Microwave absorption diagnostics on the MTX tokamak

Summary Form only given, as follows. The Microwave Tokamak Experiment (MTX) is designed to investigate nonlinear electron cyclotron heating (ECH) resulting from short, high-power, microwave pulses incident on a high-density (10/sup 14/ cm/sup -3/), high-temperature (1 keV) tokamak plasma. The free-electron laser (FEL) used to supply the microwave pulses will initially operate in a single-pulse mode at a frequency of 140 GHz with pulse lengths of approximately 20 ns at a power of 1-2 GW. Ultimately, the FEL will supply pulse trains consisting of 50 pulses of 50-ns duration at a power of 8 GW. The energy supplied by the FEL pulse ( approximately=40 J) is small compared with the stored energy of the plasma ( approximately=2500 J), making it difficult to evaluate the beam-plasma interaction by measuring bulk plasma parameters for these initial experiments. To determine the FEL power balance, a set of microwave diagnostics has been developed to measure the microwave beam parameters directly. These diagnostics include a beam splitter coupled with photon drag detectors to measure the forward and reflected power of the FEL beam, a calorimeter to measure the total microwave energy transmitted through the plasma and its spatial extent, and a receiver measuring the time evolution of incident power through the calorimeter.<>