Observation of poloidal magnetic flux emission from the post-pinch phase of a plasma focus and its significance for laboratory simulation of astrophysical jets

Abstract

Astrophysical jets are plasma flows, which are observed to substantially maintain their transverse size while travelling distances orders-of-magnitude larger. They are found in many astrophysical contexts, spanning several decades in energy and size, suggesting operation of an underlying scale-invariant mechanism. Similar phenomena observed in laboratory plasmas are often studied as surrogate models for astrophysical jets under the conjecture that the scale-invariance of that as-yet-unconfirmed mechanism continues to hold down to laboratory spatial and energy scales. The plasma focus is one such laboratory plasma device which offers the advantage of diagnostic accessibility at a relatively modest resource cost. The present paper uses the plasma focus to address one of the intriguing aspects of the astrophysical jet phenomenon. Theoretical models of astrophysical jets require presence of a poloidal magnetic flux but there is no observational basis for assuming its existence. Indeed, there is a fundamental theoretical impossibility of existence of poloidal magnetic flux in the natural symmetry of the jet phenomena about its axis in the context of magnetohydrodynamics. The next best evidence in support of the poloidal magnetic flux hypothesis of such theoretical models would be to look for it in surrogate experimental simulations of astrophysical jets. In this context, this paper demonstrates a new diagnostic method for detection of poloidal magnetic flux emission from a plasma focus. The results indicate that poloidal magnetic flux continues to be emitted even after the disruption of the plasma focus pinch phase and shows evidence of its being decoupled from the externally supplied discharge current. This observation is interpreted along with previous knowledgebase in terms of a conjecture regarding the scale-invariant mechanism that might also be involved in astrophysical jet phenomena.