Measurement of Relative Flux of Fractional-Energy Emissions Using Beam Emission Diagnostic

Fraction of a neutral beam particle with the different energy has been investigated in the Large Helical Device. We adopt a low-energy (40keV-3MW) neutral beam injection system in order to improve the ion temperature. A visible-spectrometer coupled intensified charge coupled device detector has been installed in order to measure a hydrogen beam emission spectrum inside of a target plasma. The spectral resolution and the reciprocal dispersion are 0.21nm and 1.4nm/mm, respectively. We typically use the 40ms sampling times with the 20ms exposure times. We have clearly observed the beam emission spectra from a hydrogen neutral beam with the energy of full, half and 1/3. We have also estimated the fraction of the full-energy beam component from the beam emission intensity. Total injection beam power is improved by increasing of the fraction of the full-energy beam component.