Ion temperature measurement in a plasma column using pulsed CO2 collective scattering and heterodyne detection

We describe a pulsed CO2 laser scattering experiment set up to measure the ion temperature of a magnetically stabilized arc plasma (ne≂1021 m−3, Te≂5 eV). Sensitivity and spectral resolution considerations led us to use heterodyne detection with a separate local oscillator and a multichannel rf frequency analyzer. The forward scattering angle is chosen to be 5° in order to match the expected ion feature spectrum to the receiver bandwidth and also to eliminate spontaneous fluctuations from the small-k larger-amplitude signal. Experimental scattering spectra illustrate the apparatus sensitivity to discharge current and gas mixture. Ion-acoustic resonances are resolved as well as the spectral signatures from various mixed ion species plasmas. The ion temperature appears to be determined to ±10% once Te and ne are known from other measurements. Applications to high temperature fusion plasmas are discussed.