IR Beam Pipes and Assembly
14th KEKB Accelerator Review CommitteeFebruary 09-11, 2009
K. Kanazawa

Contents• Overview• Possible assembling procedure• 80K surface• High power SR on a plated surface• Remaining issues• SummaryOverview (1)Copper duct
50 µm gold plating

Bellows

LER

BPM

SR on thechamber wall
~25 kW (~1m)
Bellows

BPM ?
Bellows(no space !)HER
Warm bore, the vacuum chambers are
independent from the cryostat.

Warm bore, the vacuum chamber
is fixed to the cryostat

Pumps are not fixed yet.

Overview (2)Copper duct
50 micron gold plating
Bellows

BPM

BPM in thecryostat

HER vacuum chamber
must have a clearance
against the direct SRfrom QCSR as far as 10m from the IP.

Bellows

HER

Warm bore~80K cold bore

Bellows between the cryostat andthe vacuum ducts

Possible assembling procedure

The connecting flanges of QCSLD chamber and IP chamber become
inaccessible during assembling. IP chamber and SVD must be assembled infront of QCSLD outside the Belle detector.

80K surface (1)• Basic property– If an ambient pressure of a gas is lower than the vapor
pressure at 80 K, vacuum property of the surface isgoverned by adsorption isotherm.
– If an ambient pressure of a gas is higher than the vapor
pressure at 80 K, the gas condenses on the surface. Thesurface works as a cryopump for the gas.
• If the temperature of the triple point of a gas (meltingtemperature) is higher/lower than 80K, the surface is covered
with solid/liquid.

80K surface (2)Interaction with gas species.
GasVapor pressure at80K (Pa)

80K surface invacuum (~10-8 Pa)

With SR gas load(~10-5-10-7 Pa)

Exposed toatmosphere (~105Pa)

H2(Tc.p. = 33.6 K)

AIAI

AI

CH4103 (S-G)

AI

AI

AI or Growth ofsolid methane

H2O<<10-17 (S-G)

Cryopumping

Cryopumping

Growth of ice

CO8x104 (L-G)

AI

AI

AI

N2

1.4x105 (L-G)

AI

AI

AI

O23x104 (L-G)

AI

AI

AI

CO2

10-5 (S-G)

AI
Gas source if dry iceexistsAI
Gas source if dryice exists

Growth of dry ice

AI means that the interaction follows the adsorption isotherm.
S/L-G means the vapor pressure is given by solid/liquid-gas equilibrium.

80K surface (3)• 80K surface does not work as a cryopump formain gases during photodesorption such as H2,CH4, CO, CO2.
• An accidental exposure to air results in a growthof ice on the surface. This ice may be a gas source
if the temperature of the surface of the ice is muchhigher than 80K. For safety, a mild bake-out
system should be supplied.

High power SR on a plated surface (1)
SRSR

SR?

??

force
Au
Cu
Cooling
water

Localized SR induces
temperature gradientand resulting
compressing force tothe central part.

The central partwill swell andplated gold
comes off torelease the force.

A part of gold
evaporate due to thehear from SR.

High power SR on a plated surface (2)• Vertically localized SR will induce a temperature
gradient near the heated region. This results in acompressing force to the heated part. This is amechanically unstable condition for the plated
layer if strong sticking force does not exist.
• If the plated gold gets a damage or not, a model
test using electron beam will be necessary.

Remaining issues• BPM in a cryostat.
• More realistic vacuum chamber design.
• Pumping scheme and pressure estimation.

Summary••
•
•

•
•
•

All vacuum chambers in IR are required to be made of copper and withan inside gold plating of 50 µm.
In HER downstream IP, direct synchrotron radiation from QCS should
avoid vacuum chambers as far as 10m.
In the present design, IP chamber and SVD must be assembled in frontof QCSLD outside the Belle detector.
An accidental exposure to air results in a growth of ice on the 80K
surface. For safety, a mild bake-out system or equivalent procedure
should be supplied.
The stability of the gold plating under intense synchrotron radiationneeds experimental verification.
There is no experience for BPM in a cryostat at KEK. Useful
information is needed.
Consideration on a pumping scheme is still remaining.