Upgrade of magnetized coaxial plasma gun system to generate high flux spheromak

Magnetized coaxial plasma guns (MCPGs), also known as compact toroid injectors (CTIs), can control the total trapped flux of the ejected spheromak by adjusting the initial stuffing field between the electrodes. TAE technologies developed MCPGs for TAE's C-2 series devices, as part of the particle fueling system [1]. We also conducted spheromak merging experiments using two MCPGs on the CTI testbed [2] and reported that it is possible to generate an FRC by colliding two spheromaks. Ejected spheromaks have a maximum flux of 1 mWb and lose some flux before CTs collide. The upper limit of the trapped flux generally depends on the geometry of the electrode design [3]. In order to expand the operating regime with high trapped flux, we redesigned the electrodes. New electrodes are 3x larger and the stuffing coil energy has been increased to improve attainable flux. By using this new MCPG configuration, we expect that the upper limit of the trapped flux can expand up to 15 mWb. We will present the details of the upgraded MCPG systems as well as preliminary results of spheromak formation.

[1] T. Asai, etc. Nucl. Fusion 57 076018 (2017)

[2] T. Matsumoto, et al., Rev. Sci. Instrum. 89, 10E108 (2018)

[3] C. G. R. Geddes, et al., Phys. Plasmas 5, 1027 (1998)