[Dsg-rtpc] Backpressure

[Sebastian Kuhn]

Dear Bob,

Thanks for your response - we did indeed modify the “chimney” to minimize its length and did see an effect from it.

I’m sorry for keeping coming back to the other items. I believe as long as you just give the green light to the DSG they can help us set up the differential pressure readout between 4He buffer and RTPC (both hardware and software). This would be needed soon - if we wait too long, we won’t be able to test our system before moving things into the Hall.

Finally, about the gas bottles: We did a careful measurement and believe that we can - barely - run with a minimum of 200 sccm flow rate to the RTPC. Given a standard gas supply bottle (the ones we have seem to have a volume of about 40 liters), this means that we will lose about 7 atm of pressure in these bottles per day. They seem to come with roughly 140 atm when delivered fresh, so this would give each bottle a life time of at most 20 days. Including tests before and after the experiment, we should budget 100 days of continuous running which corresponds to 6 bottles minimum (to avoid running them completely down). However, to be sure, we should have at least 2 spare bottles (we may well be forced to run at a higher flow rate). So if we have 6 bottles stored in the gas shed already, I would ask that we order 2 more to be sure. I am sure that members of the DSG can check my numbers. The point is that we should not risk running out of gas at the end of the experiment.

Thanks, and see you on Monday - Sebastian

On Jan 21, 2020, at 7:53 AM, Bob Miller <rmiller at jlab.org<mailto:rmiller at jlab.org>> wrote:

Hi Sebastian,

First question; yes you can modify the 1" nylon line as you like.

The other requests will be looked at after all the currently scheduled work for the changeover is complete.

Please check your inventor of gas and if you would like some ordered, send me a final number and I will get it ordered.

Regards,
Bob

________________________________
From: Sebastian Kuhn <kuhn at jlab.org<mailto:kuhn at jlab.org>>
Sent: Friday, January 17, 2020 3:48 PM
To: Bob Miller <rmiller at jlab.org<mailto:rmiller at jlab.org>>
Cc: JIWAN POUDEL <jpoud001 at odu.edu<mailto:jpoud001 at odu.edu>>; Mohammad Hattawy <mohammad.hattawy at gmail.com<mailto:mohammad.hattawy at gmail.com>>; dsg-rtpc at jlab.org<mailto:dsg-rtpc at jlab.org> <dsg-rtpc at jlab.org<mailto:dsg-rtpc at jlab.org>>; Nathan Baltzell <nbaltzel at odu.edu<mailto:nbaltzel at odu.edu>>; Narbe Kalantarians <narbe at jlab.org<mailto:narbe at jlab.org>>; Eric Christy <meric.christy at gmail.com<mailto:meric.christy at gmail.com>>
Subject: Re: Backpressure

Sorry, forgot to attach the photo…



On Jan 17, 2020, at 3:42 PM, Sebastian Kuhn <kuhn at jlab.org<mailto:kuhn at jlab.org>> wrote:

Dear Bob et al.,

thank you and the DSG people for quickly setting up the “chimney” I requested. One question: Would we be allowed to cut that (very long) exhaust line? I understand that right now much of it coils up on the ground, where it doesn’t do us much good but creates a lot of volume (many liters, if my math is correct) that have to be filled with HeCO2 before the “chimney effect” can even start to work. Ideally, we would like to shorten it to not much more than needed to reach the present exhaust height.

Secondly, I’d like to come back to my earlier request to slightly change the interconnections on the gas panel for the differential pressure meter which presently has one side connected to the 4He buffer volume (highlighted in the attached photo). I would like to connect the other side of this meter to the RTPC pressure line (with a T) as indicated in green. That way, this meter will measure the differential pressure between the 4He buffer and the RTPC, which is our most sensitive pressure differential we have to keep an eye on.

Right now, I believe the port on the slow controls readout unit meant for this differential pressure meter is being used alternatively to monitor the ambient pressure in the EEL via a 2000 Torr probe that we happened to have. Ideally, we would like to rather add another dedicated port of that purpose (and another “virtual” meter in the slow control readout panel) so we can monitor both. But in any case the pressure difference between RTPC and 4He buffer is more crucial, and in the Hall we will have an “ambient pressure” readout anyway. So if we are short on readout channels (or programming time), we should just revert that port to its originally intended purpose.

Finally, speaking of HeCO2 gas bottles: I wanted to make sure that we have enough for the actual run - I believe, presently we have 6 in the gas shed but we may potentially need 8, and perhaps even 10 to be extra sure we have enough headroom. So it might be good to order 4 more of those bottles if possible.

Thanks, and have a nice weekend - Sebastian


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