sPHENIX HCal discussion

[Edouard Kistenev <kistenev AT bnl.gov>]

John, I am sure you are correct in your cost analysis. Please tell your machinists that we’ll want modules locked into a common load bearing structure what will help with chosing absorber material (for example - if structure is not welded - inner layer of Al and outer of Steel -  by keeping strength distributed and mass consentrated in a single layer you will only improve the performance a).

About scintillators - they can also be injection molded but …. I do not know. I think it will be advantageous to have them lumious but that can probably be improved by increased thickness etc. If this proposal will get serious consideration - I’ll give it a thought and consider different approaches.

Edward

On Sep 11, 2017, at 2:02 PM, John Lajoie <lajoie AT iastate.edu> wrote:

Hi Edward,

    Thanks for sending out a drawing of what you proposed at the general meeting on Friday - it's very helpful.

    I think the mechanical structure you are proposing could be a very straightforward evolution of what we have now (in steel). If you built the existing structure (with small mods for the scintillator) and just instrumented it with scintillator on the back it could cost a little less because you don't have to worry about the mechanical tolerances of the gaps, but by definition it would (a) be able to hold the weight of the EMCal, and (b) have the same amount of absorber as it does now.   Still, this iteration is likely going to be a little more than $1M for the mechanical structure - it's still a lot of stainless steel.

    You can gain some additional savings by making the plates thicker, that will reduce machining. If you reduced the radial size of the steel so that it was about half an interaction length  - which gets me to what I think that's what you are proposing in your slides - you certainly won't cut the remaining cost in half, as most of the cost is in machining.  Of course, then you will still need to make sure that the reduced structure is stiff enough to hold the EMCal, but it is probably OK if the thickness of the plates is increased by a factor of two.

    There would be some additional savings on the scintillator and electronics, since we are reducing the number of channels by four, but you would still need to pay to have them assembled, shipped, etc.  My offhand feeling, from working with the BoE's and RLS for some time, is that you would overall save less than a million (before contingency), but that could be worked out in more detail.  Not chump change, but not a large bite out of the larger problem.

    I think we would want to try, as much as possible, to use the existing calorimeter readout scheme for the tiles.  Anything else is an R&D project that I don't think we would have time for.

    I'll have a talk with our machinists that build the current prototype to see if they can give use some back-of-the envelope numbers for potential cost savings with this kind of a structure. Without a detailed design it might be difficult but they might be able to estimate it as deltas from the current design (as I did above).

Regards,
John Lajoie

On 9/11/2017 10:00 AM, Edouard Kistenev wrote:

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John Lajoie

Professor of Physics

Iowa State University

 

(515) 294-6952

lajoie AT iastate.edu

Contact me: john.lajoie

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