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Fast wave heating and current drive in tokamaks
KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
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 [en]
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
Keyword [sv]
Fysik
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-118ISBN: 91-7283-954-6 (print)OAI: oai:DiVA.org:kth-118DiVA: diva2:6969
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
List of papers
1. Self-consistent simulations of ICRH in ITB plasmas
Open this publication in new window or tab >>Self-consistent simulations of ICRH in ITB plasmas
2001 (English)In: AIP Conf. Proc.: October 29, 2001, 2001, 414-417 p.Conference paper, Published paper (Other academic)
Abstract [en]

The RF power partition and power deposition on resonant ion species during ICRH depend strongly on the distribution functions of the heated ions. The distribution functions in turn depend on RF interactions and Coulomb collisions with the background plasma. It has previously been found that the finite ion orbit width, as well as the RF induced transport of resonant ions, are important for describing the distribution functions. This is particularly important in ITB plasmas, where low central current density results in broad orbits. To simulate ICRH in ITB plasmas the SELFO code has been upgraded to self-consistently calculate the wave field and the distribution functions of several ion species, including beam injected ions. Simulations of hydrogen minority heating of a deuterium, JET-like, ITB plasma have been made for different antenna phasings, with and without NBI. The distribution functions of both hydrogen and deuterium have been simulated. Finite orbit width and RF induced particle transport effects are shown to have a large impact on the partition of RF power absorption between hydrogen and deuterium, and thereby on the power transfer to the background.

Keyword
plasma radiofrequency heating, cyclotron resonance, ions, collision processes, electromagnetic wave absorption, Monte Carlo methods, antennas in plasma
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-12706 (URN)10.1063/1.1424221 (DOI)
Conference
RADIO FREQUENCY POWER IN PLASMAS:14th Topical Conference
Note
QC 20100506Available from: 2010-05-06 Created: 2010-05-06 Last updated: 2010-07-14Bibliographically approved
2. Self-consistent RF modelling of beam and ICRF heated plasmas
Open this publication in new window or tab >>Self-consistent RF modelling of beam and ICRF heated plasmas
2002 (English)In: Proceedings of the Joint Varenna-Lausanne International Workshop, Varenna, Italy 2002 / [ed] Connor, J. W.; Sauter, O.; Sindoni, E., 2002Conference paper, Published paper (Other academic)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-12707 (URN)
Note
QC 20100506 Available from: 2010-05-06 Created: 2010-05-06 Last updated: 2010-07-14Bibliographically approved
3. Effects of finite drift orbit width and RF-induced spatial transport on plasma heated by ICRH
Open this publication in new window or tab >>Effects of finite drift orbit width and RF-induced spatial transport on plasma heated by ICRH
Show others...
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.

Keyword
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:nbn:se:kth:diva-12712 (URN)10.1088/0029-5515/44/8/008 (DOI)000223954400008 ()2-s2.0-4344607797 (Scopus ID)
Note
QC 20100507Available from: 2010-05-07 Created: 2010-05-07 Last updated: 2017-12-12Bibliographically approved
4. Modelling of minority ion cyclotron current drive during the activated phase of ITER
Open this publication in new window or tab >>Modelling of minority ion cyclotron current drive during the activated phase of ITER
2005 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 45, no 12, 1510-1523 p.Article in journal (Refereed) Published
Abstract [en]

Neoclassical tearing modes, triggered by the long-period sawteeth expected in tokamaks with large non-thermal α-particle populations, may impose a severe β limit on experiments with large fusion yields and on reactors. Sawtooth destabilization by localized current drive could relax the β limit and improve plasma performance. 3He minority ion cyclotron current drive around the sawtooth inversion radius has been planned for ITER. Several ion species, including beam injected D ions and fusion born α particles, are however also resonant in the plasma and may represent a parasitic absorption of RF power. Modelling of minority ion cyclotron current drive in an ITER-FEAT-like plasma is presented, including the effects of ion trapping, finite ion drift orbit widths, wave-induced radial transport and the coupled evolution of wave fields and resonant ion distributions. The parasitic absorption of RF power by the other resonant species is concluded to be relatively small, but the 3He minority current drive is nevertheless negligible due to the strong collisionality of the 3He ions and the drag current by toroidally counter-rotating background ions and co-rotating electrons. H minority current drive is found to be a significantly more effective alternative.

