Y. A. Gorelov

The Electron Cyclotron Resonant Heating System on the DIII-D Tokamak

Abstract In the DIII-D electron heating and current drive installation, up to six gyrotron microwave generators in the 1-MW class at pulse lengths up to 5 s have been operated simultaneously. The frequency for all the gyrotrons is 110 GHz, corresponding to the second harmonic of the electron gyrofrequency at 2 T. The peak generated power has been >4 MW with peak injected power slightly greater than 3 MW. The radio frequency (rf) generators are located remotely and are connected to the tokamak by up to 100 m of evacuated circular corrugated waveguide carrying the HE1,1 mode with overall transmission efficiency, including coupling to the waveguide, of up to 75%. Ancillary equipment for polarization control, beam switching, power monitoring, control of launch direction, and system protection has been developed. The system has been used to support a wide variety of physics experiments, including control of magnetohydrodynamic modes, current density profile modifications, basic plasma heating and current drive, transport studies, and rf-assisted start-up. The gyrotron complex is being upgraded by the acquisition of additional tubes with 5- to 10-s pulse length capability.

Transmission lines power measurements for the 110 GHz electron cyclotron heating system on DIII-D and gyrotron operational performance

Operational trends for the six-gyrotron electron cyclotron heating system on DIII-D are presented. Losses in the transmission lines were measured and values close to theoretical were attained for one of the lines with the existing components. Improved alignment and reduction of the number of miter bends in the lines will increase the power transmitted through the waveguide to the DIII-D tokamak.

Millisecond microwave annealing: Driving microelectronics nano

The efficient deposition of high frequency microwave energy into the top several microns of a semiconducting material was experimentally demonstrated as a highly effective mechanism for rapid thermal annealing. Simulations show that absorbed power densities of 4 and 32kW∕cm2 produce average Si heating rates of 325 000 and 10000000°C∕s up to 1300°C. Conduction of thermal energy from the absorption region into the bulk substrate yields peak cooling rates that exceed 1000000°C∕s after the microwave pulse subsides. At the peak temperature, thermal gradients of 5 and 20°C∕μm exist for the aforementioned power densities of 4 and 32kW∕cm2. The application of a 4.5ms, 6kW∕cm2 pulse of 110GHz radiation resulted in an experimentally measured Si heating rate of 275000°C∕s. Applying this millisecond microwave anneal technology to ultrarapid annealing for shallow implanted dopants resulted in ultrashallow junctions that were 14–16nm deep with sheet resistances between 500 and 700Ω∕square and an estimated active dopant...

HIGH POWER LONG PULSE PERFORMANCE OF THE DIII-D GYROTRON INSTALLATION

At DIII-D, five 110 GHz gyrotrons are operating routinely for 2.0 s pulses at generated power levels {ge}750 kW per gyrotron. A sixth gyrotron is being installed, which should bring the generated power level to >4 MW and the injected power to about 3.0 MW. The output power now can be modulated by the plasma control system to fix T{sub e} at a desired value. The system is being used as a tool for control of current diffusion, for current profile control and other experiments leading to advanced tokamak operation.

LAUNCHER PERFORMANCE IN THE DIII-D ECH SYSTEM

The thermal performance of three different designs for the steerable mirrors on the ECH launchers installed in the DIII‐D tokamak has been evaluated theoretically and experimentally. In each case the disruption forces must be minimized while providing a low loss reflecting surface. One design uses all Glidcop® material, but shaped so that the center is appreciably thicker than the edge. A second design is graphite with a molybdenum surface brazed to the graphite. The latest design is laminated copper/stainless steel construction with a thin copper reflecting surface. All three mirrors employ passive radiative cooling. The mirror temperatures are measured by resistance temperature devices (RTDs) which are attached at the back surfaces of the mirrors. The temperature increases are moderate for the laminated mirror, which has the best overall performance.

Upgrades and performance of the electron cyclotron heating system on DIII-D

The Electron Cyclotron Heating (ECH) system on DIII-D 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, 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 degrees both poloidally and toroidally, were used for real-time neoclassical tearing mode control and suppression with increased poloidal scanning speed up to 60 deg/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 being manufactured at Communications and Power Industries (CPI).

The 110 GHz Microwave Heating System on the DIII‐D Tokamak

OAK-B135 Six 110 GHz gyrotrons in the 1 MW class are operational on DIII-D. Source power is > 4.0 MW for pulse lengths {le} 2.1 s and {approx} 2.8 MW for 5.0 s. The rf beams can be steered poloidally across the tokamak upper half plane at off-perpendicular injection angles in the toroidal direction up to {+-} 20{sup o}. measured transmission line loss is about -1 dB for the longest line, which is 92 m long with 11 miter bends. Coupling efficiency into the waveguide is {approx} 93% for the Gaussian rf beams. The transmission lines are evacuated and windowless except for the gyrotron output window and include flexible control of the elliptical polarization of the injected rf beam with remote controlled grooved mirrors in two of the miter bends on each line. The injected power can be modulated according to a predetermined program or controlled by the DIII-D plasma control system using real time feedback based on diagnostic signals obtained during the plasma pulse. Three gyrotrons have operated at 1.0 MW output power for 5.0 s. Peak central temperatures of the artificially grown diamond gyrotron output windows are < 180 C at equilibrium.