Dependence of Plasma Parameters in Hydrogen Pellet Ablation Cloud on the Background Plasma Conditions

UV-visible spectra of the radiation from hydrogen pellet ablation clouds have been measured in the Large Helical Device. The temporal development of the Balmer-α line intensity shows a peaked profile with FWHM (full width at half maximum) of approximately 150 µs. The electron temperature Te, electron density ne, and plasma volume V are evaluated by fitting of the measured spectra with a complete LTE (local thermodynamic equilibrium) model. The results shows that Te is almost unchanged, while ne and V increases and decreases monotonically, respectively, in the dominant time period around the intensity peak. The same analyses made for several different magnetic configurations have revealed that ne has a tendency to become higher when the magnetic field strength is higher, while no clear dependence on the magnetic axis position has been observed. On the other hand, Te shows little dependence either on the magnetic field strength or the magnetic axis position.