High-voltage crowbar protection for the large CDF axial drift chamber

The central outer tracker (COT) is a big cylindrical drift chamber that provides charged particle tracking for the collider detector at Fermilab experiment. To protect the COT, the large stored energy in the high-voltage (HV) system needs to be removed quickly when a problem is sensed. For the HV switch, a special-order silicon-controlled-rectifier was chosen over more readily available integrated gate bipolar transistors because of layout and reliability questions. The considerations concerning the HV switch, the prototype performance, and the experience of more than two years of running are described.