Re: SiPM vs Planacon

[Carl Zorn <carl.zorn@jlab.org>]

Monday, March 19, 2007

Elton was asking about gain adjustment of the individual channels of  
the planacon.

As it stands now, the device takes one HV.  Adjustments in gain  
variance can be made
by making an individual array of compensating resistors on an  
external board.  This scheme
(devised and implemented by Vladimir Popov) has been used to great  
success on the multichannel
Hamamatsu phototubes.  So far, it has not been implemented on the  
planacons because their
channel variance is much smaller (about 50%) than the Hamamatsu case  
(3:1 or worse).  But the
scheme could be implemented with the Burle tubes too.


All the best,

..............Carl

carl.zorn@jlab.org
757-269-7449 (office)
757-584-7449 (pager)


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On Mar 16, 2007, at 6:52 PM, Elton Smith wrote:

>
> Hi George,
>
> Since my trip to Paris got delayed... yeah I know a bummer.... I had
> nothing better to do but to go over the document you sent. Might as  
> well
> make some comments in advance of the collaboration meeting.
>
> Segmentation and Floor term:
>
> Any uncorrected difference in gains between channels will certainly
> contribute to the floor term in the resolution.  The contribution to
> sigmaE/E should behave roughly as sigmaG/G, where G is the average  
> gain
> per channel, and sigmag~sigmaG/sqrt(n), where g is the gain of an
> individual channel, and n is the number of channels that contribute  
> to the
> measurement. For discussion sake I take n~5 (is this roughly  
> right?), so
> sqrt(n)~2.2. Assuming we want to keep the floor term to less than  
> 1%, this
> implies that sigmag/G <~2.2%. Any non-uniformity in the light  
> collection
> should have the same effect. But it seems to me that one can  
> correct for
> this by including the correct weighting factors when computing the  
> energy.
> Am I not correct? In other words, the non-uniformity does not have an
> intrinsic addition to the resolution. Or am I missing something?
>
> Added note: Your comment later about the planacons and light  
> collection
> through the light guides is certainly valid in this regard if  
> individual
> gains cannot be adjusted. This is a question for Carl: Can one  
> adjust the
> gains of the 16 individual segments of the planacon? As far as I  
> remember
> there is a single HV input, so what is the gain uniformity?
>
> SiPM option:
>
> General comment: From the data I have seen so far of the SiPM  
> tests, my
> main concerns are gain and efficiency, not necessariy DR. However,  
> Carl
> may have some more data for us soon.
>
> I)
>
> Gain: Accordint to Carl (in coversations with SensL), the gain of the
> SiPMs is actually 10^5, with 10^6 only after an amplification  
> stage, so
> not much different than the planacon tubes.
>
> Photoelectrons per MeV(p.3 second bullet): From your numbers, 16  
> p.e./MeV
> energy desposited, but 20 MeV-> 2.4 MeV deposited, so I conclude  
> that we
> get 1.9 p.e./Mev incident energy. This seems off by a factor of 4  
> from the
> number at the top of page 4 that gives 8p.e/MeV incident energy.  
> What is
> missing?
>
> II)
>
> One item missing from the list is the issue of heat dissipation  
> inside the
> magnet. This would be a similar problem for both SiPMs and planacons,
> except that the planacons are outside the solenoid enclosure so  
> bringing
> the light out has the benefit of getting the electronics out of an
> enclosed space. There were also questions about 15% humidity  
> controls...
> this also needs to be addressed.
>
> DR: With all the concern about the dark rate, it appears that the  
> rates
> are actually acceptable for the calorimeter. It would be good to  
> specify a
> maximum dark rate at a temperature above the due point (or where  
> one can
> reasonably cool). If the SiPMs meet this spec we are finished, no  
> need to
> do much better.
>
>
> Planacon options
>
> I
>
> Linearity: Should this be 300 microA?
>
> II
>
> Nonuniformity: This is a very valid point, both for the light  
> guides as
> well as gain control of each channel. (See my first question/comments)
>
> Conclusions:
>
> While I am very hopeful that the SiPMs will meet their expected
> performance, so far I have not seen the data to validate our optimism.
> Perhaps you and Zisis have some data from SensL that corroborate your
> assessment.
>
>
> Enough for now. Cheers, Elton.
>
>
>
> Elton Smith
> Jefferson Lab MS 12H5
> 12000 Jefferson Ave
> Suite # 16
> Newport News, VA 23606
> elton@jlab.org
> (757) 269-7625
>
> On Wed, 14 Mar 2007, George Lolos wrote:
>
>> Hi Elton and Elke:
>>
>> Here's the critical review of the two BCAL read-out options.  I  
>> believe
>> that I have addressed most - if not all the issues - but I  
>> consider my
>> job done.  No more work out of me until the Collaboration  
>> Meeting :-) !
>>
>> Cheers,
>>
>> George
>>
>