Studies on the implosion of pinches with tailored density profiles

Abstract

This paper presents the results of experimental and theoretical studies of imploding metal-puff Z-pinches. The experiments were carried out on the MIG high-current pulse generator at a current level of about 2 MA and a current rise time of about 100 ns. A plasma gun was used to produce a plasma column with a tailored density profile through which the main electromagnetic pulse of the MIG generator was passed. The experiments have shown that pinches of this type, being compressed, are resistant to dynamic magneto-Rayleigh–Taylor (MRT) instabilities. The experimental results were analyzed using one-dimensional radiation magnetohydrodynamic simulations. It has been shown that in a pinch with a tailored density profile, the formation of a high-temperature plasma at the pinch axis and the generation of x-rays occur at the stagnation stage, i.e. under conditions close to Bennett equilibrium. At this stage, flute-like MRT instabilities develop, causing the pinch to decay.

Effect of tailored density profiles on the stability of imploding Z-pinches at microsecond rise time megaampere currents

“…In general, the implosion pattern is quite consistent with the mechanism proposed in [20]: the radiator mass preheated by the shock wave 'is heated quasiadiabatically as long as the implosion continues'. Similar conclusions were obtained in [35,[42][43][44][45]. Unfortunately, the radiator mass cannot be determined within the framework of the snowplow model used by us, and we plan to carry out this work in the near future by using other diagnostics.…”

“…The radius of the optical image, measured for the center of the gap with an error of ±0.2 cm, fits well the curve representing r pinch (t) in figure 5(a). The stable implosion observed for the TDP mode (see figures 6(a) through (d)) is similar to the implosion of an Mg metal puff Z-pinch with a TDP that was driven by the MIG generator (2 MA, 100 ns) [35]. It can be seen that, as predicted in [9], the TDP operated as a switching device, providing an opportunity of stable pinch implosion at a current rise time of 1 µs.…”

“…On the one hand, this flash could be associated with a shock wave arrived at the axis. Such a shock wave, as shown in [35][36][37][38], can move away from the current sheath (acting as a magnetic piston) for a distance of 0.5-1 cm. On the other hand, the bright flash could occur due to the arrival of light ions at the pinch axis.…”

Scaling of rise time of drive current on development of magneto-Rayleigh-Taylor instabilities for single-shell Z-pinches

“…However, it should be noted that the effects of current peak on the process of plasma formation are not considered in the paper, which could affect the developments of MRTs by changing the perturbation seed, the temperature and density profile. [36,54] With other parameters corresponding to Fig. 1, effect of the current rise time τ on the development of MRTs is studied.…”

Effect of the plasma self-radiation on the growth of thermal filamentation instabilities in imploding Z pinches

“…In Z-pinch plasmas, various types of magnetohydrodynamic instability may develop. The most dangerous of these are Rayleigh-Taylor instabilities whose growth is caused by the pressure of the magnetic field created by the current flowing through the pinch [2][3][4][5][16][17][18][19][20]. In terms of the MagLIF concept, to suppress this type of instability, it is supposed to use an external magnetic field whose induction vector is directed axially, that is parallel to the direction of the current.…”