A linear beam device (10) having a multi-stage depressed collector is provided with means that quickly removes the total voltage across the collector electrodes (22-32) upon detection of an arc between the collector electrodes. The linear beam device (10) comprises a cathode (12) and an anode (16) spaced therefrom that are operable to form and accelerate an electron beam. A collector having a plurality of successive collector electrodes (22-32) is arranged downstream from the anode (16) to collect electrons of the electron beam. At least one power supply (42, 52, 62, 72, 82) is coupled to the collector and provides a plurality of distinct voltage levels to respective ones of the collector electrodes (22-32). The power supply (42, 52, 62, 72, 82) comprises a plurality of serially coupled filter capacitors (46, 56, 66, 76, 86), with each one of the filter capacitors (46, 56, 66, 76, 86) being charged to a respective difference (V-V5) between adjacent ones of the distinct voltage levels. A crowbar circuit (40) or other means is coupled across the plurality of filter capacitors (46, 56, 66, 76, 86). The crowbar circuit (40) or the other means reduces the total voltage across the plurality of filter capacitors (46, 56, 66, 76, 86) to zero upon detection of an arc between any two of the collector electrodes (22-32). According to an embodiment of the invention, the power supply further comprises a plurality of diodes (48, 58, 68, 78, 88) respectively coupled across the plurality of serially coupled filter capacitors (46, 56, 66, 76, 86). The diodes (48, 58, 68, 78, 88) prevent reversal of voltage of a corresponding one of the filter capacitors (46, 56, 66, 76, 86) upon operation of the crowbar circuit (40) or other means.