.
    Dynamics of density cavities generated by frictional heating: Formation, distortion, and instability2015Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, nr 23, s. 10120-10125Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A simulation study of the generation and evolution of mesoscale density cavities in the polar ionosphere is conducted using a time-dependent, nonlinear, quasi-electrostatic model. The model demonstrates that density cavities, generated by frictional heating, can form in as little as 90 s due to strong electric fields of ∼120 mV/m, which are sometimes observed near auroral zone and polar cap arcs. Asymmetric density cavity features and strong plasma density gradients perpendicular to the geomagnetic field are naturally generated as a consequence of the strong convection and finite extent of the auroral feature. The walls of the auroral density cavities are shown to be susceptible to large-scale distortion and gradient-drift instability, hence indicating that arc-related regions of frictional heating may be a source of polar ionospheric density irregularities.

  • 1178. Zhao, M. L.
    et al.
    Chen, Y. P.
    Guo, H. Y.
    Ye, M. Y.
    Tendler, Michael
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Li, G. Q.
    Luo, Z. P.
    Modeling of divertor geometry effects in China fusion engineering testing reactor by SOLPS/B2-Eirene2014Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 21, nr 5, s. 052503-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The China Fusion Engineering Testing Reactor (CFETR) is currently under design. The SOLPS/B2-Eirene code package is utilized for the design and optimization of the divertor geometry for CFETR. Detailed modeling is carried out for an ITER-like divertor configuration and one with relatively open inner divertor structure, to assess, in particular, peak power loading on the divertor target, which is a key issue for the operation of a next-step fusion machine, such as ITER and CFETR. As expected, the divertor peak heat flux greatly exceeds the maximum steady-state heat load of 10MW/m(2), which is a limit dictated by engineering, for both divertor configurations with a wide range of edge plasma conditions. Ar puffing is effective at reducing divertor peak heat fluxes below 10MW/m(2) even at relatively low densities for both cases, favoring the divertor configuration with more open inner divertor structure.

  • 1179. Zhou, M.
    et al.
    Ashour-Abdalla, M.
    Berchem, J.
    Walker, R. J.
    Liang, H.
    El-Alaoui, M.
    Goldstein, M. L.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran T.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Khotyaintsev, Y. V.
    Ergun, R. E.
    Wilder, F. D.
    Russell, C. T.
    Strangeway, R. J.
    Zhao, C.
    Paterson, W. R.
    Giles, B. L.
    Pollock, C. J.
    Torbert, R. B.
    Burch, J. L.
    Dorelli, J. C.
    Gershman, D. J.
    Avanov, L. A.
    Lavraud, B.
    Chandler, M. O.
    Observation of high-frequency electrostatic waves in the vicinity of the reconnection ion diffusion region by the spacecraft of the Magnetospheric Multiscale (MMS) mission2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 10, s. 4808-4815Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report Magnetospheric Multiscale observations of high-frequency electrostatic waves in the vicinity of the reconnection ion diffusion region on the dayside magnetopause. The ion diffusion region is identified during two magnetopause crossings by the Hall electromagnetic fields, the slippage of ions with respect to the magnetic field, and magnetic energy dissipation. In addition to electron beam modes that have been previously detected at the separatrix on the magnetospheric side of the magnetopause, we report, for the first time, the existence of electron cyclotron harmonic waves at the magnetosheath separatrix. Broadband waves between the electron cyclotron and electron plasma frequencies, which were probably generated by electron beams, were found within the magnetopause current sheet. Contributions by these high-frequency waves to the magnetic energy dissipation were negligible in the diffusion regions as compared to those of lower-frequency waves.

