Lower hybrid low power microwave active control system design, installation and testing on Alcator C-Mod

Current profile evolution will be controlled and sustained in the Alcator C-Mod advanced tokamak lower hybrid current drive experiment by use of 3 MW of 4.6 GHz lower hybrid current drive (LHCD) now being installed and tested. LHCD and an existing 5 MW ICRH capability are to be used to develop regimes with high confinement, high β_n and high bootstrap fraction and extend them to quasi-steady-state conditions. This paper will describe the design, installation and testing of the low power microwave active control system used in the experiment. The LHCD low power microwave active control system uses vector modulators to provide a phase and amplitude controlled driver for each of twelve 4.6 GHz, 250 kW klystrons. Phase and power output of each klystron are monitored by an I-Q detector and the resulting signals are used in digital controllers for closed-loop control of the klystron phase and amplitude to preset values.