Staged Z-pinch: a target for fusion and a possible source for interstellar propulsion

Author: Dr. Hafiz Ur Rahman, President & Chief Scientist, Magneto-Inertial Fusion Technology Inc.

Abstract: The gas-puff Staged Z-pinch (SZP) is a magneto-inertial fusion concept in which an annular liner of a high-Z material, such as Ar or Kr, implodes onto a column of target plasma of D or DT fuel. The success of the concept necessarily requires mitigation of the magneto-Rayleigh-Taylor instability, which develops on the surface of the imploding liner and can feed through to the target and disrupt the pinch. One well-known method of MRTI mitigation is by axial pre-magnetization. As the liner implodes, a modest initial magnetic field Bz0 is amplified significantly due to flux conservation inside the liner plasma, and the resulting magnetic field line tension acts against MRTI growth. Recent experiments on a 1-MA, 100-ns driver at the Nevada Terawatt Facility at the University of Nevada, Reno, demonstrated that Bz0 = 0.1-0.2 T can significantly mitigate MRT growth of a SZP with initial liner radius of about 1.3 cm. DD neutron yields of 109-1010/shot were measured and appear to be isotropic and of thermonuclear origin. MACH2 MHD simulations show reasonable agreement with measured neutron yields at the 1-MA level, and also show favorable yield scaling to 10-MA and 20-MA machines, providing a path towards scientific breakeven and beyond. As the footprint and wall-plug efficiency of such a high-current machine is important to consider, the use of linear transformer driver (LTD) technology to improve driver/load energy coupling, and compact switch assembly (CSA) technology to decrease driver size, are also discussed as part of a conceptual design for future experiments and a possible future interstellar propulsion system.

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