Formation of double shell during implosion of plasma metal puff Z-pinches

Abstract

This work presents the results of experimental and theoretical research of impact of tailored density profile and application of external axial magnetic field on initial spatial distribution of the plasma density in the plasma metal puff Z-pinch and on its implosion dynamics. It has been discovered that upon implosion of the plasma metal puff Z-pinch some stripes interpreted as the system of two coaxial shells appear on the optical images. With the help of numerical simulation, the formation of the plasma liner consisting of a mixture of carbon and bismuth ions and formed by the expansion of the plasma jet of the arc burning on the bismuth electrode has been considered in this work. It has been shown that the lightweight carbon ions facilitate formation of the density distribution smoothly decreasing with the increase in radius, that, in turn, leads to suppression of the Rayleigh-Taylor instability in the current sheath upon further implosion. It has also been demonstrated that availability of the two types of ions in plasma considerably different in mass leads to formation (in the compression phase) of a double shell with externally located heavy ions. It has also been revealed that the application of the external axial magnetic field leads to reduction in the plasma metal puff Z-pinch initial diameter.

Studies on the implosion of pinches with tailored density profiles

“…Comparing the plots given in figure 6(a) with figure 6(b), we see that the calculated characteristics of the K-shell radiation are rather close to but higher than the respective quantities obtained in experiments on the MIG facility. This discrepancy can be associated with many factors that were not taken into account in the calculations, such as the presence of impurities resulting in diffusion of ions of various substances into the pinch plasma [51,52], the zippering effect, the error in determining the XRD sensitivity, etc. However, the main factor is probably the growth of MRT instabilities that arise at the stage of pinch stagnation, as can clearly be seen in figures 3(c) and (d).…”

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

“…On the other hand, the bright flash could occur due to the arrival of light ions at the pinch axis. In imploding metal-puff Z pinches, light ions move 20%-30% faster than heavy metal ions [28]. To clarify this point, further investigations are needed, which we intend to perform in the future.…”

“…The radial density profile that occurred during the expansion of the PJ was simulated using a previously developed twodimensional quasi-neutral hybrid model [27,28]. The amount of mass m jet (t) entering the PJ due to the erosion of the vacuum arc electrodes was determined using radiographic measurements.…”

Numerical model of high current plasma source

“…The average cathode current density here is the total current divided by the surface area of the cathode. In various experiments, a current from tens of kiloamperes to several megaamperes was passed through similar plasma sources [2][3][4]. Considering that the diameter of the cathode rod in the plasma gun was several millimeters, the average cathode current density reached 10 5 -10 6 A/cm 2 .…”

“…Under such conditions, the specific cathodic erosion in interrupters remains close to the canonical cathodic specific erosion measured in low-current arcs (of the order of 15-170 µg/C for various metals [5]). By measuring the masses of plasma liners by various methods, it was concluded in [1][2][3][4] that the specific erosion of plasma sources (Fig. 1.)…”