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  • 1.
    Alvarez Ruiz, Jesus
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Melero-Garcia, Emilio
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Kivimäki, Antti
    Coreno, M.
    Erman, Peter
    KTH, School of Engineering Sciences (SCI), Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Richter, R.
    Synchrotron radiation induced fluorescence spectroscopy of SF62005In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 38, p. 387-Article in journal (Refereed)
    Abstract [en]

    The fluorescence of gaseous SF6 was investigated after excitation with 25-80eV synchrotron radiation photons. The total UV-Vis-near IR fluorescence yield was recorded and interpreted in terms of inner valence excitations/ionizations and double excitations in SF6. Dispersed fluorescence measurements in the 400-1000 nm spectral range reveal excited S, S+, F and F+ fragments as solely responsible for the emission. The fluorescence intensity of some of the observed atomic transitions was monitored as a function of the excitation energy. Single, double and triple excitations as well as direct ionizations and shake-ups are proposed as the triggering processes responsible for the creation of the emitting fragments.

  • 2. Bengtsson, Lennart
    et al.
    Rachlew (Källne), Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Wagner, Friedrich
    Sustainable energy supply and consumption by 2050 and outlook towards the end of the century: Possible scientific breakthroughs2016In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 45, no Suppl. 1):, p. 1-4Article, review/survey (Refereed)
  • 3.
    Bergsåker, Henric
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Drake, James R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Metal impurity fluxes and plasma-surface interactions in EXTRAP T2R2008In: PROCEEDINGS OF THE 17TH INTERNATIONAL VACUUM CONGRESS/13TH INTERNATIONAL CONFERENCE ON SURFACE SCIENCE/INTERNATIONAL CONFERENCE ON NANOSCIENCE AND TECHNOLOGY, 2008, Vol. 100Conference paper (Refereed)
    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.

  • 4. Beurskens, M. N. A.
    et al.
    Arnoux, G.
    Brezinsek, A. S.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Saarelma, S.
    Solano, E.
    et al,
    Pedestal and ELM response to impurity seeding in JET advanced scenario plasmas2008In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 48, no 9Article in journal (Refereed)
    Abstract [en]

    Advanced scenario plasmas must often be run at low densities and high power, leading to hot edge temperatures and consequent power handling issues at plasma - surface interaction zones. Experiments at JET are addressing this issue by exploring the use of extrinsic impurity seeding and D-2 puffing to reduce heat fluxes. The experiments presented in this paper continue the line of advanced tokamak ( AT) scenario studies at high triangularity in JET by concentrating on the characterization of the edge pedestal and the ELM behaviour with deuterium and/or light impurity fuelling (neon, nitrogen). Both injection of extrinsic impurities and D2 puffing are shown to have a significant impact on the edge pedestal in typical JET AT conditions. The ELM energy loss, Delta W-ELM/W-dia, can be reduced to below 3% and the maximum ELM penetration depth can be limited to r/a > 0.7, thus enhancing the possibility for sustainable internal transport barriers at large plasma radius. These conditions can be achieved in two separate domains, either at a radiated power fraction (F-rad) of 30% or at a fraction of > 50%. At the lower Frad the ELMs are type I and a high pedestal pressure is maintained, but the occasional large ELM may still occur. At F-rad > 50% the pedestal pressure is degraded by 30-50%, but the ELMs are degraded to type III. The intermediate regime at F-rad similar to 40% is unattractive for ITB scenarios because large type I ELMs occur intermittently during the predominantly type III ELM phases (compound type I/III). F-rad = 30% can be obtained with D-2 fuelling alone, whereas neon or nitrogen seeding is needed to achieve F-rad > 50%. Only a limited number of tests have been carried out with nitrogen seeding, with the preliminary conclusion that the plasma edge behaviour is similar to that with neon seeding once the radiated fraction is matched.

  • 5.
    Brunsell, Per
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Olofsson, K. Erik J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Yadikin, D.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Kuldkepp, Mattias
    KTH, School of Engineering Sciences (SCI), Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rachlew, Elisabethth
    KTH, School of Engineering Sciences (SCI), Physics.
    Resistive wall mode feedback control experiments in EXTRAP T2R2007In: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, 2007, p. 544-547Conference paper (Refereed)
    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.

  • 6.
    Brunsell, Per R.
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Kuldkepp, Mattias
    KTH, School of Engineering Sciences (SCI), Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Hedqvist, Anders
    KTH, School of Engineering Sciences (SCI), Physics.
    Yadikin, Dimitry
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Reversed field pinch operation with intelligent shell feedback control in EXTRAP T2R2006In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 46, no 11, p. 904-913Article in journal (Refereed)
    Abstract [en]

    Discharges in the thin shell reversed field pinch (RFP) device EXTRAP T2R without active feedback control are characterized by growth of non-resonant m = 1 unstable resistive wall modes (RWMs) in agreement with linear MHD theory. Resonant m = 1 tearing modes (TMs) exhibit initially fast rotation and the associated perturbed radial fields at the shell are small, but eventually TMs wall-lock and give rise to a growing radial field. The increase in the radial field at the wall due to growing RWMs and wall-locked TMs is correlated with an increase in the toroidal loop voltage, which leads to discharge termination after 3-4 wall times. An active magnetic feedback control system has been installed in EXTRAP T2R. A two-dimensional array of 128 active saddle coils (pair-connected into 64 independent m = 1 coils) is used with intelligent shell feedback control to suppress the m = 1 radial field at the shell. With feedback control, active stabilization of the full toroidal spectrum of 16 unstable m = 1 non-resonant RWMs is achieved, and TM wall locking is avoided. A three-fold extension of the pulse length, up to the power supply limit, is observed. Intelligent shell feedback control is able to maintain the plasma equilibrium for 10 wall times, with plasma confinement parameters sustained at values comparable to those obtained in thick shell devices of similar size.

  • 7.
    Brunsell, Per
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Yadikin, Dmitriy
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Zanca, P.
    Active control of multiple resistive wall modes2005In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 47, no 12 B, p. B25-B36Article in journal (Refereed)
    Abstract [en]

     A two-dimensional array of saddle coils at M-c poloidal and N-c toroidal positions is used on the EXTRAP T2R reversed-field pinch (Brunsell P R et al 2001 Plasma Phys. Control. Fusion 43 1457) to study active control of resistive wall modes (RWMs). Spontaneous growth of several RWMs with poloidal mode number m = 1 and different toroidal mode number n is observed experimentally, in agreement with linear MHD modelling. The measured plasma response to a controlled coil field and the plasma response computed using the linear circular cylinder MHD model are in quantitive agreement. Feedback control introduces a linear coupling of modes with toroidal mode numbers n, n' that fulfil the condition vertical bar n - n'vertical bar = N-c. Pairs of coupled unstable RWMs are present in feedback experiments with an array of Mc x Nc = 4 x 16 coils. Using intelligent shell feedback, the coupled modes are generally not controlled even though the field is suppressed at the active coils. A better suppression of coupled modes may be achieved in the case of rotating modes by using the mode control feedback scheme with individually set complex gains. In feedback with a larger array of Mc x Nc = 4 x 32 coils, the coupling effect largely disappears, and with this array, the main internal RWMs n = -11, -10, +5, +6 are all simultaneously suppressed throughout the discharge (7-8 wall times). With feedback there is a two-fold extension of the pulse length, compared to discharges without feedback.

