first refurbished booster rf cavity for 15hz

First Refurbished Booster RF Cavity for 15Hz

John Reid

March 7, 2012

fFermilab

• Booster RF Cavity removed from Station 8– Removed October 3, 2011– This cavity was picked to be first for the following:

• One of the lowest for radioactivity.

• Cavity had a suspected small vacuum leak.

• Cavity had performance issues when cold.

– Shipped cavity to MI-60 for initial testing before disassembly.– Cavity moved into cave at MI-60 for high power testing.– Cavity leak checked and found to have a vacuum leak on

upstream end flange.– Temporary repair was performed to allow cavity to under go

initial testing at 15Hz.– Cavity run at 15Hz with reduced gradient to measure

temperature rise of critical components.• Stem temperature > 200 F in 15 minutes running

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Leaking Cavity End Flange

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Standard Ferrite Tuner

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Cavity End Cut Open

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Bad Tuner Stem Connection

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Burnt Tuner Cone

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Burnt Fingers on Cone

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Inside Center of Cavity

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Anode Blocking Capacitor

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Anode Blocking Capacitor

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Std Operating Waveforms

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Phase Det Error – Light BlueAnode Prog – Purple – 23kVpkRF Gap Envelope – Drk BluePA Screen I - Green

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Std Operating Waveforms

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FBI – YellowFBV – GreenPlate I - Blue

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Stem Temp vs Anode Voltage

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• Parameters at 23kV anode voltage @15Hz for 12 hours.– Gradient ~52.9kV peak accelerating voltage– Blocking capacitor temperature = 140 F– High voltage filter chokes – 150 F– Inside drift tube temperature = 145 F– Drift tube temperature = 140 F– Beam tube temperature (on Mu-metal shield) = 150 F– Cavity outer shell temperature by PA = 114 F– Ceramic window outer ring temperature = 106 F– Ferrite Power removed to water = 5.9kW per tuner– Back tuner stem temperature = 165 F– Front tuner stem temperature = 175 F– Bottom tuner stem temperature = 179 F– Cavity vacuum = 1.17 x 10-7 Torr

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Conclusions

• Cavity does operate at 15Hz full gradient, BUT– Need to reduce stem temperatures – Elevated temperatures are in part due to a very small

gap (0.001 to 0.002 inches) on stem vertical connection to center section.

– Going to make a 0.005 inch tin gasket to help in sealing this high rf current connection.

• Want to do longer continuous running starting as soon as gaskets are installed.

• Consider installing cavity back in Station 8 before the end of March.

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