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

A multichannel Thomson scattering system has been developed for the CDX-U s pherical torus. The system is designed for 10 eV < T-e < 400 eV, n(e) <10(1 8) 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 di rection, enabling coverage of nearly 70% of the major-radial plasma extent. Twelve channels over the vertical minor radius provide similar to 2.5 cm s patial resolution. The main collecting lens, located 45 cm from the laser b eamline, provides high solid angle (Delta Omega similar to 0.01) light coll ection using a 15 cm diam lens. The system makes maximum usage of an optica lly fast (f/1.8) compact imaging spectrometer. An intensified charge couple d device with a GaAs photocathode provides quantum efficiency of similar to 20% at 6943 Angstrom. The combination of plasma access, multiple beam pass es, high-throughput spectrometer, and high quantum efficiency detector prov ide for very high total photon statistics in a relatively simple and inexpe nsive system. (C) 1999 American Institute of Physics. [S0034-6748(99)55401- 4].