SuperKEKB IR Design

1
SuperKEKB IR Design

• Y. Funakoshi, N. Ohuchi, F. Tawada, S. Kanazawa,
  H. Koiso, Y. Ohnishi and O. Tajima (KEK)

2
Design strategy

• Natural extension of present KEKB
• the same boundary between KEKB and Belle
• conventional flat beam scheme
• round beam
• A baseline design of SuperKEKB IR has been
  completed.
• Details are described in LoI (2004).
• We have to proceed to the technical design.

3
Machine parameters
4
Issues of IR Design
5
Place QCS magnets closer to IP
SuperKEKB
KEKB
The boundary between KEKB and Belle is the
same. ESL and ESR will be divided into two parts
(to reduce E.M. force). QCSL (QCSR) will be
overlaid with (the one part of ) ESL(ESR).
6
QCS-related parameters
( ) present KEKB Design
7
Relationship between SuperBelle and SuperKEKB
Belle Solenoid will not rotate. The HER axis will
not change. The LER axis will rotate by
8mrad. The beam pipe (and SVD) have a finite
angle of 7mrad with respect to Belle
Solenoid. QCS magnets will be set parallel to
Belle Solenoid.
8
IR magnet layout
QC2RE
QC2LP
QC1RE
HER beam
QCSR
QCSL
LER beam
QC2RP
QC1LE
QC2LE
9
Ring acceptance

• ???a0 ???
• ??????????????????????
• Ring emittance exr
• nr
• ws
• ns
• ni
• Ring b bxr
• Linac beam emittance exi
• Injection line b bxi
• ?????bxi?????(?????????)?????
• ??kicker jump?????

10
Ring acceptance vs. Linac beam emittance

• ??????????Linac beam emittance??????
• Damping ring??????????( exilt1x10-8m?)
• ????????
• ???3.5e-7m (_at_3.5GeV)-gt 1.5e-7m (_at_8GeV)
• ??2.0e-8m (_at_8GeV)

11
IR aperture strategy

• Strategy
• We will take the adiabatic construction
  scenario into consideration.
• The Linac energy switch will be realized some
  time later after the IR reconstruction is
  completed.
• This means that the both rings will have to
  accept the position beam.
• Required acceptance becomes large with this
  strategy.
• If we can construct the damping ring before the
  IR reconstruction, required acceptance will be
  drastically reduced.

12
Ring acceptanceRequirement
13
Optics(?????)

• Dynamic aperture???
• QCS higher multipole
• HER machine errors
• Belle solenoid?????
• HER local correction
• Beam-Beam effects
• Parasitic collision
• Main collision

14
HER dynamic aperture bare lattice BX/BY20/.3 cm
H. Koiso
injection beam
Required H/V 4.5/0.52 10-6m
15
Ohnishi
Dynamic Aperture for Injected Beam
Injected beam Jy/Jx 7
Injected beam Jy/Jx 4
nx 45.510 ny 43.545
LER
nx 45.510 ny 43.570
HER
required acceptance for injected beam
required acceptance for injected beam
red no machine error blue machine error
optics correction (12 lines indicate different
seed numbers.)
Estimated dynamic aperture of HER is marginal. Do
we need a local chromaticity correction also In
HER?
16
Local correction scheme also in HER?

• HER local chromaticity correction scheme is not
  compatible with installation of crab cavities in
  Tsukuba section.
• If we want to install crab cavities in Tsukuba,
  we can not adopt the local correction scheme in
  HER.
• We need to wait for the results of the experiment
  with the crab cavities in Nikko section next year.

17
Importance of dynamic effects

• Horizontal tune very close to half-integer
• Physical aperture in IR
• SR fan

18
Beam-beam simulation
Tune Survey in SuperKEKB without parasitic
collision effect. Lpeak8.3x1035cm-2s-1
(L/bunch1.66X1032, Nb5000)
Head-on

?y 0.33
(.503, .550)
Simulation by K. Ohmi
19
Estimation of dynamic effects

• Input parameters
• ?x0 0.152
• ?x variable(0.503)
• ?x 24 nm
• ?x 20 cm

?x 2.0cm ?x0.125?m
?x 2.5mrad
20
?x in IR with dynamic effects
LER IR ?x 4.78cm, ?x 98.7nm (?x0 40cm, ?x0
12nm )(red) ?x 4.45cm, ?x 217nm (?x0
20cm, ?x0 24nm )(blue)
21
HER IR ?x 4.78cm, ?x 98.7nm (?x0 40cm, ?x0
12nm )(red) ?x 4.45cm, ?x 217nm (?x0
20cm, ?x0 24nm )(blue)
22
Parameters of IR quad (LoI)
b
?x (mm)
8
12
22
21
10
16
b ??x
3.1
6.7
4.1
2.4
4.8
2.5
23
IR Horizontal physical aperture

• Dynamic effect ????????????
• IP???focusing Q???????x?????????
• ?x?????half integer??????????????????????????
• .503 -gt .505
• IR Magnet??????????????

