4. The Role of Molecular Spectroscopy in the Vacuum Ultraviolet Region for the Development of a Negative Ion Source

Abstract

Fundamental plasma processes of negative ions in a low pressure region (a gas pressure P g < 1.5 Pa) have been studied using the photodetachment technique and vacuum ultraviolet (VUV) spectroscopic measurements in the spectral range from 100 to 180 nm. Understanding the behavior of a plasma with negative ions, in particular, the correlation between H -density and vibrationally excited H 2 density, is of great interest in the field of atomic-molecular physics and ion source developments. The volume and the surface effects of negative ions are discussed taking into account the e-V, the E-V, and the RD processes, and the measured VUV spectrum is compared with the synthetic one. The cascade transition to the B 1 Σ + u state by the electron excitation contributes to the production of the highly vibrationally excited levels of the X 1 Σ + g ground electronic state.

VUV-diagnostics of a filament-driven arc discharge H− ion source

“…These transitions to the ground state are considered to be the main production channel for high vibrational states [8] in…”

Diagnostics of Recombining Plasmas in Divertor Simulator MAP-II

“…Most direct emission spectroscopy to obtain the vibrational distribution in the ground electronic state of molecular hydrogen, X 1 Σ + g , is the one by which the radiative decay from the B 1 Σ + u or C 1 Π u state is measured [41]. However, these wavelengths are in the vacuum ultraviolet (VUV) region and installing the measurement system in the divertor region is complicated.…”

Vibrational States of Hydrogen Molecules in One Third LHD Negative Ion Source

“…The sensitivity does not change in two systems. The ratio of the intensities of atomic Lyman-E, -J, and -G lines to molecular bands in one-third negative ion source is relatively higher than that measured in the small negative ion source [6]. The difference would be caused by the ionization degree and the electron temperature.…”

“…The Argon admixture in the hydrogen negative ion source does not enhance the Lyman and Werner bands. The H -density in low gas pressure region (less than 0.1 Pa) is enhanced because the electron density is increased due to Ar additive in hydrogen plasmas, and it leads to the enhancement of dissociative electron attachment to H 2 molecules [5,6]. A large size negative ion source for NBI usually uses cesium vapor admixture in it to enhance negative ion beam currents.…”

“…3 in a pure hydrogen discharge of one third LHD negative ion source. The same spectrometer with the CCD detector is used for two experiments (present experiment and the former experiment in the small negative ion source [6]). The observed atomic lines at 121.6, 102.7, 97.2, and 94.9 nm correspond to Lyman-D, -E, -J, and -G, respectively.…”