The Effect of Bootstrap Current on Ideal Magnetohydrodynamic Equilibrium State of Snake Structure.

This study investigates the impact of bootstrap current on the snake structure, which is a three-dimensional ideal MHD state observed in JET tokamak during D₂ pellet injection [1]. When the pellet ablates on-axis, it locally cools the plasma, causing the plasma current to move radially outward and create a hollow current profile. This outward shift results in the minimum value of the safety factor, q, moving outward as well. When this minimum q is near unity and off-axis, it rapidly saturates the ideal internal MHD kink mode, inducing the snake structure. The 3D snake equilibrium has been theoretically proved and computed using VMEC code [2]. On the other hand, bootstrap current will play an important role in fusion reactors, especially for the low aspect ratio tokamaks. It is worth investigating the impact of bootstrap current on the snake structure. Here, we present the analysis and comparison in various tokamaks, i.e. TCV, ITER and MAST.

[1] R.D. Gill et al 1992 Nucl. Fusion 32 723

[2] W.A. Cooper et al 2011 Nucl. Fusion 51 072002