Construction of the Interaction Region
CDCInnertube

QCSR
Support extension

IP Chamber
VXD unit

The 18th KEKB Accelerator Review Committee
KEK, 4-6 March 2013
K. Kanazawafor
KEKB Vacuum GroupIR Technical Meeting Member
IR Installation Meeting Member
SVD/IR Mechanics Meeting Member

Contents• Sketch of the interaction region• Mile-stones and task schedule• Bridge reinforcement• Installation scenario• Vacuum around IR• IP chamber• Radiation shield• SummarySketch of the Interaction Region
Phase 2QCSL

QCSRIP
PositronElectron

Belle 2Moving stage

Slide gate shieldSketch of the Interaction Region
Phase 1Al IP chamber(ID 4 cm, ~2 m long)

Moving stage
without
QCSL support

Copper ducts with BPM

Temporal shield(on the temporal stage)

Fixed temporal stage

Mile-stone and Task Schedule
Bellerotation

QCS

Specialmagnets

Bridgereinforce
ment

QCS
supportandMovingstage

IPchamberTa beampipe for
QCS

VacuumsystemInstallation scenario

Backgroundestimation
andRadiation
shieldLABM

Luminosit
y monitor

Belle

MG(Cryo)

MGMG

MG

Belle/VAC

VAC/MG(Cryo)

VAC

Belle/VAC

Belle/RSC/Acc

BM

Belle/Acc

Completefirst stage

QCSL
underfabricationDecision

Apr 2013- Feb 2014

QCSR
fabrication
start
QCSL
complete(Must end
before Oct2013)

Mar 2014- Aug 2014

In situ testof QCSL

dateNow

QCSL
test at IR- Mar 2013

Sep 2014- Dec 2014
Phase 1

Phase 2

Jan 2016- Apr 2016
May 2016- Sep 2016

Phase 3

Oct 2016

Bridgework
L sidecompleteVer. 1 final
fabrication

Selectscenario

Mechanica
l test (Lside)
Installation

Jan 2015- May2015
Jun 2015- Dec 2015

Fix
positioncomplete

QCSR
complete?
Finaladjust

complete

QCS
installationPhase 1shieldcomplete
Preparationcomplete
1 st testBeastFeedbackto var. 2 ?

Set upcompleteSystem
test

Phase 2shieldcomplete

Improvement
additional

Bridge Reinforcement

H. Yamaoka

65 Hz•The end of the bridge where QCS lies on ismechanically weak. For example thevertical oscillation of the place with 65 Hz
is one of the lowest modes of the bridge
oscillation.
•The measured amplitudes during KEKB
are tolerable if QC1E and QC1P oscillatewith the same phase (this is the mostprobable case).
•However. if a simple and effective way ofreinforcement of this part is available, it
should be done.
•The chance of the work is quite limited.
The decision should be done as soon aspossible.

Installation Scenario
Basic conditions• IP chamber is supported by VXD frame.

Both sides of IP chamber are fixed to the VXD frametransversally and are free longitudinally.

• VXD is supported by CDC.

• Connection flanges forvacuum chambers.

The R-side of VXD is aligned transversally and isfree longitudinally.
The L-side of VXD is fixed to CDC.

• QCS cryostats can move out.

Top view

Some work spaces toaccess flanges.
It will be possible to
make use of these spaces.

CDC

Little work space toaccess flanges.
It is impossible to connect
flanges by hands in thisconfiguration.
7

Installation Scenario - Baseline

T. KohrikiInstallation Scenario

Alternative Scenario with Remote vacuum seal mechanism.
•Some people feel uneasy on thesituation that VXD unit is pushed by
QCS in the baseline scenario.
•They proposed an alternative scenario
to slide VXD with manual force and aremote vacuum seal mechanism.
•The mechanism is not yet valid with amock-up test.
•However the choice of the installation
scenario has various impacts on
detailed designs of VXD andsurrounding components.
•The decision on the choice cannot bedelayed so long.

DESYVacuum around IR

Layout of vacuum components near QCS in the R side
The beam pipe in the cryostat is made of Ta (redpart in the figure). The maximum thickness of thispipe is 4 mm.
Pumps are located outside the cryostat.
The major gas load for the incoming
positron line is photon-desorbed gas.
That for the outgoing electron line isthermal outgassing.
Ta beam pipes will becoated with Au or Cu to
reduce ohmic powerloss.

electron

SR power ~ 1.4 kW

Electron cloud in the cryostat beam pipe is expected tobe suppressed by solenoid fields (~50 G is necessary).

positronVacuum around IR

Typical cross section of Ta beam pipe

Vertically elongated aperture
in QC1P(Larger aperture is preferable
but it is not available in thepresent design.)

BPM

Vacuum around IR

Layout of vacuum components near QCS in the L side
The layout issimilar to the Rside.
positronelectronVacuum around IR

Rough estimation of pressure near IP
Thermal only
P0 = 2 ×10 −7 PaPIP = 8 ×10 −7 Pa
Photon - desorption dominant
P0 = 2 ×η PaPIPpositron

P0Example: Incoming positron line
Assumptions:•The equation for a long tube gives good estimation
for a short tube
•At IP pressure is maximum•P0 is determined by the total outgassing of thecryostat beam pipe and the pumping speed there (50l/s).
•The thermal outgassing rate is 1×10-11 Torrl/s/cm2(1.33×10-8 Pa m3/s/m2).