  • 1180. Zhou, M.
    et al.
    Berchem, J.
    Walker, R. J.
    El-Alaoui, M.
    Deng, X.
    Cazzola, E.
    Lapenta, G.
    Goldstein, M. L.
    Paterson, W. R.
    Pang, Y.
    Ergun, R. E.
    Lavraud, B.
    Liang, H.
    Russell, C. T.
    Strangeway, R. J.
    Zhao, C.
    Giles, B. L.
    Pollock, C. J.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Wilder, F. D.
    Khotyaintsev, Y. V.
    Torbert, R. B.
    Burch, J. L.
    Coalescence of Macroscopic Flux Ropes at the Subsolar Magnetopause: Magnetospheric Multiscale Observations2017Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 119, nr 5, artikkel-id 055101Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report unambiguous in situ observation of the coalescence of macroscopic flux ropes by the magnetospheric multiscale (MMS) mission. Two coalescing flux ropes with sizes of similar to 1 R-E were identified at the subsolar magnetopause by the occurrence of an asymmetric quadrupolar signature in the normal component of the magnetic field measured by the MMS spacecraft. An electron diffusion region (EDR) with a width of four local electron inertial lengths was embedded within the merging current sheet. The EDR was characterized by an intense parallel electric field, significant energy dissipation, and suprathermal electrons. Although the electrons were organized by a large guide field, the small observed electron pressure nongyrotropy may be sufficient to support a significant fraction of the parallel electric field within the EDR. Since the flux ropes are observed in the exhaust region, we suggest that secondary EDRs are formed further downstream of the primary reconnection line between the magnetosheath and magnetospheric fields.

  • 1181.
    Zhou, M.
    et al.
    Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA..
    Berchem, J.
    Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA..
    Walker, R. J.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    El-Alaoui, M.
    Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA..
    Goldstein, M. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Space Sci Inst, Boulder, CO USA..
    Lapenta, G.
    Katholieke Univ Leuven, Dept Math, Ctr Plasma Astrophys, Leuven, Belgium..
    Deng, X.
    Nanchang Univ, Inst Space Sci & Technol, Nanchang, Jiangxi, Peoples R China..
    Li, J.
    Univ Calif Los Angeles, Dept Atmospher & Ocean Sci, Los Angeles, CA USA..
    Le Contel, O.
    Univ Paris Sud, UPMC Univ Paris 06, CNRS, Lab Phys Plasmas,Ecole Polytech,Observ Paris, Paris, France..
    Graham, D. B.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Lavraud, B.
    Univ Toulouse, CNRS, Inst Rech Astrophys & Planetol, UPS,CNES, Toulouse, France..
    Paterson, W. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Torbert, R. B.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA.;Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Zhao, C.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Ergun, R. E.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Marklund, Göran
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Magnetospheric Multiscale Observations of an Ion Diffusion Region With Large Guide Field at the Magnetopause: Current System, Electron Heating, and Plasma Waves2018Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, nr 3, s. 1834-1852Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report Magnetospheric Multiscale (MMS) observations of a reconnecting current sheet in the presence of a weak density asymmetry with large guide field at the dayside magnetopause. An ion diffusion region (IDR) was detected associated with this current sheet. Parallel current dominated over the perpendicular current in the IDR, as found in previous studies of component reconnection. Electrons were preferentially heated parallel to the magnetic field within the IDR. The heating was manifested as a flattop distribution below 400eV. Two types of electromagnetic electron whistler waves were observed within the regions where electrons were heated. One type of whistler wave was associated with nonlinear structures in E-|| with amplitudes up to 20mV/m. The other type was not associated with any structures in E-||. Poynting fluxes of these two types of whistler waves were directed away from the X-line. We suggest that the nonlinear evolution of the oblique whistler waves gave rise to the solitary structures in E-||. There was a perpendicular super-Alfvenic outflow jet that was carried by magnetized electrons. Intense electrostatic lower hybrid drift waves were localized in the current sheet center and were probably driven by the super-Alfvenic electron jet, the velocity of which was approximately equal to the diamagnetic drift of demagnetized ions. Our observations suggest that the guide field significantly modified the structures (Hall electromagnetic fields and current system) and wave properties in the IDR.

  • 1182.
    Zhou, Yushan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Impact of Surface Structures onDeposition and Erosion in a Tokamak2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Fusion is a potentially unlimited and environmentally friendly energy source for human society in the future. However, along the way towards the application of fusion energy there are still unresolved complications. Among them, deposition and erosion are two critical issues. Deposition of fuel and impurities brings potential long-term fuel retention which may generate safety issues and limit the economic efficiency of fusion devices. Moreover, the erosion of the vacuum vessel wall in a fusion device generates impurities which contaminate core plasma and can restrict the life time of plasma facing component. The work in this thesis focuses on deposition and erosion on tiles in the JET-ILW project, which consist of tungsten (or tungsten coating carbon fibre composited) in the divertor and beryllium in limiters.

