Advanced Space Propulsion Based on the Flow-Stabilized Z-Pinch Fusion Concept

Abstract

A fusion space thruster based on the flow-stabilized Z-pinch may be possible in the near-term and provide many advantages over other fusion-based thruster concepts. The Zpinch equilibrium is classically unstable to gross disruption modes according to theoretical, numerical, and experimental evidence. However, a new stabilization mechanism has been discovered that can stabilize these modes with plasma flow. The stabilizing mechanism was developed for a Z-pinch plasma equilibrium which has an axial velocity profile that is linear in radius. When the velocity shear exceeds a threshold, the plasma modes are stabilized. The magnitude of the peak velocity is dependent on the mode wavelength but is sub-Alfvénic for the wavelengths of experimental interest, vmax > 0.1VAka where VA is the Alfvén speed, k is the axial wave vector, and a is the characteristic pinch radius. The flow Z-pinch experiment ZaP has been built at the University of Washington to experimentally verify the sheared flow stabilizing mechanism. The experiment has achieved plasma flow velocities of 10 5 m/s and stability for almost 2000 growth times. For more information the reader is encouraged to visit http://www.aa.washington.edu/AERP/ZaP. The extension of the flow Z-pinch to a space thruster is straight forward. The plasma in a flow Z-pinch would already be moving axially, fusing, and releasing a tremendous amount of nuclear energy. The end of the Z-pinch can be left open to allow the escape of the energetic plasma. Specific impulses in the range of 10 6 s and thrust levels of 10 5 N are possible.

Case and Development Path for Fusion Propulsion

“…Because of the abundance of relatively low-cost nonradioactive fuel that can be stored as a solid at room temperature, we are investigating D 6 Li. Further, due to the very favorable scaling of fusion output with current [16,78], and emerging theoretical insights into the suppression of deleterious instabilities [79][80][81], we conclude that the pulsed Z pinch is the most direct route to fusion propulsion. The purpose of the following sections is not to offer a fusion propulsion design, nor offer in-depth details of particular experiments.…”

“…Plasma instabilities in the pinch discouraged continued research in the steady-state experiments, but short-pulsed Z pinch has shown a very favorable fusion yield scaling with peak current (∼I 4 ) [78] New theoretical insights are overcoming these Rayleigh-Taylor instabilities [79]. One of the best sustained efforts in propulsion is Shumlak et al's ZAP concept [80]. In ZAP, the pinch is stabilized by a shear flow generated by a coaxial plasma gun during the collapse of the pinch.…”

Experimental investigation of a low-energy linear plasma propulsion device

“…5) Pulsed electromagnetic propulsion devices usually use an intense surge of electrical current to create a high-speed jet of plasma 6) which can provide many advantages over the fusion-based thruster concepts and may be possible in the near-term and fusion space thruster based on the flow-stabilized Z-pinch. 7) The pulsed plasma propulsion can be generated by Z-pinch, 8) flow stabilized Z-pinch 7) and dense plasma focus. 9) The principle of linear plasma propulsion (LPP) as Z-pinch and high dense plasma focus is to run high currents through a plasma over short timescales (∼μs).…”

“…9) The principle of linear plasma propulsion (LPP) as Z-pinch and high dense plasma focus is to run high currents through a plasma over short timescales (∼μs). 7,8) Additionally, it provides many of the desired features for a fusion space thruster such as a linear device, no external field coils, high specific power, and high plasma density. It produces plasma that can be easily confined by an induced magnetic field to produce a high-density plasma column.…”

Design of Z-pinch and Dense Plasma Focus Powered Vehicles

“…1,5,6 . In order to be useful in engineering analysis, simplified Z-Pinch fusion thermodynamic models are required to give propulsion engineers the quantity of plasma, plasma temperature, rate of expansion, etc.…”