Spheromak Formation and Current Sustainment Using a Repetitively Pulsed Source

Abstract

By repeated injection of magnetic helicity (K = 2φψ) on time-scales short compared with the dissipation time (τinj << τ K ), it is possible to produce toroidal currents relevant to POP-level experiments. Here we discuss an effective injection rate, $$ \dot{K}_{\text{eff}} = 2\psi_{\text{gun}} I_{\text{gun}} \dot{L} $$ due to the expansion of a series of current sheets and their subsequent reconnection to form spheromaks and compression into a copper flux-conserving chamber. The benefits of repeated injection are that the usual limits to current amplification can be exceeded, and an efficient quasi-steady sustainment scenario is possible (within minimum impact on confinement). A new experiment designed to address the physics of pulsed formation and sustainment is described.