Radiation losses of a theta pinch plasma in the wave-length range 10–200 Å
In order to measure the radiation losses of a theta pinch plasma (electron densityne=1−5×1016 cm−3, electron temperatureTe=150−350 eV), a grazing incidence spectrograph is absolutely calibrated in the range 10–200 Å. This is done in two steps: First the measured intensity ratios of lines emitted by hydrogen-like ions are compared with their calculated values thus yielding the relative sensitivity of the instrument. The result is confirmed by incorporating well known intensity ratios of lithium-like ions. Secondly absolute calibration is possible by hanging the spectrograph on an absolutely calibrated monochromator via the branching-ratios of lithium-like ions.Radiation losses from the plasma turn out to be negligible as compared with heat conduction losses and the total energy radiated is found to be small compared with the energy content of the electrons, if the impurity concentration does not exceed 0.5 percent. The radiation is found to be predominantly emitted by the resonance lines of the oxygen and carbon ions O VI, O VII, O VIII, CV, CVI whereas continuum radiation and the contribution from other ions are negligible small.However, in discharge where the oxygen concentration reaches 5 percent, radiation losses can exceed the losses by heat conduction during the early phase of the discharge. But still the final electron temperature is not significantly influenced by the impurities.