Minority Ion Cyclotron Current Drive in Tokamaks

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

doi:10.1103/physrevlett.74.3612

Cited by 53 publications

(85 citation statements)

References 6 publications

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“…We note that j 0 can encompass both Fisch currents, 16 and the currents associated with detrapping into preferentially co-or counterpassing ions. 34,11 In this paper we do not differentiate between which of these mechanisms creates j 0 , but we note that both are consistent with an asymmetric distribution in v ʈ at the lowest order, i.e., in F 0 . The finite orbit corrected current j 1 is essentially independent of asymmetry in the lowest order distribution function, and we see that any distribution of particles have currents associated with constraint of canonical momentum conservation.…”

Section: B Currents In Asymmetric Fast Ion Distributionsmentioning

confidence: 57%

A new sawtooth control mechanism relying on toroidally propagating ion cyclotron resonance frequency waves: Theory and Joint European Torus tokamak experimental evidence

Graves¹,

Chapman²,

Coda³

et al. 2010

Physics of Plasmas

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The sawtooth control mechanism in plasmas employing toroidally propagating ion cyclotron resonance waves is extended. The asymmetrically distributed energetic passing ions are shown to modify the ideal internal kink mode when the position of the minority ion cyclotron resonance resides within a narrow region close to the q = 1 surface. An analytical treatment of the internal kink mode in the presence of model distribution function with parallel velocity asymmetry is developed. The fast ion mechanism explains the strong sensitivity of sawteeth to resonance position, and moreover is consistent with dedicated Joint European Torus ͓F. Romanelli, Nucl. Fusion 49, 104006 ͑2009͔͒ experiments which controlled sawteeth despite negligible current drive.

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Section: B Currents In Asymmetric Fast Ion Distributionsmentioning

confidence: 57%

A new sawtooth control mechanism relying on toroidally propagating ion cyclotron resonance frequency waves: Theory and Joint European Torus tokamak experimental evidence

Graves¹,

Chapman²,

Coda³

et al. 2010

Physics of Plasmas

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“…b ¼ 2 = b , and c ¼ eZB 0 =m. We note that the current driven entirely by passing ions j 0 can encompass both Fisch currents [12], and the currents associated with detrapping into preferentially co-or counter-passing ions [9,13]. Both require an asymmetric distribution in v k at the lowest order, i.e., in F 0 .…”

mentioning

confidence: 99%

Sawtooth-Control Mechanism using Toroidally Propagating Ion-Cyclotron-Resonance Waves in Tokamaks

et al. 2009

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The sawtooth control mechanism in plasmas employing off-axis toroidally propagating ion cyclotron resonance waves in tokamaks is reinvestigated. The radial drift excursion of energetic passing ions distributed asymmetrically in the velocity parallel to the magnetic field determines stability when the rational q ¼ 1 surface resides within a narrow region centered about the shifted fundamental cyclotron resonance. Magnetohydrodynamic (MHD) stability of plasmas in the presence of energetic ions is a crucial issue for present and future large tokamak experiments. Such ions include 3.5 MeV fusion alpha particles, and energetic minority ions produced by auxiliary heating methods such as from ion cyclotron resonance frequency (ICRF) waves. Ions trapped outside the region of highest magnetic field strength have been shown [1] to stabilize a key core instability known as the sawtooth, located within the q ¼ 1 rational surface, thereby lengthening the period between sequential soft-xray relaxations [2]. Without an effective means of shortening the period of sawteeth, coupling can occur with instabilities located at rational surfaces closer to the tokamak edge. Indeed, interaction of long sawteeth and performance degrading neoclassical tearing modes has been observed [3] in the Joint European Torus (JET), while improved plasma confinement is often found to coincide with small regular sawteeth.Under certain conditions untrapped, or passing, energetic ions can also strongly influence sawteeth. Sawtooth control from energetic ions injected with near tangential unbalanced neutral beams has already been demonstrated analytically, for deeply passing ions [4], numerically and experimentally [5]. The mechanism responsible was found to be due to the contribution on the n ¼ 1 internal kink mode of passing particles intersecting the q ¼ 1 rational surface. An important fast ion effect is obtained when the distribution function of passing ions is asymmetrically distributed in the velocity parallel to the magnetic field. By extending the analysis of Ref.[4] to solve for the internal kink mode across all velocity space, including barely passing trajectories, it is shown in the present contribution that the sawtooth control mechanism responsible for localized off-axis toroidally propagating ICRF waves is essentially the same as for unbalanced neutral beam injection (NBI) scenarios. Moreover, the propagating ICRF waves are more effective than unbalanced NBI because the orbit widths of the energetic ions are larger, and the parallel asymmetry of the distribution function is more strongly radially sheared. Simulations using SELFO [6] for the ICRF wave field and distribution function are applied to a key demonstration JET discharge [7] with localized off-axis ion cyclotron current drive (ICCD) counter to the Ohmic current. Analytical and full numerical calculations [8] of the internal kink mode with the simulated JET ICRF distribution function [9] demonstrate ideal instability when the deposition of the resonating ions is very close to the ...

