A low-cost multichannel Thomson scattering system for CDX-U

A multichannel Thomson scattering system has been developed for the CDX-U spherical torus. The system is designed for 10 eV < T-e < 400 eV, n(e) <10(18) m(-3), which includes typical and predicted central and edge conditions in CDX-U. The system uses two laser passes to double the scattered photons from a 5 J ruby laser. The beam path is vertical through the similar to 66 cm (elongated) diameter of the plasma and is movable in the major-radial direction, enabling coverage of nearly 70% of the major-radial plasma extent. Twelve channels over the vertical minor radius provide similar to 2.5 cm spatial resolution. The main collecting lens, located 45 cm from the laser beamline, provides high solid angle (Delta Omega similar to 0.01) light collection using a 15 cm diam lens. The system makes maximum usage of an optically fast (f/1.8) compact imaging spectrometer. An intensified charge coupled device with a GaAs photocathode provides quantum efficiency of similar to 20% at 6943 Angstrom. The combination of plasma access, multiple beam passes, high-throughput spectrometer, and high quantum efficiency detector provide for very high total photon statistics in a relatively simple and inexpensive system. (C) 1999 American Institute of Physics. [S0034-6748(99)55401-4].