Chemical vapor deposition diamond window for high-power and long pulse millimeter wave transmission

Abstract

To satisfy the electrical and thermomechanical requirements for a continuous wave millimeter wave beam transmission, a window assembly using a large size synthesized diamond disk has been developed. Such window systems are needed as a vacuum barrier and tritium shielding in future electron cyclotron heating systems for fusion plasma heating and noninductive electron cyclotron current drive. The diamond used in this study was manufactured by chemical vapor deposition (CVD) and consists of a polycrystalline diamond disk 96 mm in diameter and 2.23 mm thick. The disk was built into an assembly in which two Inconel tubes were bonded on both sides of the plate to provide vacuum shielding and water cooling to the edge of the disk, leaving an effective window aperture of 83 mm. It will be shown that, as a result of the high thermal conductivity and low dielectric loss exhibited by this grade of CVD diamond, the temperature increase of the window due to the absorption of high-power millimeter wave radiation could be minimized by simple water edge cooling at room temperature. During transmission of a focused Gaussian beam of 170 GHz, 110 kW, 10 s, the temperature increase at the center of the window reached a steady state condition at a value of approximately 40 K, in good agreement with calculated values. Water-edge-cooled CVD diamond windows promise to provide a practical technical solution for the transmission of continuous millimeter wave transmission in excess of 1 MW.

Development of reliable diamond window for EC launcher on fusion reactors

“…The windows are located just before the closure plate in each transmission line. In order to allow a 1 MW mm-wave transmission per window, a synthetic poly-crystalline diamond window has been developed [4,5] and is now a standard window for high power mm-wave transmission. In terms of safety, the window is a tritium barrier, which is the same boundary as a vacuum vessel (primary boundary).…”

Thermal desorption behavior of deuterium implanted into polycrystalline diamond

“…The ECH/ECCD system with high power radio frequency (rf) power source has been developed in JAERI (Japan Atomic Energy Research Institute) for ITER (International Thermonuclear Experimental Reactor). A vacuum window is one of the most important components in the ECH/ECCD system development [1][2][3][4][5]. Diamond is the leading candidate for rf windows.…”

Design activities on helical DEMO reactor FFHR-d1

“…Performance of CW gyrotrons has been improved recently, and the maximum power reaches ∼2 MW/170 GHz [40,41] and 1.9 MW/77 GHz gyrotrons [42]. The other main components of ECH system have been developed for the ITER ECH system such as the transmission line [43], the MOU [44], and the diamond window [45,46]. Those components are directly applicable to the FFHR system.…”