Ion Energy Distributions for a High Power Helicon Plasma Source

The high power helicon source, developed at the University of Washington is capable of depositing up to 100 kW of peak power into the plasma. Measured source electron densities using argon are near 2x10$^{20}$ m$^{-3}$ with electron temperatures of 5-7 eV. The HPH system has been operated in a pulsed manner with shot durations ranging from 30 $\mu $s to several milliseconds and ambient magnetic field strengths (B$_{0})$ ranging from 60 to 500 G. Langmuir probe measurements, at the exit of the helicon source and further downstream, show a peaked spatial profile. Both the time of flight and Mach probe measurements indicate a supersonic axial flow. Ion energy distributions as a function of axial distance away from the source region have been obtained using a retarding field analyzer. The distributions show a dually peaked population flowing downstream away from the discharge. The special profile of the energy distributions show increasing directed ion energies several centimeters downstream of the helicon coil region. Maximum sustained directed ion energies using argon are near 55 eV. Detailed results of the helicon source and ion energy distributions will be presented.