Installation and operation of the 400 kW 140 GHz gyrotron on the MTX experiment

The authors describe the installation and operation of the 400 kW 140 GHz gyrotron used for plasma heating on the Microwave Tokamak Experiment (MTX). The gyrotron system comprises a high-voltage (80 kV) modulated power supply, a multistation CAMAC computer control, a 5 T superconducting magnet, a series of conventional copper magnets, a circulating fluorinert (FC75) window cooling system, a circulating oil cooling system, a water cooling system, and microwave frequency and power diagnostics. The microwave power measured at the MTX tokamak input is typically 200 kW for a gyrotron output of approximately 400 kW. Losses in the system arise from power in modes other than the desired TE 15,2 mode, transport losses in the Vlasov sidelobes, small waveguide losses to the Vlasov, and small losses in the quasi-optical beamline. Individual MTX shots with the gyrotron have shown a stored energy increase of 1 kJ in the plasma in high density plasmas, and central electron temperature increases of up to 800 eV have been obtained. Even larger temperature increases have been observed recently in low density plasmas