Optimization of an m = 0 multi-loop helicon source configuration for linear plasma devices: A comparative study with Boswell and half-helix antenna designs

This article presents the physics for determining an appropriate helicon plasma source for the linear experimental advanced device (LEAD) through tripartite mutual verification encompassing theoretical analysis, code simulation, and experimental validation. Using the HELIC code, plasma excitation processes were simulated with three antenna configurations: m = 1 half-helix, m = 1 Boswell, and m = 0 single-loop helicon antennas, and complemented by theoretical analysis. Key parameters including plasma impedance ( R p ) and energy deposition profiles along radial ( P r ) and axial ( P z ) directions were comparatively analyzed, revealing significantly enhanced R p , P r , and P z values for the loop antenna configuration as compared with other configurations. Wave propagation equation solutions predicted a primary plasma generation layer at the antenna center; numerical simulations identified an additional plasma formation region at the antenna boundary, indicative of edge Landau damping effects. Interestingly, stronger axial magnetic fields do not necessarily result in higher plasma densities, especially for m = 0 antenna configurations. Experimental validation conducted with an m = 0 multi-loop plasma source confirmed these findings. Both theoretical analyses and experimental studies on large-volume plasma generation utilizing this innovative source elucidated the underlying mechanisms responsible for the remarkable low mode transition threshold of 150-watt input power and demonstrated significantly enhanced plasma confinement properties.