UK ECAL Meeting, 16 October 1997
UK ECAL Meeting, 16 October 1997
Revised (2nd time) Minutes of UK CMS ECAL Meeting
on Thursday Oct. 16, 1997
at RAL
changes marked by **
Present
Name Institution
---- -----------
A.Presland University of Bristol
R.Head University of Bristol
D.Cockerill RAL
R.Tapper University of Bristol
G.Heath University of Bristol
H.Heath University of Bristol
D.Imrie Brunel University/RAL
D.Graham IC
J.Hays IC
G.Davis IC
D.Britton IC
J.Connolly RAL
P.W.Jeffreys RAL
R.M.Brown RAL
P.S.Flower RAL
G.Patrick RAL
R.Stephenson RAL
L.Denton RAL
B.Smith RAL
1) News
R.Brown said the OST-PPARC document had been posted on the web.
URL http://hepwww.rl.ac.uk/atlas/atlas_uk/pparc/pparc_ost.html
The form has been basically agreed with Brian Foster. There are 3 annexes to
the document :
Part 1. Expected Physics: this is still being discussed
Part 2. The LHC machine and detectors: this is basically completed
Part 3. Deliverables: these now incorporates the UK's intention to deliver all
the end cap supercrystals
Comments are now invited.
R.Brown has had discussions with the referees on this modification to CMS UK's
deliverables and they have indicated that this would be acceptable.
It was felt that to formalise this modification, a letter will be required from
D.Miller to J.Fry notifying him of the change and asking him for his formal
approval.
R.Brown reported that the tenders for the coil return yoke had now been
received at CERN and were close to the estimated 20 Million CHF
There now followed a discussion on the ECAL Endcap TDR submission
2) ECAL Endcap Mechanics section
D.Cockerill presented a slide detailing the separate chapters in the TDR and
indicating their names on disk (see Index of /TDR/September)
1. General Overview TDRse18.ps
2. Lead Tungstate Crystals TDR2se18.ps
3. Mechanical design Not there yet
4. Photodector apd.frm
5. Readout Electronics electdr.pdf
6. Calibration and Light Monitoring system chapter6.ps
7. Preshower chapter7.ps
8. Detector Assembly and Integration TDR8se18.ps
9. Safety aspects TDR9se18.ps
10. Responsibilities and Organisation Not yet available
11. Cost, Funding and Profiles Not yet available
12. Detector Performance Studies TDRperformanceNEW.ps
The file" radiation" will be included in an annex.
D.Cockerill called for comments on this Scheme
R.Brown noted that there was to be a PDR ( Preliminary Design Report) to
proceed the TDR and it would be useful if we were to have as much as possible
of the TDR in the PDR. The PDR is going to the printers Thursday 23d Oct.
G.Heath asked why the electronics R and D was included under Mechanics.
DC commented that this was because the principal electronic development now
required was associated with the physical separation of the VPTs and the
Pre-amplifiers. ****
The 50 cm connecting cable capacitance of 40 pf was well matched
to the 35pf input design capacitance of the Lyon amplifier. Much of the
electronics can be the same as for the barrel but the mechanics are
specific.and the modularity will also be different. The signal from the end cap
is also lower than that from the barrel.
There was general discussion on the scheme and the following points were
proposed:
More details of the Electronics should be in a separate section.
The VPT's should have a separate chapter
It was hoped that it would be possible to use Russian VPT data in the TDR.
The meeting then considered chapter 3 in detail, and a document containing an
initial draft of some of this chapter was circulated.
D. Cockerill asked for specific commitments from institutions to take on TDR
work. He also stated that RDMS (Russia) should be fully involved. A copy of
the file should be sent to Russia so that they can proof read and be invited
to comment
The following sections of the TDR were allocated as follows, attention is drawn
to points raised during the discussions.
