IR Vacuum Chamber
Basic design consideration for SuperKEKB
22 Feb. 2005
KEKB Vacuum GroupKen-ichi Kanazawa

Contents• From KEKB to SuperKEKB– Experience in KEKB and Design Principle forSuperKEKB• Preliminary Design Layout of IR VacuumChambers• Summary and Next StepFrom KEKB to SuperKEKB

Synchrotron Radiation (SR) (1)KEKB
On the whole,
COOLING IS NOTSUFFICIENT.
• For the incoming
beam line, SR from far
magnets was notconsidered seriously.

SuperKEKB• Provide cooling every
possible SR irradiation.

From KEKB to SuperKEKB

Synchrotron Radiation (SR) (2)KEKB• The exact path of the SR
from QCS and its spread
were not strictly taken into
account in the first design.
• This caused a hightemperature at unexpected
portions of a vacuum
chamber.
– Deformation of vacuum
chamber– Motion of magnets.

SuperKEKB• The design of QC magnets in
the LoI looks trying to give a
sufficient clearance for the SR
down to QC2.
• The design of the beam ductlayout also tried to avoid theSR.
• However, the design should bechecked against the fact thatthe two beams and the SR don’t lie in the same plane.

From KEKB to SuperKEKB

Detector Background
KEKB• Back scattering of the SR
from QCS by a HER Al
beam duct became a noise
source. (Cu has a smaller
cross section of the backscattering than that of Al.)• Shields against thedetector backgroundshould have been
incorporated from the first
design.

SuperKEKB• Chamber material: Cu(cooling, shielding, small
back scatter of SR)• Beam ducts avoid the SR
down to 8m (HERdownstream) and 5m (LERdownstream) from IP.
• Shield should be taken into
consideration from the firstdesign.

From KEKB to SuperKEKB

Higher Order Mode (HOM) (1)KEKB• The HOM power turned
into heat in IR is, in theunit of the loss factor,
around 474 V/nC.
(Estimated from thetemperature rise ofcooling water)• Heat up of the bellows
will be unacceptable levelin Super KEKBSuperKEKB• Extrapolation from KEKB
gives as a heat by HOM
about 100kW ×(bunchlength factor).
• Is the compact HOM
absorber possible?
• The cooling for HOM will
be a big problem.
• The comb type bellows isexpected to be durable.

From KEKB to SuperKEKB

Higher Order Mode (HOM) (2)KEKB• Avoid a local cavity
structure as possible asone can.
• Flange gap is filled withHelicoflex

SuperKEKB• Design principle of theinner shape of chambers issame as KEKB.
• The pump slot must be
designed carefully not tocause the heat up of NEG.
• Flange gap will be filled
MO type gasket.
• The design of thebranching part is simmiler
to KEKB.

From KEKB to SuperKEKB

Electron Cloud
SuperKEKB• TiN coating for the
positron beam duct toreduce multipactoring.
• Solenoid is also
necessary to confine
photoelectrons.

KEKB• No measures
NEG coated Cu Chamber
Cu Chamber (no coating)TiN coated Cu Chamber

Electron Monitor Current after Beam Conditioning
1.2 10-5

E>30eVElectron Monitor Current [A]

1 10-5

8 10-6

6 10-6

4 10-6

2 10-6

0
0500

1000
LER Beam Current [mA]

1500

2000

The reduction of bothphotoelectron yield andsecondary electron yield bya TiN coated chamber.

From KEKB to SuperKEKB

OthersKEKB• NEG (Non EvaporableGetter)+Sputter Ion Pumpscheme.
• Bellows is welded to avacuum chamber.
• The pressure of thepositron (LER) incomingline (within 10m from IP)
is higher than expected.

SuperKEKB• The same scheme withexchangeable NEG. ( aspossible as one can)• Easily repairable design(mechanically detachablebellows etc).
• Denser distribution ofpumps.

Beam duct layout Right hand side (1)•In HER , all ducts are expected to avoid SR.
•The BPM at the end of the QCS chamber is possible only if the electrodes clear
the inner bore of QCSR.
HER ducts avoid SRIPHER

SR:179 kWLER

Beam ducts
separate.
BM:Beam Position Monitor, BL:Bellows

Manageable
in installation ?

Beam duct layout Right hand side (2)•The space for the pump must be reserved in the magnet.

HER:Rectangular cross section.
HER ducts avoid SR.

HER

LER

BM:Beam Position Monitor, BL:Bellows

Beam duct layout Left hand side (1)•Flange connection in the bore of QCS-L (magic flange).
•The ducts of LER from QCSL to QC2LP escape SR
LER ducts avoid SR.
LER

SR:65kWIP
Magicflange
Beam ducts
separate

BM:Beam Position Monitor, BL:Bellows

Beam duct layout Left hand side (2)•The space for the pump must be reserved in the magnet.
SR hits the LER duct wall.
LER:Rectangular cross section
LERHER

BM:Beam Position Monitor, BL:BellowsSummary and Next Step (1)Summary• Based on the experience in the KEKB IR vacuum
system, the new beam duct layout is shown.
– Two rings separate at about 1.5m from IP.
– HER downstream ducts avoid SR down to 8m from IP.
– LER downstream ducts avoid SR down to 5m from IP.
– The comb type bellows will be used and the flange gap
will be filled with MO type gasket.
– Seeking easy repair

Summary and Next Step (2)Next Step• To make the design more concrete:– Cooling structures and pumps should be added in thedesign.
– The interference with magnets must be checked and benegotiated.
– Manageability of flange connection should be checked.
– How to fix a beam duct should be designed.
– HOM absorber near the branching part should bestudied.