Cross-validation of analytical models for computation of disruption forces in tokamaks

Abstract

Electromagnetic forces generated during hard-to-predict transient events, represent a serious constraint for the operation and design of tokamaks. A sudden loss of plasma stability, triggering plasma thermal and current quenches, leads to the induction of eddy currents in the conducting structures surrounding the plasma column. Interaction of these currents with the magnetic field is responsible for a j×B local force that might compromise the integrity of the device. Here we evaluate the effect of poloidal currents induced in the wall on the local and global forces. To test the earlier analytical predictions (Pustovitov and Kiramov 2018 Plasma Phys. Controlled Fusion 60, 045011), we consider a circular tokamak by the numerical tool CarMa0NL (Villone et al 2013 Plasma Phys. Controlled Fusion 55, 095008). The results confirm the necessity of incorporating the poloidal currents into the task, as these strongly affect the local stress distribution and the global radial force. The overall agreement between analytical and numerical computation is an additional evidence that CarMa0NL is a sound tool for the prediction of disruption forces in tokamaks. At the same time, the simulation conditions in which the agreement is less satisfactory allow to identify which are the most restrictive assumptions of the analytical model, pointing out the way for future theoretical work.

Analysis of Electromagnetic Loads on the Vacuum Vessel during Thermal Quench in the TRT Tokamak

“…Comparison with the exact results of numerical simulations performed using the CarMa0NL code and given in [31,32,49] confirmed the necessity of considering the poloidal currents when solving the problem. The analytical predictions as a whole were also confirmed, including those given by Eqs.…”

“…In a similar formulation, the disruption-induced wall forces were considered analytically in [23][24][25][26] for the plasma and wall with circular cross sections. Here, the plasma and wall are vertically elongated, but it can be expected that the main dependencies found in [23][24][25][26] should also manifest themselves in our case too [22,31,32]. In particular, we will check the prediction that a strong radial force can be generated during the TQ before the CQ start, although the presence of dangerous electromagnetic loads in tokamaks is usually associated with the current quench [6,7,[11][12][13][14][15][16][17][18][19][33][34][35][36][37][38][39][40][41][42][43][44], sometimes explicitly noting that the force is proportional to [7,36,42].…”

“…The effect of the current on the wall forces was discussed in [25,45], and then in [31,32,46,47]. In [45], it was numerically shown for the first time that the poloidal currents induced during disruptions in the IGNITOR tokamak can have a considerable effect on both the total radial force and the normal force acting on the wall.…”

“…(7) and (15). The additional analytical study [50], performed after it was demonstrated in [31,32] that the local forces depend on the plasma position relative to the wall, showed that the plasma position has almost no effect on the integral radial force when both terms in Eq. ( 10) are taken into account.…”

Sideways forces on asymmetric tokamak walls during plasma disruptions

“…Calculations are performed with CarMa0NL code [25,26,40,43,44], which solves evolutionary equilibrium of 2D plasma in the presence of 3D volumetric conductors. This means that the plasma is supposed to be in equilibrium at each time instant.…”