Developments on Proposed CLIC Crab Cavity Roger M. Jones University Manchester, UK/ Cockcroft Institute, Daresbury, UK. Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

Personel Faculty: Roger M . Jones (Univ. Manchester/CI), Amos Dexter, Graeme Burt (Univ. Lancs/CI) Postdoctoral Research Associate: Praveen K. Ambattu (CI) collaborating Institutes: CERN, ASTeC, CI, University of Manchester, University of Lancs. Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

Crab Cavity Overview Crab cavities are required for CLIC and LHC upgrade Crab cavity is a deflection cavity operated with a 90o phase shift. Particle at the centre of the bunch gets no transverse momentum kick and hence no deflection at the IP. Particle at the head gets a transverse momentum that is equal and opposite to the momentum kick of particles in the tail. The quadrupoles change the rate of rotation of the bunch. Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

Design Issues Phase stability RF Source Power requirements Pulsed heating on the iris Gradient Wakefield Suppression Frequency separation of nearby modes Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

Crab Design Equations Luminosity reduction factor (Consequence of no crab cavity) Relation between displacement at IP and transverse kick at the crab cavity Kick depends on relative time of arrival t (note voltage kick defined from eV=pc) Displacement for late arrival at time to: Kick voltage Vmax required from system to achieve a rotation angle of r: Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

Transverse Kick for 3 TeV CM To minimise required cavity kick R12 needs to be quite large and hence we situate the cavity close to IP (~25 m) For 20 mrad crossing and using as 12 GHz structure At 20 MV/m transverse gradient we are investigating 18-cell structures. Requires 2 MW RF for a SW design. Vertical kicks caused by parasitic modes in the cavity (prefer R34 to be small) Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

Phase for less than 2% L/L Crabbed crossing angle with phase jitter Δx Interaction point electron bunch positron bunch Luminosity reduction factor S is given as 0.06 0.02 20 mrad 30 GHz 12 GHz Crossing angle Phase error (degrees) and Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

Crab Cavity R&D Overview Verify prototype designs for the CLIC crab cavity system LLRF controls, Investigate synchronisation technology. Establish breakdown limits for copper X-band dipole structures Incorporate suitable damping scheme for LOM, HOM and SOMs. Measure prototype crab cavity system at CTF3, Measure wakes and investigate behaviour of crab cavities with beam Ensure that the system including the crab cavity can continue to meet the luminosity specification taking full account of linac and beam delivery system wakefields. Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

Proposed Gradient Tests Here we purposely optimise the dipole mode kick and we are required to identify the gradient that is sustainable. Proposed test on high-field dipole structures at SLAC -discussions with V. Dolgashev Initial on non-damped single cell and multiple cell structures. Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

Optimised Rsh RF field simulation in CST Microwave studio The structure used is a single cell cavity with periodic boundary condition enforced at either ends Structures are taken to be copper Figures of merit such as the quality factor, R/Q , peak fields and group velocity/ cavity coupling are simulated and compared for various cavity dimensions giving the first dipole frequency at 12 GHz and for various phase advance/cell (2π/3, 5π/6 and π radians) Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

Phase advance per cell, ö radians Cell Parameters Ci 2Li Re 2Lc Ri Cell structure Lc Half cell length Li Half iris thickness Ci Iris curvature (=Li) Re Equator radius Ri Iris radius 12.5  (SW) 10.417 5  /6 (TW) 8.333 2/3 (TW) Length of the cell, 2Lc mm Phase advance per cell, ö radians Periodic boundary condition Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

Shunt Impedance vs Iris radius and Thickness 2p/3 mode 5p/6 mode 5p/6 mode p mode Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

Vtrans/Emax 2p/3 5p/6 p Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

Frequency separation (%) for the π (standing) mode =2/3 =5/6 Group velocity (% of vel. of light) for the 2π/3 and 5π/6 (travelling) modes = Frequency separation (%) for the π (standing) mode Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

Vtrans/Hmax =2/3 =5/6 = Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

Cavity Development Schedule 1.1 Cavity designs (needs 2.1) (Due May 09) 1.2 Input coupler design (Due Jan 10) 1.3 Manufacture and test prototype stacks (Due Jul 10) 1.4 Manufacture and low power tests of full structure (Due Jan 11) Testing includes, cavity tuning, matching couplers and bead pull to determine mode frequencies and field flatness. These fabrication requirements aims to be synergetic with the fabrication demands of the main linac. The fabrication effort will be strongly intermeshed with the CLIC main linac development program/team. Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

Wakefield and Beam Dynamics 2.1 Simulation of crab wakefields and design of wakefield suppression of LOM, HOM and SOM (Due May 10) 2.2 Study of manufacturing tolerances on wakefield and phase stability performance (Due Jan 11) 2.3 Beam dynamic simulation and emittance dilution in crab cavity (Due May 10) 2.4 Main linac wakefield simulation (Due May 10) 2.5 Beam dynamic simulation of emittance dilution and BBU for main linac (Due May 10) 2.6 Stretched wire measurements to probe HOMs in the crab cavity and main linac. (Due Jan 11) Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

LLRF development 3.1 Develop phase control concepts. (Due May 09) 3.2 Performance simulation of possible CLIC crab cavity LLRF systems. (Due Jan 10) 3.3 Develop and test phase control components. (Due Jan 11) 3.3 Provision of control system for cavities at CTF3. (Due Jan 11) Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

Testing at CTF3 4.1 High power tests on crab cavity (Due Apr 11) 4.2 Measure cavity wakefields (Due Apr 11) (May not be possible at CTF3 but is at ASSeT SLAC) 4.3 Measure deflection of a beam by a single cavity at CTF3 (Due Apr 11) 4.4 Test phase stability of two crab cavities (Due in follow on project) Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)