Confinement and compression of magnetic flux by plasma shells

Abstract

Confinement and compression of magnetic flux by plasma shells is of interest for a variety of applications associated with keV x-ray production in pulsed-power driven Z-pinch plasma radiation sources ͑PRS͒. Confinement of a B z field with a B field of the pinch current can help stabilize the implosion of a shell from a large initial radius. Compression of the azimuthal magnetic flux in the PRS ͑secondary͒ circuit with a plasma shell driven by B field of the primary circuit may represent a new opportunity for using a low-cost, relatively slow pulsed power to generate large amounts of keV x rays. The magnetic field has to be compressed and/or confined by low-mass plasma shells emitting soft x-ray radiation that limits the temperature and conductivity of the shell plasma. The thickness of a plasma shell is established self-consistently during the implosion, and it is not obvious whether or not the shell becomes thick enough to confine or compress the magnetic flux. The results of analytical theory and numerical simulations demonstrate that the flux-compressing capability of a low-beta plasma shell is surprisingly good because the shell is shown to dynamically adjust its thickness so that it always remains of the order of its skin depth. The self-similar profiles of confined magnetic field predicted by the theory are consistently reproduced in the simulations.

Heating of on-axis plasma heating for keV X-ray production with Z-pinches

“…Already when the shell traveled the distance comparable to its initial thickness ( mm, see Fig. 1), the established density profile becomes close to that predicted theoretically [27]. The Ohmic heating of the shell is compensated by radiative cooling of the argon plasma.…”

“…As the argon shell intensively radiates, its temperature is low and the plasma shell thickness is shown to be determined only by the magnetic field skin depth [27]. Therefore, this magnetic field must exist in the shell plasma also at the shock wave and quasi-adiabatic compression stages.…”

“…At the same time, the difference in initial radial density distribution is known to make little effect on the K-shell yield predicted by 1-D radiation-hydro models [2]. Indeed, a distributed fuzzy shell transforms itself into a thin shell during a 1-D simulation of implosion [27], producing essentially the same K-shell yield. The effect of higher observed keV radiated energy for initially diffuse density profiles can be reasonably explained by an enhanced 2D stability of implosion in the more filled-in part of the gas flow [2].…”