1. Ralf Eichhorn CLASSE, Cornell University

2. Ralf Eichhorn, Cornell – Cornell’s HOM Beamline Absorbers – TTC Topical Meeting on CW-SRF 2013 2 2 ps bunch length, 2*100 mA beam current Broad HOM spectrum (90 % below 50 GHz) 200 W HOM power per cavity (average) strong HOM suppression of monopole, dipole, quadrupole modes with Q < 10,000

3. 3 Cornell CESR HOM Load Ferrite absorber tiles Water cooled Cornell ERL injector HOM Load 3 types of absorber tiles One was charging up  Operated at 80 K Complicated to mount Ralf Eichhorn, Cornell – Cornell’s HOM Beamline Absorbers – TTC Topical Meeting on CW-SRF 2013

4. 4 Full-circumference heat sink to allow >500W dissipation @ 80K Broadband SiC absorber ring Includes bellow sections Flanges allow easy cleaning Zero-impedance beamline flanges 5K intercept 40 to 80K intercept SiC absorber ring brazed to metal ring Shielded bellow Flange for disassembly Flange to cavity Ralf Eichhorn, Cornell – Cornell’s HOM Beamline Absorbers – TTC Topical Meeting on CW-SRF 2013

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6. 6 Frequency [MHz] No HOM Loads With HOM Loads Courtesy: N. Valles Q 0 > 2*10 10 for the fundamental mode

7. Ralf Eichhorn, Cornell – Cornell’s HOM Beamline Absorbers – TTC Topical Meeting on CW-SRF 2013 7 Are we happy?

8. Ralf Eichhorn, Cornell – Cornell’s HOM Beamline Absorbers – TTC Topical Meeting on CW-SRF 2013 8 We have a vacuum to vacuum leak in HTC 3

9. Ralf Eichhorn, Cornell – Cornell’s HOM Beamline Absorbers – TTC Topical Meeting on CW-SRF 2013 9 Tungsten becomes porous under brazing cycle SiC Absorber Tungsten (to match CTE) 700 C braze

10. Ralf Eichhorn, Cornell – Cornell’s HOM Beamline Absorbers – TTC Topical Meeting on CW-SRF 2013 10 SiC is not a nice material Strong outgasing High particle contamination Tends to chip

11. Ralf Eichhorn, Cornell – Cornell’s HOM Beamline Absorbers – TTC Topical Meeting on CW-SRF 2013 11 How reliable is the material? Measured on a sample Finding on a full cylinder

12. Ralf Eichhorn, Cornell – Cornell’s HOM Beamline Absorbers – TTC Topical Meeting on CW-SRF 2013 12 Shrink-fitting SiC to Ti-5 400 C, 0.002 inch interference at RT So far survived 2 thermal cycles (77 K and back)

13.  Very smooth pumpdown curves, no gas burps  Exposure to nitrogen does not ‘wash-out’ bakeout benefit  Exposure to air (moisture) completely ‘wash-out’ bakeout benefit Courtesy: Y. Li Ralf Eichhorn, Cornell – Cornell’s HOM Beamline Absorbers – TTC Topical Meeting on CW-SRF 2013

14. 14 Flange to Cavity Thermal Shrink Fit Ti Cylinder with integral cooling Use AlN instead of SiC?

15. Ralf Eichhorn, Cornell – Cornell’s HOM Beamline Absorbers – TTC Topical Meeting on CW-SRF 2013 15 Are we happy? Maybe not! – What is the best broad-band absorbing material? – How reliable is it? – How to realize the vacuum barrier? – How much should we care about cleaning issues? – …..