Field and Current Amplification in the SSPX Spheromak

Abstract

Recent results from the SSPX spheromak experiment at Livermore show peaked temperature and pressure profiles with low fluctuation levels, core transport coefficients near tokamak L-mode levels, and evidence that the device is operating near a beta limit. These results point to the need for obtaining significant magnetic field amplification. We have added a pulse-forming network to extend the discharge duration and a new set of bias magnetic field coils (which provide a uniquely flexible vacuum field configuration), to explore the physics of magnetic field generation in the spheromak. The bias coils allow low density, high Te ~ 150 eV operation and reduce the threshold current needed to form and maintain the spheromak by about a factor of 2, thereby lowering the fluctuation level. With a flat 3 msec current pulse, we observe steadily increasing field amplification throughout the discharge. We have installed a hyper-resistivity model for helicity transport in the 2d CORSICA code to simulate the observed current amplification. Numerical simulation of the evolution of the magnetic field topology (e.g. internal q-profiles) using the 3d resistive MHD code NIMROD will also be discussed.