How Can ComPASS EM Codes Solve the SRF Problems at JLab?

1. How Can ComPASS EM Codes Solve the SRF Problems at JLab? • Review of original work plans on EM at JLab in ComPASS proposal • As code users to work with code developers, how these work plans are addressed our SRF problems at JLab. • Story telling how these codes have solved or to solve our BBU problems at CEBAF and FEL. • Stress out the multipactoring, RF-thermal cooling, and ERL efficiency simulations and problem solutions in next two years. Haipeng Wang, ISRFST, Jefferson Lab Webex presentation to ComPASS all hands meeting, September 5-6, 2009

2. Original ComPASS NP work plans on EM at JLab FY07 • EM: Provide Low Loss cavity shape for the 12 GeV Upgrade for benchmark of Omega-3P, on its simulated modes, and heat generation due to the rf surface resistance by comparing to commercial codes, analytical estimates and experimental data. FY08 • EM: Supply a 12 GeV CEBAF Upgrade SRF cavity design and measurement data for rf heat generation analysis and cavity thermal modeling for codes benchmark. Benchmark T3P and VORPAL simulations in short and long range wakefields with JLab SRF cavities’ simulations and measurement. Provide experimental data for 3D multipactoring analysis for VORPAL and Pic3P. FY09 • EM: Benchmark self-consistent 3D multipactoring simulations against experimental data. Verify model of HOM damping against experimental data. Comparison of HOM power generated in the JLab FEL SRF cavities to VORPAL and T3P’s predictions. FY10 • EM: Benchmark self-consistent low energy beam simulation against experimental data for a DC (or RF) gun in photoinjector. VORPAL or T3P is used to determine the effects of HOM heating on energy recovery in an ERL and the design of ELIC crab cavities. FY11 • EM: Use VORPAL, Omega3P, T3P, Pic3P to design and optimize high gradient and high current SRF structures for ERLs, ELIC and injectors and to support the design of electron cooling for ELIC. Use VORPAL, Pic3P to simulate the performance of the photoinjector.

3. Actual funding was cut in half and cycles was one year delay FY07 • EM: Provide Low Loss cavity shape for the 12 GeV Upgrade for benchmark of Omega-3P, on its simulated modes, and heat generation due to the rf surface resistance by comparing to commercial codes, analytical estimates and experimental data. FY08 • EM: Supply a 12 GeV CEBAF Upgrade SRF cavity design and measurement data for rf heat generation analysis and cavity thermal modeling for codes benchmark. Benchmark T3P and VORPAL simulations in short and long range wakefields with JLab SRF cavities’ simulations and measurement. Provide experimental data for 3D multipactoring analysis for VORPAL and Track3P. FY09 • EM: Benchmark self-consistent 3D multipactoring simulations against experimental data. Verify model of HOM damping against experimental data. Comparison of HOM power generated in the JLab FEL SRF cavities to VORPAL and T3P’s predictions. FY10 • EM: Benchmark self-consistent low energy beam simulation against experimental data for a DC (or RF) gun in photoinjector. VORPAL or T3P and Pic3P is used to determine the effects of HOM heating on energy recovery in an ERL and the design of ELIC crab cavities. FY11 • EM: Use VORPAL, Omega3P, T3P, Pic3P to design and optimize high gradient and high current SRF structures for ERLs, ELIC and injectors and to support the design of electron cooling for ELIC. Use VORPAL, Pic3P to simulate the performance of the photoinjector. Done, but not fully completed yet. Done, but not fully completed yet. Start to work on these. Start to work on these.

4. Linkages between code users and code developers • SRF Problems • Multipactoringin cavity/coupler • Dynamic Lorentz Force Detune (DLFD) • Magnetic shielding in CM • Pit/bump in H-enhancement • Field Emission (FE) • Thermal/magnetic quench • HOM damping and power handling • ERLs in ER efficiency • klystron/IOT/magnetron design • RF absorbers (SiC or ferrite) • Field parameters to BCs • Low temperature bake • EP verses BCP ( and BEP) • Design optimizations • Cavity shape and FPC/HOM coupler choice • Beam Breakup (or Mm/Mp BBU) • sapphire loss in SRF cavity • Non-relativistic, space-charge dominated BD in SRF gun • Structure design optimization • Functions Desired (in 3D) • Solution accuracy • nonlinear/lossy/anisotropic materials • particle-field interaction with full Maxwell’s solution • wake-impedance calculation • multi-physics with EM • mechanical (thermal, deformation, fluid dynamics) • chemical (electro-physical-chemistry ) • surface mophology (photo-electron, SEY, FE, RF vortices around pit/defect/GB, Cooper pairs formation) • Inverse problem • parameterized models • Codes/platforms integration and automation • User manual/interface friendly • Particle tracking/in-cell in real fields • Practical Examples • Spherical cavities benchmark • MP in TE011/crab and sapphire-loaded cavities • C100/C50 CM shields • SRF gun design • HOM load designs • Understood a BBU at CEBAF • (Thanks to your ACD group) • 4-spoke cavity design • Multiple field effect on BD • multi-beam excitation scheme of wakefield and impedance interpolation • Surface pit/bump on Nb • Cost reduction on HLRF of ILC Color code in SRF Problems: have been touched by commercial codes or ComPASS codes; Being or can be addressed by ComPASS codes; Simulations could help to understand experimental data