3.2.1 Introduction David Britton
3.2.2 Constraints Dave Cockerill & David Britton
3.2.3 Geometry considerations David Britton
3.2.4 Endcap Modularity ECD (Electrical Control and Design group)
(John Connolly, Brian Smith & Len Denton)
3.2.5 Supercrystal Construction ECD
3.2.6 Backplate support/cooling ECD
3.2.7 Radiation Shielding David Cockerill
It was noted that recent work from Mika Huhtinen had indicated
a high residual radiation level on the end caps on shut down This therefore
needed to be taken into consideration during the design phase. It may be
necessary to work from behind shields, where servicing or maintenance is
anticipated. It should be possible to remove modules to a safe environment and
replace them without compromising personnel. M.H.'s work had also shown that
the holes in the polyethylene radiation shield to allow cables through should
be as small as practicable and filled to make them more impermeable to
neutrons. Neutron leakage even through small holes would contribute
significantly to radiation damage.
3.2.8 Readout electronics ECD
The spatial layout of the electronics needs to be defined. This will also
require knowledge of the end cap modularization.
3.2.9 Service requirements David Cockerill
It may be possible to take out some of the services at eta = 3. This would
then alleviate some of the service load in the 53 degree crack.
Cooling will be a problem as the preshower runs at -5·C and the end caps at
18C. It may be necessary to use heating strips or take steps and to ensure the
local atmosphere is above it's dew point at -5·C
3.2.10 Manufacture Helen Heath
Attention was drawn to the modularity of the system i.e. End plate, crystals,
Electronics. and the provision of a Data Base.
3.2.11 Construction ECD
Attention was drawn to the need to assemble on the surface at CERN. It was
felt that the work to be done should be detailed so that CERN could
appreciate both the necessity of assembling there and the limited resources
required. This is an area where RDMS can make a significant contribution.
3.2.12 Installation & Commissioning ECD
J.Connolly stressed that the assembly cannot be translated from the horizontal
to the vertical.
The mechanical design is now much more rational and the D's can be pulled
apart with the services, ( except water ) following them.
Careful consideration must be given to the problems associated with high
activation levels.
3.2.13 Maintenance planning ECD
J.Connolly noted that this need only be a single paragraph of a few clear
sentences.
3.2.14 Survey David Cockerill
It is important that allowance is made for the difference in the dimensions of
the magnet with field on and field off these can change by more than 2 cm. The
exact change is difficult to calculate as it depends on the quality of the
steel used. Attention was also drawn to the problems that would arise if the
barrel, end cap and coil are not con-centric.
3.2.15 Timescale - MS Gant chart John Connolly
3) VPT chapter
Derek has sent a version to CERN
4) Endcap Trigger
Greg heath presented his latest work on the endcap trigger
Transparencies may be found under
http://www.phy.bris.ac.uk/~heath/endcap/
in the following files:
giftmeet_oct97.ps Contains the 'words'
default_trigtow.ps ) Have endcap pictures
trigtow_oct97.ps )
boards.ps Is the picture showing readout boards
There are still problems in matching the modularity to the fermi readout
boards. Greg was able to show considerable improvements in the spread in
crystal numbers per trigger tower by optimisation. There may be problems
associated with the fact that the signal from the end cap to the electronics
will be less than the signal from the barrel.
5) Simulation input - status of ECAL Endcap
There is now more space behind the end caps.
The distance to the extreme edge of the end cap has gone up from 1.700 to
1.711. For good resolution we ideally need an extra 2.4 cm thus would like
to increase the distance to 1.736.
Simulation results were presented by H Heath, J Hays and D Graham.
*******
The effect of different materials used in alveolar walls was considered :
in particular steel or air. Initial results suggest a significant
degradation of the resolution of the reconstructed energy with steel.
The effect of crystal length on energy loss was studied, with 20cm and
22cm crystals at phi = 45 degrees, and at eta = 1.8. The relative losses
were 29.4% and 13.3% for 100 GeV gammas and 17.7 % and 8.3% for 50 GeV
gammas.
6) Calibration and monitoring section R Brown
R.Brown felt that the end cap should be calibrated as a D in a beam line.
This will need careful consideration as it will be necessary to tilt the
assembly to 26·
It may also be necessary to make the measurements in a magnetic field, but
the smaller VPT's may be more stable than the ones used for OPAL.
