The Coupler Protection System Upgrade for Lower Hybrid Current Drive on Alcator C-Mod

The MIT Plasma Science and Fusion Center (PSFC) Alcator C-Mod project has implemented a lower hybrid current drive (LHCD) system that uses 12 VKC-7849 Varian (CPI) klystron transmitters to supply up to 3 MW source power at 4.6 GHz. Power from each transmitter is split eight ways using a complex system of waveguides to drive the 96-channel coupler array. The existing Coupler Protection System (CPS) monitors directional coupler forward and reflected power signals at 60 locations in the system and provides 60 channels of voltage standing wave ratio (VSWR) protection for the coupler array. To further improve coupler protection and provide remote adjustability an upgrade to the CPS is underway. The most efficient approach to this upgrade has been to use an existing fast digitizer board design having MDS+ data system communication capabilities and reserve field programmable gate array (FPGA) circuitry. Working closely with the digitizer board manufacturer and designers, D-TACQ Solutions, PSFC engineers are developing CPS fault protection logic for twelve each of the ten channel, 14 bit, 6 MSPS/channel digitizer boards with associated custom rear transition modules (RTM). These boards will provide the protection and data acquisition functions needed to allow programmable, optimized protection and monitoring for the coupler and accessibility to the existing MIT PSFC MDS+ data acquisition and control system. Details of the CPS upgrade system will be presented.