Plasma temperature measurements using black-body radiation from spectral lines emitted by a capillary discharge

Optically thick spectral line emssion from plasmas is often difficult to use for the diagnosis of plasma parameters. We demonstrate a technique for temperature measurement using the peak intensity of optically thick lines as their intensities approach a black-body distribution. Recording optical emission in the wavelength range 300-1000 nm from a plasma formed by radio-frequency heating and electrical discharges in a 0.2 m long capillary plasma, we show that the high wavelength Rayleigh-Jeans form of the black-body emission can be fitted to the most intense spectral lines to give a measurement of plasma temperatures in the 1-1.5  eV range. The temperature measurement technique should have wider applicability in diagnosing plasmas with optically thick spectral lines.