Brown, RM (Bob)

From:	rmb@v2.rl.ac.uk
Sent:	14 July 199917:57
To:	rmb@mailbox.rl.ac.uk

Subject:	Fw:  Changed ECAL deliverables letter, 1st draft to David Miller

From:	RALH EP: DAVEC	"Dave Cockeril I"
To:	DMILLER
CC:	RMB
Subj:	Changed ECAL deliverables letter, 1st draft to David Miller

Tues, Oct 7th, 1997

Hi David

Here is the letter we would like to send to you, as Chairman of the PPESP, outlining our proposed changed deliverables for the CMS ECAL.  Do you have any comments or changes?  We would give more detail about the changes at the next CMS Management Committee meeting in Oct/Nov if required.  We also propose to forward this letter to Brian Foster and to our referee, John Fry.

Many thanks

Dave Cockerill.

Letter of notification to the PPESP:

Further rationalisation of the CMS ECAL Endcap design

CMS has recently reviewed the overall design of the detector in order to optimise the interfaces between the different subsystems and to match costs to available resources.  This has resulted in some significant changes, some of which bear directly on the UK contributions to the project.

In the case of the ECAL, the changes to the overall design are:

-	a smaller radius for the barrel ECAL
-	an increase in crystal size
-	a flat cylindrical inner surface for the barrel ECAL
-	the positioning of the barrel preshower inside the tracker volume rather than within the ECAL volume (the preshower will only be installed, if needed, for high luminosity running)
-	the addition of a further 2 hadronic interaction lengths for the barrel HCAL behind the new barrel ECAL.

Furthermore, as the endcap design has progressed over the last few months, detailed design changes have been found necessary compared to the original design presented to the PPESP.  These result in a significant simplification of the tasks to be undertaken at a regional centre.  As a consequence the UK groups wish to update the deliverables specified in the PPESP/97/22 document of June 1997.  The changes and proposed deliverables are outlined in this letter.

1)	Supercrystal assembly

The design of the supercrystal has been considerably simplified by the removal of the preamp readout.  The preamp readout together with all the subsequent components of the ECAL electronics chain will now be located on the rear side of the ECAL Endcap support plates.

The supercrystal now comprises only the crystals, the alveolar support structure, the VPT's and the monitoring fibres.  This considerably reduces the number of services and readout channels which previously had to be incorporated within each supercrystal.  Separate cooling, to remove the power dissipated by the preamps, no longer has to be incorporated within the supercrystal.

2)	ECAL Endcap Channel count

The crystal size has been increased from 25 x 25 mm**2 to 25.9 x 25.9 mm**2.  In addition, the layout of the CMS Barrel ECAL has changed: the crystals are now placed at a smaller radius.  This reduces the volume subtended by the endcaps since they are now placed at a shorter distance from the intersection point.

The channel count is now 10,750 for each endcap, a reduction of 9% from the 12,000 channels quoted in PPESP/97/22.

268 supercrystals are now needed for each endcap plus 60 smaller supercrystals to complete the inner and outer perimeters, in comparison to the 350 stated in the PPESP document.

3)	Regional Centre

There has been considerable discussion within the CMS ECAL Finance and Technical boards about the number of Regional Centres needed for the CMS ECAL.

The CMS ECAL project manager has recommended that the UK be the sole Regional Centre for the construction of the ECAL Endcap supercrystals.  This will reduce the overheads that had been part of the previous planning where two Regional Centres had been expected, one in the UK and one led by the RDMS (Russia/Dubna Member States) groups.

The UK fully backs the recommendation of the ECAL project manager.  Indeed this will give the UK an enhanced role within CMS.  It is an important marker for the regard with which the CMS UK ECAL community is held.  It shows the UK obtaining key international strategic roles well beyond that expected from the level of the UK financial contribution to the project.

The new organisation has been discussed with our RDMS colleagues.  They are keen to participate in the UK Regional centre and are considering long term placements, resident in the UK, to assist in the project.  We will be seeking ways to facilitate their presence in the UK.

Proposed changes in the deliverables

The UK has rediscussed the use of the resources speciified in PPESP/97122.

With the same hired and allocated manpower stated in PPESP/97/22 we now wish to deliver 536 simplified supercrystals, and 120 smaller supercrystals, to equip both endcaps.

In the updated Table 3.4 in PPE5P197122 #703k were allocated for front end housings and connectors (#663k and #40k respectively) for one endcap.  With this allocation we wish to deliver the simplified housings and connectors needed for the supercrystals on both endcaps.
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