A multichord spectrometer using an 8×8 anode photomultipliera)

A multianode photomultiplier (8×8 anodes of 2.5×2.5 mm2) is used to detect a collection of spectra in a high dispersion echelle spectrometer. A cylindrical lens is placed at the output slit to increase the dispersion at the photomultiplier. The cross talk between adjacent spectra is non-negligible (although <5%), resulting in some interspectral distortion. This is removed by solving a system of simultaneous equations, one for each channel, obtained from the measured cross-talk coefficients. The spectrometer has been used on the COMPASS-D tokamak to measure ion temperatures and fluid velocities.