The scaling laws of a cold gas-blanket experiment

Abstract

Abstract Experimental investigations of a cold gas-blanket surrounding a fully ionized plasma core have been performed. The gas blanket is produced in the F-1 rotating plasma device having a purely poloidal magnetic field, B ⩽0.5 T, major radius R = 0.3 m, electron density in the range of 10 21 m −3 , electron temperature T = 5 eV and rotation velocity υ ϕ = 10 5 m/s. It is found that the transverse particle diffusion is classical and the scaling of the plasma density, n b , with the neutral hydrogen density at the wall, n 1w , follows the law n b ∝ (n 1 w B 2 ) 1 3 agreeing with theory based on the momentum and particle balances. The scaling of the temperature with the power input cannot be accounted for on the basis of the transverse heat-balance alone. The thickness of the boundary layer decreases with increasing power input, but the maximum power input compatible with a gas-blanket could not be determined due to the Alfven critical-velocity effect, which limited the rotation velocity at the insulator surfaces. The minimum power input needed to maintain an impermeable plasma core was found to be 0.25 MW.