Analysis of the direction of plasma vertical movement during major disruptions in ITER

Abstract

The plasma movement in the upward direction (away from the X-point) after the thermal quench (TQ) of major disruptions in ITER is favourable for the machine design, since the downward movement causes larger electromagnetic (EM) load due to the induced eddy and halo currents. Vertical directions of plasma movement after the TQ in ITER are investigated using the predictive mode of the DINA code. Three dominant parameters in determining the direction of plasma movement are identified: (i) the rate of plasma current quench (plasma temperature after the TQ), (ii) the width of plasma current mixing area just after the TQ (change of the internal plasma inductance l i ) and (iii) the initial vertical position of plasma column before the TQ. It is shown that the reference ITER plasma moves upwards after the TQ, if the electron temperature after the TQ is less than 10 eV and the drop of l i does not exceed 0.2 for the present reference initial vertical position (55.5 cm above the centre of the machine). It is also shown that the operational domain leading to the upward movement is considerably large for disruptions with fast current quench, which could generate quite severe EM load due to the induced eddy current combined with the induced halo current if the movement is downwards.

Analytical model of wall forces produced by kink perturbations in tokamaks

“…It is known [2][3][4][5]7,8,[10][11][12][13][14][15][16][17]20,22,[33][34][35][36][37] that the force on the wall during the disruptions in tokamaks depends on the halo current, which is the part of the plasma current that flows in the conducting structure and has a return path through the plasma. 14,15,22,33,34 In Ref.…”

Complete 3D MHD simulations of the current quench phase of ITER mitigated disruptions

“…We attribute this change of direction to the stronger drop in l i (3) for case #2. It was found in [18] that large drops of the internal inductance during major disruptions in ITER lead to downward displacements. Similarly for the ASDEX-Upgrade tokamak [20], it was found that drops of l i in lower single-null plasmas cause a "vertical dragging effect" that moves the plasma downwards.…”

Modeling of Plasma Current Decay during Disruptions Caused by Massive Impurity Injection

“…In these experiments, a rupture disk (RD) has been used to realize quick injections of gas. In addition, at the downstream of the RD, orifices of different diameters (6,12, and 45 mm) have been used to control the amount of the injected impurity gas. The current decay times τ c for each RD have been fitted with an exponential curve using 80% to 20% of I p0 (cf.…”

“…employing the NP of the plasma current center. Since there is no universal NP [6], however, the halo current should be decreased during a VDE, in particular caused by a slow current quench. In DIII-D, a reduction of the halo current was observed by shutting down the plasma very quickly by means of a massive impurity injection [7].…”