Twisted Waveguide Accelerating Structures: Potential and Challenges

1. Twisted Waveguide Accelerating Structures: Potential and Challenges Mohamed Awida University of Tennessee at Knoxville

2. Acknowledgement Dr Yoon Kang Dr Aly Fathy Dr Josh Wilson This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE

3. Outline • Introduction (Motivation, TWG Potential, Geometrical Features of TWG) • Twisted Analog to SNS Cavities (Scaled for 2.8 GHz) • A More Practical Accelerator (1.3 GHz) • Towards A More Attractive Accelerating Structure (1.3GHz, comparison to Tesla) • Summary

4. Introduction

5. Motivation--Cost Tesla Cavity Cavity Iris *linearcollider.org How to simplify the structure in such a way to make it easy to fabricate and so inexpensive? *fnal.org

6. Motivation--Trapped Modes • Trapped modes are localized modes that could exist within the accelerator cavities F. Marhauser, et. al. “Trapped Modes in Tesla Cavities,” PAC99

7. Motivation--Trapped Modes • Existence of trapped modes within an accelerator cavity could be a severe problem • Damping of trapped modes seems impossible due to their localization within the cavity, which prevents a coupling to the HOM dampers mounted to both ends of the beam pipes • As a consequence the energy of a trapped mode can achieve considerable values after several bunch passings • This effect gives additional heat load for the cooling system that has to be taken into account Is there any way to attain an accelerator free from trapped modes? F. Marhauser, et. al. “Trapped Modes in Tesla Cavities,” PAC99

8. Slowing Down the Wave • Wave can be slowed down by:- • Iris loading (corrugated structures) • Dielectric loading • Having it traveling along an elongated spiral path

9. TWG Potential First proposed by Kang in 2000* • The structure basically performs as a (multi-cell) single cavity • Localized trapped modes shouldn’t exist (Modes are distributed along the whole structure) • Higher order modes could be damped by the conventional HOM dampers at the ends *Y. Kang , “Twisted waveguide accelerating structure,” in 9th Workshop on Advanced Accelerator Concepts, Aug. 2000

10. TWG Potential Cont. More fundamental properties of the twisted waveguide cavity structures for particle accelerationwere investigated by Wilson* Higher Twist Rate Slower Wave structure can be used for different particle beta Twisted WG Fast-Wave Slow-Wave Straight WG TEM-Limit *J . Wilson, et. al., “Applications of Twisted Hollow Waveguides as Accelerating Structures” in NST 09

11. Twisted WG Looks like cavities! Cross-Section Longitudinal-Section

12. Twisted WG Cross-Section • In principle, cross-section could be any • However, certain cross-sections leads to twisted analogs of the common accelerating structures Twisted analog to the disk loaded slow –wave structure Twisted analog to an elliptical accelerating structure J . Wilson, et. al., “Twisted Waveguides for Particle Accelerator Applications ,” in IMS 09

13. Twisted WG Cross-Section Cont. Cross-section definition in terms of standard spline geometry parameters [0,Rf] [c1*Rf*cos(θ),c1*Rf*sin(θ)] θ [Rt,0] M. Awida et. al., “Building Twisted Waveguide Accelerating Structures” in PAC 09

14. Twisted WG Cross-Section Cont. θ=π/3 θ θ=π/4 θ=π/5 Theta basically controls the cavity-like and iris-like thicknesses

15. Twisted WG Cross-Section Cont. Rt=12*scale Rt=24*scale Rt controls the iris-like opening

16. Twisted Analog to SNS Cavities (Scaled for 2.8 GHz)

17. Twisted Analog to SNS • Twisted analog to an elliptical • cavity • Non relativistic particles βg=0.61 • Scaled to operate at 2.8 GHz • Twist Rate=96.2 rad/m 63.5 mm 260 mm CST Model

18. CST Simulations--Fields Pi-like mode

19. CST Simulations--Dispersion

20. Experimental Results • Carried out by Wilson * • Twisted guides were terminated • by copper endplates to form a • cavity • Small probes on each end to • measure S21 • Fields appear sinusoidal • toward center of cavity • End effects dominate • close to copper walls *J . Wilson, et. al., “Applications of Twisted Hollow Waveguides as Accelerating Structures” in NST 09

