From: Matthew Worcester (mworcest@hep.uchicago.edu)
Date: Thu Apr 27 2006 - 22:23:43 CDT
Hi Chris,
Now that I know how you did the PMT placement in RAT, I think I understand
why there are too many pmts in RAT. ReactorFsim's calc actually used
R2 = 350 cm, so it got the pmt coverage right, but overestimated the
number of pmts if you actually put the photocathode at R2-20 cm. I agree
that putting something like SetPMT into RAT would be nice, then the number
of pmts could be automatically set by pmt coverage and R2 in RATDB.
Matt
On Thu, 27 Apr 2006, Chris Tunnell wrote:
> Stan is correct, I just added a 'for loop' from 0 to Npmt on some array
in ReactorFsim that stored PMT locations, and then dumped the coordinates
to a file. You can see the file in CVS at
data/pmtcoordinates_spherical_id.dat. There are also scripts in the util
directory to go from that format to RATDB. I don't remember changing the
coverage, so I don't know why it is off, but this was nearly a year ago.
>
> Currently, the 20 cm from the tank distance seems right in RAT (though
the part of the PMT the measurement is made from could be different), but
the number of PMTs is too high. We have 27% coverage instead of 24.35%.
This has been a known problem for a while, but nobody really knew
specifics about the coverage other than 25% when asked, so I made a
ticket in RATTRAC about it:
>
> http://nu.ph.utexas.edu/bw/trac/ticket/36
>
> If you could close that when you figure it out. It sounds like you
would benifit from adding a feature to RAT that did what ReactorFsim did:
added PMTs until a certain coverage is met.
>
> My numerical work just now:
>
> To calculate the area of coverage per PMT at a certain radius: pi *
(r_pmt)^2 / (4 * pi * r_photocathode^2) = (20.16/2)^2 / (4 * (350-20)^2)
= 0.00023325 = a. Yet a*1044 = 0.2435 and a*1160 = 0.27057. You can use
the coverage per PMT at a radius for overall coverage.
>
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