February 17-18, 2010 R&D ERL Andrew Burrill R&D ERL SRF Electron Gun Andrew Burrill February 17-18, 2010 SRF Electron Gun

February 17-18, 2010 R&D ERL Andrew Burrill SRF Electron Gun What are we building? ½ cell SRF injector with an independently cooled demountable cathode stalk designed for use with CsK 2 Sb photocathodes What makes this unique? –Ability to couple 1 MW of RF power to the gun via 2 coaxial couplers  Novel pringle tip FPC to improve coupling and reduce beam effect on beam –Plans to deliver up to 500 mA average current from the gun –Cathode delivery system can be outfitted with a wide variety of cathode materials from metals to dispensers –Use of a quarter wavelength RF choke joint for the cathode insertion. –High Temperature Superconducting Solenoid 2

February 17-18, 2010 R&D ERL Andrew Burrill SRF Electron Gun - Physics ParameterUnitsValue FrequencyMHz Iris radiuscm5 Equator Diametercm37.9 Cavity lengthcm25 Beam kinetic energyMeV2 Peak electric field MV/m35.7 Peak magnetic fieldA/m58740 (73mT) Stored energyJoule8.37 Ratio of Bmax/EmaxmT/(MV/m) Ratio of Emax/Eacc QRs (geometry factor)  111 R/Q  62 Qe (external Q) Power inputMW1 Maximum currentmA500 Emittance at 1.4 nC  m rms normalized 1.4 Cathode recessmm1 Cathode spot sizemm diameter5 Emission phaseDegrees25 Longitudinal loss factor V/pC0.7 Transverse loss factorV/pC/m32 3

February 17-18, 2010 R&D ERL Andrew Burrill SRF Electron Gun Fabrication & Testing one polycrystalline & one large grain gun fabricated Polycrystaline at Jlab for processing and testing Initial VTA testing complete 4

February 17-18, 2010 R&D ERL Andrew Burrill Cavity Processing Cavity was tuned to pre- determined frequency prior to shipment to Jlab Cavity was given a bulk, 140 um BCP treatment 10 hours at 600  C Furnace treatment 25 um BCP, HPR, Assembly Ultrasonic thickness measurements are being taken along the way. –To date show an actual etch rate ~60% of the sample etch rate. 5

February 17-18, 2010 R&D ERL Andrew Burrill Cavity Testing Summary Preliminary VTA test completed last week on the cavity without the VTA cathode inserted. –Goal was to measure the performance of the cavity independent of the choke joint. Data shows signs of multipacting/ radiation in the cavity requiring further investigation –Multipacting analysis did not look at the cavity without the cathode stalk as this is not a useful operational mode of the cavity Low Field Q value was 1e10 in line with superfish simulations Goal for the next test is the install the VTA cathode and provide a DC bias to help suppress multipacting in the choke region. –This should help identify the location of the multipacting 6

February 17-18, 2010 R&D ERL Andrew Burrill Preliminary Cavity Test Data 7

February 17-18, 2010 R&D ERL Andrew Burrill SRF Electron Gun Cryomodule 8

February 17-18, 2010 R&D ERL Andrew Burrill Summary Cavity is progressing well in the processing and testing phase FPC conditioning should take place by end of April Hermetic String Assembly complete by end of August Installation into cryomodule by December Testing in early