Analysis of the mechanism of soft x-ray emission from a spherical pinch radiation source (SPX II)

A qualitative analysis of the soft X-ray emission from SPX II, a spherical pinch radiation source, has been carried out. An aluminum foil (> 1.9 mg/cm2), which transmits only radiation above 800 eV, was used as window. High sensitivity Kodak DEF 392 film was used to measure the radiation after the window. The relative soft X-ray output vs machine discharge voltage is shown in Fig. 1. Argon was the working gas and the background pressure was 2 Torr. The soft X-ray output increases with discharge voltage, as expected. Fig. 2 shows the soft X-ray output as a function of the background gas pressure for Helium, Argon, and Neon. The machine discharge voltage was 20 kV. The results seem to indicate that, for all gases, the optimum pressure lies between 1 and 3 Torr. Since the soft X-ray yield depends on the imploding velocity of the wave that compresses the central plasma of the spherical pinch, the authors have developed an analytical snowplow model to predict the imploding velocity. This model yields: where Δt is the time taken by the wave to go from r = 0.02 m to the center r = 0, ρ0 is a function of gas and pressure, and α can be determined from the discharge current. The straight line is the model prediction and the courses are the measured results. Good agreement between the prediction and the experimental results is observed