24
Fan of SR

• Consideration of the particle distribution in the
  phase space
• Effects of dynamic-b and dynamic-emittance
• These effects are very large with the horizontal
  tune very close to the half integer.
• We took 9ex (3 sx, 3sx) into consideration.

25
IP ?x, ?x from beam-beam simulation (Ohmi,
Ohnishi)
6.64mrad
295?m
??x6.7mrad
??x280?m
?x(??x)/(??x) 4.18cm
?x?x/?x 2.30cm
?x?x?x 0.128?m ??x 7.46?m
??x(??x)(??x) 1.88?m
26
Enlargement of SR fan due to dynamic effects
xx0 0.1, nx .510
27
Fan of SR with dynamic effects
9ex (3 sx, 3sx) is taken into account.
xx0 0.1, nx .510
nx .510 -gt ?x1.4mrad nx .503 -gt ?x2.5mrad
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IR Vacuum system design (??)

• ??
• SR
• ??path?3??????
• ?????????????
• Detector background??????????
• HOM
• HOM power???(??)
• SuperKEKB, ???KEKB???????
• HOM absorber???
• ??????????????(??????)
• ????
• ???????????????(??????Belle ?????)

29
From KEKB to SuperKEKBHigher Order Mode (HOM) (1)
??

• KEKB
• The HOM power turned into heat in IR is, in the
  unit of the loss factor, around 474 V/nC.
  (Estimated from the temperature rise of cooling
  water)
• Heat up of the bellows will be unacceptable level
  in Super KEKB

• SuperKEKB
• Extrapolation from KEKB gives as a heat by HOM
  about 100kW ?(bunch length factor).
• Is the compact HOM absorber possible?
• The cooling for HOM will be a big problem.
• The comb type bellows is expected to be durable.

30
From KEKB to SuperKEKBHigher Order Mode (HOM) (2)
??

• KEKB
• Avoid a local cavity structure as possible as one
  can.
• Flange gap is filled with Helicoflex

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

31
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

32
Summary and Next Step (2)
??

• Next Step
• To make the design more concrete
• Cooling structures and pumps should be added in
  the design.
• The interference with magnets must be checked and
  be negotiated.
• Manageability of flange connection should be
  checked.
• How to fix a beam duct should be designed.
• HOM absorber near the branching part should be
  studied.

33
Detector beam background issues (Tajima)
34
Belle Detector
Detector will be upgrade to work under BGx20 SVD
will work under BGx30 (rbp 1.5 ? 1.0 cm) Almost
same structure
PID
3.5 GeV (LER)
ECL
8.0 GeV (HER)
CDC
KLM
SVD
35
(No Transcript)
36
Rad. Bhabha BG sim. for Super-KEKB
Barrel
BWD EndCap
FWD EndCap
Realistic design based on discussion with QCS
group
Expected BG from other sources
with heavy metal total 1.5 ton
L25x1034 /cm2/s
4 of total BG
L1034 /cm2/s
O. Tajima
37
Average Vacuum 2.5x10-7 Pa
??
Suppressed by Neutron shield
Beampipe radius 1.5?1cm
1st layer
BGx33 (several MRad/yr)!? (sim. for particle
shower)
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Summary
??

• Backscattering of QCS-SR is not serious, but
  strongly depends on IR chamber configuration
• Vacuum level is very important
• Original design (5x10-7 Pa) is serious ? BGx25
• w/ further effort (2.5x10-7 Pa) ? BGx18
• Increasing of Touschek origin BG
• Smaller bunch size higher bunch currents are
  reason
• Might be reduced by further study
• Radiative Bhabha origin BG can be suppressed
• Beampipe radius 1.5cm ? 1cm
• Further simulation study of shower particles into
  SVD is important

-30
39
???

• ???????????
• QCS RD???
• ?????
• ??????????????????????????
• ??????
• ????????
• ??SuperKEKB IR Meeting?????

40
Spare slides
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LoI (Ohuchi)
42
LoI (Tawada)
43
LoI (Tawada)
44
LoI (Tawada)