Measuring the compression velocity of a Z pinch in an axial magnetic field

Abstract

This paper presents the results of measuring the velocity of the plasma boundary during the compression of a metallic gas-puff Z pinch in an axial magnetic field. The experiment was conducted on the IMRI-5 facility (current pulse of 450-kA amplitude with a 450-ns rise time); the initial magnetic field Bz0 was varied in the range of 0.15–0.6 T. To measure the compression velocity, B-dot probes were used successfully. The data obtained with the B-dot probes agree with the results obtained by other methods [visible imaging and determination of the pinch radius as a function of the time-varying pinch inductance L(t)]. It is shown that the plasma compression velocity is (1–1.5) × 107 cm/s at Bz0 = 0 and 0.6 × 107 cm/s at Bz0 = 0.6 T.

Effects of a Preembedded Axial Magnetic Field on the Current Distribution in a Z -Pinch Implosion

“…These advances follow three decades of experimental [7][8][9][10][11][12][13][14][15] and theoretical [16,17] research. Some of the magnetized-plasma implosion experiments [7,8,11,[18][19][20][21] reveal new and unpredicted phenomena, yet to be fully understood, which dramatically differ from those observed in implosion experiments without preembedded axial magnetic field. These include significant changes in the plasma dynamics and radiation emission properties, specifically, (i) the formation of helical structures [18,19], (ii) larger than predicted implosion time and plasma radius at stagnation [19][20][21] accompanied by strong mitigation of instabilities [11,19], and (iii) reduction of the continuum [7,8] and K-shell emission [11].…”

“…(i) B z significantly slows down the plasma implosion and increases the final stagnation radius [19][20][21], while simulations using the NRL 1-D radiation-MHD code [36] predict that the B z counter-pressure is too low to have such significant impact on the plasma dynamics. In our experiment, the implosion time for B z0 = 0.4 T is ∼ 35% longer than for B z0 = 0, while simulations, assuming the entire current flows in the imploding plasma, predict an implosion longer by only ∼ 2%.…”

Hybrid MHD/PIC Simulation of a Metallic Gas-Puff Z-Pinch Implosion

“…Compression dynamics is regulated by solving the system of the electric circuit equations with the following circuit parameters: L0=25 nG, C0=3,2 µF, initial voltage U(0)=40 kV. In the case of the short circuit the circuit provides current I(t)=Imaxsin((π/2t0)t), where t0 is about 450 ns, Imax -about 450 kА, which is in compliance with current source characteristics used in the experiment [1,2].…”

“…The metallic gas-puff z-pinch are formed by injecting high-current vacuum arc plasma into a vacuum gap the electrodes of which are under the voltage supplied by a generator to produce the z pinch. A number of studies [1][2][3] show that the plasma liners thus generated have a smoothly decreasing with an increase of radius density profile (so called tailored profile). According to [4], the liner with density profile subject to power law of density reduction suppresses the development of Rayleigh-Taylor instability during the implosion of the z-pinch that results in more homogeneous compression involving almost all substance of the liner.…”

“…In case of compression of a sharp boundary liner, the Rayleigh-Taylor instabilities develop in the current sheath that makes only a part of the liner substance to compress [5]. As some experimental researches [1][2] reveal, the liner formed by injecting the high current arc plasma compresses homogeneously without any visible disturbances typical for the developed Rayleigh-Taylor instability.…”