Development of a Low-Energetic Metastable Helium Beam Injector for Electric Field Diagnostics by Laser-Induced Fluorescence Method in Inertial Electrostatic Confinement Plasmas

Progresses in development of a metastable helium atomic beam injector as a beam prove for electric field diagnoses are described, which is applicable to a high electric potential region in inertial electrostatic confinement plasmas where a solid probe can hardly be utilized. Configuration refinement of setup of a skimmer to take a collimated diagnostic beam out of the gas jet resulted in a drastic enhancement of the beam density because of reduced scattering effect by reflected atoms. Also a magnetron-discharge system has been developed which can produce a race-track-shaped plasma with a 5 cm long straight section capable of strong interaction with the injected beam. In preliminary d.c. experiments the present system shows an extremely low accessible operating helium gas pressure of less than 2 mPa