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Photonic Bandgap Accelerator Experiments

Photonic Bandgap Accelerator Experiments. Roark A. Marsh, Michael A. Shapiro, Richard J. Temkin Massachusetts Institute of Technology, Plasma Science and Fusion Center Work supported by DOE HEP. Collaborators. Continuing collaboration with Jake Haimson and HRC

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Photonic Bandgap Accelerator Experiments

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  1. Photonic Bandgap Accelerator Experiments Roark A. Marsh, Michael A. Shapiro, Richard J. Temkin Massachusetts Institute of Technology, Plasma Science and Fusion Center Work supported by DOE HEP

  2. Collaborators • Continuing collaboration with Jake Haimson and HRC • 6 Cell structure was designed, built, and tested by Evgenya Smirnova, now at LANL • Wakefield simulations in collaboration with Kwok Ko at SLAC, and John DeFord at STAAR, Inc. • Breakdown experiments were designed to be tested, and in collaboration with Sami Tantawi and Valery Dolgashev at SLAC

  3. Outline • 17.14 GHz Experimental Results • Lab • 6 Cell Traveling Wave Structure • Wakefield Simulations • Wakefield Measurements • 11.424 GHz Planned Experiments • Single Cell Breakdown Structures • Design of PBG Breakdown Structure • Future PBG Improvements and Experiments

  4. Outline • 17.14 GHz Experimental Results • Lab • 6 Cell Traveling Wave Structure • Wakefield Simulations • Wakefield Measurements • 11.424 GHz Planned Experiments • Single Cell Breakdown Structures • Design of PBG Breakdown Structure • Future PBG Improvements and Experiments

  5. MIT 17 GHz Accelerator 700 kV 500 MW Modulator HRC Relativistic beam Klystron: Microwave Power Source 25 MW @ 17.14 GHz Structure Test Stand Photonic Bandgap Accelerator 25 MeV Linac: 0.5 m long 94 cells

  6. Motivation • Acceleration demonstrated but what about HOMs? • 2D Theory predicts all HOMs in propagation band • PBG HOM Damping in practice is more complicated • 3D Structure with disk loading (irises/plates) • Propagation band means damping, but how much? • HOM Simulations need to be backed by experiments • Beam excitation of wakefields using 6 Cell structure

  7. Experimental Setup • Structure is unpowered • DC injector produces a train of bunches • Matched load on input port • Diode detector observations made through output port and vacuum chamber windows Diode Load 1/17GHz = 60ps 100ns Horn & Diode

  8. Experimental Setup Pictures Matched Load Output Port Window View from Below Chamber Window

  9. PBG Multi-Bunch Simulation Output Port Matched Load • Bunch train with 1 mm rms bunch length and 17.5 mm spacing driven through structure Chamber window

  10. PBG Multi-Bunch Simulation Output Port Matched Load • Bunch train with 1 mm rms bunch length and 17.5 mm spacing driven through structure Chamber window

  11. PBG Multi-Bunch Simulation Output Port Matched Load • Bunch train with 1 mm rms bunch length and 17.5 mm spacing driven through structure Chamber window

  12. PBG Multi-Bunch Simulation Output Port Matched Load • Bunch train with 1 mm rms bunch length and 17.5 mm spacing driven through structure Chamber window

  13. PBG Multi-Bunch Simulation Output Port Matched Load • Bunch train with 1 mm rms bunch length and 17.5 mm spacing driven through structure Chamber window

  14. Cold Test of PBG HOMs Low Q Lattice HOMs • 17.14 GHz • Q = 4000 • group velocity = 0.0109 c • Lattice HOMs • Q < 250

  15. Simulation of PBG Lattice HOMs • Electric field from HFSS simulations of PBG • Train of bunches means harmonics of 17.14 GHz • Dipole mode not observed Lattice HOM: 34 GHz, Q = 100 Fundamental: 17 GHz, Q = 4000

  16. Measured 17 GHz Beam Loading • Output Port diode measurement • No fitting parameters, excellent agreement Pb (Theory)

  17. Measured 34 GHz Wakefields • Output Port diode measurement • Awaiting theory, please help… Quadratic fit

  18. Experimental Results Summary • Summary of measurements for 100 mA average current • Observations made on Chamber window as well as Output Port • Multiples of 17.14 GHz observed up to 85.7 GHz with heterodyne receiver

  19. Outline • 17.14 GHz Experimental Results • Lab • 6 Cell Traveling Wave Structure • Wakefield Simulations • Wakefield Measurements • 11.424 GHz Planned Experiments • Single Cell Breakdown Structures • Design of PBG Breakdown Structure • Future PBG Improvements and Experiments

  20. SLAC Setup • TM01 Mode Launcher • Single Cell SW Cavity • Input and end cells for matching • Central test cell • New design uses PBG as central test cell

  21. X Band PBG Structure Test • SLAC test stand with reusable TM01 mode launchers • MIT designed PBG structure for high power testing • Under construction

  22. Design Results • Designed to have ½ field in each pillbox coupling cell, only full field region is in PBG “test” cell • Coupling optimized by minimizing S11 reflection from TM01 Mode launcher Field on axis S11 Coupling reflection

  23. X Band PBG Single Cell Structure • Central PBG test cell • Pillbox matching cells • First iris radius varied to optimize coupling ½ Field Full Field PBG Structure Experiments, AAC 2008

  24. Electric Field Plots • Electric field plots: top and side views • 6.6 MW in = 100 MV/m gradient = 180 MV/m surface field on iris

  25. Magnetic Field Plots • Magnetic field plots: top and side views • 6.6 MW in = 100 MV/m gradient = 0.8 MA/m surface field on inner rod

  26. Outline • 17.14 GHz Experimental Results • Lab • 6 Cell Traveling Wave Structure • Wakefield Simulations • Wakefield Measurements • 11.424 GHz Planned Experiments • Single Cell Breakdown Structures • Design of PBG Breakdown Structure • Future PBG Improvements and Experiments

  27. PBG Structures, The Next Generation • 1st PBG structure test made using: • a/b = 0.18 • Triangular lattice of cylindrical rods • 3 rows of rods • Relatively high pulsed heating on inner row of rods • Next generation: PBG with low pulsed heating, high gradient, low lattice HOMs • Planned additional tests of improved PBG structures at 11.424 GHz, at SLAC and at 17.14 GHz, at MIT

  28. Summary and Conclusions • Measured beam loading in PBG structure • Excellent agreement with theory • Measured HOMs at 34 GHz (waiting for theory…) • X-band standing wave PBG structure designed for SLAC, under fabrication • First high gradient, breakdown tested PBG structure • Future Plans • Better PBG structures • Testing at SLAC, and MIT

  29. Thank You • Any Questions?

  30. Abstract Damping wakefields is a critical issue in the next generation of high gradient accelerators. Photonic bandgap (PBG) structures have unique properties that offer significant wakefield damping. Experimental measurements of wakefields excited by an 18 MeV electron beam in a 6 cell, 17.14 GHz metallic PBG traveling wave accelerator structure are reported. Theory calculations including traveling wave beam coupling, and wakefield simulations using T3P and Analyst are discussed. Good agreement is obtained between theory and experiment. Design and status of an 11.424 GHz standing waves PBG breakdown experiment to be performed at SLAC are discussed. Current status and future plans for design work including future X-band PBG breakdown structures, and improved pulsed heating performance PBGs will be discussed. Work supported by DOE HEP, under contract DE-FG02-91ER40648

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