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

[Rory Miskimen]

> On Feb 28, 2018, at 10:50 AM, David Lawrence <davidl at jlab.org <mailto: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 <mailto:davidl at jlab.org>
> (757) 269-5567 W
> (757) 746-6697 C
> 
> 
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