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MuCool Cavity RF Simulation Studies

Explore in-depth simulation studies conducted by Z. Li for accelerator modeling using the ACE3P suite at SLAC and LBNL. Topics include modeling effort, cavity design optimization, coupler modifications, and dark current effects. Learn about multiphysics modeling tools and applications in RF component design.

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MuCool Cavity RF Simulation Studies

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  1. MuCool CavityRF Simulation Studies Zenghai Li LixinGe, Chris Adolphsen, SLAC, Daniel Bowring, Derun Li, TianhuanLuo, LBNL MAP Collaboration Meeting 06/21/2013

  2. Outline • Multi-physics Modeling tool ACE3P • Modeling effort with ACE3P • 805 MHz Be-wall modular cavity • 201 MHz cavity (Tianhuan’s talk) • Cavity length study • Summary and outlook Z. Li - RF Simulation Studies, MAP 6/21/2013

  3. Accelerator Modeling with EM Code Suite ACE3P SLAC’s suite of conformal, higher-order, C++/MPI based parallel finite-element electromagnetic codes. Implemented on NERSC super computers https://slacportal.slac.stanford.edu/sites/ard_public/bpd/acd/Pages/Default.aspx ACE3P (Advanced Computational Electromagnetics3P) Frequency Domain: Omega3P – Eigensolver (damping) S3P – S-Parameter Time Domain:T3P – Wakefields and Transients Particle Tracking: Track3P – Multipacting and Dark Current EM Particle-in-cell:Pic3P– RF guns & klystrons Multi-physics: TEM3P – EM, Thermal & Structural effects • Have been applied to cavity and rf component design for various accelerator projects • Cavity design and optimization, HOM damping, coupler design,multipacting, thermal and mechanical analysis, etc • As numerical probe to help understand experimental data (e.g. identifying trapped modes, understand bead-pull results, MP barriers, etc) Z. Li - RF Simulation Studies, MAP 6/21/2013

  4. Be-Wall Modular Cavity Modular cavity 104.4 mm in length • Coupler optimization • MP simulation and mitigation - for B=0T and B=3T • Shape optimization • TiN coating • Thermal analysis Z. Li - RF Simulation Studies, MAP 6/21/2013

  5. The Coupler • Side coupling • Reduced height waveguide to reduce transverse size, step transition to full height • Beta=1.35 Z. Li - RF Simulation Studies, MAP 6/21/2013

  6. MP Around Coupler Iris – initial design • Waveguide stub: 36.85mm • Iris neck rounding: 6.25mm simulation using Track3P Resonant particles on iris neck region and end of the waveguide stub B=3T B=0T • Resonant particles only occur around coupler iris region • Strong MP barrier around 7.5 MV/m Z. Li - RF Simulation Studies, MAP 6/21/2013

  7. Coupler Modification to Minimize MP Band (h) 43mm stub, racetrack neck (c) 36.85mm stub, 12mm rounding Z. Li - RF Simulation Studies, MAP 6/21/2013

  8. MP Around Coupler Iris – Prototype Design WG stub:43mm, racetrack iris neck (h) Coating Area (Z-X plot) • B=3T • B=0T cavity outer wall coupler neck Z. Li - RF Simulation Studies, MAP 6/21/2013

  9. Field Enhancement at Viewport • Frequency shift due to viewport: 23kHz/port • B field at viewport: 0.78*B_coupling_slot Z. Li - RF Simulation Studies, MAP 6/21/2013

  10. MP at Viewport, TiN Coating Area B=3T MP, need coating (coating area) B=0T Z. Li - RF Simulation Studies, MAP 6/21/2013

  11. MP on Be Wall, B=3T • Two point MP resonant particles on Be window • Impact energies much higher than energy of peak SEY (~ 250eV) • Not likely to MP (though high energy field emission current possible) F. Le Pimpec, et al, SLAC-TN-04-046 \ LCC-0146 Z. Li - RF Simulation Studies, MAP 6/21/2013

  12. Fields at Pump Slot E field B field No significant enhancement at the slots Z. Li - RF Simulation Studies, MAP 6/21/2013

  13. Field in waveguide • Single step transition from reduced height waveguide to full height waveguide • Field is ~3.6 times the field in full height waveguide Z. Li - RF Simulation Studies, MAP 6/21/2013

  14. Thermal Mechanical Modeling Using TEM3P • Using same data structure as EM components of ACE3P • RF heat load calculation using higher-order EM fields from Omega3P/S3P/T3P • Higher-order thermal and mechanical solvers • Realistic linear and nonlinear material properties • Calculate geometry distortion and effect on RF Z. Li - RF Simulation Studies, MAP 6/21/2013

  15. Modular Cavity Material Composition Stainless steel with copper coating inside Stainless Steel Copper ring Beryllium wall Courtesy David Martin Z. Li - RF Simulation Studies, MAP 6/21/2013

  16. RF Thermo-Elastic Simulation Results Cooling channel added to minimize ΔT across the Be endplate B Fields Z. Li - RF Simulation Studies, MAP 6/21/2013

  17. 201 MHz cavity MP Analysis See Tianhuan’s talk for details Cavity Model Curved window Coupler region Z. Li - RF Simulation Studies, MAP 6/21/2013

  18. 201 MHz Cavity MP Comparison – with vs without external B field See Tianhuan’s talk for details NO external B field With 3T external B field NO resonant particles on Window Z. Li - RF Simulation Studies, MAP 6/21/2013

  19. Dark Current Effect vs Cavity Length • Using a simple pillbox cavity model under strong B field • Calculate • Impact Energy: V • FN current: J • “Impact power” : V*J v.s. cavity length, Es and effective gradient Eacc • --> To understand parameter optimization for cavities under strong magnetic field Z. Li - RF Simulation Studies, MAP 6/21/2013

  20. Dark Current - Impact Energy & V*J (beta_FN=50) Es=25MV/m max at L=81mm • At same Es • Max V*J at around 80mm length • V*J drops by more than factor of 2 at a length of lambda*/2 • But, higher V*J with longer length for the same effective accelerating gradient (next slide) Z. Li - RF Simulation Studies, MAP 6/21/2013

  21. V*J at Same Effective Acc Gradient • Effective Gradient: 25MV/m • Longer cell require higher ES to achieve same acceleration gradient – higher V*J • Optimal RF power requirement at L~100 mm (5mm space between cavities assumed for packing factor) ES/Gaccvs cavity length (due to Ttransient) PACC/L Testing cavities of different lengths will help understanding the effects of DC, and parameters for cavity optimization Z. Li - RF Simulation Studies, MAP 6/21/2013

  22. Summary and Outlook ACE3Pis a suite of high performance computing EM thermal/mechanical codes Modular cavity prototype design • Coupler geometry optimized • MP analyzed, mitigation of MP at coupling iris and viewport incorporated in the engineering design • Thermal stress analyzed using TEM3P, cooling channels incorporated in the thermal design to reduce stress on Be wall • Cavity being manufactured 201 MHz cavity simulation • MP analysis with realistic external B field map (Tianhuan, Lixin) Outlook – simulation effort with ACE3P • Assist users on using ACE3P • Support rf design and optimization of cavity and components • Modular cavity and test setups • Dark current and RF breakdown studies Z. Li - RF Simulation Studies, MAP 6/21/2013

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