PowerPoint-Pr

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Axial Power Input in Photocathode Electron
Guns D. Janssen, FZR, Germany, V. Volkov, BINP,
Novosibirsk, Russia,
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Power input in RF guns

• In normal and superconducting
• RF guns the cathode can be separeted by a
• vacuum gap from the surrounding cavity
• Idea This gap can be used for coaxial
• input of RF power
• Advantages
• No additional RF input coupler necessary
• No emittance growth by nonsymmetric
• RF fields in the coupler plane
• No RF losses by the coaxial line around
• the cathode
• Optimal arrangement of magnetic coils
• in the normal conducting case is possible
• Easy to make the RF input variable by a
• quarter wave filter in the superconducting
  case

Vacuum gap
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First operation of a SRF gun
D.Janssen et al., NIM-A, Vol. 507(2003)p314-317 T
4.2K, Q 2.5108, Ezmax 22MV/m E 900keV, I
520µA
RF power input
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New SRF Gun Cavity design
Cathode transfer rod
Poster WPAP007
LN2 reservoir
cathode cooler
cathode
HOM filter
choke filter
gun half-cell
He-vessel
power coupler
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Coupler plane of the cavity
HOM coupler
HOM coupler
Pic-up flange
Main coupler flange
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Beam tube with higher order mode and main
coupler
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RF power input around the cathode
Power input
Bellows for adjustment of Qext and heat isolation
LN2 cooling
Quarter wave choke
cavity
Tube for cathode exchange
cathode
Warm RF window
L
Cold RF window
?z
Power input
End of the cryostat
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External quality factor and heat load of a
cathode-RF coupler
Field parameters for Eacc 25MV/m Ezmax(r0)
50MV/m, Urmax 6.5kV Esmax 43.6MV/m, Bsmax 0.11T
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Summary

• In RF electron guns a coaxial gap between cathode
• and cavity can be used for RF power input.
• This special input coupler
• is easy adjustable,
• create no additional emittance growth and
• produce in the superconducting case a small heat
• load even at large RF power