Measurement of neutral hydrogen density in a helicon plasma

Abstract

Summary form only given. A new laser based diagnostic system has been developed at West Virginia University to measure neutral hydrogen density in the edge of high temperature plasmas. The diagnostic is based on the principle of two photon absorption laser induced fluorescence (TALIF). 205 nm photons from a frequency tripled dye laser are injected co-propagating into the plasma chamber where they excite the 1s-3d transition in neutral hydrogen. The 3D state then decays back to the 2s state emitting light at 656 nm. Emission is collected perpendicular to the injected light using a high-speed gated photomultiplier tube detector. The emission signal intensity is directly proportional to the ground state hydrogen density. Absolute calibration is obtained by performing TALIF measurements on neutral krypton using the same laser, light collection, and detector. With the tabulated atomic absorption rates of the hydrogen and krypton, as well as knowledge of the wavelength response of the detector, TALIF measurements of krypton provide an absolute calibration of the entire system. We present initial results from the TALIF system obtained using a target hydrogen plasma created in a helicon plasma source.