[Halld-pid] Fwd: PMT choice for TOF

[Beni Zihlmann]

Hi All,
I would like to address Elton's main concern the lifetime of the PMTs.

After 1000 hours of running at 0.1mA the gain reduces by about a factor 
of 2.
According to my calculations below the highest current PMT is 0.062mA so
after about 1400 hours of running the gain would be reduced by about a 
factor
of 2. The HV is about 1600V for a pristine 10-stage PMT to get a gain of 
10^6.
The maximum HV is 2000V for such a PMT with a gain of about 6*10^6. So we
have some headroom to adjust the PMT high voltage to retain a gain of 10^6
for some time, but at least twice such that we can run for about 3000 hours
with sufficient gain. That is not perfect but would mean we can run for 
at least
one year. At the end of one year running (120days full running) one 
would have
to assess the situation and may consider to replace the 8 PMTs of the 
innermost
paddles left and right of the beam hole of the two planes. At that point 
we would
also have enough experience with the TOF to take educated decisions on what
we need as amplifications and operating parameters for the 8-stage PMTs in
the high luminosity running.
I hope this makes sense to you too.

cheers,
Beni




> Hi all,
>
> See my comments attached. Cheers, Elton.
> Elton Smith
> Jefferson Lab MS 12H5
> 12000 Jefferson Ave
> Suite #16
> Newport News, VA 23606
> (757) 269-7625
> (757) 269-6331 fax
>
> On 12/13/11 11:54 AM, Mark M. Ito wrote:
>> Folks,
>>
>> Yesterday Beni sent out an email summarizing thinking on the choice 
>> of phototubes for the TOF (see below).
>>
>> Recall that there is a problem with PMT lifetime for the high rate 
>> counters near the beamline, especially at 10^8 photons/s. The choice 
>> of PMT's is central to how we deal with this problem.
>>
>> Please have a look. He is asking for feedback so that we can make a 
>> decision soon.
>>
>>   -- Mark
>>
>> -------- Original Message --------
>> Subject: 	[Halld-pid] PMT choice for TOF
>> Date: 	Mon, 12 Dec 2011 12:01:22 -0500
>> From: 	Beni Zihlmann <zihlmann at jlab.org>
>> To: 	halld-pid at jlab.org, Elton Smith <elton at jlab.org>, "Fernando J. 
>> Barbosa" <barbosa at jlab.org>
>>
>>
>>
>> Dear colleagues,
>> In order to make a final decision on the choice and strategy with regard to
>> the PMTs for the TOF I put together a few facts and findings and ask for
>> your
>> opinion.
>> Please read the attached outline set in 4 main paragraphs:
>> Purpose, Facts, Calculations and Strategies
>>
>> I am advocating strategy a) where we go with a two phase approach.
>>
>> Let me know what you think and what makes the most sense. Depending
>> on your answers we will either take a decision right away or I will call
>> for a meeting at end of this week (beginning next) so that we can take a
>> decision on this matter before Christmas.
>>
>>
>> thanks everybody,
>> Beni
>>
>>
>>
>>
>>
>>
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>
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