  • 8. Challis, C. D.
    et al.
    Joffrin, E.
    Luce, T.
    Buratti, P.
    De Vries, P.
    Hobirk, J.
    Alper, B.
    Brix, M.
    Felton, R.
    Ferron, J.
    Giroud, C.
    Gryaznevich, M.
    Hawkes, N.
    Hender, T. C.
    Howell, D.
    Menard, J.
    Murakami, M.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Saarelma, S.
    Sharapov, S.
    Tudisco, O.
    Voitsekhovitch, I.
    Zimmermann, O.
    High βN JET H-modes for steady-state application2007In: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, European Physical Society , 2007, no 3, p. 2118-2121Conference paper (Refereed)
  • 9. Conway, N. J.
    et al.
    De Bock, M. F. M.
    Michael, C. A.
    Walsh, M. J.
    Carolan, P. G.
    Hawkes, N. C.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    McCone, J. F. G.
    Shibaev, S.
    Wearing, G.
    The MAST motional Stark effect diagnostic2010In: REVIEW OF SCIENTIFIC INSTRUMENTS, Melville, NY: AMER INST PHYSICS , 2010, Vol. 81, no 10, p. 10D738-Conference paper (Refereed)
    Abstract [en]

    A motional Stark effect (MSE) diagnostic is now installed and operating routinely on the MAST spherical tokamak, with 35 radial channels, spatial resolution of similar to 2.5 cm, and time resolution of similar to 1 ms at angular noise levels of similar to 0.5 degrees. Conventional (albeit very narrow) interference filters isolate pi or sigma polarized emission. Avalanche photodiode detectors with digital phase-sensitive detection measure the harmonics of a pair of photoelastic modulators operating at 20 and 23 kHz, and thus the polarization state. The pi component is observed to be significantly stronger than sigma, in reasonably good agreement with atomic physics calculations, and as a result, almost all channels are now operated on pi. Trials with a wide filter that admits the entire Stark pattern (relying on the net polarization of the emission) have demonstrated performance almost as good as the conventional channels. MSE-constrained equilibrium reconstructions can readily be produced between pulses.

  • 10. Coreno, M.
    et al.
    Kivimaeki, A.
    de Simone, M.
    Garcia, E. Melero
    Vall-Llosera, G.
    Ruiz, J. Alvarez
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Stankiewicz, M.
    Vis-UV fluorescence studies of fragments resulting from the relaxation of molecular core hole states2007In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 76, no 3, p. C90-C95Article in journal (Refereed)
    Abstract [en]

    The absorption of soft x-ray radiation induces neutral and ionic core hole states in molecules. The relaxation of such states typically leads to a multi-step process, at the end of which photons in the visible and UV range can also be emitted from fragments. In this paper, we present results on Balmer and Lyman emission that originates from excited H atoms produced at the K-edge of the water, ammonia and methane molecules. Dissociation pathways leading to fluorescence emission are discussed.

  • 11. Corre, Y.
    et al.
    Joffrin, E.
    Monier-Garbet, P.
    Andrew, Y.
    Arnoux, G.
    Beurskens, M.
    Brezinsek, S.
    Brix, M.
    Buttery, R.
    Coffey, I.
    Crombe, K.
    de La Luna, E.
    Felton, R.
    Giroud, C.
    Hacquin, S.
    Hobirk, J.
    Huber, A.
    Imbeaux, F.
    Jachmich, S.
    Kempenaars, M.
    Litaudon, X.
    Leggate, H.
    Loarer, T.
    Maddison, G.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Rapp, J.
    Sauter, O.
    Savchkov, A.
    Telesca, G.
    Widdowson, A.
    Zastrow, K. D.
    Zimmermann, O.
    Hybrid H-mode scenario with nitrogen seeding and type III ELMs in JET2008In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 50, no 11, p. 115012-Article in journal (Refereed)
    Abstract [en]

    The performance of the 'hybrid' H-mode regime (long pulse operation with high neutron fluency) has been extensively investigated in JET during the 2005-2007 experimental campaign up to normalized pressure beta(N) = 3, toroidal magnetic field B-t = 1.7T, with type I ELMs plasma edge conditions. The optimized external current drive sources, self-generated non-inductive bootstrap current and plasma core stability properties provide a good prospect of achieving a high fusion gain at reduced plasma current for long durations in ITER. One of the remaining issues is the erosion of the divertor target plates associated with the type I ELM regime. A possible solution could be to operate with a plasma edge in the type III ELM regime (reduced transient and stationary heat loads) obtained with impurity seeding. An integrated hybrid type III ELM regime with a normalized pressure beta(N) = 2.6 (PNBI similar to 20-22 MW) and a thermal confinement factor of H-98* 98(y, 2) similar to 0.83 has been recently successfully developed on JET with nitrogen seeding. This scenario shows good plasma edge condition (compatible with the future ITER-like wall on JET) and moderate MHD activity. In this paper, we report on the experimental development of the scenario (with plasma current I-p = 1.7MA and magnetic field B-t = 1.7T) and the trade-off between heat load reduction at the target plates and global confinement due to nitrogen seeding and type III ELM working conditions.

  • 12. Corre, Y.
    et al.
    Joffrin, E.
    Monier-Garbet, P.
    Andrew, Y.
    Arnoux, G.
    Brezinsek, S.
    Brix, M.
    Buttery, R.
    Coffey, I.
    Crombe, K.
    De La Luna, E.
    Felton, R.
    Giroud, C.
    Hacquin, S.
    Hobirk, J.
    Huber, A.
    Imbeaux, F.
    Jachmich, S.
    Kempenaars, M.
    Leggate, H.
    Loarer, T.
    Maddison, G.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Rapp, J.
    Sauter, O.
    Savchkov, A.
    Tabares, F.
    Telesca, G.
    Widdowson, A.
    Zastrow, K. D.
    Zimmermann, O.
    Hybrid H-mode scenario with nitrogen seeding and type III ELMs in JET2007In: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, European Physical Society , 2007, no 3, p. 2206-2209Conference paper (Refereed)
  • 13. Corre, Y.
    et al.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Cecconello, M.
    Gravestijn, R. M.
    Hedqvist, A.
    Pegourie, B.
    Schunke, B.
    Stancalie, V.
    Radiated power and impurity concentrations in the EXTRAP-T2R reversed-field pinch2005In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 71, no 5, p. 523-531Article in journal (Refereed)
    Abstract [en]

    A numerical and experimental study of the impurity concentration and radiation in the EXTRAP-T2R device is reported. The experimental setup consists of an 8-chord bolometer system providing the plasma radiated power and a vacuum-ultraviolet spectrometer providing information on the plasma impurity content. The plasma emissivity profile as measured by the bolometric system is peaked in the plasma centre. A one dimensional Onion Skin Collisional-Radiative model (OSCR) has been developed to compute the density and radiation distributions of the main impurities. The observed centrally peaked emissivity profile can be reproduced by OSCR simulations only if finite particle confinement time and charge-exchange processes between plasma impurities and neutral hydrogen are taken into account. The neutral hydrogen density profile is computed with a recycling code. Simulations show that recycling on metal first wall such as in EXTRAP-T2R (stainless steel vacuum vessel and molybdenum limiters) is compatible with a rather high neutral hydrogen density in the plasma centre. Assuming an impurity concentration of 10% for oxygen and 3% for carbon compared with the electron density, the OSCR calculation including lines and continuum emission reproduces about 60% of the total radiated power with a similarly centrally peaked emmissivity profile. The centrally peaked emissivity profile is due to low ionisation stages and strongly radiating species in the plasma core, mainly O4+ (Be-like) and C3+ (Li-like).

