Development of broadband vacuum windows for high-power millimeter wave systems

Frequency agile sources for future electron cyclotron wave (ECW) systems require broadband windows that are suitable for high-power transmission (> 0.5 MW) in the millimeter wave range. While the relative bandwidths of single-disk or double-disk windows used in conventional monofrequent systems are of the order of 1%, the future systems require for bandwidths of 10% or even more (e.g. > 60% for the FOM-Fusion-FEM). A description of the different window types under consideration and first results of a development of suitable windows have been reported elsewhere. This paper presents an improved test apparatus as well as the latest experimental and theoretical results about broadband windows