Alpha channeling with high-field launch of lower hybrid waves

Ochs, Ian E.; Bertelli, N.; Fisch, Nathaniel J.

doi:10.1063/1.4935123

Cited by 27 publications

(19 citation statements)

References 35 publications

(21 reference statements)

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“…In addition, LHCD, but not ECCD, can tap the energy in α particles in a reactor through the α-channeling effect [77], reducing the recirculating power. The channeling is in fact most effective under high-field side launch [78,79]. LHCD also sees a stronger rf current condensation effect than ECCD, because of its higher phase velocity, a potential advantage for stabilizing NTMs.…”

Section: Pacs Numbersmentioning

confidence: 99%

Suppression of Tearing Modes by Radio Frequency Current Condensation

Reiman

Fisch

2018

Phys. Rev. Lett.

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Currents driven by rf (radio frequency) waves in the interior of magnetic islands can stabilize deleterious tearing modes in tokamaks. Present analyses of stabilization assume that the local electron acceleration is unaffected by the presence of the island. However, the power deposition and electron acceleration are sensitive to the perturbation of the temperature. The nonlinear feedback on the power deposition in the island increases the temperature perturbation, and can lead to a bifurcation of the solution to the steady-state heat diffusion equation. The combination of the nonlinearly enhanced temperature perturbation with the rf current drive sensitivity to the temperature leads to an rf current condensation effect, which can increase the efficiency of rf current drive stabilization and reduce its sensitivity to radial misalignment of the ray trajectories. The threshold for the effect is in a regime that has been encountered in experiments, and will likely be encountered in ITER. PACS numbers:Introduction: A study of the root causes of disruptions in the JET tokamak found that neoclassical tearing modes (NTMs) were the single most common cause [1,2]. Theoretical calculations in the early 1980's showed the feasibility of using rf current drive to stabilize tearing modes [3,4]. The recognition in the late 1990's that bootstrap currents were driving NTMs in hot, collisionless tokamak plasmas [5][6][7][8], led to a resurgence of theoretical work in this area [9][10][11][12][13], to experimental demonstrations of stabilization [14][15][16][17][18][19][20], and to continuing intensive attention [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. A variety of rf waves are used to drive current [41], but, for stabilizing the NTM, the most studied methods are electron cyclotron current drive (ECCD) [42] and lower hybrid current drive (LHCD) [43]. ITER is designed with an NTM ECCD stabilization capability, with continued effort to model and improve this capability [25,29,30,44]. We identify here an rf current condensation effect, previously overlooked, which can significantly facilitate island stabilization.Calculations of rf stabilization of magnetic islands assume, at present, that the local acceleration of electrons is unaffected by the presence of the island. However, the local deposition is sensitive to small changes in the temperature, and these changes can be significantly affected by the presence of an island. The effect on the local deposition becomes significant when the fractional temperature perturbation exceeds about 5% for electron cyclotron waves and 2.5% for lower hybrid waves. Temperature perturbations as high as 20% have been measured in islands in rf stabilization experiments [45].In the conventional picture of rf current drive stabilization of a rotating island, a geometric effect associated with the equilibration of the rf driven current density within the flux surfaces of the island leads to a higher current density near the center of the island than near its peripher...

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Section: Pacs Numbersmentioning

confidence: 99%

Suppression of Tearing Modes by Radio Frequency Current Condensation

Reiman

Fisch

2018

Phys. Rev. Lett.

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“…It is worth mentioning, however, that there is the potential for additional synergies between rf-stablization and hot ion mode operation, in the case of inside-launch LHCD 56,57 . While α-channeling can be used to redirect α-particle power back in to the fuel-ion population using waves that deposit their energy on the ions, it might also be used for driving toroidal current by amplifying LHWs.…”

Section: Discussionmentioning

confidence: 99%

On the merit of hot ion mode for tearing mode stabilization

Jin,

Reiman,

Fisch

2021

Preprint

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“…Although the alpha channelling effect has generally been pursued using waves in the ion cyclotron range of frequencies (Fisch 1995; Herrmann & Fisch 1997), recently it was shown that there are ways of launching the LH wave that can exploit the alpha channelling effect (Ochs, Bertelli & Fisch 2015 a , b ). The preferred launching techniques avoid launching the LH wave from the low field side of the tokamak.…”

Section: Effect Of Lh Frequency On CD Characteristicmentioning

confidence: 99%

Studies of challenge in lower hybrid current drive capability at high density regime in experimental advanced superconducting tokamak

Ding

et al. 2017

J. Plasma Phys.

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Aiming at a fusion reactor, two issues must be solved for the lower hybrid current drive (LHCD), namely good lower hybrid wave (LHW)-plasma coupling and effective current drive at high density. For this goal, efforts have been made to improve LHW-plasma coupling and current drive capability at high density in experimental advanced superconducting tokamak (EAST). LHW-plasma coupling is improved by means of local gas puffing and gas puffing from the electron side is taken as a routine way for EAST to operate with LHCD. Studies of high density experiments suggest that low recycling and high lower hybrid (LH) frequency are preferred for LHCD experiments at high density, consistent with previous results in other machines. With the combination of 2.45 GHz and 4.6 GHz LH waves, a repeatable high confinement mode plasma with maximum density up to 4.5 × 10 19 m −3 was obtained by LHCD in EAST. In addition, in the first stage of LHCD cyclic operation, an alternative candidate for more economical fusion reactors has been demonstrated in EAST and further work will be continued.

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Alpha channeling with high-field launch of lower hybrid waves

Cited by 27 publications

References 35 publications

Suppression of Tearing Modes by Radio Frequency Current Condensation

Suppression of Tearing Modes by Radio Frequency Current Condensation

On the merit of hot ion mode for tearing mode stabilization

Studies of challenge in lower hybrid current drive capability at high density regime in experimental advanced superconducting tokamak

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