1 / 19

Ali Nassiri and Geoff Waldschmidt Accelerator System Division Advanced Photon Source

A Brief Report on the Status of Rf Deflecting Cavity Design for the Generation of Ultra-Short X-Ray pulses at APS. Ali Nassiri and Geoff Waldschmidt Accelerator System Division Advanced Photon Source. ICFA Mini-Workshop on “Frontiers of Short Bunches in Storage Rings”

olin
Download Presentation

Ali Nassiri and Geoff Waldschmidt Accelerator System Division Advanced Photon Source

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. A Brief Report on the Status of Rf Deflecting Cavity Design for the Generation of Ultra-Short X-Ray pulses at APS Ali Nassiri and Geoff Waldschmidt Accelerator System Division Advanced Photon Source ICFA Mini-Workshop on “Frontiers of Short Bunches in Storage Rings” Laboratori Nazionali di Frascati, 7-9 November 2005

  2. Acknowledgements Special thanks to Kenji Hosoyama (KEK), Derun Li and J. Shi ( LBNL), and Tim Koeth (Fermilab) for many productive and useful discussions. A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

  3. Feasibility study group* Undulator radiation & x-ray optics L. Assoufid R. Dejus D. Mills S. Shastri RF K. Harkay D. Horan R. Kustom A. Nassiri G. Pile G. Waldschmidt M. White Beam dynamics M. Borland Y.-C. Chae L. Emery W. Guo K.-J. Kim S. Milton V. Sajaev B. Yang A. Zholents, LBNL * All affiliated with APS except where noted A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

  4. Outline • Introduction • SC vs. RT option • Crab cavity modeling • Summary A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

  5. Parameters / Constraints: What hV is Required? Can get the same compression as long as h*V is constant V=6, h=4 V=4, h=6 Higher V and lower h: more linear chirp and less need for slits V=6, h=8 Higher h and lower V: smaller maximum deflection and less lifetime impact Cavity design and rf source issues h=7, V<6 MV? Higher h and maximum V: shortest pulse, acceptable lifetime Beam dynamics simulation study: h ≥ 4 (1.4 GHz) V ≤ 6 MV (lifetime) M. Borland, APS ps Workshop, May 2005 A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

  6. Parasitic modes (squashed geometry) TM010 Accelerating mode TM110h/TE111h TM011 frequency TM110v APS crabbing mode TE111v • Vertical crabbing mode (APS): horiz axis “squashed” • Maximize mode separation for optimized damping • HOMs above beam pipe cutoff, propogate out • Lower-order mode (TM010) may strongly couple to beam; freq. below cutoff, adopt KEKB coaxial line strategy (for SC) • Multiple cells produce multiplicity of parasitic modes (issue for SC) • Orbit displacement causes beam loading in crabbing mode; adopt KEKB criterion of y = ±1 mm (for orbit distortions ± 0.1 mm) • Generator power increased to compensate; de-Q to decrease sensitivity A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

  7. RT vs. SC rf • RF sources • for SC option are available with minimal reconfiguration • for RT are non-typical and modification is required (1 kHz) • Cavity fill time vs. susceptibility to phase noise • Long for SC cavity; makes it less susceptible • Short for RT structure; makes it more susceptible • Need to compensate frequency detuning • Due to pulse heating for RT case • From microphonics for SC case A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

  8. 9 Cells SW Deflecting Structure • Pulsed heating < 100 deg. C • BMAX < 200 kA/m for 5 μs pulse (surface) • Limited available power ≤ 5 MW • EMAX < 100 MV/m (surface) V. Dolgashev, SLAC, APS seminar, June 2005 A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

  9. SC RF Cavity Study for APS • Single-cell vs. multiple-cell SC cavity configurations • Orbit displacement causes beam loading in crabbing mode; adopt KEKB criterion of y = ±1 mm (for orbit distortions ± 0.1 mm) Superconducting Deflecting Cavity Design Parameters A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