PIP = 11×η Pa

η : photo - desorption coefficient

The difference between P0 andPIP is determined by the local
outgassing and the conductanceof the beam pipe. It doesn’t
depend on the pumping speed
outside the cryostat.

Vacuum around IR
Test Ta beam pipe

A test Ta beam pipe with coolingchannels, a taper, and conflat
flanges was fabricated.
Ta pipe model for QCS withcooling path in the wall. Thispipe has a weld seam between
water and vacuum. The testwith tap water caused noleakage at least for months.

Thermal outgassing ofthe Ta pipe. ‘Very low’(H. Hisamatsu)

Vacuum around IR

Photon-induced desorption of Ta, Au, and Cu (2nd)

Photo-desorption coefficients of Cu, Ta,and Au-coated Ta. Ta and Au-coating havea sufficiently low photo-desorptioncoefficient.
(At PF BL21, εcr = 4 keV, by Y. Tanimoto)Vacuum around IR

Consideration on IR pressure•At least, the pressure around the IP (±5m) must not affect the overall average designpressure of the ring (1×10-7 Pa). Therefore the target pressure in this region must be
less than 1 × 10-7 × 3000/10 =3 × 10-5 Pa. A consideration on the beam-gas Rutherford
scattering requires much lower pressure in the QC magnets where β is large.
• The main gas source in this region is photon-desorbed gas due to the direct SR fromthe last bend. If a photo-desorption coefficient η is assumed to be 1 × 10-6
molecules/photon, The average pressure of this region will be a few × 10-6 Pa.
•It was shown that Ta and Au-coating have a sufficiently low photo-desorption
coefficient. It was also shown Ta has a very low thermal outgassing rate.
•Still we are looking for an idea to improve IP pressure.

IP Chamber
Cut View

Electron

S. Koike

PositronIP Chamber
Design feature

HIP = Hot IsostaticPressing

1~2 µm10~20 µm

1~2 µm•The central
straight partconsists of double
tube. Paraffinruns betweenthem.
•The connection
between double
tubes is done by
Ti-Ti EBW.

IP Chamber
R&D•

Done– Stress analysis••

For the temperature difference between the two tubes at the center.
Changing support position of beam pipe•
•
•
•
•
•

Precise machining of Be pipes
NC machining of ridges
Be-Ti brazing
Ti-Ta HIPEBW near by HIP
Pulsed sputter coating of Cu inside 2 cm Al pipe and its uniformity check– Fabrication test•

To be done (in preparation)– Stress analysis•

Check the strength under dynamic force•••

Au coating on Ti pipe
Effect of EBW on the coating
Simulation welding between inner and outer Ti pipes– Fabrication test•

Ta part will be fabricated in FY 2013 and the first version of IP chamber will appear
within FY 2013

IP Chamber
Cooling

The coolant is paraffin. The flow ofparaffin can absorb a heat of ~270W
for a temperature rise of 10℃.
WL: 210W (Ta)e−
WL: 190 W (Ta)SRQ: ~ 50 W
SRB: 100 W

Heat: 400 W.
Water cooling, ID 4 mm, L = 600 cm, v = 2 m/s∆T of water ~ 4°C
Heat transfer coefficient to water: 1.1×104 W/m2/ °C∆T ~ 5 °C (between water and pipe)
Ta will be coated with Au or Cu toreduce the wall loss.

WL: 70 W (bulk Au)
SRQ: few W

WL: 140 W (Ta)WL: 270 W (Ta)SRQ: ? W
SRB: 130 W

e+T. Kohriki

IP Chamber

Are steep ridges permissible?
Gentle ridge

Steep ridge

Newridge

Since the height of the ridge is only
0.5 mm, structures of impedance dueto the sharpness of ridges appears inhigher frequencies than a 6mm bunchspectrum.
Steep ridges are OK.
(K. Shibata, Y.H. Chin)

IP Chamber

Tip scattering on a ridge

T. Ishibashi, et al

Ta sample

Set upCHESS (Cornell Univ.) G2 beam line
Photon energy : 9 keVSlit : 2 mm (H) by 0.05 mm (V)
Detector angular resolution : 0.2 degree (FWHM)

Ratio of the scattered photon. The slopeof the taper inside the pipe is 1.23
degree.

Radiation shield
Phase 2

There are two majorradiation sources in theinteraction region. One is theLER horizontal collimator(upstream) to cut the halo
created by Touschek effect.
The other is the downstream
LER beam pipes hit by offmomentum positrons andgamma rays due to theradiative Bhabha process.
(Y. Funakoshi, Y. Ohnishi)

The present design seems
insufficient to keep theexperimental hall free fromradiation.
(H. Nakayama and T. Sanami).
Further investigation isnecessary.

Radiation shield
Phase 1

Now on-going estimationof the beam loss at phase
1 suggests this structure issufficient for Phase 1.
(Y. Ohnishi, T. Sanami)

Summary• With the progress of the construction ofSuperKEKB, the number of tasks to be solved forthe interaction region is increasing.
• Among them,– We must make decision on the bridge reinforcement assoon as possible.
– The choice of the installation scenario has verious side
effects. It cannot be delayed so long.

• And,– We are still looking for an idea to improve IP pressure.