  • 14. Crombé, K.
    et al.
    Andrew, Y.
    Biewer, T. M.
    Blanco, E.
    Brix, M.
    De Vries, P.
    Fonseca, A.
    Giroud, C.
    Hawkes, N. C.
    Joffrin, E.
    Mantica, P.
    Meigs, A.
    Naulin, V.
    Pinches, S.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Tala, T.
    Whiteford, A.
    Influence of rotational shear on triggering and sustainment of internal transport barriers on JET2009In: 36th EPS Conference on Plasma Physics 2009, EPS 2009 - Europhysics Conference Abstracts, 2009, p. 797-800Conference paper (Refereed)
  • 15. De Angelis, R.
    et al.
    Baruzzo, M.
    Buratti, P.
    Alper, B.
    Barrera, L.
    Botrugno, A.
    Brix, M.
    Figini, L.
    Fonseca, A.
    Giroud, C.
    Hawkes, N.
    Howell, D.
    De la Luna, E.
    Orsitto, F.
    Pericoli, V.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Tudisco, O.
    Localization of MHD modes and consistency with q-profiles in JET2010In: NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH: SECTION A - ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT    , 2010, Vol. 623, no 2, p. 734-737Conference paper (Refereed)
    Abstract [en]

    The measurement of the safety factor q in tokamaks, which describes the winding of the helical magnetic field lines, is very important especially for the achievement of advanced scenarios. The motional Stark effect diagnostic can provide a direct measurement of the magnetic field orientation but the derivation of the q-profiles requires a simulation of the magnetic equilibrium taking into account inputs from several other diagnostics. This analysis can be affected by large errors. In order to validate the results, q-profiles are compared with the radii of MHD modes, which can be attributed to surfaces of known q.

  • 16. De Angelis, R.
    et al.
    Orsitto, F.
    Brix, M.
    Hawkes, N.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Botrugno, A.
    Buratti, P.
    Fonseca, A.
    Howell, D.
    Pericoli, V.
    Tudisco, O.
    Current profile measurements in JET Advanced Tokamak scenarios2009In: 36th EPS Conference on Plasma Physics 2009, EPS 2009 - Europhysics Conference Abstracts, 2009, p. 721-724Conference paper (Refereed)
  • 17.
    Drake, James Robert
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Yadikin, Dmitriy
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hedqvist, Anders
    KTH, School of Engineering Sciences (SCI), Physics.
    Kuldkepp, Mattias
    KTH, School of Engineering Sciences (SCI), Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Experiments on feedback control of multiple resistive wall modes comparing different active coil arrays and sensor types2006In: IAEA-F1-CN-149, 2006, p. Paper EX/P8-11-Conference paper (Refereed)
  • 18. Ekedahl, A.
    et al.
    Petrzilka, V.
    Baranov, Y.
    Biewer, T. M.
    Brix, M.
    Goniche, M.
    Jacquet, P.
    Kirov, K. K.
    Klepper, C. C.
    Mailloux, J.
    Mayoral, M-L
    Nave, M. F. F.
    Ongena, J.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Influence of gas puff location on the coupling of lower hybrid waves in JET ELMy H-mode plasmas2012In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 54, no 7, p. 074004-Article in journal (Refereed)
    Abstract [en]

    Reliable coupling of the lower hybrid current drive (LHCD) to H-mode plasmas in JET is made feasible through a dedicated gas injection system, located at the outer wall and magnetically connected to the antenna (Pericoli Ridolfini et al 2004 Plasma Phys. Control. Fusion 46 349, Ekedahl et al 2005 Nucl. Fusion 45 351, Ekedahl et al 2009 Plasma Phys. Control. Fusion 51 044001). An experiment was carried out in JET in order to investigate whether a gas injection from the top of the torus, as is foreseen for the main gas injection in ITER, could also provide good coupling of the LH waves if magnetically connected to the antenna. The results show that a top gas injection was not efficient for providing a reliable LHCD power injection, in spite of being magnetically connected and in spite of using almost twice the amount of gas flow compared with the dedicated outer mid-plane gas puffing system. A dedicated gas injection system, set in the outer wall and magnetically connected to the LHCD antenna, is therefore recommended in order to provide the reliable coupling conditions for an LHCD antenna in ITER.

  • 19. Ekedahl, A.
    et al.
    Rantamaki, K.
    Goniche, M.
    Mailloux, J.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    et al,
    Effect of gas injection during LH wave coupling at ITER-relevant plasma-wall distances in JET2009In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 51, no 4Article in journal (Refereed)
    Abstract [en]

    Good coupling of lower hybrid (LH) waves has been demonstrated in different H-mode scenarios in JET, at high triangularity (delta similar to 0.4) and at large distance between the last closed flux surface and the LH launcher ( up to 15 cm). Local gas injection of D-2 in the region magnetically connected to the LH launcher is used for increasing the local density in the scrape-off layer ( SOL). Reciprocating Langmuir probe measurements magnetically connected to the LH launcher indicate that the electron density profile flattens in the far SOL during gas injection and LH power application. Some degradation in normalized H-mode confinement, as given by the H98(gamma,2)-factor, could be observed at high gas injection rates in these scenarios, but this was rather due to total gas injection and not specifically to the local gas puffing used for LH coupling. Furthermore, experiments carried out in L-mode plasmas in order to evaluate the effect on the LH current drive efficiency, when using local gas injection to improve the coupling, indicate only a small degradation (Delta I-LH/I-LH similar to 15%). This effect is largely compensated by the improvement in coupling and thus increase in coupled power when using gas puffing.