  10. Damping Parasitic Modes f < fc A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

  11. Coaxial transmission lines Rejection filter not shown LOM Damping • Damping load is placed outside of cryomodule. • Ridge waveguide and coaxial transmission lines transport LOM / HOM to loads • Efficiency of deQing was simulated by creating the TM010 mode with an axial antenna. • Stability condition for LOM achieved when Q < 12,900 for 100 mA beam current. • Unloaded Q of LOM was 4.34e9. • Coaxial beam pipe damper with four coaxial transmission lines, damped the LOM to a loaded Q of 1130. Rejectionfilter Coaxialtransmissionline Excitationantenna A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

  12. Deflecting mode filter Waveguide to damper load Single-Cell Deflecting Cavity: Rejection Filter • Deflecting mode creates surface currents along the coaxial beam pipe damper, but does not propagate power. • When a resistive element is added, there is substantial coupling of power into the damping material. • A radial deflecting mode filter rejects at ~ -10 dB. • Performance improvement pursued as well as physical size reduction. A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

  13. Design A Configuration • Ten single-cell cavities with KEK-type coaxial beam pipe damper and rejection filter • Ion pump/valves/bellow assembly will need at least 0.4m on both sides of the cavity assembly. • The total space required by the following physical arrangement is ~ 2.6 m. • Beam impedance considerations may require different cavity configuration • Upstream/Downstream location of coaxial beam pipe damper may be significant • Downstream location may increase beam impedance excessively • Configuration change would require additional space Input Coupler Coaxial Damper Rejection Filter Coaxial Beam Pipe A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

  14. Issues with KEK-Type Layout @ 2.8 GHz • Alignment of coaxial beam pipe dampers (CBD) will be difficult. • Thickness of (CBD) as modeled is 4mm which includes the cooling channel. Rigidity and mechanical stability and cooling capabilities are questionable • Rejection filter may be difficult to implement efficiently. • Results of stress analysis of cavity performed by KEK required stiffening of KEK cavity - tuning by deformation was abandoned. • CBD also functions as tuner in KEK design. This will require a separate adjustable CBD for each cavity. • CBD tuner will require more space and increase complexity • KEK locates CBD on the upstream side of the cavity due to possible impedance issues – will require more space. A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

  15. Design B with Waveguide Dampers: Monopole Modes • Waveguide dampers are placed near cavity to intercept leakage fields of the LOM*+ • LOM couples to waveguide and is strongly damped Qext= 500. • Other monopole modes also couple to TE10 waveguide mode and are strongly damped. Power Flow and Efield vector plot of LOM * A. Nassiri, APS/ANL + D. Li, LBL A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

  16. Design B with Waveguide Dampers: Dipole Modes • Coaxial input coupler considered to permit variable coupling. • Deflecting dipole mode couples to waveguide as TE20 mode and is rejected by > 30 dB in current configuration due to waveguide cutoff frequency. • “Degenerate” deflecting mode couples to TE10 waveguide mode and is strongly damped. • Asymmetric cavity may no longer be necessary depending on HOM spectrum. A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

  17. Input Coupler Waveguide Damper Coaxial Damper Design B Configuration • Ten single-cell cavities with waveguide damper. • The total space required by ten single-cell cavities in the following physical arrangement is ~ 2.4 m assuming ion pump/valves/bellow assembly installed on both ends. • Additional dampers may be required based on full HOM analysis A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

  18. R&D Plan • Feasibility study completed • SC rf technology chosen • Finalize RF system design, refine simulations • Observe assembly and testing of KEKB crab cavities in 2005, 2006 • Model impedance effects (parasitic modes, head-tail) • Conduct proof of principle tests (beam dynamics, x-ray optics) • Chirp beam using synchrobetatron coupling (transient) (W. Guo) • Install 1 MV RT S-band structure, quarter betatron tune (M. Borland, W. Guo, A. Nassiri) (AIP) • Install warm model of SC rf cavity (passive), parasitic mode damping (K. Harkay, A. Nassiri) (AIP) A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

  19. Summary • We believe x-ray pulse lengths ≤ 1 ps achievable at APS • SC RF chosen as baseline after study of technology options • Recent simulation results on LOM and HOM damping are encouraging. • Input coupler design is underway • Beam impedance calculation may have appreciable effect on final design • Proof of principle R&D is underway: beam/photon dynamics • Operational system possibly ≤ 4 yrs from project start A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

More Related