Current channel evolution in ideal Z pinch for general velocity profiles

Recent diagnostic advances in gas-puff Z pinches at the Weizmann Institute for the first time allow the reconstruction of the current flow as a function of time and radius. These experiments show an unexpected radially-outward motion of the current channel, as the plasma moves radially-inward [C. Stollberg, Ph.D thesis, Weizmann Institute, 2019]. In this paper, a mechanism that could explain this current evolution is described. We examine the impact of advection on the distribution of current in a cylindrically symmetric plasma. In the case of metric compression, with |v_r| proportional to r, the current enclosed between each plasma fluid element and the axis is conserved, and so the current profile maintains its shape. We show that for more general velocity profiles, this simple behavior quickly breaks down, allowing for non-conservation of current in a compressing conductor, rapid redistribution of the current density, and even for the formation of reverse currents. In particular, a specific inward radial velocity profile is shown to result in radially-outward motion of the current channel, recovering the surprising current evolution discovered at the Weizmann Institute.Comment: 12 pages, 6 figure

Perspectives on Physics of E×B Discharges Relevant to Plasma Propulsion and Similar Technologies

This paper provides perspectives on recent progress in understanding the physics of devices in which the external magnetic field is applied perpendicular to the discharge current. This configuration generates a strong electric field that acts to accelerate ions. The many applications of this set up include generation of thrust for spacecraft propulsion and separation of species in plasma mass separation devices. These "“E X B” plasmas are subject to plasma–wall interaction effects and to various micro- and macroinstabilities. In many devices we also observe the emergence of anomalous transport. This perspective presents the current understanding of the physics of these phenomena and state-ofthe-art computational results, identifies critical questions, and suggests directions for future research.Y. Raitses and I. D. Kaganovich gratefully acknowledge partial financial support by the AFOSR grant (No. FA9550–17-1–0010) and assistance in preparation and fruitful discussions with I. Romadanov, Eduardo Rodriquez, and J. B. Simmonds. The work of A. Smolyakov was supported in part by the Natural Sciences and Engineering Research Council of Canada (NSERC) Canada, by the AFOSR grant (No. FA9550-18-1-0132), and by Compute Canada, and he acknowledges fruitful discussions with O. Chapurin, S. Janhunen, M. Jimenez, O. Koshkarov, I. Romadanov, and D. Sydorenko. The contribution of E. Ahedo and M. Merino was supported by the Government of Spain, National Development and Research Program, Grant No. PID2019-108034RB-I00, and they thank J. Navarro and P. Fajardo for their contribution. M. Keidar and I. Schweigert gratefully acknowledge the AFSOR grant (No. FA9550-19-1-0166). I. Schweigert was partly supported by the Russian Science Foundation (Grant No. 17-19-01375). S. Tsikata acknowledges support from CNES (Centre national d’ etudes spatiales, France). F. Taccogna gratefully acknowledges financial support from the Italian minister of university and research (MIUR) under the project PON “CLOSE to the Earth” No. ARS ARS01–00141. R. Gueroult and N. J. Fisch were supported by Nos. DOE DESC0016072 and NSF PHY-1805316. A. Bourdon and P. Chabert gratefully acknowledge financial support of the French National Research Agency (L’Agence nationale de la recherche) ANR grant (No. ANR-16-CHIN-003-01) and Safran Aircraft Engines within the project POSEIDON Israel Science Foundation, Grant 1581/16