Formation of an anisotropic electron velocity distribution function and production of multicharged ions in the micropinc
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MA DYNAMICS
Formation of an Anisotropic Electron Velocity Distribution Function and Production of Multicharged Ions in the Micropinch Discharge Plasma A. N. Dolgov, N. V. Zemchenkova, N. A. Klyachin, and D. E. Prokhorovich National Research Nuclear University, Moscow Engineering Physics Institute, Kashirskoe sh. 31, Moscow, 115409 Russia Received May 21, 2010; in final form, June 17, 2010
Abstract—Analysis of the results of polarimetric measurements of Xray line radiation of multicharged ions in a Zpinch discharge indicates that the formation of an anisotropic electron velocity distribution in the neck of the current channel and the generation of highly charged ions are separated in time. The generation of a fast electron beam in the longitudinal ohmic electric field in the stage of plasma compression in the neck results in the polarization of Xray bremsstrahlung continuum. In the stage of expansion of the hot dense micropinch plasma, the radial electric field prevails, due to which Xray line radiation of multicharged ions becomes linearly polarized. DOI: 10.1134/S1063780X10121025
1. INTRODUCTION
nature of this phenomenon by analyzing the experi mental data.
Fast electrons generated in the plasma of a high current Zpinch discharge operating in a heavyele ment medium can substantially affect the spectrum of discharge plasma radiation. In particular, the effect of fast electrons manifests itself in the polarization of radiation of multicharged ions [1–5]. Experimental results indicate that the generation, excitation, and emission of highly charged ions occur at the instant at which a “hot spot” (or micropinch)—a domain with an electron temperature of Те ≈ 2–3 keV, an electron density of ne ≈ 1022 cm–3, and a radius of r ≥ 5 µm [6– 8]—forms in the neck of the discharge current chan nel. The line radiation spectrum of multicharged ions is rather complicated, separate lines being superim posed. Therefore, timeintegrated measurements turn out to be inapplicable to recover the true line profiles and the relative line intensities averaged over the emis sion time and, thus, to determine the conditions in which radiation is emitted. Since the time of micropinch formation is very short, study of the micropinch radiation dynamics is a difficult technical task that requires application of equipment with a picosecond time resolution. Moreover, since the time scatter in the instant of micropinch formation reaches a few tens to several hundred nanoseconds, special methods for synchronization of the recording devices with the process under study should be applied. Taking into account the aforesaid, the polarization mechanism of line radiation of multicharged ions from the plasma of a pinch discharge operating in a heavyelement medium still remains discussable. The objective of the present study was to elucidate the
2. EXPERIMENTAL LAYOUT AND RESULTS The experiments were carried out using a highcur rent vacuumspark device. Two versions of the dis charge device with different discharge initiation schemes were us
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