Amplification of spontaneous emission of neon-like argon in a fast gas-filled capillary discharge
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TEMPERATURE PLASMA
Amplification of Spontaneous Emission of Neon-Like Argon in a Fast Gas-Filled Capillary Discharge K. Kolaceka, J. Schmidta, V. Bohaceka, M. Ripaa, O. Frolova, P. Vrbaa, J. Strausa, V. Pruknera, A. A. Rupasovb, and A. S. Shikanovb a Institute
of Plasma Physics, Academy of Sciences of the Czech Republic, Za Slovankou 3, 182 00 Prague 8, Czech Republic b Lebedev Physical Institute, Russian Academy of Sciences, Leninskiœ pr. 53, Moscow, 119991 Russia Received March 9, 2007; in final form, April 16, 2007
Abstract—The evolution of the CAPEX facility and its basic diagnostics are described. The experiments carried out in the last modification of this facility accomplished with the demonstration of amplified spontaneous emission of neon-like argon (Ar8+) at the wavelength 46.88 nm. The first version of the facility, CAPEX1, operated with a plastic capillary and had a short high-power passive prepulse and an imperfect gas-filling system. In the second version, CAPEX2, a ceramic capillary was used, the prepulse amplitude was lowered, and the gas-filling system was improved. In the third, most successful version, CAPEX3, the capillary bending was reduced, a longer external prepulse was used, and the gas-filling system was further optimized. For each version, results of X-ray measurements are presented and interpreted. PACS numbers: 52.25.Dg, 52.25.Fi, 52.27.Cm, 52.30.Cv DOI: 10.1134/S1063780X08020086
1. INTRODUCTION Capillary discharges have been known as stable sources of optical, UV, VUV, and soft X-ray (SXR) emission since the middle of the past century. After the possibility of creating X-ray lasers pumped by optical lasers was demonstrated, capillary discharges became the most promising candidates for use as an alternative active medium for X-ray lasers. Research efforts in this direction met with success first for evacuated capillaries [1–3] and then for gas-filled ones [4]. Experiments with gas-filled capillaries carried out in the group headed by Prof. J. Rocca (Colorado State University) resulted in creating an X-ray laser suitable for numerous applications. It took almost 10 years to reproduce these results in other laboratories [5–8]. In the scheme of electron-collisional excitation pumping, which is usually realized in gas-filled capillaries, the upper level of neon- or nickel-like ions is populated via electron collisions. The diameter of gasfilled capillaries (3–6 mm) is substantially larger than that of evacuated capillaries used in the scheme of recombination pumping (≤1 mm), because, in the latter case, the plasma should be efficiently cooled due to its permanent contact with the capillary wall. In gas-filled capillaries, the growth rate of the discharge current reaches a value of (1–4) × 1012 A/s, which is quite enough for the plasma to be rapidly detached from the capillary wall due to the Z-pinch effect. In this case, the wall is evaporated insignificantly, so the amount of the material to be heated is relatively small.
In [5, 7], the role of the preionization current was pointed out.
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