Muon Collider Design Workshop, 12/8~12/2008 TM110 Deflecting/Crabbing Cavity for Muon Emittance Exchange ? Haipeng Wang, Robert Rimmer Jefferson Lab

Muon Collider Design Workshop, 12/8~12/2008 Talk Outlines Motivation: After muon 6D emittance cooling in helix channel, using TM110 mode of RF cavities instead of absorbers combining with dipole chicanes to exchange transverse emittance (too large) to longitudinal emittance (too small) before (pre) acceleration. This is an open question to implement this technique. Review principle of TM110 mode RF cavity Examples of past and present applications of deflecting/crabbing cavities in different projects. Design challenge and limitation of practicable cavity.

Muon Collider Design Workshop, 12/8~12/2008 Principle of Deflecting Mode of a RF cavity Panofsky-Wenzel Theorem: W. K. H. Panofsky and W. A. Wenzel, Review of Scientific Instruments, Nov. 1956, p967. also M. J. Browman, LANL, PAC93, May 17-20, 1993, Washington D.C. USA. Panofsky’s theorem implies that for any given RF mode, no matter who (E or B) deflecting the beam, there is must an non-zero transverse gradient of longitudinal component of the electric field. TM110 is one of such modes. Two rod type, TEM mode is another one. There are also other “exotic” modes, like off-axis TM010 mode, sideway TM012 mode. Transverse verses longitudinal impedance based on Panofsy’s: R t /Q  (R // /Q)/(ka) 2 k=  c a=off-axis distance where to assess the R //. Deflecting force: E B Deflecting crabbing Aberration terms B

Muon Collider Design Workshop, 12/8~12/2008 Scaling laws of RF deflecting cavities /2 a Cylindrical pillbox Here  =u 11 r/a, u 11 =3.832, is root of J 1, J 1 /J 2 is first/second order of Bessel function. for r  0, R  /Q=64.16  which is wavelength independent. For a 800 MHz cavity, Two-rod transmission line ~ /2 d0d0 dcdc Reference: C. Leemann and C. G. Yao, LINAC 1990, Albuquerque, NM, p233. for a 800MHz cavity, d 0 =2cm, d c =5cm R  /Q=  which is wavelength dependent. TM110 mode TEM dipole mode

Muon Collider Design Workshop, 12/8~12/2008 Scaling laws of RF deflecting cavities /2 a Cylindrical pillbox Two-rod transmission line ~ /2 d0d0 dcdc For a 800 MHz cavity with a 50mm beam aperture, two–rod type is only about 45% in efficiency of pillbox type, and even less than the elliptical cavity. But its transverse dimension is 55% or less than the pillbox type. Squashing elliptical cavity in transverse dimension is in wrong direction for the transverse kick (will give vertical kick instead).

Muon Collider Design Workshop, 12/8~12/2008 Application Examples of Deflecting/Crabbing Cavities Particle separation: (CEBAF separator) Temporal beam diagnostics: (injector/gun emittance measurement, BPM, BCM) Crab-crossing in colliders (KEK B Factory, LHC, ILC, ELIC, eRHIC…) X-ray pulse compression: (APS crab cavity R&D) Emittance exchange: (AWA, FELs, Muon pre- acceleration?...) Most technical challenge to those designs are for high current accelerators (circular) which require heavy damping on parasitic modes (LOM, SOM, HOM, SPBM) and single high- Q deflecting mode CW operation, so SRF structure. For muon (single pass) EMX, the damping might not required.

Muon Collider Design Workshop, 12/8~12/2008 CEBAF Normal Conducting Separator Cavity Quick fact and number: Q cu is only ~5000 (structure wise), the stainless steel cylinder only takes less than 5% of total loss. Each cavity is two-cell, ~ long, can produce 400kV deflecting voltage with 1.5kW input RF power. The maximum surface magnetic field at the rod ends is ~14.3mT. Need water cooling on the rods. Can kick beam into three experiment halls simultaneously.

Muon Collider Design Workshop, 12/8~12/2008 Crab Crossing in Linear and Circular Colliders Robert Palmer invented “Crab crossing” in Feb at SLAC to reduce head-on collision luminosity loss due to bremsstrahlung. Just the second day after Peshi Chen reported this possible mechanism. Since then, the first group to use SRF cavities to do the “crab crossing” in a circular collider is KEKB. A global crabbing scheme to increase luminosity has shown a good result recently. Other crab cavities for LHC, ILC are aggressively

Muon Collider Design Workshop, 12/8~12/2008 KEKB Crab Cavity Developments elliptical squashed shape

Muon Collider Design Workshop, 12/8~12/2008 KEKB Crab Cavity Commissioning Curtsy of K. Hosoyama: KEK elliptical crab type cavity, 508.9MHz, Started from 1994 Superconducting Nb, one cavity per ring, global crab scheme in KEKB operation.

Muon Collider Design Workshop, 12/8~12/2008 ILC Crab Cavity Developments (FNAL/SLAC/Cockcroft Intitutes) Collaboration has been worked on this project for many years. So far the 3.9 GHz 9cell, slightly squashed elliptical superconducting cavity has been chosen for the ILC local crabbing scheme. Cavity VTA test has been done and to be integrated into a cryomodule. A lot of bead-pulls, simulation of HOM/LOM/SOM work have been done. All LOM/SOM/LOM damping by coaxial couplers have been designed and simulated. Prototyping in on going.