  • 20. Erman, P.
    et al.
    Karawajczyk, A.
    Rachlew-Källne, Elisabeth
    KTH, Superseded Departments, Physics.
    Riu, J. R. I.
    Stankiewicz, M.
    Franzen, K. Y.
    Moen, A. W.
    Veseth, L.
    Non Franck-Condon effects in photoionization of molecular oxygen2000In: Physica scripta. T, ISSN 0281-1847, Vol. 62, no 4, p. 294-300Article in journal (Refereed)
    Abstract [en]

    We present a theoretical and experimental analysis of non Franck-Condon effects in photoionization to the b (4)Sigma(g)(-), state of O-2(+). Experimentally, by dispersing the synchrotron radiation induced O-2(+) b (4)Sigma(g)(-) a (IIu)-I-4 fluorescence we derive the b (4)Sigma(g)(-), State vibrational branching ratios in the excitation energy range 21-34 eV. The vibrational branching ratios reveal features in the region 21-28 eV indicating strong non Franck-Condon effects. The experimental results have been analysed by computing ab initio the vibrational population branching ratios using a many-body perturbation method. Additionally the autoionizing neutral states existing in this energy region have been studied. We have computed the energies of the valence states up to an energy of 30 eV their transition moments for excitations from the ground state, and autoionization rates. Our calculations show, that strong non Franck-Condon effects recorded in the branching ratio spectrum (below 25 eV) are actually caused by the narrow 3 sigma(g) --> sigma(u) shape resonance, and its coupling to the 1 pi(u) --> pi(g) channel.

  • 21.
    Frassinetti, Lorenzo
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Saarelma, S.
    Lomas, P.
    Nunes, I.
    Rimini, F.
    Beurskens, M. N. A.
    Bilkova, P.
    Boom, J. E.
    de la Luna, E.
    Delabie, E.
    Drewelow, P.
    Flanagan, J.
    Garzotti, L.
    Giroud, C.
    Hawks, N.
    Joffrin, E.
    Kempenaars, M.
    Kim, Hyun-Tae
    Kruezi, U.
    Loarte, A.
    Lomanowski, B.
    Lupelli, I.
    Meneses, L.
    Maggi, C. F.
    Menmuir, S.
    Peterka, M.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Romanelli, M.
    Stefanikova, E.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Dimensionless scalings of confinement, heat transport and pedestal stability in JET-ILW and comparison with JET-C2017In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 59, no 1, article id 014014Article in journal (Refereed)
    Abstract [en]

    Three dimensionless scans in the normalized Larmor radius rho*, normalized collisionality nu* and normalized plasma pressure beta have been performed in JET with the ITER-like wall (JET-ILW). The normalized energy confinement and the thermal diffusivity exhibit a scaling with rho* consistent with the earlier results obtained in the carbon wall JET (JET-C) and with a gyro-Bohm scaling. In the pedestal, experimental results show that the stability is not dependent on rho*, qualitatively in agreement with the peeling-ballooning (P-B) model. The nu* dimensionless scaling shows that JET-ILW normalized confinement has a stronger dependence on collisionality than JET-C. This leads to a reduction of the difference in the confinement between JET-ILW and JET-C to approximate to 10% at low nu*. The pedestal stability shows an improvement with decreasing nu*. This is ascribed to the increase of the bootstrap current, to the reduction of the pedestal width and to the reduction of the relative shift between pedestal density and temperature position. The beta dimensionless scan shows that, at low collisionality, JET-ILW normalized confinement has no clear dependence with beta, in agreement with part of the earlier scalings. At high collisionality, a reduction of the normalized confinement with increasing beta is observed. This behaviour is driven mainly by the pedestal where the stability is reduced with increasing beta. The P-B analysis shows that the stability reduction with increasing beta at high nu* is due to the destabilizing effect of the increased relative shift.

  • 22.
    García, Emilio Melero
    et al.
    KTH, Superseded Departments, Physics.
    Álvarez Ruiz, Jesús
    KTH, Superseded Departments, Physics.
    Erman, Peter
    KTH, Superseded Departments, Physics.
    Kivimäki, Antti Eerik
    KTH, Superseded Departments, Physics.
    Rachlew-Källne, Elisabeth
    KTH, Superseded Departments, Physics.
    Rius Riu, Jaume
    KTH, Superseded Departments, Physics.
    Stankiewicz, Marek
    KTH, Superseded Departments, Physics.
    Veseth, V.
    Neutral dissociation of superexcited states in nitric oxide2003In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 293, no 1, p. 65-73Article in journal (Refereed)
    Abstract [en]

    Near-infrared dispersed fluorescence measurements of 13 different atomic multiplets of neutral atomic fragments from photon induced neutral dissociation processes in NO are reported. For excitation of the molecules narrow band synchrotron photons of energy 17.2-25.8 eV were used. Neither Rydberg series nor other molecular states in NO known so far can account for the collected data. From ab initio calculations we try to obtain more information regarding the NO precursor states, and the mechanism behind the observed neutral dissociation.

  • 23.
    Gravestijn, Robert
    et al.
    KTH, Superseded Departments, Physics.
    Drake, James R.
    KTH, Superseded Departments, Alfvén Laboratory.
    Hedqvist, Anders
    KTH, Superseded Departments, Physics.
    Rachlew, Elisabeth
    KTH, Superseded Departments, Physics.
    Comparison of confinement in resistive-shell reversed-field pinch devices with two different magnetic shell penetration times2004In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 46, no 1, p. 11-22Article in journal (Refereed)
    Abstract [en]

    A loop voltage is required to sustain the reversed-field pinch (RFP) equilibrium. The configuration is characterized by redistribution of magnetic helicity but with the condition that the total helicity is maintained constant. The magnetic field shell penetration time, tau(s), has a critical role in the stability and performance of the RFP Confinement in the EXTRAP device has been studied with two values of tau(s), first (EXTRAP-T2) with tau(s), of the order of the typical relaxation cycle timescale and then (EXTRAP-T2R) with tau(s), much longer than the relaxation cycle timescale, but still much shorter than the pulse length. Plasma parameters show significant improvements in confinement in EXTRAP-T2R. The typical loop voltage required to sustain comparable electron poloidal beta values is a factor of 3 lower in the EXTRAP-T2R device. The improvement is attributed to reduced magnetic turbulence.

  • 24. Hawkes, N. C.
    et al.
    Andrew, Y.
    Challis, C. D.
    DeAngelis, R.
    Drozdov, V.
    Hobirk, J.
    Joffrin, E.
    Lotte, P.
    Mazon, D.
    Rachlew, Elisabeth
    KTH, Superseded Departments, Physics.
    Reyes-Cortes, S.
    Sattin, F.
    Solano, E.
    Stratton, B. C.
    Tala, T.
    Valisa, M.
    Efda Jet Workprogramme,
    The formation and evolution of extreme shear reversal in JET and its influence on local thermal transport2002In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 44, no 7, p. 1105-1125Article in journal (Refereed)
    Abstract [en]

    In JET discharges where lower hybrid heating and current drive (LHCD) is applied early during the current ramp, a region of the plasma with zero current density is formed near the axis. At the boundary of this region the current density is large and B-theta increases rapidly over a small distance. In the central region the safety factor, q, is effectively infinite, but this falls steeply in the boundary region. Outside the boundary region q reaches a minimum, where the magnetic shears equivalent to r/q (dq/dr) becomes zero. The formation of this region of zero current is dependent on both the heating and the current drive effects of the LHCD. When LHCD is switched off the current profile begins to relax towards the resistive peaked current distribution of fully inductive tokamak operation. If LHCD is not used in the current rise then these current profiles are not established. Although the physical mechanism exists to drive the central plasma current below zero, in most cases it appears to be prevented from going negative. At least one MHD mechanism has been identified which could be responsible for this. The presence of the zero central current is closely linked to the periodic relaxation events seen in these discharges. In these discharges, internal transport barriers have been observed with additional heating powers substantially below the values required to obtain barriers in monotonic q profile cases.

