1. 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)

2. 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)

3. 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)

4. 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)

5. 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)

6. 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)

7. 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)

8. 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)

9. 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)

10. 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)

11. 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)

12. 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)

13. 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)

14. 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)

15. 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)

16. 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)

17. 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)

18. 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 CTF (Due Jan 11)
Roger M. Jones (2nd Collaboration Meeting on X-band Accelerator Structure Design and Test-Program, KEK, May 13th - May 15th 2007)

19. Testing at CTF3 4.1 High power tests on crab cavity (Due Apr 11)
Measure cavity wakefields (Due Apr 11)
(May not be possible at CTF3 but is at ASSeT SLAC)
Measure deflection of a beam by
a single cavity at CTF (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)