Numerical study of magnetic island suppression by RF waves in large tokamaks

Abstract

The suppression behaviour of magnetic island growth using electron cyclotron heating and lower hybrid current drive is analysed. A quasi-linear model is developed for island suppression, including the local peaking effect of the resistivity and the RF-driven current within the island. Pulsed launching of lower hybrid waves synchronized with the plasma diamagnetic rotation frequency can strongly suppress the magnetic island.

On the stabilization of neoclassical magnetohydrodynamic tearing modes using localized current drive or heating

“…Similar techniques for the prevention of resistive tearing modes and disruption control have been proposed and studied previously. [16][17][18][19][20][21][22][23][24][25][26][27][28] In this work, the prevention and stabilization of neoclassical tearing modes have been emphasized.…”

“…A number of proposals have been suggested and studied relative to stabilizing magnetic island formation in tokamaks which are resistive MHD unstable. In particular, these methods include using applied resonant field errors with negative feedback, [11][12][13][14][15] local heating of the island region, [16][17][18][19][20][21][22][23] and local current drive mechanisms. [24][25][26][27][28] We extend these studies and use a similar procedure to study the local heating and current drive effects on neoclassical MHD tearing modes.…”

Tearing mode stabilization in tokamaks with lower hybrid waves

“…phasing at the X point). The problem can be analysed by inserting the computed induced electric field E (ρ, t), or an equivalent J RF (ρ, t) = E /η (η being the resistivity), into the equation for the evolution of the island width w [1][2][3][4][5][6][7][8][9][10][11]. This has been accomplished by basically following the formalism of Ref.…”

“…It is therefore optimized using feedback techniques, namely modulating the heating power in phase with the island rotation. Non-inductive current drive inside the island is expected to act in the same way, but to be substantially more efficient [1][2][3][4][5][6][7][8][9]. Rutherford's theory of the non-linear tearing mode evolution shows that co-current driven at the island O point and counter-current at the X point are stabilizing, the former method being more efficient [3].…”

“…This was proposed theoretically several years ago [1][2][3][4][5], but never experimentally validated, although inconclusive results, obtained under unfavourable experimental conditions, have been reported [24]. Indeed, it has often been reported that in lower hybrid current drive (LHCD) experiments, the m = 2 mode was destabilized.…”