Study of a scalable large-area radio-frequency helicon plasma source

Abstract

A large-area planar spiral antenna has been installed on the linear laboratory device VINETA. For low radio-frequency (RF) powers the induction coil is operated in the inductive discharge mode with typical plasma densities of n ≈ 1 × 1016 m−3 and electron temperatures of Te ≈ 5 eV. At higher RF powers a transition to the helicon wave sustained discharge mode is observed, in which the density increases by a factor of 200 and Te drops by a factor of 2. Detailed measurements of the helicon wavefield show that a helicon wave with azimuthal mode number m = 0 is launched. Due to the larger wave excitation region of the m = 0 discharges the width of the plasma density profile in the helicon mode increases by a factor of 1.5 compared with the standard VINETA helicon operation with a helical m = +1 antenna.