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“Testing a 100kv / 20A SolidState Fast Switch and ModAnode Regulator at the APS” ASD – RF Group Argonne National Laboratory Office of Science U.S. Department of Energy A U.S. Department of Energy Office of Science Laboratory Operated by The University of Chicago “Testing a 100kv / 20A Solid-State Fast Switch and Mod-Anode Regulator at the APS” Mercury - containing ignitron crowbars are commonly used to protect klystrons from arc damage. When an arc occurs, the crowbar closes and rapidly discharges the energystorage capacitor. An alternative way to protect a klystron is to use a switch that opens during an arc, using series arrays of insulated-gate bipolar transistors (IGBTs). Pioneering Science and Technology Office of Science U.S. Department of Energy Ideal switch: 1) Zero resistance or forward voltage drop in the on-state. 2) Infinite resistance in the off-state. 3) Switch with infinite speed. 4) Would not require any input power to make it switch. Choice involves voltage, current, switching speed, drive circuitry, load, and temperature effects. Most desirable primary characteristics are fast switching speed, simple drive requirements and low conduction loss. Pioneering Science and Technology Office of Science U.S. Department of Energy High Power MOSFET: Has high input impedance and fast switching speed. For low voltage applications, power MOSFETs offer extremely low on-resistance, RDS(on), and approach the desired ideal switch. In high voltage applications, MOSFETs exhibit increased RDS(on) resulting in lower efficiency due to increased conduction losses. BJTs Low conduction loss. BJTs and IGBTs have similar ratings in terms of voltage and current. The presence of an isolated gate in an IGBT makes it simpler to drive than a BJT. BJTs require that base current be continuously supplied in a quantity sufficient enough to maintain saturation. • BJTs have a much slower performance than MOSFETs. Pioneering Science and Technology Office of Science U.S. Department of Energy IGBTs IGBT technology offers a combination of the low conduction loss of a BJT and the switching speed of a power MOSFET. IGBTs, like MOSFETs, are transconductance devices and can remain fully on by keeping the gate voltage above a certain threshold. The IGBT has high input impedance and fast turn-on speed like a MOSFET. Although turn-on speeds are very fast, turn-off (tailing) of the IGBT is slower than a MOSFET. Until recently, the feature that limited the IGBT from serving a wide variety of applications was initial IGBTs had current fall times of around three microseconds. Pioneering Science and Technology Office of Science U.S. Department of Energy STAGE 1 M ODIFICATIONS, UVC 1.9 MW DC POWER SYSTEM FOR SR (SECTORS 38 + 40) and RF1 DRIVES TEST BED FUSED DISCONNECT MOTORIZED/FUSED DISCONNECT MATCHING TRANSFORMER VAC SCR'S SGR3 M 13.2 1.4 KV KV : REGULATOR TR SET 0 - 1400 VARIABLE VAC Vc FAST SWITCH V MA 1.9M W I Fil. 0 TO -95KVDC @20A Vc KLY LLRF TEST BED CROWBAR LLRF Pioneering Science and Technology + HLRF to TEST BED V MA I Fil. OUTSIDE BUILDING 420 - Typical 100KW RF KLY RF1 HLRF to RF1 Typical 700KW RF + INSIDE BUILDING 420 Office of Science U.S. Department of Energy Major parameters for fast opening switch transmitter system from Diversified Technologies, Inc. (DTI). Pioneering Science and Technology Office of Science U.S. Department of Energy DTI SOLID STATE OPENING SWITCH / MOD ANODE SUPPLY D C -100KV @20A INPUT C FAST + K 2mH 1? FIL. PWR 25VDC 20A H FAST OPENING SWITCH MOD ANODE REGULATOR (LINEAR) WIRE TEST DUMP RELAY 10K 1K 13M 1uF MA 100M 13M VIN Vc 4M VMA Vc-VMA IMA Pioneering Science and Technology Office of Science U.S. Department of Energy Pioneering Science and Technology Office of Science U.S. Department of Energy Pioneering Science and Technology Office of Science U.S. Department of Energy Solid-state switch plate rated at 3.3 kV, 100A continuous; 36 plates are connected in series to achieve over 100 kV switch capability. Pioneering Science and Technology Office of Science U.S. Department of Energy Pioneering Science and Technology Office of Science U.S. Department of Energy Pioneering Science and Technology Office of Science U.S. Department of Energy Pioneering Science and Technology Office of Science U.S. Department of Energy Pioneering Science and Technology Office of Science U.S. Department of Energy Ch.1 = cathode voltage Ch.2 = cathode current Ch.3 = diode current Ch.4 = over current fault Input = 80kV from spotknocker (fault caused by arc test – output to ANL dummy load) Pioneering Science and Technology Office of Science U.S. Department of Energy Ch.1 = cathode voltage Ch.2 = cathode current Ch.4 = over current fault Input = 100kV from spotknocker (fault caused by arc test – output connected to ANL dummy load) Pioneering Science and Technology Office of Science U.S. Department of Energy Series opening switches have substantial advantages over crowbars in the protection of RF amplifiers (klystrons). 1) Nearly immediate resumption of operation after an arc, during klystron conditioning. 2) Solid – State opening switches use no ignitron crowbars, therefore no mercury. 3) IGBTs can be much less expensive than vacuum tubes due to expected longer lifetimes. 4) Removal of crowbars can significantly lower stresses on upstream power components. Pioneering Science and Technology Office of Science U.S. Department of Energy 5) Opening switches are made with excessive voltage capability, so the switch can operate even if several devices fail (IGBTs always fail shorted). 6) Because the energy – storage capacitor does not discharge during an arc, the RF could be turned again immediately after the arc clears. It is possible the beam may be retained during an arc. - Pioneering Science and Technology At APS, the accelerator beam will continue for approximately 30µs without RF. If a fault would clear within this time and the opening switch were to reclose, it is possible that no beam restart would be required. Office of Science U.S. Department of Energy