X-ray emission was used to diagnose the plasma formation in a gas-puff pulseddischarge device. X-ray pinhole images were collected simultaneously with x-ray spectra from Ar and Kr gases. X rays were emitted from z-pinched regions (50-100 }-tm in diameter) along a collinear track formed by the plasma implosion of a hollow gas jet. Spectral analysis indicated Ar plasma formation with electron densities of -2 X 10 21 cm -J. The Ar plasma temperature was -1 keV, based on a collisional-radiative transport model. Li-like satellite lines were classified in Ar XVI with atomic structure calculations. The Kr x-ray spectrum (6-8-A region) was dominated by Ne-like Kr XXVII lines. New spectral transitions were classified in Na-like Kr XXVI and F-like Kr XXVIII. The wavelength calibrations in the Kr spectrum were obtained from exploded-AI-wire plasma generated in coincidence with the plasma implosion formed in the puff gas.
Single mode operation was exhibited on the Israeli tandem free-electron laser (FEL). This enabled judicious measurements of narrow spectral linewidth, frequency chirp, and relaxation-oscillation effects. Exact 3D simulations of the FEL oscillator showed good agreement with the measurements, and permitted an estimation of the fundamental Schawlow-Towns linewidth limit of the FEL (including "a effect") as well as technical noise linewidth limits. We estimate that with voltage-controlled stabilization high-power (10 kW) tunable (over 60% bandwidth) quasi-cw coherent ͓͑Dn͞n͒ rms ഠ 10 210 ͔ mm-FIR (far infrared) radiation is attainable in the tandem FEL. [S0031-9007(99)09370-9]
The lasing of a Van de Graaff electrostatic accelerator-free-electron laser ͑EA-FEL͒ with an internal cavity is reported. An EA-FEL employing an internal cavity is a FEL configuration that has a potential to operate at high average power, high frequency, and possibly in a continuous wave ͑cw͒ mode. The initial lasing provided a pulsed radiation power of 1 kW at 100.5 GHz frequency. The FEL operated with a 1.4 A, 1.4 MeV electron beam in a recirculation ͑depressed collector͒ configuration. It utilizes a high quality (QϷ30 000) Talbot effect resonator and a Halbach-type wiggler placed internally in the center of the accelerator tank. Nonlinear features of the oscillation power buildup and decay near saturation and mode hopping were observed and are interpreted.
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