  • 25. Hawkes, N. C.
    et al.
    Stratton, B. C.
    Tala, T.
    Challis, C. D.
    Conway, G.
    DeAngelis, R.
    Giroud, C.
    Hobirk, J.
    Joffrin, E.
    Lomas, P.
    Lotte, P.
    Mailloux, J.
    Mazon, D.
    Rachlew, Elisabeth
    KTH, Superseded Departments, Physics.
    Reyes-Cortes, S.
    Solano, E.
    Zastrow, K. D.
    Observation of zero current density in the core of JET discharges with lower hybrid heating and current drive2001In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 8711, no 11, p. art. no.-115001Article in journal (Refereed)
    Abstract [en]

    Simultaneous current ramping and application of lower hybrid heating and current drive (LHCD) have produced a region with zero current density within measurement errors in the core (r/a less than or equal to 0.2) of JET tokamak optimized shear discharges. The reduction of core current density is consistent with a simple physical explanation and numerical simulations of radial current diffusion including the effects of LHCD. However, the core current density is clamped at zero, indicating the existence of a physical mechanism which prevents it from becoming negative.

  • 26.
    Hedqvist, Anders
    et al.
    KTH, Superseded Departments, Physics.
    O'Mullane, Martin
    Nordquist, Jonas
    KTH, Superseded Departments, Physics.
    Rachlew-Källne, Elisabeth
    KTH, Superseded Departments, Physics.
    Zastrow, Klaus-Dieter
    JET Joint Undertaking, United Kingdom .
    Contributions of thermal charge exchange excitation to the Rydberg series of Cl16+2000In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 33, no 3, p. 375-382Article in journal (Refereed)
    Abstract [en]

    Spectra from the Rydberg series 1s-np for the principal quantum numbers n greater than or equal to 8 of Cl16+ are observed on the JET tokamak. Individual lines up to n = 15 are resolved. The line intensity of n = 10 is enhanced, relative to the underlying 1/n(3) scaling, due to charge exchange collisions with neutral deuterium in the ground state. The observations are compared with predictions based on available partial charge exchange cross section data. There is generally good agreement, however, some details of the predicted n-shell distribution are different from those observed in the experiment.

  • 27. Hobirk, J.
    et al.
    Imbeaux, F.
    Crisanti, F.
    Buratti, P.
    Challis, C. D.
    Joffrin, E.
    Alper, B.
    Andrew, Y.
    Beaumont, P.
    Beurskens, M.
    Boboc, A.
    Botrugno, A.
    Brix, M.
    Calabro', G.
    Coffey, I.
    Conroy, S.
    Ford, O.
    Frigione, D.
    Garcia, J.
    Giroud, C.
    Hawkes, N. C.
    Howell, D.
    Jenkins, I.
    Keeling, D.
    Kempenaars, M.
    Leggate, H.
    Lotte, P.
    De La Luna, E.
    Maddison, G. P.
    Mantica, P.
    Mazzotta, C.
    McDonald, D. C.
    Meigs, A.
    Nunes, I.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Rimini, F.
    Schneider, M.
    Sips, A. C. C.
    Stober, J. K.
    Studholme, W.
    Tala, T.
    Tsalas, M.
    Voitsekhovitch, I.
    De Vries, P. C.
    Improved confinement in JET hybrid discharges2009In: 36th EPS Conference on Plasma Physics 2009, EPS 2009 - Europhysics Conference Abstracts, 2009, p. 150-153Conference paper (Refereed)
  • 28. Hobirk, J.
    et al.
    Imbeaux, F.
    Crisanti, F.
    Buratti, P.
    Challis, C. D.
    Joffrin, E.
    Alper, B.
    Andrew, Y.
    Beaumont, P.
    Beurskens, M.
    Boboc, A.
    Botrugno, A.
    Brix, M.
    Calabro', G.
    Coffey, I.
    Conroy, S.
    Ford, O.
    Frigione, D.
    Garcia, J.
    Giroud, C.
    Hawkes, N. C.
    Howell, D.
    Jenkins, I.
    Keeling, D.
    Kempenaars, M.
    Leggate, H.
    Lotte, P.
    De La Luna, E.
    Maddison, G. P.
    Mantica, P.
    Mazzotta, C.
    McDonald, D. C.
    Meigs, A.
    Nunes, I.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Rimini, F.
    Schneider, M.
    Sips, A. C. C.
    Stober, J. K.
    Studholme, W.
    Tala, T.
    Tsalas, M.
    Voitsekhovitch, I.
    De Vries, P. C.
    Improved confinement in JET hybrid discharges2012In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 54, no 9, p. 095001-Article in journal (Refereed)
    Abstract [en]

    A new technique has been developed to produce plasmas with improved confinement relative to the H 98,y2 scaling law (ITER Physics Expert Groups on Confinement and Transport and Confinement Modelling and Database ITER Physics Basics Editors and ITER EDA 1999 Nucl. Fusion 39 2175) on the JET tokamak. In the mid-size tokamaks ASDEX upgrade and DIII-D heating during the current formation is used to produce a flat q-profile with a minimum close to 1. On JET this technique leads to q-profiles with similar minimum q but opposite to the other tokamaks not to an improved confinement state. By changing the method utilizing a faster current ramp with temporary higher current than in the flattop (current overshoot) plasmas with improved confinement (H 98,y2=1.35) and good stability (β N3) have been produced and extended to many confinement times only limited by technical constraints. The increase in H 98,y2-factor is stronger with more heating power as can be seen in a power scan. The q-profile development during the high power phase in JET is reproduced by current diffusion calculated by TRANSP and CRONOS. Therefore the modifications produced by the current overshoot disappear quickly from the edge but the confinement improvement lasts longer, in some cases up to the end of the heating phase.

  • 29. Horvath, Akos
    et al.
    Rachlew (Källne), Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Nuclear power in the 21st century: Challenges and possibilities2016In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 45, no Suppl. 1, p. 38-49Article, review/survey (Refereed)
    Abstract [en]

    The current situation and possible future developments for nuclear power—including fission and fusion processes—is presented. The fission nuclear power continues to be an essential part of the low-carbon electricity generation in the world for decades to come.

    There are breakthrough possibilities in the development of new generation nuclear reactors where the life-time of the nuclear waste can be reduced to some hundreds of years instead of the present time-scales of hundred thousand of years. Research on the fourth generation reactors is needed for the realisation of this development. For the fast nuclear reactors, a substantial research and development effort is required in many fields—from material sciences to safety demonstration—to attain the envisaged goals. Fusion provides a long-term vision for an efficient energy production. The fusion option for a nuclear reactor for efficient production of electricity has been set out in a focussed European programme including the international project of ITER after which a fusion electricity DEMO reactor is envisaged.

