Development of Excited Helium Beam Injector for Electric Field Measurement by Laser-Induced Fluorescence Method

A 2¹S metastable helium atomic beam injector was studied for a beam probe of electric field diagnoses, which is applicable to high electric potential region in Inertial Electrostatic Confinement Fusion (IECF) plasmas where a solid probe can hardly be utilized. With deuterium background gas (~0.1Pa) which is the minimum operation pressure of the IECF devices, the beam density was found to decrease ten times lower than beam density without background gas because of collisional effect. Also, plasma parameters in a-magnetron-discharge-based exciter were evaluated by means of Langmuir probe and emission spectroscopy. These results strongly imply a high excitation rate of ~10^-4 into 2¹S metastable state.