Study of the dynamics of the electrode plasma in a high-current magnetically insulated transmission line
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DYNAMICS
Study of the Dynamics of the Electrode Plasma in a High-Current Magnetically Insulated Transmission Line Yu. L. Bakshaeva, A. V. Bartova, P. I. Blinova, A. S. Chernenkoa, S. A. Dan’koa, Yu. G. Kalinina, A. S. Kingsepa, V. D. Koroleva, V. I. Mizhiritskiœa, V. P. Smirnova, A. Yu. Shashkova, P. V. Sasorovb, and S. I. Tkachenkoc a Russian
Research Centre Kurchatov Institute, pl. Kurchatova 1, Moscow, 123182 Russia b Institute of Theoretical and Experimental Physics, ul. Bol’shaya Cheremushkinskaya 25, Moscow, 117259 Russia c Institute for High Energy Densities, Russian Academy of Sciences, Izhorskaya ul. 13/19, Moscow, 125412 Russia Received January 31, 2006; in final form, June 05, 2006
Abstract—A series of experiments was carried out in the S-300 facility (3 MA, 0.15 Ω, 100 ns) to study the behavior of a section of a magnetically insulated transmission line (MITL) at current densities of up to 500 MA/cm2 and linear current densities of up to 6 MA/cm (i.e., at parameters close to those expected in a fast Z-pinch fusion reactor projected in Sandia National Laboratories). The surface explosion of the ohmically heated MITL electrode is accompanied by the formation of a plasma layer on its surface. This can deteriorate of the transmission properties of the line because the vacuum gap is short-circuited by the plasma produced. The parameters of the electrode plasma and its effect on the MITL transmission properties were investigated experimentally. Possible consequences of the above effects are evaluated, and MHD simulations of the electrode explosion and the subsequent spread of the plasma layer are performed. It is shown that the time during which an MITL segment preserves its transmission properties conforms to the requirements of the conceptual fusion reactor. PACS numbers: 52.58.Lq DOI: 10.1134/S1063780X07040010
1. INTRODUCTION In Sandia National Laboratories (USA), a conceptual project has been developed of a fast Z-pinch inertial fusion reactor [1]. One of its main components is a recyclable magnetically insulated transmission line (MITL). MITLs are commonly used to transfer energy in various schemes of high-power high-current pulsed generators. The Sandia project, however, intends to use them at extremely high energy fluxes and current densities. In particular, the total current is expected to be I ≈ 60–90 MA. No experience in working at such extremely high parameter values has been acquired yet. When the MITL electrode is ohmically heated, its surface can explode, forming a surface plasma layer. The electrode explosion in a recyclable MITL can lead to the loss of its transmission properties for the following reasons: (i) an unacceptable decrease in the MITL effective conductance, (ii) an increase in the ion-current leakage from the positive electrode through the MITL vacuum gap due to the formation of a plasma layer, and (iii) the bridging of the vacuum gap by the plasma produced.
Therefore, studying the behavior of the electrode material in an MITL and the operation of the MITL itself under such sever
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