Helicon plasma source excited by a flat spiral coil

We have characterized a new helicon plasma source with an end-launch antenna configuration. Power at 13.56 MHz is coupled via a four-turn flat spiral coil into an m=0 helicon mode with the application of a weak (B≳5 G) axial magnetic field. Plasma parameters were measured with Langmuir probes, and the structure and absorption of the helicon wave fields were determined with magnetic induction probes. Plasma densities of 1011–1012 cm−3 were produced in argon for pressures in the 1–100 mTorr range with a 5–60 G magnetic field. Radio frequency power absorption occurs primarily via collisionless Landau damping for pressures below 5–10 mTorr and collisional damping dominates at higher pressures. Single pass absorption occurs for magnetic fields less than 20 G. This source does not require a separate source chamber, and thus combines the compactness of flat coil inductively coupled sources with the advantages of remote plasma generation found in wave supported sources. The source can be easily optimized for a variety of operating conditions, because the helicon parallel wavelength is not constrained.