“ testing a 100kv / 20a solid-state fast switch and mod-anode regulator at the aps”

A U.S. Department of EnergyOffice of Science LaboratoryOperated by The University of Chicago

Argonne National Laboratory

Office of ScienceU.S. Department of Energy

“Testing a 100kv / 20A Solid-State Fast Switch and Mod-Anode Regulator at the APS”ASD – RF Group

Pioneering Science andTechnology

Office of Science U.S. Department

of Energy

“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 energy-storage 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).



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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.



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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.



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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.



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BUILDING 420

I Fil.

BUILDING 420

-

+

SGR3

MATCHING TRANSFORMER

FUSED DISCONNECT

REGULATOR

VAC

TR SET

SCR'S

MOTORIZED/FUSEDDISCONNECT

LLRF

M

OUTSIDE INSIDE

:13.2 KV

HLRF

VARIABLE VAC

1.4KV

0 - 1400

STAGE 1 MODIFICATIONS, UVC 1.9 MW DC POWER SYSTEM FOR SR (SECTORS 38 + 40) and RF1 DRIVES TEST BED

Typical100KW RF

KLY HLRF-

+

Typical700KW RF

LLRF

to RF1

to TEST BED

CR

OW

BA

R

1.9MW

0 TO-95KVDC @20A

V MA

I Fil.

V MA

TESTBED

RF1KLY

Vc

FASTSWITCH

Vc



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Major parameters for fast opening switch transmitter system from Diversified Technologies, Inc. (DTI).



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FASTOPENINGSWITCH

DUMPRELAY

100M

VIN

1?

1uF

Vc

Vc-VMA

IMA

MOD ANODEREGULATOR

(LINEAR)

CFASTC

WIRETEST

MA

13M

1K

4M

VMA

10K

13M

-100KV@20AINPUT

D

2mH

DTI SOLID STATE OPENING SWITCH / MOD ANODE SUPPLY

FIL.PWR

25VDC20A

+K

-H



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Solid-state switch plate rated at 3.3 kV, 100A continuous; 36 plates are connected in series to achieve over 100 kV switch capability.



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Ch.1 = cathode voltage Ch.2 = cathode current Ch.3 = diode currentCh.4 = over current faultInput = 80kV from spotknocker (fault caused by arc test – output to ANL dummy load)



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Ch.1 = cathode voltage Ch.2 = cathode current Ch.4 = over current faultInput = 100kV from spotknocker

(fault caused by arc test – output connected to ANL dummy load)



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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.



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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.

- 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.

“ testing a 100kv / 20a solid-state fast switch and mod-anode regulator at the aps”

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