Status of the heavy ion beam probe system in the Large Helical Device.

A heavy ion beam probe (HIBP) system has been installed into the Large Helical Device (LHD) to measure the spatial profile of the plasma potential and density fluctuations. The optimization of the HIBP system, especially the beam injector, is described. The negative ion beam is required for the MeV beam production in a tandem accelerator. A sputter-type heavy negative ion source has been developed as an intense Au(-) beam source to produce Au(+) beams with energy in the MeV range. The extraction electrodes and the Einzel lens system of the ion source have been designed taking into account the beam optics, and installed into the real machine. Throughout the plasma diagnostics on LHD experiments, the consumptions of vaporized caesium and gold target are being characterized for practical operations. In addition, the experimental charge fractions are compared with the theoretical fractions for understanding the charge-changing behavior of Au(-) ions and optimizing the fraction of Au(+) ions at the exit of the tandem accelerator of the HIBP system.

Charge-exchange-induced two-electron satellite transitions from autoionizing levels in dense plasmas.

Order-of-magnitude anomalously high intensities for two-electron (dielectronic) satellite transitions, originating from the He-like 2s(2) 1S0 and Li-like 1s2s(2) (2)S(1/2) autoionizing states of silicon, have been observed in dense laser-produced plasmas at different laboratories. Spatially resolved, high-resolution spectra and plasma images show that these effects are correlated with an intense emission of the He-like 1s3p 1P-1s(2) 1S lines, as well as the K(alpha) lines. A time-dependent, collisional-radiative model, allowing for non-Maxwellian electron-energy distributions, has been developed for the determination of the relevant nonequilibrium level populations of the silicon ions, and a detailed analysis of the experimental data has been carried out. Taking into account electron density and temperature variations, plasma optical-depth effects, and hot-electron distributions, the spectral simulations are found to be not in agreement with the observations. We propose that highly stripped target ions (e.g., bare nuclei or H-like 1s ground-state ions) are transported into the dense, cold plasma (predominantly consisting of L- and M-shell ions) near the target surface and undergo single- and double-electron charge-transfer processes. The spectral simulations indicate that, in dense and optically thick plasmas, these charge-transfer processes may lead to an enhancement of the intensities of the two-electron transitions by up to a factor of 10 relative to those of the other emission lines, in agreement with the spectral observations.