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

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Abstract
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.