Muon Collider Design Workshop, 12/8~12/2008 LOM HOM(TE111) SOM FM Crab cavity for LHCs’ squash ratio is chosen to optimize mode separation Dx Optimize Crab Cavity’s Squash Ratio Dy Curtsy of L. Xiao and Z. Li of SLAC.

Muon Collider Design Workshop, 12/8~12/2008 Crab Cavities for Light Sources Use transverse-deflecting rf cavities to impose a correlation (“chirp” between the longitudinal position of a particle within the bunch and the vertical momentum. The second cavity is placed at a vertical betatron phase advance of n  downstream of the first cavity, so as to cancel the chirp. With an undulator or bending magnet placed between the cavities, the emitted photons will have a strong correlation among time and vertical slope. This can be used for either pulse slicing or pulse compression. Slitting yy   X-rays A. Zholents, P. Heimann, M. Zolotorev, J. Byrd, NIM A 425(1999), 385 X-ray pulse compression

Muon Collider Design Workshop, 12/8~12/2008 Squashed elliptical cavity shape optimization MWS,ANSYS, HFSS and Gdfidl simulation by J. Shi and G. Waldschmidt

Muon Collider Design Workshop, 12/8~12/2008 Squashed elliptical cavity shape comparison Scaled KEK and JLab-ANL-LBNL’s crab cavity shapes to 800MHz

Muon Collider Design Workshop, 12/8~12/2008 Elliptical squashed SRF cavity R&D for APS (JLab/LBNL/AL/Tsinghua Univ.) First time vertical test achieved design gradient!Single-cell 2.815GHz Nb crab cavity Rarc Rbp rcav zcav rcon

Muon Collider Design Workshop, 12/8~12/2008 Waveguide HOM Damped Cavity Structure for APS R // /Q and R t /Q Calculated from MWS eigen solver Bench Qext measurement by using RF absorbers on WG ports Clamping copper parts (low contact loss) Weak coupling to VNA Rotatable antennas to suppress the unwanted modes.

Muon Collider Design Workshop, 12/8~12/2008 TM110 Cavity Replace Wedge Absorber? No gas or liquid to vacuum interface windows. No scattering, no straggling Original from Y. Derbenev and R. P. Johnson EPAC 2006, WEPLS019 E TM110 E

Muon Collider Design Workshop, 12/8~12/2008 TM110 cavity used in Trans/Long Emittance Exchange 1.M. Cornacchia and P. Emma, Phys. Rev. ST Accel. Beams 5, (2002). 2.P. Emma, Z. Huang, K.-J. Kim and P. Piot, Phy. Rev. ST Accel. Beams 9, , (2006). M in (x, x', z,  ) phase space a is cavity radius  and  are dispersion and momentum compaction Factor respectively

Muon Collider Design Workshop, 12/8~12/2008 Emittance Exchange Simulations and Experiments Curtsy of G. Wei and J. Power  (  x,  y,  z )=

Muon Collider Design Workshop, 12/8~12/2008 TM110/TE111 Modes Cell-to-Cell Coupling and Double-Chain Model Bane, K. L. & Gluckstern, R. L. (1993), 'The Transverse Wake Field of a Detuned X-band Accelerator Structure', Part. Accel. 42, (SLAC-PUB-5783) Curtsey of J. Shi, Tsinghua Univ. Beijing, China B field enhancement when operates in pi mode

Muon Collider Design Workshop, 12/8~12/2008 Magnetic Field Enhancement at Iris of TM110 Multi-cell Cavity Thanks K. Tian at JLab Magnitude of the magnetic field on the 3- cell cavity. Note the large field enhancement along the iris. Thanks to G. Waldschmidt

Muon Collider Design Workshop, 12/8~12/2008 Multi-cell TM110 and Loaded Structure of Crabbing Cavities APS 4-cell crab cavity, 2.815GHz, 0 mode, 8MV total needed periodic damping LOM/SOM/SPBM/HOM modes HOM coupler LOM/SOM coupler JLab/Cockcroft Inst./Lancaster Univ. UK 200MHz for LHC LC scheme Curtsy of Z. Li and L. Xiao from SLAC:LHC crab cavity in IP4 GC scheme, 800MHz prototype phase I with LOM/SOM/SPBM/HOM modes couplers Parallel Bar advanced, 400MHz for LHC, 499MHz for CEBAF 11GeV.

Muon Collider Design Workshop, 12/8~12/2008 TEM Parallel Bar (Half-Wave) Deflecting Structure recent study for low frequency application more efficient more compact no LOM but acceleration mode in HOM J. Delayen, H. Wang, LINAC 2008’s paper. E field B field Parameter Ω3P Analytical model Unit Frequency of  -mode 400 MHz λ/2 of  -mode mm Frequency of 0-mode MHz Cavity length ∞ mm Cavity width 500 ∞ mm Bar length mm Bar diameter (2R) 100 mm Bar axes separation (2A) 200 mm Aperture diameter 1000mm Deflecting voltage V t * MV Ep *Ep * MV/m Bp *Bp * mT U * J G Ω R t /Q Ω * at E t =1MV/m

Muon Collider Design Workshop, 12/8~12/2008 Summary Using crab cavity for muon emittance exchange is an interesting idea. Detail study is just starting. We need simulations with a real field map including fringe field of cavity and dipole magnets. If technical feasible, this scheme will solve absorber’s problem and lower cost. NC and SC deflecting/crabbing cavity development experience in other projects can be brought in to see the technical limitation. Low frequency, larger aperture crab cavity structure without HOM damping is needed for the emittance exchange section.