Study of the termination phase of plasma production and the formation of magnetic flux breakthroughs during wire array implosion

Abstract

The phenomenon of magnetic flux breakthrough into a wire array during its implosion was studied experimentally at the Angara 5 1 facility. It is shown that breakthroughs develop in the final stage of plasma production from the wire material and occur near the initial wire position. The spatial distributions of the azi muthal magnetic field within tungsten, molybdenum, copper, and aluminum wire arrays were studied using magnetic probes. The distributions of the azimuthal magnetic field B ϕ (z, t) along the array height in different stages of implosion were measured, and the characteristic dimensions of regions with a nonuniform magnetic field that appear during magnetic flux breakthroughs at the outer boundary of the wire array plasma were determined. The dimensions of these regions are compared with those of the regions with depressed plasma radiation observed in frame and time integrated X ray images. The dynamics of the distribution B ϕ (z, t) in regions with a nonuniform magnetic field during breakthroughs of the azimuthal magnetic flux is compared with that of the spatial distribution of pinch radiation in the frame X ray images in different stages of implo sion. The experimental data on the characteristics of spatially nonuniform breakthroughs of the magnetic flux into the wire array are analyzed using the plasma rainstorm model proposed by V.V. Aleksandrov et al. (JETP 97, 745 (2003)). The plasma density in the region of magnetic flux breakthrough is estimated.

Progress in researching the implosion of nested arrays of mixed composition and the generation of soft x-ray power pulse

“…The times of the end of plasma production on the outer T pl out and inner T pl in arrays were determined from measurements of the derivative of the total current dI/dt and voltage U (see curves 1 and 2 in figures 2(a)-4(a)) in the following way. Based on the experiments [37,52] with single wire arrays made of various substances, it was shown that at the stage of the end of plasma production, when ṁ → 0, in the region where the wires (or fibers) are located, the magnetic flux breaks into the interior of the array. This leads to an increase in the inductance of the wire array and a violation of the proportionality between the voltage U and the derivative of the total current dI/dt.…”

“…However, the final stage of compression of wire arrays [36][37][38] and thin metal shells [39] is accompanied by the development of various instabilities. One of the main and dangerous types of instabilities of the outer boundary of the plasma, accelerated by the pressure of the magnetic field of its own current, is the magnetic Rayleigh-Taylor (MRT) instability.…”