An optimized F-number matching system for the Advanced Toroidal Facility's Thomson scattering plasma diagnostic

The design of the Thomson scattering collection optics for the Advanced Toroidal Facility (ATF) has been optimized with respect to throughput efficiency. This optimization was accomplished within constraints imposed by existing com ponents and previous design work by utilizing a lens system to f-number match to the spectrometer array and by reconfiguring the ends of the optical fiber bundles which transmit light to the array. Estimates of spectrometer coupling efficiency as a function of input f-number, input slit size, and wavelength were obtained by tracing rays through a computer model of the spectrometers. This model was developed with a commercial optical design code and was used to select the magnification of the f-number matching optics and the configuration of the optical fiber bundles. The computer model was verified by direct measurements of the spectrometer throughput efficiency. Good agreement between the measurements and the results of the model was obtained for all cases. Limits on the maximum allow able input slit size were developed based on stray light and spectrometer resolution considerations. These limits imposed additional constraints on the magnification of the matching optics. A significant improvement in throughput efficiency was obtained (as compared to the case with no matching optics) while still retaining acceptable spectrometer resolution and stray light rejection. This improvement in system throughput efficiency should increase the dynamic range of the ATF Thomson scattering piasma diagnostic.