5. BBU@CEBAF Cause Investigation-Inverse Problem • R. Kazimi et al. EPAC 2008 paper PP087

6. BBU@CEBAF Cause Investigation-Inverse Problem • Z. Li, H. Wang et al. SLAC-PUB-13266 and JLab-TN-08-026, 2008 • Feedback and lessen to learn: • Better QA on cavity fabrication and dumbbell tuning • Bead-pull/cavity tuning QA only fundamental but HOMs • Full HOM QA in VTA before cryomodule assembly • Confirmation: • Bead-pulls on those defense cavities will be done very soon • R/Qs can be calculated base on bead-pull data to compare predicted and experimental values • Defense cavities are to be fully surveyed.

7. Benchmark on Spherical Cavity Models • K. Tian, H. Wang et al, PAC2009 and ICAP 2009 papers. • Analytical solution available in high accuracy • Fixed mesh density to calculate up to 10HGz HOMs • Code evaluated: Omega3P, VORPAL MWS, HFSS, ANSYS Single Sphere for surface H-field Double Sphere for surface E-field Relative Err.=|fsim-fa|/fa • More data coming from Analyst and VORPAL Relative Err.=||hsim|-|ha||/ |ha| Relative Err.=||esim|-|ea||/ |ea|

8. Pit, Hole, Bump and Grain Boundary on Trapped Vortices and H-field Enhancement • G. Ciovati and A. Gurevich, PRST A&B, 11, 122001 (2008) • V. Shemelin, H. Padamsee, TTC-Report 2008-07 • h~ rn n=-1/3, C. Reece, SRF-840302, Cornell University, 1984 • h up to 3, J. Knobloch, SRF Workshop, 1999 • h up to 5, V. Shemelin, TTC-Report-2008-07, 2008 G. Ciovati & A. Gurevish V. Shemelin & H. Padamsee TE111 mode X. Zhao & A. Valente

9. Magnetic Shielding in Cryomodule Design • G. Cheng et al. JLab-TN-08-015, 2008 • ANSYS simulations for nonlinear magnetic material: • B-H curve, temp. material dependent. • 20 mils shield thickness verses 9 meter long shield • In the 3-D linear model, when an axial external field of 2 Gauss is applied, it is found that the flux density in the outer shield exceeds the saturation limit of 8,000 Gauss. • An H-field survey on Renascence cryomodule has been done and the experimental data do not agree with simulation data. • C50 cryomodules have lower Q0, could blame to magnetic shield or dogleg RF waveguide loss on copper coating or ceramic window eye lid. See a typical cavity’s graph on Q0 vs. Eacc. • QA programs are implemented. • Both simulation and measurement could not tell us the true story.

10. Multipactoring Simulations in SNS HOM Coupler • J. F. Deford, Breakdown Workshop, Boulder, CO, Aug. 10, 2009 • Lixin Ge, ICAP 09 Conference, San Francisco, CA, Sep. 3, 2009 • Chet Neiter, and Peter Stoltz, Tech-X, MP simulations on waveguides and cavities by VORPAL • Excellent mulations and movie revealed a great detail of this MP • for understanding • The ultimate goal is not to remove the HOM coupler from high beta cavities at SNS although it is feasible, but to avoid it in the design • Other projects like ADSs might follow. 2 3 1

11. RF-Thermal Management Problems in Renascence Cryomodule • C Reece et al. SRF 2007 paper WEP62. • We are currently working on VORPAL and TEMP3P to address this challenge • Not only through SciDAC but also SBIRs.

12. Long-rang Wakefield and Impedance Calculations • H. Wang et al. ERL 2007, PAC 2007 paper WEPMS070. Multiple beam wake excitation scheme. • F. Marhauser et al. PAC 2009 paper FR5PFP094, ERL 2009. Impedance spectrum extrapolation method. • Set up field (power) monitors on WG ports can let us do the HOM load design and ERL efficiency calculation.

13. HOM Load Design and Measurement for High Current Structures • H. Wang et al. PAC 2007 paper WEPMS070. • F. Marhauser et al. PAC 2009 paper WE6RFP009. • Wakefield solver with lossy materials can let us design a real HOM load CEBAF HOM load at 2K

14. Summary • SRF problems challenge many expects of the current state of art ComPASS EM simulations • Both software and hardware developments need advanced models and algorisms • Simulation itself, by its limitation, can not replace our R&D experiments. But it can help to understand our data and guide our R&D works and designs. • Cryomodule engineering design and structure integration definitely need multi-physics simulations to work and to be benchmarked. • SCiDAC ComPASS is a right vehicle to meet those challenges but is less funded to the NP program. • JLab needs ComPASS’s expert codes and their supports and running them on our local clusters and at NERSC. • We need stress out the simulation solution for multipactoring and rf-thermal problems not from CST-PS or ANSYS but from ComPASS codes in next two years.