Modeling Liner Compression of FRCs: Obstacles and Advances

Compression of a field-reversed configuration (FRC) by an imploding solid liner is a possible path to magnetized target fusion. It is critical to the success of such experiments to perform full-up multidimensional computational simulations of them. However, there are numerous difficulties in performing those simulations. The interacting physical processes involved introduce disparate time scales. For example, the FRC itself has near-vacuum buffer-field regions that have extremely high Alfven velocity, while the implosion of the liner proceeds at a much slower pace. These strongly differing time scales impose stringent accuracy requirements. The lifetime of an FRC of sufficient density to provide interesting fusion output is on the order of 10 ms while the implosion times of liners of sufficient thickness to survive acceleration to the requisite velocity are somewhat longer than 20 ms. Hence, the FRC must be formed and translated into the liner after the liner implosion begins, so that the FRC formation fields may perturb the liner. Our previous simulations of the experiment have addressed formation separately from the liner implosion and merged the FRC into the liner simulation, preventing proper assessment of this issue. Experimental success hinges on realizing the magnetic inhibition of thermal conduction to prevent loss of plasma energy. Our previous simulations of the final stages of FRC compression have often failed because of inaccuracy in the numerical treatment of the parallel flux.