In recent years, there has been great interest in the intense plasma flows generated by plasma focus facilities, which are widely used in various fields. In particular, laboratory experiments on modeling astrophysical jets developed, for which plasma focus facilities also proved to be in demand [1].
However, there has not been an unambiguous point of view on the mechanisms of flow launch until now. The most popular mechanisms were cumulative plasma outflow either at the stage of compression of the plasma current sheath (PCS) to the axis, or during the development of constrictions already on the body of the formed pinch [2, 3]. The paper presents experimental data and a theoretical model that make it possible to formulate a fundamentally new look on the physics of the launching mechanism of plasma ejection in a plasma focus discharge.

Experimental studies of the stage of the plasma jet generation at the ISPF-M plasma focus facility at the Kurchatov Institute have shown that the source of the plasma outflow propagating along the axis of the discharge system is a local region inside the PCS in its upper part. It shows that the plasma bunch moves in a well-defined direction upward from the anode, rather than in symmetrical directions, which would be expected, for example, when plasma flows out of a pinch constriction. A characteristic feature of this region is the presence of a radial component of the electric current, which leads to the appearance of a vertical component of the plasma velocity due to Ampère force. Already at the initial stages of the plasma bunch movement, it has a supersonic character, which leads to the formation of a shock wave. In this case, the upper boundary of the PCS is destroyed, which can lead to the reconnection of magnetic field lines and currents and the formation of a compact plasma bunch with a trapped magnetic flux propagating along the axis of the system, in accordance with the model formulated in [4].

The shadowgram of the discharge in argon at the second harmonic of the Nd:YAG laser (532 nm) 40 ns after the peak of the derivative of the discharge current corresponding to the phase of maximum pinch compression (a) and the shadowgram of the discharge in hydrogen at the fundamental harmonic (1064 nm) 29 ns (b) and 62 ns (c) after the peak of the derivative.

1. V.S. Beskin, V.I. Krauz, S.A. Lamzin, Physics – Uspekhi 66, 327 (2023).
2. N.V. Filippov, et al., Applied Physics (Prikladnaya Fizika) 5, 43 (1999).
3. S. N. Polukhin, at al. Plasma Physics Reports 46, 127 (2020).
4. K.N. Mitrofanov et al. JETP 119, 2010 (2014)

V. Krauz, V.  Beskin, M. Medvedev,  A. Kharrasov, V. Myalton
JETP Letters 122, issue 10 (2025)