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A series of 139 GHz microwave scattering experiments has been performed on the Versator II tokamak (B. Richards, Ph.D. thesis, Massachusetts Institute of Technology, 1981 ) to study the propagation of externally launched 0.8 GHz lower-hybrid waves. During lower-hybrid current drive, the launched waves are found to follow a highly directional resonance cone in the outer portion of the plasma. Wave power is also detected near the center of the plasma, and evidence of wave absorption is seen. Scattering of lower-hybrid waves in k space by density fluctuations appears to be a weak effect, although measurable frequency broadening by density fluctuations is found, δω/ω = 3 × 10[sup -4]. In the detectable range (2.5 < N[sub ] < 5.5) the N[sub ] spectra inferred from the scattering measurements are quite similar above and below the current drive density limit. Numerical modeling of these experiments using ray tracing is also presented. [ABSTRACT FROM AUTHOR]

Increases in average density have been observed during lower-hybrid current-drive experiments (LHCD) on the Versator II tokamak [Phys. Rev. Lett. 48, 152 (1982)], and on other LHCD experiments where inductive-Ohmic and lower-hybrid current drive are combined. In the present experiment it is found that this density increase is the result of an improvement in global particle confinement time τ[sub p] in comparison to purely Ohmic discharges with similar plasma parameters. Furthermore, it is found that the improved confinement deteriorates when the anomalous Doppler relaxation instability of the anisotropic high-energy electron tail becomes unstable during LHCD, and the loss rate of tail electrons increases. However, energetic electron losses alone are at least an order of magnitude too small to explain this deterioration in particle confinement. [ABSTRACT FROM AUTHOR]

The first linac-based visible free-electron-laser oscillator was operated in February 1987 at a wavelength of 525 nm with and without a wiggler taper. Peak output power of 29 kW with a macropulse average power of 1.1 W was observed. The cavity dielectric mirrors were damaged at approximately 21 kW/cm2 of average intracavity power. [ABSTRACT FROM AUTHOR]