Clarification of fundamental processes in negative ion plasma

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Formation and destruction processes of negative ions were studied to clarify the factors affected by plasma-surface interaction at the wall of a plasma source confining a negative ion plasma. Simple dependence of negative ion density upon surface characteristic parameter like work function or tungsten coverage rate was not found obvious, but the negative ion density and/or the VUV spectrum of the light emission from the plasma appeared to be dependent upon plasma volume parameters as well. Electron energy distribution functions, perturbation upon extracted negative hydrogen ion (H^-) current due to laser injection into the ion source extraction region, and transport of perturbed plasma by photodetachement were investigated to clarify the effect of neutral collisions. A precise measurement of electron energy distribution function revealed the high energy component occupied larger portion than the one in a simple Maxwell distribution function. This corresponds to more frequent formation of vibrationally excited hydrogen molecules in the plasma. The collision processes were found influential upon the transport of H^- in hydrogen plasma through two mechanisms. The first is the deceleration of plasma due to neutral collision damping, and the second is an enhanced transport of H^- toward the extraction hole, which is presumed caused by a combination with the local electric field. Velocity distribution functions of neutral hydrogen atoms and molecules were measured by mass separated time-of-flight analysis. When the velocity distribution functions of D_2 molecules were fitted to Maxwell distribution functions, the molecular translational temperature increased with the discharge power up to a critical one, and then decreased against further increase of the power. The above experimental observations should form a set of key components to be taken into account for modeling the atomic and molecular processes in a negative ion containing plasma.