1. Review 09/2010 page RF System for Electron Collider Ring Haipeng Wang for the team of R. Rimmer and F. Marhauser, SRF Institute and Y. Zhang, G. Krafft and S. Derbenev, CASA

2. Review 09/2010 page Medium Energy EIC Top Layout Three compact rings: 3 to 11 GeV electron Up to 12 GeV/c proton (warm) Up to 60 GeV/c proton (cold)

3. Review 09/2010 page Electron collider ring figure 8 layout 2 MEIC collider ring 134.989 m R=57.495 m 60° 379.609 m 20.000 m 239.167 m RF insertion Low energy High current High energy Low current

4. Review 09/2010 page Electron Beam Stacking Structure for 5GeV 3 <3.3 ps (<1 mm) 0.4 pC 1.334 ns (40 cm) 0.750 GHz 10-turn injection 33.3 μs (4 pC) 40 ms (~5 times radiation damping) 25 Hz 40 s (1000 bunch trains), average current=3 A Microscopic bunch duty factor 2.47x10 -3 average current=0.3 mA Macroscopic bunch duty factor 8.33x10 -4 From CEBAF SRF Linac Stored beam in collider ring revolution time=3.33 μs, 2501 bunches per ring

5. Review 09/2010 page Existing RF systems in storage rings: normal conducting 4 BESSY PEP-II Two examples Rimmer and Allen etc Marhauser and Weihreter etc

6. Review 09/2010 page Existing RF systems in storage rings: superconducting 5 Two examples CESR-III B-cell KEKB-TRISTAN Furuya and Akai etc. Padamsee and Chojnacki etc Design ParametersUnitsOriginal CESR-III, Cornell Univ.Original KEKB, Japan cavity parametersCESR-III CavityKEKB-HER cavity frequencyMHz499.765509 number of cell11 R/Q = Ueff^2/(w*W)Ohm89.093.0 R/Q/cellOhm89.093.0 material independent geometry factor G = R s *Q 0 Ohm270.0250.0 R/Q*GOhm2403023250 acitve lengthm0.30.243 insertion lengthm2.863.01 operating temperatureKelvin4.2 BCS surface resistance R BCS nΩnΩ97.2100.8 residual surface resistance assumed R res nΩnΩ13.0 total surface resistance R s nΩnΩ110.2113.8 Q05.0E+082.2E+09 shunt impedance (R=Ueff^2/P)MΩMΩ4.5E+042.0E+05 input power (total losses)kW324.9571.2 Pcavity (surface losses)kW0.007610.00079 Pbeam (beam loading)kW320.00562.50 Pbeam (beam loading on crest)kW324.9571.2 average beam currentA0.551.4 minimum gap voltage requiredkV581.8401.8 accelerating gradientMV/m1.971.68 Qext matched Q0/(1+Pbeam/Pcavity)2.00E+058.90E+04 coupling factor (Q0/Qext)2.50E+032.47E+04 total radiated powerMW1.284.50 energy loss per turnMeV2.333.21 beam energyGeV5.38 rf effective accelerating voltageMV2.333.21 synchronous phase, 0 is on crestdeg10 rf peak voltage requiredMV 2.3633.264 number of cavities needed 48 insertion lengthm11.44024.080 straigh section length in storage ringm Preliminary Cost Exercisefrom BNL per Jim Rose 2008 costs per cavity$$1,200,000 total investment costs + RF power$$3,395,000 total investment costs (cavities only)$$4,800,000 total costs (w/o power bill)$13,580,000 cryoplant$ RF to AC power per year$ operational costs per year$could favor SRF after 5-10 years

7. Review 09/2010 page Synchrotron radiation power RF system in storage ring: Technology of choice 6 High Current Low Energy High Energy Low Current Klystron power Power coupler and RF window Beam excited HOMs HOM damping by waveguide or coaxial coupler Liquid helium Cooling, 4.2K DI water cooling <300K High gradient for CW Bunch head-tail instability Large beam aperture ceramics ferrites Low RF Frequency Low gradient for CW Normal conducting cavity RF acceleration Low broadband and narrow band HOM impedance cavity Superconducting cavity Warm HOM windows and loads <600kW for CW RF power Beam loading control

8. Review 09/2010 page Scaled RF system for MEIC Electron ring: normal conducting 7 BESSY: <100kW E acc =6MV/m Conditioned up to 30kW CW in 5 days. 11GeV 5GeV Marhauser and Weihreter

9. Review 09/2010 page Scaled RF system for MEIC electron ring: superconducting 8 11GeV 5GeV JLab High Current 750MHz, 5-cell, 1A cavity Only single-cell is preferred due to a heavy HOM damping requirement in storage ring, But space is limited. Rimmer and Wang etc

10. Review 09/2010 page Initial HOM Analysis: beam current excitation 9 FFT S. H. Kim and H.Wang Time averaged HOM power normalized to R/Q (W/  = Amp 2 ) is current square drive term. It has no information of the cavity but with assumed HOM damping Qext. For example, if we have a HOM resonated at 2.25GHz with R/Q of 10  and Q external of 100, we have 1kW HOM power from the beam in this mode. When we design a high current cavity, we have to avoid HOM frequencies sitting on the beam excitation resonances. H. Wang etc PAC2005 TPPT086.

11. Review 09/2010 page Initial HOM damping analysis: Impedance and HOM power 10 BESSY CWCT copper cavity impedance measurement s Marhauser and Weihreter, EPAC 2004 Impedance scaling from BESSY NC RF cavity in same shape but in different frequency scale: monopole modes around 2.25 GHz have to be avoid by either changing the cavity shape (safe to park) or damping totally with Qext< 100, otherwise 50kW (on resonance HOM power will come out to the HOM loads. Following is an example (H. Wang etc PAC 2005) for JLab High Current 5-cell cavity design to avoid HOM resonance by choosing different cavity shapes.

12. Review 09/2010 page MEIC electron ring RF system Summary: Pros and Cons 11 SCRF favors to High Energy, Low Current Operation NCRF favors to Low Energy, High Current Operation