UC San Diego

Gas-puff Z-pinches are intense pulsed x-ray or neutron sources. In gas-puff Z-pinches, a pulsed current is delivered to a cylindrical gas column, leading to an implosion of plasma until it stagnates on axis and generates x-rays or neutrons. The distribution of the current within the imploding plasma greatly impacts the kinetic energy of the imploding plasma, the state of the stagnated plasma and therefore the radiation achieved. This dissertation examines the delivery of current in conventional pulsed power drivers and the latest pulsed power systems based on linear transformer driver technology throughout the implosion process.

A spectroscopic technique exploiting the polarization properties of the Zeeman effect allow for local measurements of the azimuthal magnetic field (Bθ) in the high density conditions of the implosion phase.

This technique was employed on the CESZAR LTD (500 kA peak current, 180 ns rise time) and on a conventional, slower rising driver (300 kA peak current, 1500 ns rise time). Experiments on the conventional driver, performed at the Weizmann Institute of Science, Israel, found that over 80% of the current flowed within the imploding plasma. In addition, a pre-embedded axial magnetic field was shown to produce radial profiles of Bθ consistent with MHDsimulations.

On the CESZAR LTD, 50% or less of the current was flowing within the imploding plasma. The radial charge state distribution observed on the CESZAR driver indicates that a trailing plasma composed of higher charge states and lower densities carries a significant portion of the current.

Furthermore, modifications to the electrode geometry of the LTD and to the initial gas density profile greatly impact the plasma-current coupling. Installing pins in the cathode oriented toward the anode improved the plasma-current coupling, ostensibly by creating a favorable initial breakdown plasma. Using a relatively short valve opening duration led to an increase from ∼ 50% to ∼ 70% of current in the plasma early in the implosion.