Ion temperature in the ASTRAL helicon plasma source

Ion temperature is measured in the ASTRAL (\textbf{A}uburn \textbf{S}teady s\textbf{T}ate \textbf{R}esearch f\textbf{A}ci\textbf{L}ity) helicon plasma source by means of a diode laser based Laser Induced Fluorescence (LIF) diagnostic. ASTRAL produces plasmas with the following parameters: n$_{e}$ = 10$^{10}$ to 10$^{13}$ cm$^{-3}$, T$_{e}$ = 2 to 15 eV and T$_{i}$ = 0.03 to 0.5 eV. A series of 7 large coils produce an axial magnetic field up to 1.3 kGauss. A fractional helix antenna is used to introduce rf power up to 2 kWatt. The 1.5 MHz bandwidth diode laser has a Littrow external cavity with a mode-hop free tuning range up to 15 GHz and with a total power output of about 15 mW. The wavelength is measured by a wavemeter and frequent monitoring prevents wavelength drift. For Ar plasma, the laser tuned at 668.61 nm, is used to pump the 3d$^{4}$F$_{7/2}$ Ar II metastable level to the 4p$^{4}$D$_{5/2}$ level. The fluorescence radiation between the 4p$^{4}$D$_{5/2 }$and the 4s$^{4}$P$_{3/2 }$levels (442.6 nm) is monitored by a PMT. Other diagnostics are presently installed on the plasma device. They included a RF compensated Langmuir probe which is used to measure both electron temperature and plasma density. A spectrometer which features a 0.33 m Criss-Cross Scanning monochromator and a CCD camera is used for spectroscopy studies of the plasma.