Protection and fault detection for Lawrence Berkeley Laboratory neutral beam sources

Testing of TFTR neutral beam (NB) sources has begun at the LBL Neutral Beam System Test Facility (NBSTF). Operation at 120 kV, 65 A, 0.5 sec should be achieved soon. Because NB sources spark down frequently during conditioning, the main accelerating (accel) power supply must be interrupted within a few microseconds to avoid degrading the voltage holding capability, or even the damaging, of the NB source. A variety of improper magnitudes and/or ratios of voltages, currents, and times can occur and must be recognized as fault conditions in order to initiate a prompt interruption of the accel power supply. This paper discusses in detail the key signals which must be monitored and the manner in which they are processed in fault detector circuitry for safe operation of LBL NB sources. The paper also reviews the more standard interlocks and protective features recommended for these sources.