Design of Advanced Photonic Bandgap Accelerator Structures

1. Design of Advanced Photonic Bandgap Accelerator Structures M. A. Shapiro, R. A. Marsh, B. J. Munroe, R. J. Temkin MIT Plasma Science and Fusion Center (see also R. A. Marsh et al., PBG Wakefields Expt.) Work supported by DOE HEP

2. Introduction to PBG Accelerator Research HOM and Wakefields Simulation Advanced PBG Structures Conclusions OUTLINE

3. Motivation Advanced Structures Needed for Wakefield Damping Slots for damping SLAC Damped Detuned Structure MIT PBG Structure Shintake Choke- Mode Structure

4. PBG Cavity, triangular lattice a/b=0.15, TM01 –like mode 2a b defect Photonic Bandgap Cavity • Fundamental mode TM01 in bandgap • 2D Lattice theory says: no HOM confined in defect • For a/b<0.2, only low frequency bandgap exists Pillbox Cavity, TM01 mode

5. Accelerator with PBG cells Accelerator parameters Disk loaded PBG structure. Open to free space for HOM damping. Irises as in disk loaded waveguide.

6. Accomplishments: PBG Accelerator Expt. • First successful experimental PBG accelerator demonstration. • Tested to gradient 35 MeV/m, limited by available power E. I. Smirnova et al., Physical Review Letters (2005).

7. Introduction to PBG Accelerator Research HOM and Wakefields Simulation Advanced PBG Structures Conclusions OUTLINE

8. Lattice Dipole HOMs • Pillbox Dipole Mode • 23 GHz • Q = 9500 • Lattice Dipole Mode • 24.9 GHz • Q = 63 • HFSS simulations show HOMs in PBG structure • Field not confined in central region (defect), but in lattice • Low Q, Q<300

9. Spectrum of Lattice HOMs • Simulations explain HOM continuum spectrum measured Cold test Lattice HOMs Log Amp (dB) HFSS

10. Conventional wakefield theory (K. Bane et al., 1987) can be used for PBG wakefields calculation Requires r, Q for each mode Calculations underway at MIT SLAC codes (T3P) can be used to simulate wakefields in PBG structure We collaborate with SLAC and STAAR, Inc. on wakefields simulations in PBG structures. Wakefields Theory and Simulations

11. Animation of Beam Transit

12. Introduction to PBG Accelerator Research HOM and Wakefields Simulation Advanced PBG Structures Conclusions OUTLINE

13. First PBG structure built at 17 GHz Tested at MIT for gradient, wakefields Second PBG structure being built for gradient testing at 11.424 GHz (MIT/SLAC collaboration) Future PBG structures at 11, 17 GHz are being designed Reduced pulsed heating Gradient 100 MeV/m Low breakdown rate Free of wakefields Plans for Advanced PBG Structures

14. PBG Structure Detuning Lattice rotated by 30 deg. from cell to cell • Structure allows detuning dipole modes TM11 23.0 GHz TM11, Q=72 17.13 GHz TM01

15. Pulsed Heating SLAC DDS Structure ΔT=55OC for 70 MV/m (Z. Li et al., SLAC-PUB-8647, 2000) PBG Structure H-field distribution ΔT=40OC for 70 MV/m gradient, Hmax=0.56 MA/m, 100 ns pulse length

16. New Ideas for Optimized PBG Structures Complex Mag E • Optimize structure for dipole mode • damping and reduced pulsed heating • Shaped rods, not circular • Distortion of lattice geometry • Similar to proposal of G. Werner et al. (Colorado) for dielectric PBG design Complex Mag H Example of PBG structure with elliptical rods to improve pulsed heating ΔT=11OC for 70 MV/m gradient, Hmax=0.3 MA/m, 100 ns pulse length

17. PBG structure under investigation for linear collider Wakefields in form of Dipole HOMs calculated. Lattice HOMs with low Q Calculation results can be compared to PBG wakefields experiment (next talk). Collaboration with SLAC and STAAR Inc. on wakefields in PBG structure Advanced PBG accelerator under design for testing 11 and 17 GHz 17 GHz structure for test at MIT, 11 GHz at SLAC Reduced pulsed heating, comparable to DDS Extremely low HOM wakefields, much lower than in DDS Conclusions