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 (∼70%), high β_n (∼3) and high confinement (H_H∼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.