Sensitive dependence of hydrogen Balmer-alpha laser-induced fluorescence signal from hydrogen neutral beam on background magnetic field

Abstract

A previously unreported result for the dependence of a laser-induced fluorescence (LIF) signal from the H-alpha (Balmer-alpha) transition in a hydrogen neutral beam passing through a background of neutral hydrogen gas is presented. The LIF signal from a 30kV beam is found to be enhanced and the fine-structure line amplitudes in the H-alpha spectrum are seen to vary significantly with an applied perpendicular magnetic field over the range of 0–0.01T. The phenomenon has also been observed and investigated in a background electric field of ∼0–300V∕cm, and in the presence of crossed perpendicular magnetic and electric fields, demonstrating that the magnetic-field effect is due to the motional Stark electric field perceived in the beam reference frame as it passes through the magnetic field. The effect has been studied with variations of background neutral gas pressure, laser power, and polarization direction and at different locations along the neutral beamline. The phenomenon could be exploited as a low-field diagnostic technique in environments that are not appropriate for magnetic probes.