Development of a high speed crowbar for LANSCE

Each of the four 200 MHz Final Power Amplifiers (FPAs) in the LANSCE proton linac has its own capacitor bank and crowbar. The dissipation in the 10 Ω crowbar limiting resistor is as high as 67 kW, and oil cooling is used. Our stated upgrade goal was to substantially reduce the limiting resistor dissipation and eliminate the oil cooling. Early tests showed that the fault energy quickly rose to unacceptable levels as the current limiting resistance was reduced. FPA arcs are normally quenched by interrupting the FPA modulator current, and the crowbar waits 10 μs for this to occur. The successful upgrade strategy was to replace the 10 Ω resistor with a 3 Ω air cooled resistor and to add a high speed crowbar circuit which operates only if there are simultaneous arcs in the FPA and its modulator. This paper describes the high speed circuit and its interface with the existing crowbar. Test results are also given