Frequency Doubling the Thomson Scattering Diagnostic for the Helicon Plasma Experiment (HPX)*

HPX’s Thomson Scattering (TS) diagnostic at the Coast Guard Academy Plasma Laboratory (CGAPL) employs a 2.5 J Nd:YAG laser that operates at its first and second harmonic, 532 and 1064 nm respectively. HPX continues to progress toward utilizing high densities (10¹³ cm^-3 and higher) at low pressure (.01 T) reputed by many helicon experiments. HPX temperatures will likely remain in the 3 eV - 6 eV regime and produce ~10 nm doppler-shifted photon wavelengths. A high-performance spectrometer utilizing a volume-phase-holographic grating and a CCD camera with a range of 380-1090 nm and resolution of 1024x1024 has been assembled to collect these slightly shifted photons, emitted from the plasma by the laser’s second harmonic (532 nm). A new polychromator has been from General Atomics is optimized for TS measurements of 5 eV < T_e < 2000 eV over a 109-degree scattering angle.  A linear actuated periscope with a zero-order half-wave plate to rotate the first harmonic polarization has been constructed to redirect the laser beam so both wavelengths can both be used in succession and give a self-consistent measurement. The current status of the diagnostic development, spectrometer, polychromator, and collection optics system will be reported.