sPHENIX HCal discussion

[John Lajoie <lajoie AT iastate.edu>]

Dear HCAL'ers:

    Below are some notes from the HCAL meeting held this past Tuesday. The purpose of the meeting was to review design issues associated with the tiles, light collection and LED calibration for the inner and outer HCAL's.

Regards,
John Lajoie

Notes/Action Items from HCAL Engineering Meeting 3/7/17

The purpose of this meeting was to review the status of the tile, light collection and LED/fiber design and plan the course forward to completing the design. Rich Ruggiero presented a set of slides on the updated designs, they are available in the CDS agenda at:

https://indico.bnl.gov/conferenceDisplay.py?confId=2929

The key decisions and action items from this meeting were:

1. Rich presented a set of designs that include fixturing to hold the tile in place in the inner and outer HCAL sectors. One key element is that in some cases the tiles must be shortened to clear the combs at the inner and outer radius.

For the outer HCAL, the tiles must be reduced by 4mm at the inner radius and by 13mm at the outer radius. For the inner HCAL the tile must be reduced by 4mm at the outer radius. After some discussion, it was agreed that these reductions would likely not affect the response of the calorimeter.  This should be checked in simulations, and the tiles for the v2.1 beam test will be of the reduced size so they will be checked again in the 2018 test beam.  It was decided that all tiles should be reduced, not just those in the region of the combs, to avoid creating nonuniformities in the calorimeter acceptance.

2.  The light block in the tiles is now longer, with a tapped hole to allow a bracket to be screwed into place to fix the tile at the outer radius.  It also includes holes for alignment pins that are to be used with the tile test fixture at Uniplast. Another change to the light block is that it includes a new cylindrical connector for the fiber (more later).

3. For the outer HCAL, at the inner radius, Rich proposed another injection molded alignment bracket be mounted in the tile.  This would also require alignment pins in the absorber plates, an additional expense. There was also some concern about variance in the width of the tiles.  After some discussion, it was decided to remove the locating block from the bottom of the tiles and use some kind of shim/filler to make up the 4mm gap allowing the tiles to be aligned at the bottom. A solution for this and it’s integration with the support ring and magnet supports is something we need to look at carefully. By removing the locating block from the scintillator tiles we allow the design of the tiles to move forward and be finalized.

For the inner HCAL, foam tape on the end of the scintillator tiles at the inner radius should be sufficient. The outer radius bracket, as shown would center the tile in the gap.  After some discussion it was decided this may not be necessary and the tiles could be held to one side of the gap, but the design will continue with the intention of centering the tile in the gap. 

4. The inner HCAL end plates may need modifications to the end plate to accomodate access to the electronics and shelf to hold them in place.

5.  The fiber ferrule on slide 8 needs some R&D by physicists. How long does the 3mm fiber need to be?  Would it be sufficient to frost the LED and use a 1 inch or so air gap?   Rich can't do much more on this right now, needs physicist input.

6. The optical fiber connector was discussed.  The main concern is light leaks in the fiber connector. It was suggested to include a rubber grommet that would make a light seal between the connector and mounting cylinder.

Based on these discussions/decisions, Rich can proceed with the tile design, mounting brackets, clips and light block (including the fiber mounting cylinder).

--

John Lajoie

Professor of Physics

Iowa State University

 

(515) 294-6952

lajoie AT iastate.edu

Contact me: john.lajoie