The alcator C-Mod lower hybrid current drive experiment transmitter and power system

Alcator C-Mod is a high-field, high-density, diverted, compact tokamak, which, in its present form uses inductive current drive and is heated with 5 MW of ICRF auxiliary power. C-Mod is in the process of being upgraded with a 4.6 GHz Lower Hybrid heating and current drive system. The purpose of the experiment is to develop and explore the potential of "Advanced Tokamak Regimes", i.e., regimes with high bootstrap fraction (similar to70%), high beta(n) (similar to3) and high confinement (H-H similar to 1-2) under quasi-steady-state conditions. In this paper, an overview of the RF transmitter, high-voltage power supply and controls and protection systems for the Lower Hybrid Project is given. The transmitter will use twelve 250 kW klystrons operating simultaneously which will result in a total directed power of nearly 3 MW for a planned pulse width of 5 seconds. An expected upgrade of four additional klystrons will result in a total directed power of 4 MW. All klystrons will be powered in parallel by a single solid-state pulse-step-modulated (PSM) power supply with a rating of 50 kV and 208 amperes. Commissioning of the power supply is expected in February of 2002 with initial transmitter operation in late 2002.