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ILC Crab cavity development

This document discusses the development of crab cavities and their unique properties in transverse momentum rotation. It covers technical issues, cavity design, frequency selection, wakefields, phase stability, and more. Collaboration with Fermilab and phase control system development are also mentioned.

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ILC Crab cavity development

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  1. ILC Crab cavity development Cockcroft Institute 12-13th January 2006 Graeme Burt – Lancaster University

  2. What is a crab cavity? • A crab cavity imparts a transverse momentum to the bunch. • The bunch continues to rotate outside the cavity. Crab Cavity IP l/2 Drift space

  3. Why is a crab cavity different from an accelerating cavity? • Use of the magnetic field of a TM110 horizontal dipole mode • The field gives a phase-dependant transverse momentum kick to the beam horizontal vertical Beam Magnetic field Electric field cross section

  4. Technical issues on cavity to cavity phase jitter Tolerance for a 20mrad crossing angle with 1.3 GHz cavities • 3% voltage stability  • ~2 degrees cavity to beam phase error  • 0.022 degrees phase jitter unknown, thought to be possible electron bunch Δx positron bunch Interaction point

  5. What might a Superconducting crab cavity system look like? 4m-5m • Require up to 4 9-cell cavities in each BDS • Need space for cryostat, input/output couplers, tuning mechanisms… to IP Cryostat RF Amplifier RF Amplifier RF Amplifier Feedback loop Phase Control System Synchronisation with other cavity Reference Phase

  6. Study of cavity shape As the beampipe radius is increased the transverse voltage decreases and the cell-to-cell coupling increases. Beampipe radius

  7. Fermilab cavity, other cavities and technical advancement • Current deflecting cavity exists at Fermilab, 13 cells per cavity, 6.1MV/m at 3.9GHz • We are studying variations on current cavity design for 1.3GHz and 2.6 GHz. • Also undertaking more general studies.

  8. Technical issues relating to choice of crab cavity system frequency Size • There cannot be magnets on the extraction line opposite the crab cavity hence, as the cavity will be close to the IP, it should be as short as possible. Wakefields • Transverse wakefields increase with frequency. Phase stability • Phase jitter tolerances are relaxed for higher frequencies, (although not time jitter tolerance)

  9. Beam dynamics - Action of Quadrupoles Dashed = back of bunch Solid = front of bunch QD0 Crab Location QF1

  10. Location of the crab cavity • The displacement of a particle at the IP is directly related to the beta-function. The displacement of particles at the IP due to the influence of the crab cavity is a function of bx at the crab cavity location. bx by 4 Ratio of kick with and without final doublet 3 my 2 1 mx 10 20 30 40 50 Distance of CC to IP

  11. Location of the crab cavity (effect on space required) Active length required to achieve 10mrad bunch rotation for 1TeV CM assuming 6MV/m transverse deflecting voltage Active length (m) 1.3GHz 3.5 2.5 The full crab cavity system length will be equal to the active length multiplied by a packing factor (typically ~2) 1.5 3.9GHz 0.5 CC distance from IP (m) 10 20 30 40 50

  12. Order of modes in an dipole cavity TM010 accelerating mode Higher order modes TM110v TE111v Need to extract the fundamental mode TM011 frequency Extraction of the lower order mode and the higher order modes is essential to minimise disruption of the beam. v-vertical h-horizontal TE111h TM110h crabbing mode

  13. Wakefield- R/Q Monopole modes (m=0) do not contribute to transverse wakes, and m=2 modes are very small close to r=0. R/Q for dipole modes in the FNAL CKM cavity

  14. Wakefield- Trapped modes Placing a short in the beampipe will shift the resonant frequency of a mode due to the parallel electric field on the surface.

  15. Wakefield- Simulation Crab cavity Deflected beam Collaboration with L. Bellantoni at FNAL. Bunch angle Undeflected beam Wakefield Kick Current simulations show that the bunch transverse position tolerance at the crab cavity is 250microns.

  16. Wakefield study - Low power warm cavity model • Construction of a dipole mode cavity model to investigate higher and lower order modes. HOM coupler Input coupler VNA

  17. Phase control system development • Tests need to be carried out to understand the difficulties that need to be overcome in order to achieve the required phase stability. • Can phase be effectively controlled over the distances involved? • How well would current phase control systems cope with the crab cavity system requirements and where would improvements be needed?

  18. ERLP phase measurement It is planned to place two deflecting cavities on the ERLP and to measure their phase stability using the beam deflection.

  19. Conclusions • Crab Cavity Project • ASTeC and Lancaster Engineering Department • Design of crab cavities • Integration of Crab cavity into the BDS • Wakefield/trapped mode investigation • Phase control system

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