[Halld-pid-upgrade] [New Logentry] DIRC window and PMT installation

[jrsteven at jlab.org]

Logentry Text:
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After the first water fill test yesterday we noticed some potential optical issues inside the box.  We noticed some smudges on the inner surface of the window that we didn't identify before it was first installed and the upper and lower mirrors had collected significant dust during the water fill test.  The water test without flow left a puddle on the lower mirror which we believe resulted in the dust accumulation.

So this morning, we removed the window and placed it upside-down, so Greg could lean the inner surface.  Several smudges were removed but there remain some imperfections which will be documented.  Greg also cleaned the upper and lower mirrors, which brought the mirrors back to the quality we had before the water fill test.

[figure:1]

Finally Greg and Maria installed the lower half of the dark box and 2 PMT rows to validate the installation procedure and optical coupling.  The PMT modules were connected to an SSP and Low Voltage to confirm their communication and are installed with both the optical fiber and LV cables attached.  The HV cables will be attached just before the dark box is closed.  The compression of the cookies can cause them to protrude past the edge of the PMT, so Maria has trimmed the width by 2 mm to avoid this overlap between the cookies of neighboring rows.

[figure:2]

Tomorrow we will continue installing PMTs on the lower (south optical box), as Bill and Andrew have already assembled and cabled all the required modules.

Lessons learned:
1) For the upper optical box window, we will place it in the clean room as soon as it arrives and clean both sides before installing.
2) The static water test may have been responsible for the accumulation of particulates on the upper and lower mirrors.  So we will only fill the boxes from now on if they are connected to complete plumbing to cycle the water and remove any particulates through filtration before emptying.

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