Initial magnetic field compression studies using gas-puffZ-pinches and thin liners on COBRA

Abstract

This magnetic compression of cylindrical liners filled with DT gas has promise as an efficient way to achieve fusion burn using pulsed-power machines. However, to avoid rapid cooling of the fuel by transfer of heat to the liner an axial magnetic field is required. This field has to be compressed during the implosion since the thermal insulation is more demanding as the compressed DT plasma becomes hotter and its volume smaller. This compression of the magnetic field is driven both by the imploding liner and plasma. To highlight how this magnetic field compression by the plasma and liner evolves we have separately studied Z-pinch implosions generated by gas puff and liner loads. The masses of the gas puff and liner loads were adjusted to match COBRA's current rise times. Our results have shown that Ne gas-puff implosions are well described by a snowplow model where electrical currents are predominately localized to the outer surface of the imploding plasma and the magnetic field is external to the imploding plasma. Liner implosions are dominated by the plasma ablation process on the inside surface of the liner and the electrical currents and magnetic fields are advected into the inner plasma volume; the sharp radial gradient associated with the snowplow process is not present.

Measurements of the spatial magnetic field distribution in a z-pinch plasma throughout the stagnation process

“…In general, spectroscopic methods based on the Zeeman effect for the determination of magnetic fields in plasmas, are limited due to their sensitivity to density-or temperature-induced broadenings [4,5]. Alternative approaches to Zeeman spectroscopy are based on Farady rotation [6][7][8][9], B probes [10][11][12][13] or proton beam deflectometry [14][15][16][17][18]. Yet each of the methods has its own difficulties.…”

Experimental investigation of a low-energy linear plasma propulsion device

“…Magnetic probes are commonly used as an electrophysical diagnostic tool in pinch experiments to measure the current and to estimate the strength of the inductive notch. 24,25) The CS velocity is measured by using a magnetic probe in the propulsion part of the experiment. With the help of the current, the plasma exits from the accelerated region to large velocities regions and forms a long column of linear plasmas that are over 40 cm long with a radius of 1.5 cm.…”

Design and construction of a single-axis, low-frequency magnetic probe (B-dot probe) calibrated with a LCvar Helmholtz resonant circuit

“…A small single-axis magnetic probe (also known as B-dot) has been designed and constructed to measure the pulsed magnetic field in a Circular Demountable Toroidal Field Coil (CDTFC) [1]. Similar phenomena like electromagnetic thrusters [2], lightning in transmission lines [3], magnetic field compression by puff-gas Z pinches [4], nano-second high voltage generation, high electrical current measurements in pulsed power systems [9], radio-frequency plasma measurements [10], and many other pulsed transient experiments make use of B-dot probes. Measurement of these pulsed transient phenomena can be a challenging task when the probe must be sensitive to all three components of the magnetic field, have enough sensitivity to detect low magnetic fields of some Gauss, and in some cases have a good response in frequency of some GHz.…”

“…For pulsed magnetic measurements such as lightning in transmission lines [3] it is necessary a frequency response of up to 2.5 MHz. Magnetic field compression studies by puff-gas Z pinches [4] need magnetic field measurements that last 300 ns in time. To measure both high currents and voltages in pulsed power systems [9] a calibrated B-dot probe up to 4 GHz in frequency is required.…”