[Halld-pid-upgrade] [Revised Logentry] PMT installation and cookies

[mpatsyuk at jlab.org]

Logentry Text:
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Having low voltage on we checked the DAQ communication with the modules.
We could check if the module is responding, temperature and voltage.
One module on the bracket 17 did not respond, we inspected possible connection failures, misconnection, low voltage problem, but did not find any problems. So that the problem should be inside the box: bad connection of the optical fiber or bad module.

We opened the box. The plan was:
1. Detach bracket 17 and check the cabling for the module which was not communicating
2. In case we need to exchange the optical fiber, we need to detach also bracket 18, as they are attached to the same fiber

So we detached bracket 17, checked the fiber and discovered, that the fiber is not working, not the module. [figure:1]

Since the problem was in the fiber, and the same fiber is attached to two brackets, we had to detach bracket 18 too. We were lucky, that this is the last two rows and that only two brackets were connected to the same fiber (unlike all the other brackets which are connected by four).

When we detached two brackets, we noticed, that MaPMTs tend to stick to the cookies: [figure:2]

Through the part of the window behind the brackets 17 and 18 we could see the beautiful DIRC interior. The wedges in the bar boxes on the right: [figure:3]

Some more wedges and kaleidoscopic pattern in the bars through the oily window: [figure:4]

Again radiators on the right (sorry): [figure:5]

And some more PMTs on the left: [figure:12]

Can not help posting more of the gorgeous theater-looking DIRC interior: [figure:6]

After the first try to apply the bracket 17 we saw that a large area for one of the PMTs did not have coupling. So we decided to reattach the bracket. We detached the bracket, did not wipe the window, changed cookies and attached it again. We see quite prominent bubbles: [figure:7]

And that's the same photo without arrows: [figure:8]

We realized that there is just too much oil on the window. The oil is quite viscose, it creates a non-even landscape by dripping from the modules above and all the residual oil which we put on bracket 17 while trying to attach it. So we decided to wipe the window. We cleaned in with isopropanol and then applied bracket 17. Now the coupling was perfect almost right away: [figure:9]

While enjoying the view of the good coupling (it is really nice!) we noticed that there is quite some dust on the mirror: [figure:10]

That's a better figure of the dust on one of the side mirrors: [figure:11]

After that we did two iterations with the bracket 18, and at the second iteration managed to have only some small bubbles, which will be summarized in an attached pdf.

Lessons learned:
1. It is much easier to apply PMTs in the horizontal orientation of the window
2. It is hard to say why sometimes bubbles are formed, and sometimes not: too oily window definitely spoils the coupling, but we see that even attaching a bracket to a clean window does not guarantee a good coupling from the first try
3. massaging the module does not quite help
4. allowing for several iterations, one can achieve good coupling.

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This is a plain text email for clients that cannot display HTML.  The full logentry can be found online at https://logbooks.jlab.org/entry/3645047
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