Performance and Upgrades for the Electron Cyclotron Heating System on DIII-D

Abstract

The electron cyclotron heating (ECH) system on the DIII-D fusion reactor consists of six 110-GHz gyrotrons with 6 MW installed power for pulses limited administratively to 5 s in length. The transmission coefficient is better than −1.1 dB for four of the transmission lines, which is close to the theoretical value. A new depressed collector gyrotron was recently installed and is injecting up to 720 kW of power into DIII-D during 2013 tokamak operations. Three of the four dual waveguide launchers, which can steer the RF beams ±20°both poloidally and toroidally, were used for real-time neoclassical tearing mode control and suppression with increased poloidal scanning speed up to 60°/s and positioning accuracy of the beams of ±2 mm at the plasma center. The ECH capabilities on DIII-D are being steadily updated, leading to increased experimental flexibility and high reliability of the system. In the past year, the ECH system reliability reached 87% for 2352 successful individual gyrotron shots into DIII-D. Planning is under way for the addition of two new depressed collector gyrotrons, one at 110 GHz, 1.2 MW and another at 117.5 GHz, 1.5 MW generated power, both of which are in the test stage at Communications and Power Industries.

Protection of the DIII-D Vessel, Diagnostics and Windows from Microwaves Injected by the ECH/ECCD System

“…Reflected power monitors used as sniffers are installed in each transmission line at the last miter bend before the tokamak. These 4-port rf power monitors are sensitive to the transmission direction, wave polarization, and rf mode content [4]. A mirror with vacuum on both sides picks off the forward and reflected signals and is followed by a window.…”

Performance History and Upgrades for the DIII-D Gyrotron Complex

“…The next group of gyrotrons to be added to the DIII-D complex will all be depressed collector tubes [4]. Two of these are 110 GHz tubes and all the rest will generate 117.5 GHz, a frequency which is better for current drive and heating at the highest performance levels on DIII-D.…”

“…The gyrotron system on DIII-D began operation with 1 MW class tubes in 1997 and since then has been steadily increased in capability [4]. The overall reliability over the past 9 years on a single gyrotron basis has been about 85% even though four of the gyrotrons are operated in pairs on single power supplies, hence a fault in one causes two tubes to be lost for the plasma shot.…”

Plans for the electron cyclotron heating system on J-TEXT

“…Electron cyclotron resonance heating (ECRH), recognized as a kind of efficiently auxiliary heating method, has been widely used on many tokamaks and stellarators [1][2][3][4][5][6].…”