  • 30. Itala, E
    et al.
    Ha, D T
    Kooser, K
    Huels, M A
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Nommiste, E
    Joost, U
    Kukk, E
    Molecular fragmentation of pyrimidine derivatives following site-selective carbon core ionization2011In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 184, no 3-6, p. 119-124Article in journal (Refereed)
    Abstract [en]

    Ionization-site-dependent fragmentation of three cyclic biomolecules - uracil, 5-bromouracil and thymine - has been studied using electron-energy-resolved photoelectronphotoion-photoion coincidence spectroscopy. Previous studies concerning ionization site dependent fragmentation have mainly been carried out with linear molecules. The results reported here show that all studied molecules have dicationic fragmentation channels whose intensity depends on the initial core-ionization site, although these channels cover only a relatively small fraction of the total fragment yield. The present study shows on one hand, that it is often the surrounding bond(s) of the ionized atom that will break following the initial core ionization, and on the other hand, that some specific fragmentation channels can display strong site-dependency where there is no direct correlation between the ionization site and the bond breakage locations.

  • 31. Itala, E.
    et al.
    Ha, D. T.
    Kooser, K.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Huels, Michael A.
    KTH, School of Engineering Sciences (SCI), Physics.
    Kukk, E.
    Fragmentation patterns of core-ionized thymine and 5-bromouracil2010In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 133, no 15, p. 154316-Article in journal (Refereed)
    Abstract [en]

    Photofragmentation of thymine and 5-bromouracil into cation and neutral fragments following the core ionization by soft x-rays using photoelectron-photoion-photoion coincidence technique has been studied. The fragment ion mass spectra were recorded in coincidence with the C 1s photoelectron spectra. In the case of thymine, deuterated samples were used to identify fragments. Deuteration or bromination allowed us to study not only the main fragmentation channels of these pyrimidine bases, but also to investigate if replacement of an exocyclic functional group affects molecular fragmentation. We found that the dominant fragmentation channels involve only one starting geometry, and the base ring and other bond cleavages, leading to the detected fragments, are essentially identical between thymine and 5-bromouracil. In addition, the relative intensities of the strongest fragmentation channels were determined and compared with calculated appearance energies using ab initio unrestricted Hartree-Fock theory. (C) 2010 American Institute of Physics. [doi:10.1063/1.3505140]

  • 32. Itala, E.
    et al.
    Huels, M. A.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Kooser, K.
    Hagerth, T.
    Kukk, E.
    A comparative study of dissociation of thymidine molecules following valence or core photoionization2013In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 46, no 21, p. 215102-Article in journal (Refereed)
    Abstract [en]

    We have studied the fragmentation of gas phase thymidine following valence and core ionization using synchrotron radiation, combined with electron energy and ion mass resolved detection in coincidence. To identify certain fragment masses C-13 labelled thymidine was also used. We find that in large part, the photofragmentation of thymidine can be described as separated thymine and 2-deoxy-D-ribose cations. However, also the intact thymidine radical cation, formation of intact base and sugar cations from glycosidic bond cleavage and several new thymidine-specific fragments are observed after valence ionization. Conversely, at the photoionization of C 1s electrons neither parent thymidine cations nor any fragments above 55 amu were detected, and only ion pairs with small masses survive core ionization, Auger decay and the subsequent Coulomb separation of the DNA sub-unit. This demonstrates the genotoxic nature of soft x-rays which in cells induce complex clustered damage similar to those yielded by heavy particles.

  • 33. Itala, Eero
    et al.
    Kooser, Kuno
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Levola, Helena
    Ha, Dang Trinh
    Kukk, Edwin
    Gas-phase study on uridine: Conformation and X-ray photofragmentation2015In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 142, no 19, article id 194303Article in journal (Refereed)
    Abstract [en]

    Fragmentation of RNA nucleoside uridine, induced by carbon 1s core ionization, has been studied. The measurements by combined electron and ion spectroscopy have been performed in gas phase utilizing synchrotron radiation. As uridine is a combination of d-ribose and uracil, which have been studied earlier with the same method, this study also considers the effect of chemical environment and the relevant functional groups. Furthermore, since in core ionization the initial core hole is always highly localized, charge migration prior to fragmentation has been studied here. This study also demonstrates the destructive nature of core ionization as in most cases the C 1s ionization of uridine leads to concerted explosions producing only small fragments with masses <= 43 amu. In addition to fragmentation patterns, we found out that upon evaporation the sugar part of the uridine molecule attains hexagonal form.

  • 34. Itala, Eero
    et al.
    Levola, Helena
    Ha, Dang Trinh
    Kooser, Kuno
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Kukk, Edwin
    Photofragmentation of Serine Following C 1s Core Ionization-Comparison with Cysteine2016In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 120, no 28, p. 5419-5426Article in journal (Refereed)
    Abstract [en]

    Photofragmentation pathways of doubly ionized serine molecules are investigated and compared with those of cysteine. The main motivation for the study is to investigate if an atomic substitution within the same group of elements, namely, replacing sulfur (in cysteine) with oxygen (in serine), causes a major change in the C 1s core ionization induced dissociation pattern in the molecules of an otherwise identical structure. The results show that in serine there is a single completely dominant fragmentation channel producing the (CNH2-4+, COH1-3+) pairs, whereas in cysteine there are also many other fragmentation channels. The employed experimental method was the photoelectron-photoion-photoion coincidence (PEPIPICO) technique combined with synchrotron radiation tuned to ionize desired core levels. Molecular dynamics calculations were also carried out in order to extract information on the fragmentation and the neutral final fragments.

  • 35. Itälä, E.
    et al.
    Kooser, K.
    Hägerth, T.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Huels, M. A.
    Kukk, E.
    Photofragmentation of a DNA nucleoside thymidine; Valence-vs. core ionization2012In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 388, no PART 2, p. 022078-Article in journal (Refereed)
    Abstract [en]

    The photofragmentation of free thymidine molecule has been studied using combined electron- and ion spectroscopy. The results show that valence- and core ionization processes produce very different fragmentation patterns and that regardless of the photon energy, the photoionization leads almost always to dissociation of the thymidine molecule.

  • 36. Itälä, E.
    et al.
    Kooser, K.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Huels, M. A.
    Kukk, E.
    Soft x-ray ionization induced fragmentation of glycine2014In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, no 23, p. 234305-Article in journal (Refereed)
    Abstract [en]

    X-ray absorption commonly involves dissociative core ionization producing not only momentum correlated charged fragments but also low-and high-energy electrons capable of inducing damage in living tissue. This gives a natural motivation for studying the core ionization induced fragmentation processes in biologically important molecules such as amino acids. Here the fragmentation of amino acid glycine following carbon 1s core ionization has been studied. Using photoelectron-photoion-photoion coincidence technique, a detailed analysis on fragmentation of the sample molecule into pairs of momentum correlated cations has been carried out. The main characteristics of core ionization induced fragmentation of glycine were found to be the rupture of the C-C a bond and the presence of the CNH2+ fragment.

