Study of capillary discharges for soft X-ray lasers

Summary form only given, as follows. Since the first demonstration of a compact discharge pumped soft X-ray laser by Rocca et al. (1994), there is an increasing interest in the study and the development of such tabletop systems with a high energetic efficiency. At GREMI, we developed two fast capillary discharge devices based on different pulsers. In the first experiment, the discharge is driven by a Blumlein generator allowing high injected power density in low pressure argon filled, 3 to 10 cm in length, 4 mm in diameter, polyacetal capillaries. Argon time-integrated spectra show that highly ionized argon states, up to Ar/sup 7+/, are efficiently produced at rather low values of the stored energy (<20 J). Time-resolved soft X-ray spectroscopy is in progress in order to facilitate the observation, if produced, of excited states of Ar IX at the origin of the lasing transition while scaling to larger input energy is under development. In the second experiment, we developed a low inductance system based on preionized direct discharges of a knob capacitor bank into evacuated, 0.8 to 3 cm in length, 1 mm in diameter, capillaries of polyethylene, polyacetal or teflon. The soft X-ray photons are emitted from a plasma column resulting from the capillary wall ablation. In case of polyethylene capillaries, the spectrum consists essentially of C IV, C V and C VI carbon lines. Using a constant input power density of 70 GW/cm/sup -3/, we observed an exponential growth of the C IV H/spl alpha/ at 18.2 nm and H/spl beta/ at 13.5 nm line intensities as a function of the capillary length (0.8 to 1.6 cm) which seems to indicate an amplification.