Conference Paper

Commissioning of the Lower Hybrid Current Drive System on Alcator C-Mod

Plasma Sci. & Fusion Center, MIT, Cambridge, MA
DOI: 10.1109/FUSION.2005.252948 Conference: Fusion Engineering 2005, Twenty-First IEEE/NPS Symposium on
Source: IEEE Xplore

ABSTRACT A lower hybrid current drive (LHCD) system has been developed for current profile control of advanced tokamak experiments on Alcator C-Mod. LHCD along with Ion Cyclotron Radio Frequency (ICRF) heating will be used to develop regimes with high confinement, high betan and high bootstrap fraction and extend them to quasi-steady-state conditions. This paper will describe the commissioning and initial operation of the LHCD system that includes a 50 kV, 208 A pulsed-power supply, twelve 250 kW Klystron transmitters, a 96 waveguide launcher and required control, protection and data acquisition systems

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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<sub>n</sub> 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.
    Fusion Engineering, 2003. 20th IEEE/NPSS Symposium on; 11/2003
  • [Show abstract] [Hide abstract]
    ABSTRACT: A combined model for current profile control and MHD stability analysis has been used to identify stable operating modes near the ideal stability limit (βN 3) in the Alcator C-Mod tokamak. These discharges are characterized by relatively high fractions of bootstrap current (fBS = 0.70) and non-monotonic profiles of the safety factor with qmin > 2. In the absence of a conducting shell, stability was determined by the onset of the low (n = 1) external kink mode. In these studies, current profile control in the plasma periphery (r/a 0.5) was provided by 2.5-3.0 MW of LHCD power. Internal and edge transport barriers were introduced into the model calculations in the form of density transitions. Excellent wave accessibility and absorption were still found in the presence of an H-mode-like edge density barrier. However, the presence of these barriers resulted in about a 10% decrease in the stability limit, from βN 3 to βN 2.7.
    Nuclear Fusion 05/2002; 40(6):1251. · 3.24 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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<sub>n</sub> (∼3) and high confinement (H<sub>H</sub>∼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.
    Fusion Engineering, 2002. 19th Symposium on; 02/2002

Full-text (2 Sources)

Available from
Jun 5, 2014