These considerations need not go in the TDR.
7) Update on the Mechatronics design and the electronics chain
J Connolly presented the position on the Mechanical design.
Proposed allocation of engineering design work with RDMS
RDMS
Back support plate
Super crystal mounting
Fixation to the HCAL
Build and installation plans
RAL
Crystal geometry
Super crystal mechatronics
Readout electronics ( it will not be possible to just copy the barrel)
Overall dimension and layout scheme
The arrangement will be non exclusive with an emphasis on collaboration.
To this end there should be regular ECAL endcap engineering meetings at CERN
where engineering design proposals are presented for review and approval.
There is a significant problem associated with radiation levels and the
electronics. The original design with the pre amplifiers mounted on the back
of the crystals exposed them to high radiation levels.
The proposed design now anticipates the electronics being mounted behind
the end plate and behind a polyethylene shield, which, provided good
hermaticity is maintained with respect to neutrons, should provide
sufficient shielding. There will be problems associated with matching the
cable capacitance and space considerations but overall a much more rational
modularization can be achieved and the heat loading on the crystals is
reduced.
J Connolly showed a carbon fibre sample of the alveolar unit Nikoli had made
in Russia, with an inner wall thickness of 400 mu and 200mu outer walls. He
understood that the inner surfaces could be made very smooth and asked for
physics input on the question of reflective coating and light collection.
J Connolly suggested that Nikoli should make a 3 by 3 alveolar unit, and
then make 4 off so a 36 array could be tested in the test beam. A request
should be made for the appropriate crystals.
It is important that all electronic components are radiation tested.
It was felt that a case should be made for the end cap and the barrel work
to proceed in parallel to ensure a coherent development and production
program. ***********
R.Stephenson presented developments on the front end electronics of the
endcap. He has been carrying out checks on the Lyon preamp to ascertain
whether it is viable to use a 50 cm cable between the VPT and the preamp.
Initial tests suggest a 40pf cable would, for a gain of 8, increase the
rise time to 18ns and the noise by 700 electrons.
Richard emphasised the need for careful screening and noted that the cable
would have to be twin screened coax.
8) ECAL Endcap beam tests at CERN
7 VPT's have arrived from Russia, together with the two already delivered
make 9.
V. Katchanov is due to arrive at CERN with 9 endcap shape crystals on 21st
October. Paul Lecoq has organised for the crystals to go through the
preparation, ACOSS and Tyvec wrapping schedule foreseen for production.
D.Cockerill will take out 9 Stephenson type amplifiers together with 1 VPT
to act as a spare. The original RAL distribution boxes will be reused. The
aim is to measure the number of photoelectrons per MeV from each crystal,
with coupling grease and VPT system.
The tests should start with low intensity to ensure any radiation blackening
can be carefully monitored. There can be a 20% loss in yield for 100 rad.
If run time is available from 9 to 10 Nov tests were foreseen with Lyon
preamplifiers. If the opportunity arises a VPT should be tested for
nuclear counter effect by masking the tube.
The 50 cm cable links should be tested with appropriately screened cable.
Great care will have to be taken over earth loops and cooling. G.Davis
volunteered to be present during the run to help with this when needed.
9) VPT's
D.Imrie reported that he had now received 21 VPT's from Electron tubes,
7 off of 3 types. There were 2 sizes of grid in Cu, and identical grid
sizes of Ni and Cu. The quantum efficiency given was the same as for the
Russian tubes but the stated gain differed although no voltage was given.
These will be tested at RAL.
10)Quadrant prototype model
It was felt that the plaster models so far built were invaluable. It was
also felt that the next area of modelling that was critical was the
coaxial part of the stiffening supporting the crystals. A small prototype of
the back of the alveolar unit should be made, detailing the stiffening and
flatness of the back.
11)The next meeting will be at IC at 10-30 on Wednesday 17 Dec.
The aim will be to plan the next 12 months work.
P.S. Flower
24.10.97
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