[en] MIT and PPPL have joined together to fabricate a high-power lower hybrid current drive (LHCD) system for supporting steady-state AT regime research on Alcator C-Mod. The goal of the first step of this project is to provide 1.5 MW of 4.6 GHz rf [radio frequency] power to the plasma with a compact launcher which has excellent spectral selectivity and fits into a single C-Mod port. Some of the important design, construction, calibration and testing considerations for the launcher leading up to its installation on C-Mod are presented here

[en] An antenna-transmitter system for driving current in the LHRF has been installed in Alcator C-Mod. The antenna is a grill consisting of 4 poloidal rows of waveguides, each with 24 guides in the toroidal direction. Power is supplied by 12 klystrons capable of 250 kW operation at a frequency of 4.6 GHz. Thus the total source power is 3 MW, with about 1.5 MW available to be coupled to the plasma. Power supply and heat throughput limits in C-Mod limit the pulse length to 5 s, which however represents several current redistribution times. With 90 deg. phasing, the n parallel spectrum is sharply peaked at 2.3 and the range 1.5 < n parallel < 3.5 can be accessed dynamically by varying the phase of the klystrons. The system is in the commissioning phase with klystron power limited to ∼20 kW and pulse length to 10 ms. Early results from plasma operation are discussed

[en] 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 (LHCD) system. The purpose of the experiment is to develop and explore the potential of 'Advanced Tokamak Regimes' under quasi-steady-state conditions. In this paper, an overview of the RF transmitter and the controls and protection systems for the Lower Hybrid Project is given. The transmitter will use 12 250 kW klystrons operating simultaneously which will result in a total nominal power at the klystrons of nearly 3 MW for a planned pulse width of 5 s. Active control system vector modulators provide phase and amplitude drive for each klystron, and I-Q detectors are used to monitor phase and amplitude. These feedback signals are used in digital controllers for closed-loop control of klystron phase and amplitude to preset values. An expected upgrade of four additional klystrons will result in a total nominal power of 4 MW. The transmitters have been tested to full power, and installation of the lower hybrid current drive experiment on the C-Mod Tokamak is expected in 2004/2005

[en] MIT and PPPL have joined together to fabricate a high-power lower hybrid current drive (LHCD) system for supporting steady-state AT regime research on Alcator C-Mod. The goal of the first step of this project is to provide 1.5 MW of 4.6 GHz rf power to the plasma with a compact launcher which has excellent spectral selectivity and fits into a single C-Mod port. Some of the important design, construction, calibration and testing considerations for the launcher leading up to its installation on C-Mod are presented here