MHD Stability of a Magnetized Target During Non-Self-Similar Compression

General Fusion is designing a magnetized target fusion test reactor that will compress a toroidal plasma inside a liquid metal cavity to heat it to fusion conditions. A magnetized plasma will heat adiabatically if rapidly compressed in a flux conserver (FC) following simple scalings in self-similar geometry.

In practice, variation of geometry from self-similarity complicates the equilibrium and stability calculations that drive the design process.  Here we present computations of the plasma stability evaluated for the entire compression of realistic FC geometries. Sequences of equilibria are generated using CORSICA under ideal and adiabatic compression, conserving both the safety factor and entropy profiles. The ideal MHD stability is then computed with DCON. The initial plasma pressure and current density profiles are varied to optimize the stability boundaries.  Geometry was found to affect the stability mainly via the q profile.  Most cases with q0<1 are found to be n=1 unstable, while those with q0>1 can be susceptible to low n modes. However, viable initial equilibria are found that remain stable throughout the compression.