[Halld-cpp] CPP Meeting minutes 2/28/2018

Ilia Larin ilarin at jlab.org
Thu Mar 1 00:11:09 EST 2018


 Hi Rory,

for UMass drift time measurements it might be interesting to compare
regular threshold with high signal threshold (~100 mV) distributions.

 Ilya

----- Original Message -----
From: "Rory Miskimen" <ramiskimen at gmail.com>
To: "David Lawrence" <davidl at jlab.org>
Cc: halld-cpp at jlab.org
Sent: Wednesday, February 28, 2018 2:43:40 PM
Subject: Re: [Halld-cpp] CPP Meeting minutes 2/28/2018

On Feb 28, 2018, at 10:50 AM, David Lawrence < davidl at jlab.org > wrote: 

Hi All, 

Today turned out to not be a great day for most people to meet. It ended up being 
just Ilya and I. We did have a discussion on what we would like to do with the chamber 
and any remaining beam opportunity. Here are the ideas we came up with so others 
may comment: 

1. Change the gas mixture to 90/10. We have not yet spoken with Tom/Scot on how 
difficult this is. We will do that this week. 

I think we’ll need to have Tom order a tank of 90/10 by volume. Then just move the gas regulator over to the new tank, open the valve to get gas flowing, that’s all we need to do. We will run the detector at a lower HV. 

On the way home Saturday I finally got around to looking at the gas flow calibration data I took last Nov. I did a re-calibration of the gas flow tubes because we seem to have a discrepancy between gas gain at JLab and UMass, it’s higher at JLab than UMass. To make a long story short, I believe the “80:20” by volume mix I’ve been running at UMass is approximately 75:25. The bottom line is that running the detector with an actual 80:20 at +2000 V is probably over-biasing the detector somewhat. Andrew and I will need to take some measurements with the small prototype detector to find new recommended HV’s for 80:20 and 90:10. 




2. Change the scintillator paddle position to be closer to the beam line. 

3. Machine a hole in the 10.75” steel plate and center it on the beam line. This will 
give a much closer approximation of beam conditions. The hole should be round with 
a diameter between 6.6cm and 8cm. According to my notes, the dead region in this 
chamber is 3.4” in diameter (=8.64 cm). 

The diameter of the dead-zone in the chamber is 6.8”, the radius is 3.4”. 




Studies from last year set the beam hole 
size to 2cm smaller in diameter compared to the dead region so if we follow that, 
the hole size should be ~6.6 cm. 

Yes, I think the studies we did last year indicate the hole in the iron should be 2 cm smaller than the dead zone hole. 





The final design parameter for the dead region from 
those same studies was 10 cm with a beam hole of 8cm diameter. 

Yes, that’s what I saw from our studies last year. However, the dead-zone we currently have is about 17 cm in diameter, so we would be going with a dead-zone diameter significantly smaller than what we currently have. 

Rory 






One option is to try and do both by cutting the smaller hole, taking data, and then cutting 
the larger hole. Alternatively, we could cut the larger hole and then make a plug or mask 
to get data with the smaller hole size. 
The chamber is currently out of the beam. There may be opportunity on Monday to 
reinstall it along with any of these modifications. There is also a possibility they will 
extend the run for one more week. 

Rory and Elton: please think about this and let us know what you think and if there are 
any other things you would like to do during the remainder of this run period. 

Regards, 
-David 

------------------------------------------------------------- 
David Lawrence Ph.D. 
Staff Scientist, Thomas Jefferson National Accelerator Facility 
Newport News, VA 
davidl at jlab.org 
(757) 269-5567 W 
(757) 746-6697 C 


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