Brazing of High Performance, Passively Cooled, Heat Absorbing Mirrors for Electron Cyclotron Heating Launchers

Electron Cyclotron Heating is essential for the operation of high performance plasma fusion experiments. A 6 cm diameter, 1 MW, 110GHz beam is typically guided to a specific location by a steerable mirror. This mirror is subject to design requirements that work against each other. High heat loads, and absence of convective cooling, dictate a mirror made from conductive material with a significant heat capacity and mass. These qualities tend to increase electromagnetic forces on the mirrors, complicating the design of the mirror supports.

A successful design compromise has been to make the mirror as a brazed assembly with stainless steel bars inlaid into a copper block. As power levels and pulse lengths increase, the use of higher strength copper alloys has been explored.

 Chrome Zirconium Copper, [C18150] has emerged as an attractive candidate for mirror construction. The zirconium, however, causes difficulties in brazing. We have developed a process that overcomes these difficulties, and also includes heat treatment as part of the braze cycle, so that the strength of the copper alloy is partially recovered after the high temperature braze.

 This paper describes the design challenges associated with ECH launcher mirrors, the development of a high temperature braze technique for C18150, and the latest mirror design.