  • 37.
    Jakubowska, Katarzyna
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Brix, M.
    Hawkes, N. C.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Edge Localized Mode instability influence on the q-profile measured by Motional Stark Effect diagnostic on JET2007In: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, 2007, no 1, p. 583-586Conference paper (Refereed)
  • 38.
    Jakubowska, Katarzyna
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Vall-llosera, Gemma
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Kivimäki, Antti
    CNR-INFM, Laboratorio Nazionale TASC.
    Coreno, Marcello
    CNR-INFM, Laboratorio Nazionale TASC.
    Melero García, Emilio
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Stankiewicz, Marek
    Instytut Fizyki Im. Mariana Smoluchowskiego, Uniwersytet Jagielloński.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Lyman and Balmer emission following core excitations in methane and ammonia molecules2007In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 40, no 8, p. 1489-1500Article in journal (Refereed)
    Abstract [en]

    The intensities of hydrogen Lyman-alpha and Balmer series emission lines as a result of photoexcitation of free CH4 and NH3 molecules at the C 1s and N 1s edges have been measured. For methane, the total fluorescence yield in the visible region ( 300 - 650 nm) was also recorded. Excitation functions of the Balmer lines show relative intensity enhancement of Balmer-beta emission in comparison with Balmer-alpha at higher core- to- Rydberg excitations. The Lyman-alpha emission intensity, in general, follows the relations observed in the corresponding total ion yield measurements. Additionally, the Balmer-gamma and -delta yields were measured for ammonia molecules and they show intensity maxima at photon energies shifted closer to the N 1s threshold than Balmer-alpha and -beta. A quantum defect analysis is performed to find out which core excitations are responsible for this enhanced intensity. Dissociation pathways leading to the emission in H atoms are discussed.

  • 39. Karawajczyk, A.
    et al.
    Erman, P.
    Rachlew-Källne, Elisabeth
    KTH, Superseded Departments, Physics.
    Riu, J. R. I.
    Stankiewicz, M.
    Franzen, K. Y.
    Veseth, L.
    Neutral fragmentation of superexcited oxygen molecules2000In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 61, no 3, p. art. no.-32718Article in journal (Refereed)
    Abstract [en]

    The mechanisms of neutral dissociation of oxygen molecules in the excitation energy range 15-25 eV have been studied in a dispersed fluorescence experiment. By detecting the fluorescence from excited oxygen atoms, we find that neutral superexcited O-2 states below 20 eV dissociate into O(g.s.) + O(3s,3p). At higher excitation energies (h nu = 20-25 eV) the curve-crossing interactions following excitations to members of the Rydberg c (4)Sigma(u)(-) series also yield atoms in Rydberg states (nl,n greater than or equal to 4). The experimental data are analyzed on the ground of many-body perturbation theory, calculations which indicate the structure of the predissociating states converging to the experimentally observed ones.

  • 40.
    Kato, Takako
    et al.
    KTH, Superseded Departments, Physics. Natl. Institute for Fusion Science, Japan.
    Rachlew, Elisabeth
    KTH, Superseded Departments, Physics.
    Hörling, Pontus
    KTH, Superseded Departments, Physics.
    Zastrow, Klaus Dieter
    KTH, Superseded Departments, Physics. JET Joint Undertaking, United Kingdom .
    Observations and modelling of line intensity ratios of OV multiplet line1996In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 29, no 18, p. 4241-4253Article in journal (Refereed)
    Abstract [en]

    Line intensity ratios of OV multiplet lines for the 2s3s(3)S(1)-2s3p(3)P(j) (J = 2,1,0) transitions are studied using a collisional radiative model and the results-are compared with measurements from the reversed field pinch experiments Extrap T1 and T2 at KTH. The measured line intensity ratios deviate from the predictions of the model and the possible causes for the discrepancy are discussed with regard to errors in rate coefficients and non-quasi-steady state.

  • 41. Kivimaki, A.
    et al.
    Vall Llosera, Gemma
    Coreno, M.
    Huels, M. A.
    Stankiewicz, M.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Fluorescence emission at core-to-Rydberg excitations in the N-2 molecule2009In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 42, no 18Article in journal (Refereed)
    Abstract [en]

    Fluorescence emission at the N 1s edge of the N-2 molecule has been studied with synchrotron radiation excitation. The partial fluorescence yields in the ultraviolet (250-320 nm) and visible (300-650 nm) wavelengths were collected by scanning the photon energy across the core-to-Rydberg excitations and the N 1s ionization potential (IP). When compared to the total ion yield, both fluorescence yields are most enhanced at the excitations to high Rydberg orbitals. A discrete structure appears just below the N 1s IP only in the UV yield and is assigned to core-valence doubly excited states. Dispersed fluorescence spectra in selected wavelength windows were measured at several photon energies in order to find out which fragments are responsible for the enhancement of fluorescence emission just below the N 1s IP. The excitation functions determined and considerations on de-excitation pathways indicate that the main responsible is the N+ ion.

  • 42. Kivimaki, A.
    et al.
    Vall-Llosera, Gemma
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Coreno, M.
    Huels, M. A.
    Stankiewicz, M.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Line shape narrowing in the ultraviolet yield at the N 1s -> pi* resonance of the N-2 molecule2009In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 42, no 7Article in journal (Refereed)
    Abstract [en]

    The intensity of fluorescence emission in the wavelength region of 250-320 nm has been measured across the N 1s -> pi* resonance of the N-2 molecule. It displays a narrower line shape than the total ion yield recorded simultaneously. We explain the finding by the particularities of the resonant Auger transitions from the N 1s(-1) pi* state to the D-2 Pi(g) state in N-2(+) and by the subsequent D-2 Pi(g) -> A(2)Pi(u) emission.

  • 43.
    Kivimäki, Antti
    et al.
    KTH, Superseded Departments, Physics.
    Alvarez Ruiz, Jesus
    KTH, Superseded Departments, Physics.
    Erman, Peter
    KTH, Superseded Departments, Physics.
    Hatherly, Paul
    Melero Garcia, Emilio
    KTH, Superseded Departments, Physics.
    Rachlew, Elisabeth
    KTH, Superseded Departments, Physics.
    Rius i Riu, Jaume
    KTH, Superseded Departments, Physics.
    Stankiewicz, Marek
    An energy resolved electron-ion coincidence study near the S 2p thresholds of the SF6 molecule2003In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 36, no 4, p. 781-791Article in journal (Refereed)
    Abstract [en]

    The fragmentation dynamics of the SF6 molecule following the excitations of S 2p electrons into unoccupied molecular orbitals has been studied using the energy-resolved electron-ion coincidence technique. Fragmentation patterns were found to depend on the particular excitation and on the electronic state of the molecular ion. The spectator resonant Auger decay at the 2p --> 6a(1g) resonance induces changes in the ion distributions as compared to direct photoionization. Furthermore, coincidence spectra related to the same Auger structure display different ion abundances at the 2t(2g) and 4e(g) shape resonances. Differences were also found in the Auger decay spectra. These findings give further support for the previously suggested many-electron character of the 4e(g) shape resonance.

