Runaway current termination in JT-60U

Abstract

Termination of the runaway electron current generated during plasma disruptions is found in JT-60U during simulated vertical plasma displacement events where the safety factor at the plasma surface qs decreases. For all discharges with runaway electron generation, the runaway current disappears for qs⩾2 with the appearance of spikes in the magnetic fluctuations. The growth rate of the spikes in the magnetic fluctuations decreases by an order of magnitude during the termination of runaway current. Corresponding to the loss of runaway electrons by magnetic fluctuations, heat flux pulses are measured at the inner divertor plates, which indicates interaction of the wall with the runaway electrons. The halo current during runaway termination is small and increases after runaway termination with a dominant toroidal mode of n = 1.

Disruptions in ITER and strategies for their control and mitigation

“…These numbers are consistent with previous JET observations during fast loss events [21] as well as more recent experiments with Ar MGI [22]. Also at JT-60U, a small poloidal extent of the RE heat flux of about 200 mm has been observed during fast RE loss events of less than 0.25 ms duration [23]. The above consideration assumes a RE beam in limiter configuration.…”

Disruptions, Disruptivity, and Safer Operating Windows in the High-β Spherical Torus NSTX

“…The loss of energy confinement can lead to severe thermal loads on the plasma facing components [1][2][3][4][5][6][7][8], while the electromagnetic loads from the "current quench" [9][10][11][12][13][14] can lead to excessive mechanical loads [15]. The current quench can also lead to the generation of runaway electrons [6,7,[16][17][18][19][20][21], which can result in catastrophic vessel and PFC damage [33]. Finally, if the control of the plasma vertical position [23][24][25][26][27] is lost, the plasma can drift up or down and come in contact with the vessel and PFCs; the "halo currents" [28][29][30][31][32][33][34] that are shared between those components and the plasma can lead to destructive forces [15].…”

Fuelling efficiency of massive gas injection in TEXTOR: mass scaling and importance of gas flow dynamics

“…Physics of runaway electrons, possible methods of their suppression and runaway current termination are discussed in [2,12,[17][18][19][41][42][43]. Here we consider only collisional runaway suppression and limit ourselves to a brief explanation of why the electron density must be raised extremely for the suppression to be guarantied.…”