Flow Z-pinch plasma production on the FuZE experiment

Abstract

The Fusion Z Pinch Experiment (FuZE) investigates sheared-flow stabilization of classic m = 0 and m = 1 instabilities in Z pinches with an embedded axial flow. FuZE consists of a 100 cm coaxial plasma accelerator, where neutral gas is ionized and accelerated in a pulsed electrical discharge, followed by a 50 cm assembly region, where pinches are formed. Maintaining the pinch requires continuous plasma injection provided by a deflagration mode in the coaxial accelerator. Two discharge modes, with and without deflagration, are investigated on FuZE. Pinch formation is observed with deflagration only. Plasma velocities in the assembly region are found to match the E × B velocity estimated in the accelerator based on a 1D circuit model, indicating that a 1D MHD approximation may offer a valid description of the plasma in the accelerator channel. The velocity of magnetic field propagation is found to agree with the snowplow model based on momentum conservation, and the lifetime of the pinch is shown to be in agreement with constraints imposed by mass conservation.

Whole device modeling of the fuze sheared-flow-stabilized Z pinch

“…Multi-species continuum kinetic modeling can allow for further accuracy of sheath modeling and pinch dynamics in the kinetic parameter regime [31], with hybrid approaches helping to speed up such simulations [14,17]. Other advancements include the addition of a plasmaneutral model [23] to capture plasma deflagration [20] and more accurate boundary conditions that can capture heat and particle fluxes to walls, and corresponding erosion and impurity generation [28].…”

“…Using the magnetic probes, the motion of an assumed slug of plasma injected by the gas puff valves is tracked to estimate its mass. Using this slug model, the plasma mass is determined using the force [20,21],…”

“…A combination of gas valve injection and a deflagration process ionizing remaining neutral gas sustains plasma flow to the pinch [20]. In the deflagration process, the ionization of the neutral gas propagates similar to an expansion wave in the opposite direction of the J × B force, that is upstream and opposite of the direction of the plasma velocity.…”

Time-discretization of a plasma-neutral MHD model with a semi-implicit leapfrog algorithm

“…Here we inject magnetic flux from one end of the domain while in practice the breakdown happens in the middle of the domain and the magnetic flux advects in both directions. Stepanov et al [36] discuss the physics of detonation and deflagration shack waves in such geometry. Implementing volumetric source terms can inject energy into the system representing the gas breakdown process.…”

Continuum kinetic investigation of the impact of bias potentials in the current saturation regime on sheath formation

“…7 These Z-pinch configurations are unstable to plasma instabilities, such as the sausage and kink instabilities, 10 which cause losses in nuclear fusion energy output. Experiments such as ZAP [11][12][13][14] and FuZE [15][16][17][18] show that these instabilities are stabilized by shear flow. 19 The pinch current is generated by two electrodes with a bias potential between them.…”