Floating data acquisition system for microwave calorimeter measurements on MTX

A microwave calorimeter has been designed for making 140-GHz absorption measurements on the MTX. Measurement of the intensity and spatial distribution of the free-electron laser (FEL)-generated microwave beam on the inner wall will indicate the absorption characteristics of the plasma when heated with a 140-GHz FEL pulse. The calorimeter monitors changes of temperature in silicon carbide tiles located on the inner wall of the tokamak. Thermistors are used to measure the temperature of each tile. The tiles are located inside the tokamak, about 1 cm outside of the limiter radius at machine potential. The success of this measurement depends on the ability to float the data-acquisition system near machine potential and isolate it from the rest of the vault ground system. The data-acquisition system has 48 channels of thermistor signal conditioning, a multiplexer and digitizer section, a serial data formatter, and a fiber-optic transmitter to transmit the data. Timing signals are brought to the interface through optical fibers to signal when to begin measurement while maintaining isolation. The receiver is an HP 200 Series computer with a serial data interface; the computer provides storage and local display for the shot temperature profile. The data is stored temporarily, until it can be passed to a shared resource management system for archiving