  • 44. Kukk, E.
    et al.
    Ha, D. T.
    Wang, Y.
    Piekarski, D. G.
    Diaz-Tendero, S.
    Kooser, K.
    Itaelae, E.
    Levola, H.
    Alcami, M.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Martin, F.
    Molecular dynamics of photodissociation: towards more complex systems2015In: XXIX INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC, AND ATOMIC COLLISIONS (ICPEAC2015), PTS 1-12, Institute of Physics Publishing (IOPP), 2015, article id UNSP 112105Conference paper (Refereed)
    Abstract [en]

    We present a combined experimental and theoretical study of the photodissociation of thiophene molecule using energy-resolved electron-ion-ion coincidence technique and self-consistent charge density functional tight-binding theory combined with a statistical approach. The observed complex molecular dynamics with many internal-energy-dependent fragmentation pathways is successfully described by the theoretical simulations.

  • 45. Kukk, E.
    et al.
    Ha, D. T.
    Wang, Y.
    Piekarski, D. G.
    Diaz-Tendero, S.
    Kooser, K.
    Itala, E.
    Levola, H.
    Alcami, M.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Martin, F.
    Internal energy dependence in x-ray-induced molecular fragmentation: An experimental and theoretical study of thiophene2015In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 91, no 4, article id 043417Article in journal (Refereed)
    Abstract [en]

    A detailed experimental and theoretical investigation of the dynamics leading to fragmentation of doubly ionized molecular thiophene is presented. Dissociation of double-ionized molecules was induced by S 2p core photoionization and the ionic fragments were detected in coincidence with Auger electrons from the core-hole decay. Rich molecular dynamics was observed in electron-ion-ion coincidence maps exhibiting ring breaks accompanied by hydrogen losses and/or migration. The probabilities of various dissociation channels were seen to be very sensitive to the internal energy of the molecule. Theoretical simulations were performed by using the semiempirical self-consistent charge-density-functional tight-binding method. By running thousands of these simulations, the initial conditions encountered in the experiment were properly taken into account, including the systematic dependencies on the internal (thermal) energy. This systematic approach, not affordable with first-principle methods, provides a good overall description of the complex molecular dynamics observed in the experiment and shows good promise for applicability to larger molecules or clusters, thus opening the door to systematic investigations of complex dynamical processes occurring in radiation damage.

  • 46. Kukk, E.
    et al.
    Kooser, K.
    Itälä, E.
    Trinh Ha, D.
    Urpelainen, S.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Dissociation dynamics of doubly charged CO2 and CS2 molecules as studied by electron-ion coincidence spectroscopy and simulations2012In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 388, no Part 2, p. 022084-Article in journal (Refereed)
    Abstract [en]

    Auger decay following C 1s core ionization leads to dissociating doubly ionized molecular states of CO2 and CS2. Detailed dynamics of these three- and two-body processes is investigated using electron-ion multicoincidence spectroscopy and Monte-Carlo simulations of various dissociation scenarios.

  • 47. Kukk, E.
    et al.
    Prumper, G.
    Sankari, R.
    Hoshino, M.
    Makochekanwa, C.
    Kitajima, M.
    Tanaka, H.
    Yoshida, H.
    Tamenori, Y.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Ueda, K.
    Electronic state dependence in the dissociation of core-ionized methane2007In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 40, no 18, p. 3677-3692Article in journal (Refereed)
    Abstract [en]

    Methane and deuteromethane molecules were core ionized using synchrotron radiation, and the ionic fragments from the molecular dissociation were detected in coincidence with the Auger electrons. The electron - ion coincidence spectra are analysed in terms of partial ion yields and ion kinetic energy distributions, both as functions of electron kinetic energy. The dependence of the fragmentation patterns on the electronic character of the Auger final states as well as on the excess energy available for dissociating the molecule is studied. The analysis reveals marked differences in the dissociation of the 2a(1)(-2) and 2a(1)(-1) 1t(2)(-1) states, interpreted as an `excess- energy- dependent' concerted dissociation process for the 2a(1)(-2) state and an ` electronic- state- dependent' sequential process for the 2a(1)(-1) 1t(2)(-1) state.

  • 48. Kukk, E.
    et al.
    Riu, J. R. I.
    Stankiewicz, M.
    Hatherly, P. A.
    Erman, P.
    Rachlew, Elisabeth
    KTH, Superseded Departments, Physics.
    Winiarczyk, P.
    Huttula, M.
    Aksela, S.
    Dissociation of deuteromethane following carbon 1s core ionization2002In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 66, no 1Article in journal (Refereed)
    Abstract [en]

    Energy-resolved electron-ion coincidence spectra of the deuteromethane molecule were measured following ionization by narrow-band synchrotron radiation. The ion mass spectra were recorded in coincidence with the outer and inner valence photoelectrons and with the normal Auger electrons from the decay of the carbon 1s core hole. Complementary noncoincidence ion mass spectra were measured below and above the C 1s threshold. The fragmentation patterns of the singly and doubly ionized deuteromethane under different ionization conditions are examined. Carbon core ionization is shown to open new photodissociation pathways not available in the valence ionization photon energy regime. With the aid of ab initio quantum chemistry calculations, a two-step model of the dissociation following core ionization is proposed, showing a good agreement with the experimental findings.

  • 49.
    Kuldkepp, Matias
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Hawkes, N. C.
    Schunke, B.
    Accurate polarization measurements with a dual photoelastic modulator2005In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 44, no 28, p. 5899-5904Article in journal (Refereed)
    Abstract [en]

    Measurements of the polarization effects in multimirror experiments by using a dual photoelastic modulator are described. The effect of single and multiple mirrors in polarization measurements in two and three dimensions is discussed, and experimental results show how symmetrical placement of mirrors in three-dimensional geometry can eliminate changes in the polarization. Calibration procedures for a dual photoelastic modulator and potential error sources such as misalignment of analyzer, signal dc offset, and neglect of aperture size are presented. Mirror-surface evolution and how it can disturb the polarization measurement are also addressed.

  • 50.
    Kuldkepp, Matias
    et al.
    KTH, Superseded Departments, Physics.
    Rachlew, Elisabeth
    KTH, Superseded Departments, Physics.
    Hawkes, N.C.
    Schunke, B.
    First mirror contamination studies for polarimetry motional Stark effect measurements for ITER2004In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 75, p. 3446-3448Article in journal (Refereed)
    Abstract [en]

    The motional Stark effect (MSE) diagnostic on the International Thermonuclear Experimental Reactor will need to guide the light through a labyrinth of mirrors to provide neutron shielding. Knowledge of how the mirrors change the polarization is essential for accurate determination of the q profile. The optical properties of the plasma facing mirror are also expected to change with time due to deposition/erosion. For the purpose of examining this experimentally a detector system, identical to the JET MSE system, using twin photoelastic modulators was constructed. Measurements have been performed on freshly prepared mirrors, on mirrors after exposure to plasmas in Tore Supra, and labyrinth designs. The result shows a significant effect on the optical properties and demonstrate the need for in situ monitoring. The measured properties of the labyrinth closely follow the Mueller matrix formalism. With a correct choice of material the angle change introduced by the four mirrors furthest away from the plasma will be below 1 degrees.

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