Description and preliminary results of a new photo detector for the DIII-D Thomson scattering diagnostic

A redesign of the Thomson scattering data acquisition system located on the DIII-D tokamak is undergoing its trial phase. The redesign was made necessary by several factors including the desire to improve the quality of the acquired data. In addition, the previous generation system was based on CAMAC technology, which has become difficult to maintain and is no longer supported. A big part of this improved redesign comes from the use of faster electronics allowing for greatly improved background light subtraction, the main source of noise. The past system utilized LeCroy FERA CAMAC gated integrator modules for integration and digitization. The redesigned system has been designed in a much more distributed manner. The new system consists of a number of subsystems, including: photo detectors, digitizers, distribution panels, and timing circuits. The most significant upgrade was performed on the photo detectors electronics assembly. A key feature was to make the units much more self-contained in regards to the preamplifier, background subtraction, integration, and bias circuits. The redesigned photo detectors and preliminary test results of the trial phase will be presented.