Comparison of Electrode Configurations on ZaP: Investigation of Heating Mechanisms in a Flow Z-Pinch

Abstract

The ZaP Flow Z-Pinch is a basic plasma physics experiment that investigates the effect of sheared axial flows Z-pinch stability. Two modifications are made: 1)~Installation of a perforated conducting wall to evaluate the effect on Z-pinch stability; 2)~The 10~cm diameter inner electrode is replaced with a 16 cm diameter version to evaluate the effects of adiabatic compression. It is determined that the conducting wall has no effect on the stability of the pinch. Expected effects of the inner electrode modification are increased temperature and density due to increased adiabatic compression and an increase in stable period length. Pinch density profile evolution is measured with a four-chord HeNe interferometer and temperature and magnetic field profiles are calculated with a radial heat conduction analysis. Pinch equilibrium comparison between the 10 cm and 16 cm inner electrode configurations shows that the 16 cm electrode is subject to greater non-adiabatic processes, such as shocks. Greater influence of shocks is attributed to a blunter nosecone and increased current in the accelerator for the 16 cm inner electrode. Pinch temperature for the 16 cm inner electrode is less than the 10 cm electrode due to higher linear density in the pinch and the increased size of the pinch is a result of the non-adiabatic formation process.