Crab Cavities for SuperKEKB•Parameters for the crab crossing•Performance of present crab cavities•Crab cavity for SuperKEKB•LHC crab cavity•LHC compact crab cavity•SummaryFebruary 10, 2009 KEKB review committee

K.Nakanishi

1.62

0.95

0.9

0.9

85

162

0.83

1.37

Design value (Local crab scheme)
Present value (global crab scheme)

200ｍ
1.78ＭＶ

2 cavities are required for HER.
1 or 2cavities are required for LER.

Loss factor of present crab cavity
The loss factor of the present crab cavity is k=0.877V/pC (s=6mm).
If σ-3mm, the loss factor becomes k=2.1V/pC.

HOM power for σ=3mm
s=6mm

s=3mm

Wake
K=2.1 V/pC (s=3mm)
HER 4.1A,5000-bunch Q=71 kW
LER 9.4A,5000-bunch Q=371 kW
Ferrite loss
k=0.3 V/pC (s=3mm)
HER 4.1A,5000-bunch Q=10 kW
LER 9.4A,5000-bunch Q=53 kW

Can present crab cavities be used?
HER：4.1A HOM dumper should be improved.
LER：9.4A Very difficult.

Y.Morita

Fabrication of HOM dampers•••••••••

Baking of ferrite powder
Canning of ferrite powder
HIP 1500 atm, 900 oC
Machining of ferrite surface
UTBaking
Cutting of iron base
EBW of stainless steel flange
Winding of copper pipe•••High power test: up to 10 kW
Low power test: mode damping test
Evacuation

Before Baking

T. Tajima

Before high power test

Y.Morita

Status of HOM Power(Only for LER)
φ240

The LBP HOM dumper for LER isabsorbed about 12kW at 1.6A ofbeam current.
Another type HOM dumper and asmall taper are attached to LBP ofLER cavity. It absorbs some part ofHOM power.

~15kW~12kW2.1 (with taper)

Latest design of the crab cavity for SuperKEKB
New design for SuperKEKB crab cavity was proposed.
It have no coaxial beam pipe tuner to make simple system.
To make heavily dumping, It have coaxial and waveguide type couplers.
To reduce the loss factor, diameters of upstream and downstream beam pipes are same.
No lossy material is exposed to the beam immediately.

Y.Morita
But, it looks very complicated!

1X1 when Beta>250m

71+10 kW

LHC-CC projectas an international collaboration•

Phase 0/I
– Global crab scheme– Feasibility study of the crab crossing• LUMI increase ~10%

– Crab cavity: baseline design by US-LARP– Fabrication and cold test: at KEK• not yet funded– High power tests and beam tests: ?

•Phase II– Local crab scheme– Increase LUMI by a factor of two• With small b*– Need compact crab cavities– KEK proposed a new typeK.Oide

Baseline cavity for phase 0/I
Recently US-LARP proposed a baseline cavity• The baseline design has similar properties like KEKB-CC– Elliptical/squashed cross section– Coaxial coupler•Different properties– Two-cell cavity– 800 MHz (KEKB-CC: 509MHz)– More complicated LOM/SOM/HOM coupler

Coaxial coupler
Squashed cellBaseline design, L. Xiao, LARP-CM11, 10/28/08

K.OideLocal scheme: space challenge

D2

23/04/2008, Shanghai

LHC crab cavities

12Y.P.SunRF parameters
Frequency: 800 MHz••

Compared with the baseline design;– Higher peak electric field– Lower peak magnetic field
Loss factor: 0.56 V/pC for s=3 mm (SKEKB)– Low loss factor desired for high current
operationParameter

At 2.5 MV

At 1MV

Epk (MV/m)

30.5

12.2

Bpk (mT)

69.5

27.8

R/Q (W/cavity)

111

Beam pipe radius (mm)53.1Transverse size (mm)565

US-LARP team can analyze multipacting properties of cavity.
This shape is being analyzed by them.
E-Peak

B-PeakE-field

B-field
Y.Morita

Compact crab cavity••

Compact CC is attractive for the future local crab scheme
There are many interesting designs (US-LARP, UK-EUCARD, KEK)

Rama Calaga, LARP-CM11, 10/28/08

Schematic view of e-crab

Field distribution of e-crab
This cavity required small beam separation.
Direction of deflection due to electric and magnetic fields are opposite.
Therefore the gap length must be adjusted to make high kick voltage.
If nose cone like structure is omitted, kick voltage almost vanished.
If field emission and multipacting can be suppressed as well as present crab cavity,
it can make about 1MV kick voltage.
It is not considered to apply to SuperKEKB.
It have to consider that this and other compact crab cavity designs can be apply to SuperKEKB

summary•The present crab can be applied to HER of SuperKEKB.
(Improvement of HOM absorber is required.)•New design crab cavity is required to LER of SuperKEKB.
•New design crab cavity was proposed in 2004.
•New crab cavity development is started in collaboration withLHC crab cavity group.
•Modified new design crab cavity is being analyzed by US-LARP.
•Many type of compact crab cavities are proposed, we have toconceder that if they are applicable.