Initiating the Crab System R&D

Graeme BurtLancaster University

Philippe Goudket

Daresbury Laboratory

Crab Cavity Team

Graeme Burt RA Lancaster Uni.

Amos Dexter SL Lancaster Uni.

Philippe Goudket RF Eng. Daresbury Alexander Kalinin RF Eng. Daresbury Carl Beard RF Eng. Daresbury Mike Dykes RF Group Leader Daresbury

Mike Poole (Work Package 5 Leader)

Crab Cavity work plan 2005

Analysis of requirement. Interact with international community on specification

of crab cavity solution.  Design experiment to investigate phase control

limitations. Design of cavity for phase control experiment.

Crab Cavity longer term work plan

Build and operate phase control system experiment. Design experiment to test crab cavity phase control

systems on test beam. Beam testing of cavities and control system.

Finite crossing angles

The luminosity of a collision is reduced by a finite crossing angle. The beams are rotated for a effective head-on collision, by a crab cavity.

Crabcavity

Crabcavity

Tiltedbunch

Effectivehead-on collision

finite crossingangle

Transverse deflecting dipole mode

The dipole mode of an elliptical cavity can be used to transversely deflect the beam.

Magnetic field lines of the dipole mode. Beam into page through centre point

Field is uniform in the beam direction

Sinusoidal in time

KEK-B Crab Cavity

Crab Cavities are currently under test at the KEK-B B factory, these have less stringent phase stability and lower kicks required.

Absorbing materialNotch filter

Absorbing material

Squashed Crab cavity for B-factories

Coaxial beam pipeCooling for inner conductor

(axial view)

inner conductor

"Squashed cell"

(K. Akai et al., Proc. B-factories, SLAC-400 p.181 (1992).)

Transverse deflecting dipole mode

Magnetic Field as seen by front, middle, and back of the bunch as a function of position across the cavity.

(At any instant the magnetic field is uniform across the cavity)

-1

-0.5

0

0.5

1

0 2 4 6 8 10 12

Position (cm)

No

rma

lise

d M

ag

ne

tic

Fie

ld

Crab cavity operation

B = max field in crab cavityd = distance from cavity to interaction pointfield jitter between cavities gives differing bunch rotation

mceBd2

crab

For optimum cell length

Transverse deflecting dipole mode

Magnetic Field as seen by front, middle, and back of the bunch as a function of position across the cavity for phase error.

-1

-0.5

0

0.5

1

0 2 4 6 8 10 12

Position (cm)

No

rma

lise

d M

ag

ne

tic

Fie

ld

Momentum mismatch

Δx

Differential phase jitter causes the two bunches to have a height mismatch, which can significantly reduce luminosity or cause the bunches to miss.

m

tsindBe2x o to = time bunch enters cavity

d = distance to IP

to = 0

to ≠ 0

Issues

Position of crab cavities Type of crab cavity Frequency of operation How phase jitter affects luminosity? How field stability affects luminosity? Effect of wakefields i.e. cavity harmonics Performance of phase control systems

Crab cavity phase control system

Fast phase adjust using a second klystron and fast phase difference.

Diagram by J. Frisch

Crab cavity Phase stabilization Test System

Diagram by J. Frisch