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Fast ion distributions driven by polychromatic ICRF waves on JET
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
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2005 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 47, no 9, 1439-1457 p.Article in journal (Refereed) Published
Abstract [en]

Experiments have been carried out on the JET tokamak to investigate fast He-3 and hydrogen minority ion populations accelerated by ion cyclotron range of frequencies (ICRF) waves launched with multiple frequencies (i.e. up to four frequencies separated by up to approximate to 15%). This 'polychromatic' heating is compared with single-frequency, 'monochromatic', ICRF heating of reference discharges with similar power levels. Information on the fast ion populations is provided by two-dimensional gamma-ray emission tomography and the measurements are compared with numerical modelling. Polychromatic heating with resonances in the plasma centre (R-res approximate to R-0) and on the low magnetic-field side (LFS) (R-res > R-0) is found to produce predominantly high-energy standard trapped ions, while resonances on the high magnetic-field side (R-res < R-0) increase the fraction of high-energy passing ions. Monochromatic heating with a central resonance produces stronger gamma-ray emission with the maximum emission in the midplane close to, and on the LFS of, the resonance, in agreement with the calculated radial distribution of fast ion orbits. Both the fast ion tail temperature and energy content are found to be lower with polychromatic waves. Polychromatic ICRF heating has the advantage of producing smaller-amplitude and shorter-period sawteeth, consistent with a lower fast ion pressure inside the q = 1 surface, and higher ion to electron temperature ratios.

Place, publisher, year, edition, pages
2005. Vol. 47, no 9, 1439-1457 p.
Keyword [en]
particle interaction, heated plasmas, diii-d, tokamak, absorption
National Category
Fusion, Plasma and Space Physics
URN: urn:nbn:se:kth:diva-15093DOI: 10.1088/0741-3335/47/9/006ISI: 000232428400007OAI: diva2:333134
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-02-24Bibliographically approved
In thesis
1. Fast wave heating and current drive in tokamaks
Open this publication in new window or tab >>Fast wave heating and current drive in tokamaks
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis concerns heating and current drive in tokamak plasmas using the fast magnetosonic wave in the ion cyclotron range of frequencies. Fast wave heating is a versatile heating method for thermonuclear fusion plasmas and can provide both ion and electron heating and non-inductive current drive. Predicting and interpreting realistic heating scenarios is however difficult due to the coupled evolution of the cyclotron resonant ion velocity distributions and the wave field. The SELFO code, which solves the coupled wave equation and Fokker-Planck equation for cyclotron resonant ion species in a self-consistent manner, has been upgraded to allow the study of more advanced fast wave heating and current drive scenarios in present day experiments and in preparation for the ITER tokamak.

Theoretical and experimental studies related to fast wave heating and current drive with emphasis on fast ion effects are presented. Analysis of minority ion cyclotron current drive in ITER indicates that the use of a hydrogen minority rather than the proposed helium-3 minority results in substantially more efficient current drive. The parasitic losses of power to fusion born alpha particles and beam injected ions are concluded to be acceptably low. Experiments performed at the JET tokamak on polychromatic ion cyclotron resonance heating and on fast wave electron current drive are presented and analysed. Polychromatic heating is demonstrated to increase the bulk plasma ion to electron heating ratio, in line with theoretical expectations, but the fast wave electron current drive is found to be severely degraded by parasitic power losses outside of the plasma. A theoretical analysis of parasitic power losses at radio frequency antennas indicates that the losses can be significantly increased in scenarios with low wave damping and with narrow antenna spectra, such as in electron current drive scenarios.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. xiv, 42 p.
Tokamak, JET, ITER, thermonuclear fusion, fast wave, heating, current drive, ion cyclotron resonance, polychromatic, finite orbit widths, RF-induced transport, neutral beam injection, fusion born alpha particles, magnetosonic eigenmodes, parasitic absorption, modelling, weighted Monte Carlo scheme, Fysik
National Category
Physical Sciences
urn:nbn:se:kth:diva-118 (URN)91-7283-954-6 (ISBN)
Public defence
2005-02-08, Kollegiesalen, Valhallavägen 79, Stockholm, 10:00 (English)
QC 20100506Available from: 2005-02-04 Created: 2005-02-04 Last updated: 2011-02-24Bibliographically approved

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Laxåback, MartinHellsten, Torbjörn A. K.Johnson, Thomas J.
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