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Effects of finite drift orbit width and RF-induced spatial transport on plasma heated by ICRH
KTH, Superseded Departments, Alfvén Laboratory.
KTH, Superseded Departments, Alfvén Laboratory.ORCID iD: 0000-0002-7142-7103
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2004 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 44, no 8, 892-908 p.Article in journal (Refereed) Published
Abstract [en]

The effects of RF-induced transport and orbit topology of resonant ions are analysed for high power ion cyclotron resonance heating (ICRH). These effects are found to play important roles in the details of the high-energy part of the distribution function, and affect the driven current and momentum transfer to the background plasma. The finite drift orbit width broadens the power deposition and leads to losses of high-energy ions intercepted by the wall. RF-induced transport of resonant ions across magnetic flux surfaces appears due to the toroidal acceleration of resonant ions interacting with waves having a finite toroidal mode number. Heating with waves propagating parallel to the current leads to a drift of the turning points of trapped resonant ions towards the midplane. As the turning points meet, the orbits will de-trap, preferentially into co-current passing orbits, which may ultimately be displaced to the low field side of the magnetic axis. Ions with such orbits are a typical feature in plasmas heated with directed toroidal mode spectra of waves propagating parallel to the plasma current. These ions will be subjected to a strong RF diffusion partly caused by the focusing of the wave field and partly by the Doppler shifted cyclotron resonance, as it approaches tangency with the drift orbit. The resonance condition puts a limitation on the achievable energy for these ions, which is more severe than for corresponding trapped ions. This results in a rather flat tail up to a critical energy, above which the tail rapidly decays. Heating with waves propagating anti-parallel with the plasma current curtails the energy of the trapped ions due to a vertical outward drift of the turning points of the trapped ions. Heating with symmetric spectra, in particular with waves with low magnitude of the toroidal mode numbers, gives rise to high-energy trapped ions with wide orbits, of which the maximum energy is either restricted by the fact that the RF diffusion vanishes due to cancellation of the perpendicular acceleration over a gyro orbit or by the drift orbits being intercepted by the wall. In the steady state the main source for momentum transfer to the bulk plasma comes from the finite momentum of the wave for heating with asymmetric spectra. For heating with symmetric spectra the enhanced losses of high-energy trapped ions can produce a net counter-current torque on the plasma.

Place, publisher, year, edition, pages
2004. Vol. 44, no 8, 892-908 p.
Keyword [en]
High energy ions, Ion cyclotron resonance heating, Power deposition, Spatial transport, Cyclotron resonance, High energy physics, Ions, Magnetic field effects, Natural frequencies, Orbits, Torque, Wave propagation
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-12712DOI: 10.1088/0029-5515/44/8/008ISI: 000223954400008Scopus ID: 2-s2.0-4344607797OAI: oai:DiVA.org:kth-12712DiVA: diva2:318261
Note
QC 20100507Available from: 2010-05-07 Created: 2010-05-07 Last updated: 2017-12-12Bibliographically 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.
Keyword
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
Identifiers
urn:nbn:se:kth:diva-118 (URN)91-7283-954-6 (ISBN)
Public defence
2005-02-08, Kollegiesalen, Valhallavägen 79, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100506Available from: 2005-02-04 Created: 2005-02-04 Last updated: 2011-02-24Bibliographically approved
2. Fast wave heating of cyclotron resonant ions in tokamaks
Open this publication in new window or tab >>Fast wave heating of cyclotron resonant ions in tokamaks
2004 (English)Doctoral thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH, 2004. xiv, 61 p.
Keyword
Fusion plasma, tokamak, RF heating, fast wave heating, fast wave current drive, ion cyclotron resonance, ICRH, ICRF, ICCD, RF induced rotation, RF induced transport, RF induced pinch, RF pinch, finite orbit width, fast wave current drive, self-consi
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:kth:diva-3771 (URN)91-7283-780-2 (ISBN)
Public defence
2004-06-01, 00:00
Note
QC 20100622Available from: 2004-06-01 Created: 2004-06-01 Last updated: 2010-11-15Bibliographically approved

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