Dynamic behaviors of gas/plasma mixture generated by microwave discharge jet at atmospheric pressure have been investigated in terms of the effects of working gas dynamics on the discharge characteristics, focusing on the following four points: formation of discharge jet at the ignition phase, growing speed of plasma plume in relation to gas flow rate, acceleration and deceleration of upward movement of plasma plume, and decay process of plasma column at turn-off of microwave power. Four stages are identified at the discharge ignition. The acceleration coming from buoyancy effect and the deceleration due to gas flow turbulence have been found. The decay speed of plasma column at a power shut-off is found to be influenced by the gas flow turbulence and the recombination rate.

The multiampere negative hydrogen ion source has been developed in National Institute for Fusion Science (NIFS). The ion source is a volume-production type multicusp one with an extraction area of 25×25 cm2. It is found that high density negative hydrogen ions of more than 1 × 1012 cm−3 are produced in the center of the arc chamber with a double magnetic filter configuration. A supply of a small amount of cesium vapor into the arc chamber has greatly enhanced the H− ion current and reduced the operation pressure. The H− ion current of 3.3 A has been extracted from a Cs-seeded plasma at the pressure of 0.9 Pa.

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