Magnetic island suppression by electron cyclotron current drive as converse of a forced reconnection problem

Abstract

This paper addresses one aspect of the problem of the suppression of tearing mode magnetic islands by electron cyclotron current drive (ECCD) injection, formulating the problem as the converse of a forced reconnection problem. New physical conditions are discussed which should be considered in the technical approach towards a robust control strategy. Limits on the ECCD deposition are determined to avoid driving the system into regimes where secondary instabilities develop. Numerical simulations confirming the theory are also presented.

Suppression of Tearing Modes by Radio Frequency Current Condensation

“…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].…”

Control of neoclassical tearing mode by synergetic effects of resonant magnetic perturbation and electron cyclotron current drive in reversed magnetic shear tokamak plasmas

“…To stabilize NTM, electron cyclotron current drive (ECCD) is the most widely used and straightforward method [23][24][25][26][27][28]. By emitting radio frequency electron waves localized at the magnetic islands, it can compensate the loss of bootstrap current caused by the flattening of pressure profile and modify the local plasma current gradient [29].…”

RF current condensation in magnetic islands and associated hysteresis phenomena

“…NTMs were recognised as a source of major disruptions in experiments such as JET 6,7 , and thus their stabilisation is central. Amongst proposed stabilisation approaches, driving current 8,9 at the islands with RF waves has stimulated a long list of added efforts, [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] including many experimental demonstrations [30][31][32][33][34][35][36] . By driving current at the centre of the island using ECCD 37,38 or LHCD 39,40 one may balance the lack of bootstrap current, and prevent the island growth.…”