21. Pi-Like Mode Separation “pi mode” means 180 degree phase shift per ½ turn Conventional Reactively Loaded Accelerating Structures Twisted Waveguide Accelerating Structures Near zero group velocity Finite group velocity The problem of mode separation can be dealt with more easily in in twisted periodic geometries J . Wilson, et. al., “Applications of Twisted Hollow Waveguides as Accelerating Structures” in NST 09

22. Sensitivity Analysis & Tuning Tuning can be simply done by moving the end wall (Conventional multi-cell structure needs cell by cell tuning)

23. A More Practical Accelerator (1.3 GHz)

24. Structure Parameters • Twisted analog to an elliptical • cavity • Relativistic particles βg=1 • Designed to operate at 1.3 GHz • Rf=126.8 mm • Rt=24 mm • θ=π/5.7 rad Rf θ Rt M. Awida et. al., “Building Twisted Waveguide Accelerating Structures ” in PAC 09

25. 3-Cells Results Increasing Rt will increase the R/Q value up to a certain point where the R/Q will saturate and decreases back again

26. 3-Cells Results Cont. As expected higher twist rate induces higher R/Q

27. End Wall Effect Twisted-End Wall Flat-End Wall Flat Twisted Twisted+Pipe Twisted end-wall secures a better field uniformity

28. 1.3 GHz Prototype (a) (b)

29. Particle Simulation In Twisted WG Electrons Point Source (βg=0.989) CST Particle Studio Particle Tracking Solver

30. Particle Simulation In Twisted WG βg=0.989 vp=2.967e8 βg=0.992 vp=2.973e8 βg=0.994 vp=2.979e8

31. Towards a More Attractive Accelerating Structure

32. Elliptical Cavities R=V2/P J. Sekutowicz, New Geometries: Elliptical Cavities

33. Tesla Cavity (3cells) Eacc = 9 MV/m R/Q = 1035 (1m) Epeak/Eacc = 1.98 Bpeak/Eacc = 4.15 All eigenmode solutions are normalized to one joule

34. Twisted WG Structures-What is next? • Need to achieve higher R/Q while trying to minimize Epeak/Eacc and Bpeak/Eacc and maintaining uniform Eacc • Design Goals • R/Q ~ 700 • Epeak/Eacc ~2.0 • Bpeak/Eacc ~4.0

35. Optimization (3 Cells, theta=pi/4)-Field Uniformity Ez=4.8 MV/m 27.24 rad/m Ez=6.8 MV/m 54.48 rad/m Ez=8.1 MV/m 108.96 rad/m Higher twist rate enhances the field uniformity

36. Twisted WG Parametric Study Higher twist rate degrades the quality factor (Unloaded Q assuming Copper walls)

37. Twisted WG Parametric Study Cont. Higher twist rate improves Rsh up to a certain point (Assuming Copper walls)

38. Twisted WG Parametric Study Cont. Higher twist rate enhances R/Q

39. Twisted WG Parametric Study Cont. Higher twist rate enhances the acceleration field (Assuming Copper walls – normalized to one joule)

40. Twisted WG Parametric Study Cont. Peak electric field eventually decreases with increasing the twist rate (Assuming Copper walls – normalized to one joule)

41. Twisted WG Parametric Study Cont. Peak magnetic field decreases with increasing the twist rate (Assuming Copper walls – normalized to one joule)

42. Twisted WG Trends

43. Twisted WG Structures--Final Prototypes 4.5 Turns 9 Turns Twist Rate = 54.48 rad/m Twist Rate = 27.24 rad/m Ez~4 MV/m Ez~3 MV/m R/Q=547 R/Q=252

44. Twisted WG Structures--Final Prototypes 18 Turns Twist Rate = 108.96 rad/m Eacc = 8.04 MV/m Epeak =14.1 MV/m Hpeak=27.456 KA/m R/Q = 700 Epeak/Eacc = 1.76 Bpeak/Eacc = 4.31

45. Summary • Twisted waveguides support TM-like modes with velocities slower than c • Twisted structures can be used for both relativistic and non-relativistic particle acceleration • Twisted guides can be designed to circumvent mode trapping problem • The problem of mode separation can be dealt with more easily in twisted structures • Higher twist rate secures better field uniformity, R/Q, Hpeak/Eacc, and Epeak/Eacc • Offers possibility of easier manufacturing, assemblage and tuning than conventional structures • Prototypes fabrication to be performed (Extrusion)

