Spatial structure of the neck and acceleration processes in a micropinch
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MA DYNAMICS
Spatial Structure of the Neck and Acceleration Processes in a Micropinch A. N. Dolgova, *, N. A. Klyachinb, **, and D. E. Prokhorovicha, *** a
All-Russia Research Institute of Automatics, Moscow, 127055 Russia Research Nuclear University “MEPhI,” Moscow, 115409 Russia * e-mail: [email protected] ** e-mail: [email protected] *** e-mail: [email protected]
b National
Received December 16, 2015; in final form, February 15, 2016
Abstract―It is shown that the spatial structure of the micropinch neck during the transition from magnetohydrodynamic to radiative compression and the bremsstrahlung spectrum of the discharge in the photon energy range of up to 30 keV depend on the configuration of the inner electrode of the coaxial electrode system of the micropinch discharge. Analysis of the experimental results indicates that the acceleration processes in the electron component of the micropinch plasma develop earlier than radiative compression. DOI: 10.1134/S1063780X16120047
1. INTRODUCTION As was shown in [1], the dynamics of the plasma of a noncylindrical Z-pinch discharge in a medium of low-Z elements depends on the electrode configuration. In the present study, we have observed a similar effect in a micropinch discharge, i.e., in a Z-pinch discharge in a medium of high-Z elements. Distinctive features of a micropinch discharge are high radiative losses from the pinch plasma, resulting in a high compression ratio of the pinch plasma, and record plasma densities and temperatures exceeding those in other types of pulsed discharges.
current reached its maximum value of 150 kA 1.5 μs after discharge initiation. The discharge parameters were monitored using magnetic probe 7, measuring the current time derivative. The pinching of the current channel was detected from the appearance of a dip in the current time derivative at an instant close to the maximum current, as is also observed in Z-pinches [1]. The well-developed stage of pinching, up to micropinch formation, was detected by the presence of a so-called “hot spot” in the X-ray images recorded by pinhole camera in the spectral range of hν > 3 keV [2].
2. EXPERIMENTAL LAYOUT The experiments were carried out using a high-current vacuum spark device (Fig. 1). The discharge was performed in the products of electrode erosion inside a vacuum chamber at a residual gas pressure of less than 10–2 Pa. The electrodes were made of St. 3 steel. The inner electrode (cathode 1) was a 3-mm-diameter cylinder with a conical end. The outer electrode (anode 2) was a cylinder with a 20-mm-diameter flat base. The length of the discharge gap between the coaxial electrodes was 5–7 mm. The discharge was initiated by the radial injection of the foreplasma from an auxiliary low-current discharge into the discharge gap. The circuit of the foreplasma source consisted of capacitor 3 (С1 = 0.22 μF), controlled vacuum spark dap 4, and triggering electrodes 5. The current source was high-voltage low-inductance capacitor bank 6 with a total capacitance of С2 = 12 μF. The discharg
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