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Re: [GlueX] factors in bcal readout decision
Hi Richard
Thanks for posting the table of design considerations. I have merged your
table with the one that Alex sent me and posted a bare-bones draft of a
document that can summarize our evaluation on the portal (GlueX-doc-795).
It will be updated as we work toward the workshop on April 23-24. If there
are any comments/suggestions please send them to me.
From now on I will be posting discussion of this topic to halld-cal for
any interested participants.
A note on collection of light into smaller SiPM arrays: From a cost-point,
one of our main problems is the increase of a factor of 4 in the number of
light sensors for the bcal compared to the cost book. Therefore, we should
be considering how to make larger Winston Cones to match the current
1.2cm^2 SiPM arrays to reduce the number of channels. To make the obvious
point: if we have 4200 channels, all costs per channel add up to lots of
$$. This includes cables, low voltage supplies, ADCS, TDCs,
discriminators, etc.
Cheers, Elton.
Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton@jlab.org
(757) 269-7625
On Tue, 3 Apr 2007, Richard Jones wrote:
> Colleagues,
>
> Please find attached my spreadsheet derived from our discussion of the factors driving
> the choice of readout scheme for the BCal. The items in red are highlighted because
> they are potential performance drivers.
> 1. In the case of the planacon, the relevant scale is the sector of a device devoted
> to one readout channel, eg. a 2x2 pixel section of a 8x8 anode device. The global
> variation of 1:1.5 is so large that local variations must be looked at closely. It
> can be addressed by adding additional diffusion to the light path to scramble the
> map from the BCal to the cathode surface.
> 2. In the case of the Sensl module the uniformity is probably very good (modulo
> thermal gradients), and the dark rate is the primary concern. If the photon yield
> is really as large as 8 avalanching pixels per MeV then I really believe that
> 100MHz is no problem. We should be able to confirm this quickly using the test
> beam data and the measured SiPM pde.
> 3. If photon statistics are as superabundant as we believe then there is zero
> motivation to cool these devices below 20C. Rather, we can save major costs by
> reducing the 4x4 pad readout device with a 2x2 device. How much cost reduction
> does this entail? This possibility might by itself tip the balance decisively in
> favor of the SiPM readout.
> Richard Jones
>
>
>