[Halld-pid-upgrade] DIRC meeting: Thursday 8/8 @ 1 pm Re: Postpone tomorrow's DIRC meeting (new time TBA)

[Justin Stevens]

Hi Mike,

Thanks for the reminders on previous studies of varying the index of refraction and possibility of using oil.

For the screw idea, I think the question is if the adhesive is leaching something into the water which could affect the mirrors.  It clearly still has a strong bond after 6 months in water, but Bill’s test showed that when exposed directly to water it turns opaque and seems to lose some of its stiffness.  So the possibility of other fasteners is just to remove possible contaminates from the water system.

-Justin

> On Aug 8, 2019, at 3:06 PM, Michael Williams <mwill at mit.edu> wrote:
> 
> 
> I couldn’t unmute for much of the meeting due to some drilling going on outside of my office. A few things based on today’s discussion.
> 
> Using air in the box
> 
> You’d lose about 10% of photons going into the PMTs. You’d also lose 10% of photons that exit the bars — at roughly perpendicular incidence angles. However, the photons are not typically incident on the end of the bars at 90 degrees. Recall that the DIRC works because total internal reflection occurs between the quartz bars and nitrogen already at rather moderate incident angles. This would also occur at the end of bars if the optical box was filled with air. Therefore, much of the images would be completely lost — I don’t think the DIRC would even be useful if you did this. 
> 
> Oil
> 
> We studied these oils and they lose at least 30% of the photons and were terrible to work with. Beyond this, it would cost O($100k) to fill each box, so it’d be cheaper to use water and replace the mirrors every year, and you’d definitely get better performance by doing that. 
> 
> Screws
> 
> We did consider screws early on but we were worried about breaking the mirrors and damaging the coating when we drilled through the mirrors. We also considered using clips, but for these — and the screws — we were also worried about putting pressure on the mirrors as that could also break them.  It was not clear to me from the discussion what is wrong with just using the tape that we used. What are you trying to accomplish by either using different tape or screws? 
> 
> 
> Mike
> 
> 
>> On Aug 6, 2019, at 5:23 PM, Justin Stevens <jrsteven at jlab.org <mailto:jrsteven at jlab.org>> wrote:
>> 
>> Hi All,
>> 
>> The DIRC meeting this week is rescheduled for Thursday (8/8) at 1 pm.  A preliminary agenda is posted at https://halldweb.jlab.org/wiki/index.php/August_8,_2019_DIRC#Agenda <https://halldweb.jlab.org/wiki/index.php/August_8,_2019_DIRC#Agenda>.  Please update and add items as needed.
>> 
>> -Justin
>> 
>>> On Aug 5, 2019, at 11:16 PM, Justin Stevens <jrsteven at jlab.org <mailto:jrsteven at jlab.org>> wrote:
>>> 
>>> Hi All,
>>> 
>>> Given that I’m traveling during the usual 1 pm time slot for our meeting tomorrow (Tuesday), I would like to propose that we postpone this week's meeting to a later date.  I’ll followup shortly with a proposal for the new meeting date and time.
>>> 
>>> -Justin
>> 
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