The effect of the toroidal wavenumber spectrum on the high energy tail formation during ICRH

Carlsson, Johan; Eriksson, L.‐G.; Hellsten, T.

doi:10.1088/0029-5515/37/6/i01

Cited by 23 publications

(36 citation statements)

References 17 publications

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“…The conclusion is that in a large tokamak the total energy absorption does not depend sensitively on k but the radial distribution, out to and including the limiter (orbit losses), of the energy does [2].…”

Section: Minority Ion Cyclotron Heatingmentioning

confidence: 94%

“…However, a more careful, radially resolved investigation, shows that the tail formation locally, on a specific flux surface, does depend strongly on the k -spectrum, see fig. 2 above [2].…”

Section: Minority Ion Cyclotron Heatingmentioning

confidence: 97%

“…Numerical studies, performed with the Monte-Carlo code FIDO [1], of the evolution of the resonant-ion distribution function in the presence of ICRH in toroidal geometry are presented. In particular it is pointed out how the absorption of toroidal momentum from a wave field with finite parallel wave numbers causes spatial drift and diffusion, which together with the finite orbit widths of the tail ions is shown to have a large effect on the temperature profile of the resonant ion species and also to cause losses of high-energy ions to the wall [2].Furthermore, it is found that the finite orbit width and the inward drift occuring for negative parallel wave numbers [3] each give rise to a new mechanism of minority-ion cyclotron current drive as compared to earlier models where the drift orbits of the resonant ions are confined to the magnetic flux surfaces. For high levels of coupled power these new mechanisms are found to be the dominating ones [4,5].…”

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confidence: 99%

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confidence: 99%

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Toroidal effects on ICRF heating and current drive

Carlsson¹,

Hellsten²,

Hedin³

1999

AIP Conference Proceedings

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Abstract. Numerical studies, performed with the Monte-Carlo code FIDO [1], of the evolution of the resonant-ion distribution function in the presence of ICRH in toroidal geometry are presented. In particular it is pointed out how the absorption of toroidal momentum from a wave field with finite parallel wave numbers causes spatial drift and diffusion, which together with the finite orbit widths of the tail ions is shown to have a large effect on the temperature profile of the resonant ion species and also to cause losses of high-energy ions to the wall [2].Furthermore, it is found that the finite orbit width and the inward drift occuring for negative parallel wave numbers [3] each give rise to a new mechanism of minority-ion cyclotron current drive as compared to earlier models where the drift orbits of the resonant ions are confined to the magnetic flux surfaces. For high levels of coupled power these new mechanisms are found to be the dominating ones [4,5].

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Section: Minority Ion Cyclotron Heatingmentioning

confidence: 94%

“…However, a more careful, radially resolved investigation, shows that the tail formation locally, on a specific flux surface, does depend strongly on the k -spectrum, see fig. 2 above [2].…”

Section: Minority Ion Cyclotron Heatingmentioning

confidence: 97%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Toroidal effects on ICRF heating and current drive

Carlsson¹,

Hellsten²,

Hedin³

1999

AIP Conference Proceedings

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“…A Monte Carlo method for its solution has been developed [5][6][7], and has since been successfully used for the interpretation of high-power ion cyclotron (IC) heating experiments in JET [8][9]. A review of recent work along these lines can be found in [10].…”

Section: -Introductionmentioning

confidence: 99%

Quasilinear description of radiofrequency-induced radial diffusion

Brambilla¹

2007

Nucl. Fusion

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We derive the bounce-averaged quasilinear operator in axisymmetric toroidal geometry using the standard quasilinear formalism. When specialized to resonant ion cyclotron harmonic interactions, this operator predicts the same radio-frequency-induced radial diffusion as the orbit-averaged operator (L.-G. Eriksson and P. Helander, Phys. Plasmas 1 (1994) 308) obtained using action-angle variables. By assuming the wave field known as a superposition of toroidal and poloidal Fourier modes, the quasilinear diffusion coefficients are written in a form which can be directly evaluated using the output of a spectral full-wave solver of Maxwell equations in toroidal plasmas. -Introduction.The fact that in toroidal geometry resonant cyclotron interactions inevitably cause radial diffusion of the heated ions is known since a long time [1]. As pointed out by Ryopulos et al. [2] and Hellsten [3], this is a consequence of the fact that the variation of the magnetic moment µ suffered by an ion transiting through a cyclotron resonance also causes a variation of its toroidal momentum P ϕ . This, in turn, causes the mean radius of the drift orbit to shift radially outwards or inwards, depending on the sign of the toroidal wavenumber of the hf wave. The effect has been demonstrated experimentally in the JET tokamak by launching a toroidally asymmetric spectrum of fast waves [4].An elegant form of the quasilinear (QL) kinetic equation including a term describing rf-induced radial diffusion has been derived by Eriksson and Helander [5]. A Monte Carlo method for its solution has been developed [5][6][7], and has since been successfully used for the interpretation of high-power ion cyclotron (IC) heating experiments in JET [8][9]. A review of recent work along these lines can be found in [10].The derivations of [1] and [5] are based on the action-angle variables formalism of Kaufman [11]. This approach has been called 'orbit-averaging', to distinguish it from conventional 'bounce-averaging ' [12], which is thought to be valid only in the limit of thin banana orbits. In this note we show, however, that the standard bounce-averaging procedure predicts just the same radial diffusion as orbit-averaging, unless it is explicitly or tacitly assumed that all charged particles are tied to magnetic field lines. We argue, therefore, that the real difference between orbit and bounce averaging lies in the treatment of collisions, which in Montecarlo codes, but not in bounce-averaged Fokker-Planck solvers, can be evaluated at the true position of the ions, independently from the shape and thickness of their orbit.Our derivation differs from previous ones also in an other minor technical aspect, which is, however, of practical relevance. Most derivations of the QL operator assume that the wave field in the vicinity of IC resonances can be represented in Eikonal form. Here the wave electric field is supposed instead to be given as a superposition of toroidal and poloidal Fourier modes. This is the representation used to solve Maxwell equations ...

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New mechanisms of minority ion cyclotron current drive

1998

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Minority ion cyclotron current drive is studied by solving the Fokker-Planck equation in toroidal geometry keeping the ∂/∂v-term in the quasilinear operator, hereby including the important effects of the finite orbit widths of the tail ions and the wave-induced spatial drift and diffusion. It has previously been found that the trapped ion current and the current carried by passing ions detrapped by wave-induced v ⊥diffusion are the two dominating contributions for high levels of coupled power. In this study yet another current-drive mechanism is presented, asymmetric detrapping by inward wave-induced radial drift, which occurs for negative k and is strongest for on-axis resonance where it is the totally dominating effect for high powers.

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The effect of the toroidal wavenumber spectrum on the high energy tail formation during ICRH

Cited by 23 publications

References 17 publications

Toroidal effects on ICRF heating and current drive

Toroidal effects on ICRF heating and current drive

Quasilinear description of radiofrequency-induced radial diffusion

New mechanisms of minority ion cyclotron current drive

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