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

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 T = 4.2K, Q = 2.5*10 8, Ez max = 22MV/m E = 900keV, I = 520μA RF power input

Radiation Source ELBE Mitglied der Leibniz-Gemeinschaft Dietmar Janssen New SRF Gun – Cavity design He-vessel power coupler HOM filter gun half-cell choke filter cathode cathode cooler LN 2 reservoir Cathode transfer rod Poster WPAP007

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

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 10kW Design M.Champion Development of HEPL, Stanford

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

Radiation Source ELBE Mitglied der Leibniz-Gemeinschaft Dietmar Janssen External quality factor and heat load of a cathode-RF coupler Field parameters for E acc = 25MV/m Ez max (r=0) = 50MV/m, Ur max = 6.5kV Es max = 43.6MV/m, Bs max = 0.11T

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