High Power Water Load for Lower Hybrid Current Drive at 4.6 GHz on Alcator C-Mod

We have developed a high power water load capable of absorbing 250 kW for 5 S at 4.6 GHz. These loads are required for testing and calibrating the lower hybrid current drive systems. The design and analysis of the load was done with the aid of the computer codes CST for RF and Algor and Comsol for water fluid considerations. The load consists of a stainless steel jacket with a Teflon insert. The Teflon is used as a RF impedance matching device, a water seal and is designed to manage water flow over the Teflon-water interface. This design distributes the absorption uniformly at the interface. The flow requirements are 22 gallons/minute with less than 2 psi drop. A shrink fit application to eliminate conventional seals was utilized on the Teflon insert. Initial tests resulted in 300 kW being absorbed for 500 ms with less than -26 db of reflection.