Quasi-steady sustainment of spheromak configuration by inductively driving the toroidal current.

The properties of plasma sustainment by inductively driving the toroidal current for a free-boundary spheromak were investigated experimentally by use of the TS-3 spheromak machine, in which a 290 turn OH coil is installed to drive the toroidal current. The lifetime of spheromak plasmas increased from 30μs under non OH operation to 100μs when dφ/dt with a quarter period of 70μs was applied to the plasmas. The time variation of toroidal mode spectrum observed in the current-driven spheromak agrees with the result of 3D-MHD simulation for the relaxation phenomena of spheromak plasma having initially a lower q profile than that of the minimum-energy state.