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“…For a trapped particle, this leads to the radial transport of banana tips either inwards or outwards depending on the toroidal direction of the wave. For the inward pinch with waves in the co-current direction, the fast ion orbit is eventually detrapped into co-passing orbits that reside on the low field side of the resonance ω = nω ci [9]. Experimental evidence of this effect has been obtained on the JET tokamak with high-power H and 3 He minority heating [10,11].…”

Section: Modifications Of Sawteeth Via Icrf Fast Ionsmentioning

confidence: 96%

“…For passing ion current, it is beneficial to have rather strong pitch angle scattering by keeping the average fast ion energy comparable to the critical energy [17]. Current drive, even with toroidally symmetric spectra, is possible by trapped ions due to their finite orbit widths and due to effects of non-standard orbits [9]. The trapped ion current has a dipolar shape and for typical JET parameters can exceed the current drive by passing ions [18].…”

Section: Modifications Via Ion Cyclotron Current Drivementioning

confidence: 99%

Modification of Sawtooth Oscillations with ICRF Waves in the JET Tokamak

Mantsinen

Alper

Angioni

et al. 2007

AIP Conference Proceedings

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Methods of modifying sawtooth oscillations using waves in the ion cyclotron range of frequencies (ICRF) in the JET tokamak are presented. Examples of sawtooth stabilization by ICRF-accelerated high-energy ions are shown, including experiments with ICRF-acceleration of 4 He-beam ions to simulate the effects of fusion born alpha particles. With high power ICRF heating in low-density plasmas, fast ion stabilization of sawteeth is lost and a new type of small-period and small-amplitude sawteeth appears. ICRF-induced radial pinch with toroidally asymmetric waves is found to be useful in affecting the radial profile of the ICRF-driven fast ion populations and thereby their influence on sawteeth. Ion cyclotron current drive (ICCD) applied close to the sawtooth inversion radius is effective in modifying the sawtooth period. The latest achievements include the successful application of ICCD to shorten the fast-ioninduced long-period sawteeth and thereby avoid triggering of neoclassical tearing modes (NTMs).

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Minority Ion Cyclotron Current Drive in Tokamaks

Cited by 53 publications

References 6 publications

A new sawtooth control mechanism relying on toroidally propagating ion cyclotron resonance frequency waves: Theory and Joint European Torus tokamak experimental evidence

A new sawtooth control mechanism relying on toroidally propagating ion cyclotron resonance frequency waves: Theory and Joint European Torus tokamak experimental evidence

Sawtooth-Control Mechanism using Toroidally Propagating Ion-Cyclotron-Resonance Waves in Tokamaks

Modification of Sawtooth Oscillations with ICRF Waves in the JET Tokamak

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