46. Thanks -- Questions

47. Publications • M. H. Awida, Y. W. Kang, J. L. Wilson, S-H. Kim, S-W. Lee, “Building Twisted Waveguide Accelerating Structures,” in Proc.PAC2009. • J. A. Holmes, Y. W. Kang, J. L. Wilson, Y. Zhang, M. H. Awida,, “Investigation of Beam - RF Interactions in Twisted Waveguide Accelerating Structures Using Beam Tracking Codes,” in Proc.PAC2009. • M. H. Awida, Shady F. Suleiman, A. E. Fathy, “Development of a Substrate-Integrated Ku-Band Cavity-Backed Microstrip Patch Sub-Array of Dual Linear/Circular Polarization for DBS Applications,” in IEEE Radio Wireless Symposium 2010. • S. Yang, M. H. Awida, Shady F. Suleiman, A. E. Fathy, “Low-Cost Low-Profile Dual Circularly Polarized Ku-Band Antennas for Mobile Satellite Platforms,” in Antenna Applications Symposium 2009. • M. H. Awida, A. E. Fathy, “Substrate-Integrated Waveguide Ku-Band Cavity-Backed 2x2 Microstrip Patch Array Antenna,” IEEE Antennas and Wireless Propagation Letters, vol. 8, pp. 1054-1056, 2009. Presentation_name

48. Publications • A. E. Fathy, M. H. Awida, N. Shah, W. Brian, E. Ripley, “Electromagnetic and Thermal Analysis of High Power Industrial Microwave Ovens for Metal Casting Applications,” in IEEE MTT-S Int. Microw. Symp.Workshops, Massachusetts, Boston, Jun. 2009. • M. H. Awida, N. Shah, W. Brian, E. Ripley, A. E. Fathy, “Modeling of an Industrial Microwave Furnace for Metal Casting Applications,” in IEEE MTT-S Int. Microw. Symp. Dig., Atlanta, Georgia, Jun. 2008. • M. H. Awida, A.H Kamel, A. E. Fathy, “On the Convergence of MoM for Infinite Phased Arrays,” in URSI Conference, Boulder, Colorado, Jan. 2008. • A. E. Fathy, M. H. Awida, M. J. Kuhn, J. L. Wilson, “Microwave Holographic Antennas,” in URSI Conference, Manitoba, July 2007. • M. H. Awida, A. Boutejdar, A. M. E. Safwat, H. El-Hennawy and A. Omar, “Multi-Bandpass Filters Using Multi-Armed Open Loop Resonators with Direct Feed,” in IEEE MTT-S Int. Microw. Symp. Dig., Honolulu, Hawaii, Jun. 2007. • M. H. Awida, A. Balalem, A. M. E. Safwat, H. El-Hennawy, and A. Omar, “Combined Lowpass-Bandpass Filter Response Using Different Shapes of Microstrip Dual- Mode Resonators,” Proc. of the Europ. Microwave Association, Dec. 2006. Presentation_name

49. Publications Cont. • A. Boutejdar, A. Elsherbini, S. Amari, M. H. Awida and A. Omar, “Design of a Novel Microstrip Bandstop Filter Using one Compact C Open-Loop Resonator,” in Asia-Pacific Microwave Conf., Yokohama, Japan, Dec. 2006. • M. H. Awida, A. M. E. Safwat, and H. El-Hennawy, “Miniaturized Dual-Mode Microstrip Bandpass Filters Using Meander Space-Filling Curves,” Proc. of the Europ. Microwave Association, Jun. 2006. • M. H. Awida, A. Balalem, A. M. E. Safwat, H. El-Hennawy and A. Omar “Combined Low-Pass and Bandpass Filter Response Using Microstrip Dual-Mode Resonators,” in IEEE MTT-S Int. Microw. Symp. Dig., San Francisco, California, Jun. 2006. • M. H. Awida, A. M. E. Safwat, and H. El-Hennawy, “Compact Rat-Race Hybrid Coupler Using Meander Space Filling Curves,” Microwave and Optical Technology Lett., vol. 48, no. 3, pp. 606–609, Mar. 2006. • M. H. Awida, A. M. E. Safwat, and H. El-Hennawy, “Dual-Mode Microstrip Bandpass Filter Using a Ring of Arrows Resonator,” Electron. Lett., vol. 41, no, 24, pp. 1335–1336, Nov. 2005. Presentation_name

50. Career Objective in Fermilab Be part of the Fermilab taskforce of Project X and ILC putting my solid electromagnetic background and RF experience to serve in the RF/SRF department