    For the deposition issue, micro ion beam analysis (µ-IBA) was used for observing deuterium and beryllium distributions over tile surfaces. The surface topography was obtained from SEM, optical microscope and confocal laser scan microscope. Distribution maps from IBA were compared with surface topography. To explain experimental results, modelling of ion trajectories was applied on real and artificial surfaces. Micro IBA results show that deuterium and beryllium accumulated in depressed areas, e.g. pits, cracks or craters. Modelling implies that ion gyration, surface roughness and inclination of the magnetic field could to some extent explain this non-uniform distribution of deuterium and beryllium. The same kind of issue, although on different scale length, occurs also for penetration of impurities into artificial castellation grooves, also studied experimentally in the thesis.

    For the erosion issue, the thesis includes analysis of a limiter marker tile which is designed for observing material erosion in JET. A new method to acquire erosion data from such marker tiles is proposed, by combining micro IBA and SEM image.  This method could separate the influence on IBA from roughness, a problem in applying IBA on rough surface. Similar Technique is applied to improve the interpretation of IBA measurements of deep penetration of deuterium into layered surface structures.

  • 1183.
    Zhou, Yushan
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Paneta, C.
    Possnert, G.
    Micro ion beam analysis for the erosion of beryllium marker tiles in a tokamak limiter2019Inngår i: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 450, s. 200-204Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Beryllium limiter marker tiles were exposed to plasma in the Joint European Torus to diagnose the erosion of main chamber wall materials. A limiter marker tile consists of a beryllium coating layer (7–9 μm) on the top of bulk beryllium, with a nickel interlayer (2–3 μm) between them. The thickness variation of the beryllium coating layer, after exposure to plasma, could indicate the erosion measured by ion beam analysis with backscattering spectrometry. However, interpretations from broad beam backscattering spectra were limited by the non-uniform surface structures. Therefore, micro-ion beam analysis (μ-IBA) with 3 MeV proton beam for Elastic backscattering spectrometry (EBS) and PIXE was used to scan samples. The spot size was in the range of 3–10 μm. Scanned areas were analysed with scanning electron microscopy (SEM) as well. Combining results from μ-IBA and SEM, we obtained local spectra from carefully chosen areas on which the surface structures were relatively uniform. Local spectra suggested that the scanned area (≈600 μm × 1200 μm) contained regions with serious erosion with only 2–3 μm coating beryllium left, regions with intact marker tile, and droplets with 90% beryllium. The nonuniform erosion, droplets mainly formed by beryllium, and the possible mixture of beryllium and nickel were the major reasons that confused interpretation from broad beam EBS.

  • 1184.
    Zhou, Yushan
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Possnert, G.
    Likonen, J.
    Pettersson, J.
    Koivuranta, S.
    Widdowson, A. M.
    Microanalysis of deposited layers in the inner divertor of JET with ITER-like wall2017Inngår i: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, s. 412-417Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In JET with ITER-like wall, beryllium eroded in the main chamber is transported to the divertor and deposited mainly at the horizontal surfaces of tiles 1 and 0 (high field gap closure, HFGC). These surfaces are tungsten coated carbon fibre composite (CFC). Surface sampleswere collected following the plasma operations in 2011-2012 and 2013-2014 respectively. The surfaces, as well as polished cross sections of the deposited layers at the surfaces have been studied with micro ion beam analysis methods (mu-IBA). Deposition of Beand other impurities, and retention of D is microscopically inhomogeneous. Impurities and trapped deuterium accumulate preferentially in cracks, pits and depressed regions, and at the sides of large pits in the substrate (e.g. arc tracks where the W coating has been removed). With careful overlaying of mu-NRA elemental maps with optical microscopy images, it is possible to separate surface roughness effects from depth profiles at microscopically flat surface regions.

