[Halld-pid] Fwd: PMT choice for TOF

[Mark M. Ito]

Beni,

This morning Elton and I were discussing an idea for providing a bit 
more margin for the all-10-stage solution that is on the table.

 From the exchange between you and Elton, we seem to have a lifetime 
estimate (again for the all-10-stage option) whose central range is 
significantly less than two years. That is not very comfortable. We have 
talked about using amplifiers, but building a custom PMT base would add 
another design and build component to the plan. The idea we discussed 
was to use commercial amplifiers, as a back-up in the event that 
currents and/or PMT decay rates turn out to be as high or higher than we 
expect.

We could initially run the tubes without amplifiers and as you point out 
we could raise the voltage if we see the gain start to sag 
significantly. Finally, we could add a commercial 10X amplifier 
downstream  (electronically) of the PMT for any tubes that don't look 
like they will make it to the nominal two years. These have been 
available for years (actually decades). For this last step we could 
maintain acceptable voltage steps in the first few dynodes with some 
modest lowering of the voltage, but because the last dynodes would be 
degraded, the overall gain would not be too large. This gives a better 
shot at maintaining acceptable time resolution (though likely degraded).

The amplifiers would only have to be deployed on those tubes that need 
it, likely only a few of the innermost PMT's. Hopefully, they would not 
be needed at all.

Note that we are talking here about a low-rate (10^7 photons/s) 
solution, something that will hold us for the first two years. If we 
needed to come up running at 10^8, this is clearly not a great solution.

   -- Mark

On 12/14/2011 05:15 PM, Beni Zihlmann wrote:
> 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
>>>
>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> Halld-pid mailing list
>>> Halld-pid at jlab.org
>>> https://mailman.jlab.org/mailman/listinfo/halld-pid
>>
>>
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