The present Thomson scattering system at the reversed field experiment routinely determines electron temperature and density profiles in various modes of operation but only provides a single profile of each discharge. The new system will use a Nd:YLF laser providing measurements every 20 ms. At the same time we wish to improve the accuracy of the measurement: to this end a new detection system based on filter spectrometers and avalanche photodiodes has been built. The higher throughput of the spectrometers and the higher quantum efficiency of the detectors give an improvement of signal to noise levels of almost two orders. To improve dynamic range the output is ac coupled. Noise figure of detectors has been investigated in detail. The system is novel in the way data are recorded using transient recorders with multiplexing of two channels on each input. The effective accuracy and dynamic range of this system is compared to charge integrating systems. With a look to the future we have also investigated the possible use of multi-element avalanche photodiodes. © 2001 American Institute of Physics.
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