Since both detectors should adopt the same scheme, it is an issue to be discussed in the MDI/BDS contacts for IDAC.
For the discussion, we should prepare a document to summarize the push pull issue with emphasized as ; it is a simpler and easier design of two detectors to adjust the beam level and to isolate vibrations even in deep hall.
Who will design the platform ?
Since the platform is the interface issue, it will be designed in collaboration with detector and machine people. First design has been presented at IRENG07, September 2007, SLAC, by Alain.
Two platforms each for two detectors would be better for isolation of the two detectors.
In the IR interface document,
"The off-beamline detector is shifted in transverse direction to a garage position, located 15m from the IP. "
So, we can use the 15m transverse space from the detector center if it is self-shielded. The space would be 15m minus a width of wall for non self-shielded detector.
It should be clarified how to install muon detectors in order to estimate space around the detector and location of electronic house etc. .
An effect on the second detector should be taken into account.
In LoI, coil design with correction coils should be a baseline for uniform field which must be good for anti-DID design. The correction coils do not contribute so much in the stray field issue.
For stray field in beam line, we may install compensation coil or irons to make it smaller.
In radial direction, we should fill gaps as much as possible, say 50% as Sugimoto's studies (2D model)
We agreed that we should keep 200 Gauss for safety, but set the tolerable field in a distance of 1 - 1.5m to be decided.
Present DESY design shows 300G at 3m from the detector.
Magnetic fields can be measured with various anti-DID fields and TPC requires the 30um integral error as written in the LCTPC note, i.e. ILC-NOTE-2008-048 at http://ilcdoc.linearcollider.org/ .
Two supporting systems were proposed, i.e. both has a fixed point outside of detector with different second fixtures (1) on the iron-endcap with sliding rails or (2) several rods from the coil in front of the tube. Matthieu prefers the second system for more independent scheme, i.e. decoupled the endcap opening.
At this Cambridge meeting, we will not chose the square or round tube.
We need to have a detailed opening scheme, which determines the size of IR hall. The beam pipe is an issue.
Adrian pointed out in his presentation that tungsten tube was needed for neutron shield in the endcap calorimeters.
Tungsten mask can be put innermost part of the calorimeters.
In opening process of detector, the outer endcap part is vertically split into two, then the inner part is moved out for about 3.2m in a body.
Since the proposed design has 2.3m total iron thickness, the stray field should be fine for B=3.5T.
It should be clarified how much gaps between the endcap iron plates produce stray field.
It was pointed out that the iron structure shape is not needed to be the same as the calorimeter. There is a cylindrical coil between them.
If the present calorimeter thickness is enough for physics performance without tail catcher, especially in the barrel region, minimum thickness of iron plate can be about 2 &lambda, i.e. 25cm. There may be a detector just behind of the coil-cryostat, that is, just in front of the first iron plate.
(6) End-cap design proposal by Uwe
Fine segmentation in the barrel endcap overlap region is not needed as a tail catcher. Also, length of thin (10cm thick) iron plates should be minimized for mechanical strength and installation of detectors in the interleaved gaps.
A special endcap design was proposed, where the iron yoke consists of 5 10cm thick and 3 60cm thick iron plates, that is, 2.3m total thickness of iron.
First inner 6 plates in the endcap have shorter length and they are surrounded by 1.2m thick plate which is a part of outer thick iron plates.
(7) 8 v.s.12
Uwe concluded that dodecagon (12 fold) is preferred from mechanical point of view, i.e. easier transportation and handling and less deformation, in his presentation, while the iron structure should follow the calorimeter design.
(8) Tail catcher
The ECAL and HCAL have a total absorption length of 6.7 λ. In the barrel region, there are the coil and cryostat wall whose absorption length is about 2 λ.
Do we need a tail catcher ( 5 layers of 10cm thick iron plates ) ?
(9) Future meetings
We will continue to have Webex meetings . First, we would like to gather replies to the MDI questions from sub detectors .