Axial Power Input in Photocathode Electron Guns D

Axial Power Input in Photocathode Electron Guns D. Janssen, FZR, Germany, V. Volkov, BINP, Novosibirsk, Russia, Radiation Source ELBE Mitglied der Leibniz-Gemeinschaft Dietmar Janssen

Power input in RF guns RF cavity 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 Vacuum gap Cathode Beam tube 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 Radiation Source ELBE Mitglied der Leibniz-Gemeinschaft Dietmar Janssen

First operation of a SRF gun D. Janssen et al. , NIM-A, Vol. 507(2003)p 314 -317 T = 4. 2 K, Q = 2. 5*108, Ezmax= 22 MV/m E = 900 ke. V, I = 520μA RF power input Radiation Source ELBE Mitglied der Leibniz-Gemeinschaft Dietmar Janssen

New SRF Gun – Cavity design Cathode transfer rod LN 2 reservoir cathode cooler cathode HOM filter choke filter gun half-cell He-vessel power coupler Radiation Source ELBE Mitglied der Leibniz-Gemeinschaft Dietmar Janssen Poster WPAP 007

Coupler plane of the cavity HOM coupler Pic-up flange Main coupler flange Radiation Source ELBE Mitglied der Leibniz-Gemeinschaft Dietmar Janssen

Beam tube with higher order mode – and main coupler HOM coupler (TESLA design) Main coupler Max. power 10 k. W Design M. Champion Development of HEPL, Stanford Radiation Source ELBE Mitglied der Leibniz-Gemeinschaft Dietmar Janssen

RF power input around the cathode Power input LN 2 cooling Bellows for adjustment of Qext and heat isolation Quarter wave choke cavity Tube for cathode exchange cathode Warm RF window Cold RF window L Δz Power input End of the cryostat Radiation Source ELBE Mitglied der Leibniz-Gemeinschaft Dietmar Janssen

External quality factor and heat load of a cathode-RF coupler Field parameters for Eacc = 25 MV/m Ezmax(r=0) = 50 MV/m, Urmax= 6. 5 k. V Esmax= 43. 6 MV/m, Bsmax= 0. 11 T Radiation Source ELBE Mitglied der Leibniz-Gemeinschaft Dietmar Janssen

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 Radiation Source ELBE Mitglied der Leibniz-Gemeinschaft Dietmar Janssen