First experiments looking at electric field outside the Dense Plasma Focus show axial magnetic field exists before, during and after the pinch phase

TL;DR

This study reports the first non-intrusive measurements of axial magnetic fields outside a Dense Plasma Focus device, revealing their presence before, during, and after the pinch phase, which has implications for plasma structure and ion acceleration.

Contribution

It introduces a novel technique for measuring external electromagnetic fields in plasma focus devices, confirming the existence of axial magnetic fields throughout the plasma cycle.

Findings

Axial magnetic field exists outside the plasma focus before, during, and after the pinch.

The measurement technique is non-intrusive and insensitive to non-axisymmetric plasma features.

Results support the presence of magnetic flux surfaces influencing plasma behavior.

Abstract

Recent experiments using 15 frame interferometry on PF-1000 facility in Warsaw confirm the association between neutron emission and spontaneously self-organized, relatively long lasting, finite plasma structures. A crucial aspect of this association is the simultaneous observation of an axial magnetic field, which can allow magnetic flux lines to densely cover closed surfaces creating "magnetic flux surfaces". Evolution of such 3-dimensional (3-D) magnetic field structures is necessarily accompanied by induced electric field that can provide a very long (theoretically infinite) acceleration path length along a trajectory enclosed within the magnetic structure leading to high ion kinetic energy, resulting in a high reaction rate. Associated charge and current densities can be related to electric scalar potential and magnetic vector potential measured outside the plasma. We report our first observations of these fields outside the plasma focus and discuss their general features. The reported technique is capable of unambiguous first-principles interpretation of signals in terms of quantities related to distributions of charge density and rate of change of azimuthal current density ("electromagnetic structure") in the plasma focus. It is non-intrusive and completely insensitive to non-axisymmetric aspects of plasma. Our first results show that axial magnetic field generated by azimuthal current density distribution symmetric about the axis exists before, during and after the pinch phase.