Comparison of measured and computed radial trajectories of plasma focus devices UMDPF1 and UMDPF0

Abstract

In published literature, there has been scant data on radial trajectory of the plasma focus and no comparison of computed with measured radial trajectory. This paper provides the first such comparative study. We compute the trajectories of the inward-moving radial shock and magnetic piston of UMDPF1 plasma focus and compare these with measured data taken from a streak photograph. The comparison shows agreement with the measured radial trajectory in terms of average speeds and general shape of trajectory. This paper also presents the measured trajectory of the radially compressing piston in another machine, the UMDPF0 plasma focus, confirming that the computed radial trajectory also shows similar general agreement. Features of divergence between the computed and measured trajectories, towards the end of the radial compression, are discussed. From the measured radial trajectories, an inference is made that the neutron yield mechanism could not be thermonuclear. A second inference is made regarding the speeds of axial post-pinch shocks, which are recently considered as a useful tool for damage testing of fusion-related wall materials.

Update on the Scientific Status of the Plasma Focus

“…Direct radial phase comparison is less common because of the dearth of experimental data. Figure 42 shows an outstanding comparison of computed radial trajectories with measured data from streak photograph [276]. Other more complex comparisons include combination of measured SXR profiles compared with radial dynamics [277,278].…”

“…The upper dots show the trajectory of the magnetic piston (i.e., rear of the slug), the lower dots show the trajectory of the radial inward shock (i.e., front of slug). Reproduced from[276] (Phys. Plasmas 2015, 22, 092702) with the permission of AIP Publishing.…”

Pushing the limits of existing plasma focus towards 1016 fusion neutrons with Q = 0.01

“…Inductive voltages are considered as the driver of the observed fast ion beams. Realistic simulations are achieved for axial and radial dynamics [35], fast ion beams [36] and relativistic electron beams [37], and post-pinch fast plasma flows [38], with all these having been verified against experimental measurements. The simulated neutron yields in D and D-T have been compared extensively with experimental measurements in various machines, most recently by Marciniak et al in the Polish machine PF-24 [39], with wider agreement than achievable by any other codes [2,5].…”