Development of an ultrafast gas valve in a plasma gun for PJMIF application

Until now, the fastest gas valve in a space of less than 250 cc for injecting milligrams of argon into a coaxial plasma gun is the gas valve of the HJ1 coaxial plasma gun [1] developed on the ALPHA program of the US Department of Energy ARPA-E. The ALPHA program was launched by ARPA-E in 2014 to accelerate the development of commercializable fusion power for electricity generation. The coaxial plasma gun is the critical technology for the realization of PJMIF, and the ultrafast gas valve is heart of the plasma gun. The ultrafast gas valve developed for the HJ1 plasma gun has an open-and-close time of 350 ms. An even faster gas valve has been researched and developed for the ShanghaiTech University coaxial plasma gun STG1. This ultrafast gas valve could opens and closes within 240 ms, with jitter less than 1 ms. The gas filling pressure could reach to 8 bar absolute pressure, and by regulating the filling pressure, the injected gas mass could be controlled from 1 mg to 5 mg. To achieve this, a pulse power system was designed and built to drive the motion module which we called flyer-plate. A two-stage gas injected process [2] was designed to solve the leaking and sealing problem, and a self-compiled code was also used to simulate the pulse power current and the movement of the motion module of the gas valve. A critical component of the gas valve is a spring for holding the flyer plate in place initially and to return the flyer plate to its original position to close the gas valve. An innovative, nonlinear, saucer-shape spring is developed for this purpose. The details of the engineering design and the testing of the gas valve will be presented.