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Axial Power Input in Photocathode Electron Guns

Axial Power Input in Photocathode Electron Guns D. Janssen, FZR, Germany, V. Volkov, BINP, Novosibirsk, Russia,. RF cavity. Cathode. Beam tube. Power input in RF guns. In normal and superconducting RF guns the cathode can be separeted by a vacuum gap from the surrounding cavity

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Axial Power Input in Photocathode Electron Guns

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

  2. RF cavity Cathode Beam tube 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

  3. First operation of a SRF gun D.Janssen et al., NIM-A, Vol. 507(2003)p314-317 T = 4.2K, Q = 2.5*108, Ezmax= 22MV/m E = 900keV, I = 520μA RF power input

  4. 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

  5. Coupler plane of the cavity HOM coupler HOM coupler Pic-up flange Main coupler flange

  6. HOM coupler (TESLA design) Main coupler Max. power 10kW Design M.Champion Development of HEPL, Stanford Beam tube with higher order mode – and main coupler

  7. 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 Δz Power input End of the cryostat

  8. External quality factor and heat load of a cathode-RF coupler Field parameters for Eacc = 25MV/m Ezmax(r=0) = 50MV/m, Urmax= 6.5kV Esmax= 43.6MV/m, Bsmax= 0.11T

  9. 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

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