  • 1185.
    Zhou, Yushan
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Modelling of effect from rough surface on deuterium and beryllium deposition on divertor targetManuskript (preprint) (Annet vitenskapelig)
  • 1186.
    Zhou, Yushan
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Possnert, G
    Likonen, J
    contributors, JET
    The effect of gyration on the deposition of beryllium and deuterium at rough surface on thedivertor tiles with ITER-like-wall in JET2019Inngår i: Nuclear Materials and Energy, E-ISSN 2352-1791Artikkel i tidsskrift (Fagfellevurdert)
  • 1187.
    Zyuzin, Alexander
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Zyuzin, A. Y.
    Chiral anomaly and second-harmonic generation in Weyl semimetals2017Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 95, nr 8, artikkel-id 085127Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study second-harmonic generation in centrosymmetric Weyl semimetal with broken time reversal symmetry. We calculate electric current density at the double frequency of the propagating electromagnetic field in the presence of an applied constant magnetic field, using the method of kinetic equation for electron distribution function. It is shown that the chiral anomaly contribution to second-harmonic generation in the lowest order is linearly proportional to the applied magnetic field. The limit when the chiral anomaly dominates over the Lorentz-type contribution to second-harmonic generation is discussed.

  • 1188.
    Åström, K.
    KTH, Tidigare Institutioner.
    On relativistic dust grains and extensive air showers1977Rapport (Annet vitenskapelig)
  • 1189.
    Åström, Kjell
    KTH, Tidigare Institutioner.
    Beräkning av my-mesonernas energispektrum vid jordytan i zenitriktningen1981Rapport (Annet vitenskapelig)
  • 1190.
    Öberg, Johnny
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Tuning of JET Transmission Line/Antenna System During ICRH1993Independent thesis Advanced level (degree of Master (Two Years)), 12 poäng / 18 hpOppgave
  • 1191.
    Öster, Jonas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Spatial correlation between lightning strikes and whistler observations2008Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    A whistler wave is a Very Low frequency (VLF) trace that obtains its characteristics from dispersive propagation in the magnetosphere. Field-aligned ducts of enhanced plasma density ensure the propagation from one hemisphere to the other. The origin of these signals is lightning strikes that emit radiation which spans the entire spectrum with the bulk being in the VLF band. The VLF portion can travel great distances within the Earth-ionosphere waveguide (EIWG) before penetrating through the ionosphere, and exciting a duct. The relative location, compared to the duct, of those strikes that cause whistlers is unknown. It is of interest to examine where the whistlers that have been observed at Tihany, Hungary, and Dunedin, Nerv Zealand, originate. This is one tool to gain further understanding of the properties, especially the plasma density structure, of the ionosphere and the magnetosphere. Therefore time series with observed whistlers from these stations has been correlated with lightning data obtained from the World Wide Lightning Location Network (WWLLN). The results show that whistlers observed at Tihany mainly originate from lightning in an area surrounding the magnetic conjugate point which is situated in the ocean just off East London, South Africa. This area, called the source region, has a radius slightly less than 1000 km. Whistlers also originate from lightning activity over the rest of Southern Africa and the northern parts of South America. A clear diurnal distinction is seen in that the correlation is maximized when the whistler station and the source region are covered in darkness. This is believed to relate to the diurnal variation of the ionospheric profile, which becomes more transparent to VLF waves at night. A similar diurnal correlation pattern for Dunedin was also obtained. The general correlation results for Dunedin were very sporadic. Whistler statistics for the two stations and lightning statistics for the Tihany's magnetic conjugate point are also presented. It reveals a general diurnal maximum in received whistlers in dark hours for Tihany with absolute maximum at 1 UTC and for Dunedin, the maximum occurs in the afternoon with absolute maximum at 15 UTC. It also reveals a seasonal maximum when the conjugate point is in the summer season. The lightning statistics for Tihany's magnetic conjugate point reveals a diurnal maximurn ranging from the afternoon until a couple of hour after midnight. Something worth noting is the delay between the peaks of lightning activity and whistler registration at Tihany. The lightning activity peaks around 18 UTC. The explanation is once again believed to relate to the behavior of the ionosphere in darkness.

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