Recent Experiments on Soft X-Ray Laser Development in a Confined Plasma Column*

Abstract

A series of recent experiments were performed with a new focussing system for our CO2 laser, which allowed a significantly smaller focal spot. The plasma was created by the interaction of a 1 kJoule CO2 laser with solid or gas targets. The plasma column was confined by a solenoidal magnetic field (B ≈ 50-100 kG) or was expanding freely (B =0). Spectral line radiations in the VUV region were monitored by two instruments operating initially in the spectrographic mode (spectra) and later in the monochromatic mode (time evolution of line intensities). To increase the cooling rate of the recombining plasma column, higher-Z elements were introduced into the plasma. For example, in case of a gas target, oxygen, argon or xenon were added for faster plasma cooling. For solid carbon targets, Aℓ-blades were used to increase radiation losses. Enhancement of hydrogen-like CVI 182Å line intensity and population inversion in Li-like ions (CIV, OVI, FVII, and NeVIII) were monitored for different plasma conditions. In order to change these conditions we varied the amount of higher-Z elements, CO2 laser power, magnetic field, and in the case of gas targets, we also varied the initial gas pressure. The interpretation of the time evolution, the radial and axial distribution of line intensities, together with computer simulations of the data will be presented.