Manifestation of constrained dynamics in a low pressure spark

TL;DR

This paper introduces the principle of constrained dynamics to explain solenoidal flows in dense plasma focus devices, supported by experiments with spark discharges showing magnetic flux changes.

Contribution

It proposes a new theoretical framework, the principle of constrained dynamics, to account for solenoidal flows in plasma devices, addressing limitations of previous models.

Findings

Reproducible sharp dips in current derivative signals during spark discharge.

Detection of axial magnetic flux change via diamagnetic loop.

Qualitative model explains observed phenomena using constrained dynamics.

Abstract

Some features of neutron emission from dense plasma focus suggest that the participating deuterons have energy in the range of 105 eV and have a directionality of toroidal motion. Theoretical models of these devices assume that the plasma evolves through a purely irrotational flow and thus fail to predict such solenoidal flow on the scale of the plasma dimensions. Predictions of a relaxation theory are consistent with experimental data [S K H Auluck, Physics of Plasmas,18, 032508 (2011)], but the assumptions upon which it is based are not compatible with known features of these devices. There is thus no satisfactory theoretical construct which provides the necessity for solenoidal flow in these devices. This paper proposes such theoretical construct, namely, the principle of constrained dynamics, and describes an experiment which provides support for this idea. The experiment consisted of low inductance, self-breaking spark discharge in helium at a pressure ~100 hPa between two pointed electrodes separated by 30-50 mm distance kept inside a vacuum chamber mounted on a low inductance high voltage capacitor. The current derivative signal showed reproducible sharp dips at all the extrema of the damped sinusoidal discharge. A planar diamagnetic loop centered with and perpendicular to the discharge axis consistently showed a signal representing rate of change of axial magnetic flux. A qualitative explanation of observed phenomena is obtained using a simple model using the proposed principle.