Keyword
Absorption, Electric currents, Electrons, Plasmas, Co-rotating electrons, Localized current drive, Minority ion cyclotron currents, Resonant ion drive, Tokamak devices
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-12714 (URN)10.1088/0029-5515/45/12/006 (DOI)000234452300009 ()2-s2.0-28844470775 (Scopus ID)
Note
QC 20100507Available from: 2010-05-07 Created: 2010-05-07 Last updated: 2017-12-12Bibliographically approved
5. Self-Consistent Modelling of Polychromatic ICRH in Tokamaks
Open this publication in new window or tab >>Self-Consistent Modelling of Polychromatic ICRH in Tokamaks
2003 (English)In: AIP Conference proceedings: Vol 694, 2003, 126-129 p.Conference paper, Published paper (Other academic)
Abstract [en]

Polychromatic, multi-frequency, ion cyclotron resonance heating provide a useful tool for the optimization of plasma performance in fusion devices by tailoring the fast ion distribution function. Not only can the radial profile of the fast ion distributions be modified, but also the fast energy content, the power partition on resonant species and the bulk plasma ion- and electron heating rates. This work describes finite orbit effects of polychromatic ICRH which are demonstrated using the SELFO code.

Keyword
plasma radiofrequency heating, cyclotron resonance, ion density, modelling, plasma simulation, Doppler effect, Monte Carlo methods
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-12715 (URN)10.1063/1.1638010 (DOI)
Conference
RADIO FREQUENCY POWER IN PLASMAS: 15th Topical Conference on Radio Frequency Power in Plasmas
Note
QC 20100507Available from: 2010-05-07 Created: 2010-05-07 Last updated: 2010-05-11Bibliographically approved
6. Fast ion distributions driven by polychromatic ICRF waves on JET
Open this publication in new window or tab >>Fast ion distributions driven by polychromatic ICRF waves on JET
Show others...
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.

Keyword
particle interaction, heated plasmas, diii-d, tokamak, absorption
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-15093 (URN)10.1088/0741-3335/47/9/006 (DOI)000232428400007 ()
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
7. On the parasitic absorption in FWCD experiments in JET ITB plasmas
Open this publication in new window or tab >>On the parasitic absorption in FWCD experiments in JET ITB plasmas
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2005 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 45, no 7, 706-720 p.Article in journal (Refereed) Published
Keyword
WAVE CURRENT DRIVE, JOINT EUROPEAN TORUS, DIII-D TOKAMAK, MODE CONVERSION, ICRF ANTENNAS, RESONANCE, SCENARIOS, EMISSION, SCREENS, SHEATHS
Identifiers
urn:nbn:se:kth:diva-12763 (URN)10.1088/0029-5515/45/7/020 (DOI)000231000300021 ()
Note
QC 20100510Available from: 2010-05-10 Created: 2010-05-10 Last updated: 2017-12-12Bibliographically approved
8. Influence of coupling to spectra of weakly damped eigenmodes in the ion cyclotron range of frequencies on parasitic absorption in rectified radio frequency sheaths
Open this publication in new window or tab >>Influence of coupling to spectra of weakly damped eigenmodes in the ion cyclotron range of frequencies on parasitic absorption in rectified radio frequency sheaths
2005 (English)In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 12, no 3Article in journal (Refereed) Published
Keyword
WAVE CURRENT DRIVE, H-MODE PLASMAS, DIII-D TOKAMAK, ICRF ANTENNAS, EDGE PLASMA, JET, TFTR, RESONANCE, SCREENS
Identifiers
urn:nbn:se:kth:diva-12766 (URN)10.1063/1.1851988 (DOI)000227385700022 ()2-s2.0-17044428884 (Scopus ID)
Note
QC 20100510Available from: 2010-05-10 Created: 2010-05-10 Last updated: 2017-12-12Bibliographically approved
9. Edge localized magnetosonic eigenmodes in the ion cyclotron frequency range
Open this publication in new window or tab >>Edge localized magnetosonic eigenmodes in the ion cyclotron frequency range
2003 (English)In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 10, no 11, 4371-4377 p.Article in journal (Refereed) Published
Abstract [en]

Edge localized magnetosonic modes are analyzed in toroidal plasmas. For low and medium high toroidal mode numbers they are found to propagate poloidally around the plasma. A model of these modes is developed and benchmarked against a global wave code. The eigenvalues are found to be almost independent of the aspect ratio for constant minor radius, but sensitive to the ellipticity. Magnetosonic modes localized to an annular region in the poloidal plane have been proposed as an explanation for ion cyclotron emission from the edge and strongly localized mode conversion. The appearance of such modes will also give rise to parasitic absorption at the edge during ion cyclotron resonance heating.

Keyword
emission, instability, plasmas, tokamaks, products, waves
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-12767 (URN)10.1063/1.1617315 (DOI)000185989400021 ()
Note
QC 20100510Available from: 2010-05-10 Created: 2010-05-10 Last updated: 2017-12-12Bibliographically approved

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