Status of Belle Super KEKB plan SLAC seminar
March 21st, 2003
Nobu Katayama
KEK
Status of Belle Super KEKB plan SLAC seminar
March 21st, 2003
Nobu Katayama
KEK
Outline
Belle/KEKB status
General
Beam pipe accident
SVD2
Recent physics results
Super KEKB plan
Physics
Detector study
Accelerator study
KEKB status 1999/10-2003/3/18
> 50 fb-1 in a year 2002 >50 fb-1 in 2002 LER>1.55A
HER>1A with
SRF IP leak: Longest unscheduled shutdown Oct.30~Dec 2002
Best day (03/17/2003) 462pb-1/day recorded
NK on shift!
Beam pipe accident
Oct. 29, 2002-Nov. 8, 2002 6AM, Oct. 29, 2003:New record:8.261033
Oct. 30:A vacuum problem happened
Oct. 31:A serious problem happened
After an abort, HER beam could not be injected
Leak check showed no leak
Resumed running (vacuum scrubbing)
But too much background to the detector
Beam aperture check: something inside?
Nov. 1: Opened the vacuum and inspected
No problem found
Nov. 5: Closed the vacuum to resume operation
Nov. 7: A serious leak occurred and identified
Leak is from the He cooling line of IR Be beam pipe
Structure of IP beam pipe for SVD1.4 10mm gold by
vacuum sputtering 10~30mm gold by
chemical plating 200~230mm gold by
chemical plating Inner
Surface He Beryllium part is cooled
by Helium gas. Aluminum part is cooled by water. :to reduce SR BG to reduce particle background
Pictures using optical fiber scope
Locating the leak
Leak After dismounting the beam pipe, a leak check was performed to locate the leak point
Leak was confirmed with a bubbling test
Bubbles were seen on the inner gold sputtered surface of Beryllium beam pipe
Leak is not at the joint of Be and Al
Cutting Al part of the beam pipe
Inner Beryllium beam pipe
Direction of Helium gas
position of leak
Location of the leak
Observations
A large amount of a white powder was found on the outer surface of the inner Beryllium cylinder and on those of Al rings
It looks like its following the flow of He gas
We found two types of powders
Color of one powder is clearly white
The other one looks slightly yellow
Thickness of the inner Beryllium cylinder was measured
No significant loss of Beryllium
The beam pipe was used for three months in 1999
The powder was there then although the amount was much less
Photo before re-assembly (1999)
Preliminary results of element analysis
White powder
Main components are Be and O
Probably, it is BeO
Yellow powder
Main components are Al and O
Probably, it is Al2O3 and/or Al(OH)3
Commonly found are
Carbon
Small amounts of P, K, Ca, S, Cl, Si, Mn, Fe, and Cu were found.
S and Cl are dangerous elements for corrosion of Beryllium
Si, Mn, Fe and Cu are components of Aluminum alloy
But, expert for element analysis says the amounts of S and Cl are small and are consistent with normal metal
No conclusion, yet
Cause of corrosion
Corrosion can occur on the Al and Be surfaces
What caused the corrosion is not known yet
Water, Cl or S?
Radiation?
Analysis of circulation gas is in progress
Before the accident, we had not paid attention to corrosion
Dew point had not been monitored in gas circulating system
We have never analyzed impurity of the circulating gas
Currently, to avoid corrosion
Dew point is monitored(~-20C)
An additional filter has been installed
Fresh Helium gas is added more frequently, to avoid accumulation of impurities (Most effective)
Possible causes of Helium leak
Corrosion is most suspicious
Heat stress caused by the temperature difference between two walls
Resonant HOM heating during machine study
Helium circulation system troubles
Recycled Be pipe from BP#1
Large stress at machining process (?)
Very high temperature (~300C)
When gold was spattered and the Be pipe was welded with Aluminum sections
Defect of material (?)
Still being actively investigated
SEM photos of Be surface
Beryllium is made by sintering, from a powder of 5~40mm Be particles. Some of them are missing
History of Beam Pipe and SVD
1999 2000 2001 2002 2003 BP 1 + SVD 1 BP 2 + SVD 1.2 BP 3 + SVD 1.4 BP 2 + SVD 1.6 Summer 2003
BP 4 + SVD 2! BP3 reused BP1 Be pipe SVD 1.4 electronics can survive up to 2M rad SVD 1 damaged
by back scattered
synchrotron Rad Dead wafers replaced
Much better BP4!
No? 5 buckets 5 buckets Res. HOM Paraffin He He cooling for Be Tantalum Aluminum Aluminum fwd/bwd no 20mm inside 20mm inside Au in bwd bwd no bwd Saw tooth 0.7% X0 0.9% X0 0.6% X0 Material (IP) better tolerable? standard Particle mask no 20mm inside 200mm inside Au in fwd 10mm inside 20mm outside 10mm inside Au on Be BP#4 BP#2 BP#3(1)
Daily Luminosity 2002/9-2003/3/8
Current limit 2.4A Old beam pipe
re-installed Current limit 2.2A
Comments