Direct measurements of anode/cathode gap plasma in cylindrically imploding loads on the Z machine

A Porwitzky,G Laity,D H Dolan,M R Martin,T R Mattsson,R W Lemke

doi:10.1063/1.5026225

Abstract

By deploying a photon Doppler velocimetry based plasma diagnostic, we have directly observed low density plasma in the load anode/cathode gap of cylindrically converging pulsed power targets. The arrival of this plasma is temporally correlated with gross current loss and subtle power flow differences between the anode and the cathode. The density is in the range where Hall terms in the electromagnetic equations are relevant, but this physics is lacking in the magnetohydrodynamics codes commonly used to design, analyze, and optimize pulsed power experiments. The present work presents evidence of the importance of physics beyond traditional resistive magnetohydrodynamics for the design of pulsed power targets and drivers.

Highlights

By deploying a photon Doppler velocimetry based plasma diagnostic, we have directly observed low density plasma in the load anode/cathode gap of cylindrically converging pulsed power targets
The density is in the range where Hall terms in the electromagnetic equations are relevant, but this physics is lacking in the magnetohydrodynamics codes commonly used to design, analyze, and optimize pulsed power experiments
In the last few years, interest has grown in understanding the detailed power flow physics of Z to best design future pulsed power drivers that could potentially deliver over 30 MA of current to target loads

Summary

Introduction

By deploying a photon Doppler velocimetry based plasma diagnostic, we have directly observed low density plasma in the load anode/cathode gap of cylindrically converging pulsed power targets. 3. Z2964 load current inferred from velocimetry data for anode and cathode liners overlaid with PDV plasma diagnostic signals from Z3022 illustrating that deviation occurs as plasma enters the AK gap from upstream of the load at approximately 2.8 ls.

Results

Conclusion