Re: Charge range on tracking chambers

["Fernando J. Barbosa" <barbosa@jlab.org>]

Hi Gerard,

I agree. And a simulation would be extremely helpful.

Regards,
Fernando





Gerard Visser wrote:
> Hi,
>     I would like to point out as well, that interpreting the 
> integrated charge (x*dE/dx) dynamic range (factor of 100 or whatever) 
> directly as the dynamic range requirement of the preamp is not quite 
> correct. The preamp dynamic range of signals will surely be something 
> smaller than the integrated charge dynamic range, because a track of 
> substantial length in the CDC probably must involve a large range of 
> drift times. The ASIC has a shaping time of only ~11 ns, it will not 
> see the whole pulse at once. Eventually on the ADC board where the 
> pulse is numerically integrated, we can get a larger dynamic range 
> than the preamp chip needs to provide on an instantaneous basis.
>     Still, the factor 30 is no doubt too low as a basis for preamp 
> design. But on the other hand, the GAS-1 performance surely indicates 
> more than 30, probably ~100, is available now...
>
>     Gerard
>
> p.s. It would probably be nice if some simulation addressed this 
> issue, i.e., that would require actual simulation of CDC pulse shapes 
> for various tracks and account for the electronics response. Do we 
> have anything like that?
>
> Elke-Caroline Aschenauer wrote:
>> Hall D Electronics:
>>
>> On Tue, 18 Mar 2008, Curtis A. Meyer wrote:
>>
>> Curtis,
>>
>> that is my point 30 is for sure not enough, just from dE in the mC I get
>> 100. We need this number, because it influences the asic design and our
>> dE/dx performance.
>>
>> cheers elke
>>
>>
>>> Date: Tue, 18 Mar 2008 12:31:23 -0400
>>> From: Curtis A. Meyer <cmeyer@ernest.phys.cmu.edu>
>>> To: Elke-Caroline Aschenauer <elke@jlab.org>
>>> Cc: Fernando J. Barbosa <barbosa@jlab.org>,
>>>      Daniel S. Carman <carman@jlab.org>, Simon Taylor 
>>> <staylor@jlab.org>,
>>>      Yves Van Haarlem <yvhaarle@ernest.phys.cmu.edu>,
>>>      "halld-electronics@jlab.org" <halld-electronics@jlab.org>,
>>>      halld-tracking-hw@jlab.org, Eugene Chudakov <gen@jlab.org>
>>> Subject: Re: Charge range on tracking chambers
>>>
>>> We are now trying come up with a number, but I would guess that 250 
>>> is a better
>>> factor for the CDC if we consider the path-length variations over 
>>> angles.
>>>
>>>    Curtis
>>> On Tue March 18 2008, Elke-Caroline Aschenauer wrote:
>>>> Hall D Electronics:
>>>>
>>>> On Mon, 17 Mar 2008, Fernando J. Barbosa wrote:
>>>>
>>>> Dear Fernando,
>>>>
>>>> the CDC I think needs more a dynamic range of 100. if you look to 
>>>> the dE
>>>> under 20^o and under 90^o comparing pion DE and proton dE you get 
>>>> without
>>>> modelling any fluctuation a factor of 30, If you take fluctuations 
>>>> into
>>>> account you come closer to a factor 100.
>>>>
>>>> So I think that is what we should be able to cover a factor 100 in 
>>>> dynamic
>>>> range.
>>>>
>>>> Eugene I have a question for you, how big of a problem is a 
>>>> non-linearity
>>>> in the cdc detector response for the dE/dx performance.
>>>>
>>>> cheers elke
>>>>
>>>>
>>>>> Date: Mon, 17 Mar 2008 22:02:12 -0400
>>>>> From: Fernando J. Barbosa <barbosa@jlab.org>
>>>>> To: Elke-Caroline Aschenauer <elke@jlab.org>
>>>>> Cc: Daniel S. Carman <carman@jlab.org>, Simon Taylor 
>>>>> <staylor@jlab.org>,
>>>>>      Curtis Meyer <cmeyer@ernest.phys.cmu.edu>,
>>>>>      Yves Van Haarlem <yvhaarle@ernest.phys.cmu.edu>,
>>>>>      "halld-electronics@jlab.org" <halld-electronics@jlab.org>,
>>>>>      halld-tracking-hw@jlab.org
>>>>> Subject: Charge range on tracking chambers
>>>>>
>>>>> Hi Elke,
>>>>>
>>>>> Document 747 on the portal shows the charge deposited on the CDC 
>>>>> and FDC
>>>>> detectors. These numbers were first estimated for the Electronics 
>>>>> Review
>>>>> in July 2003 and were based on geometrical constructs only. You 
>>>>> can find
>>>>> a brief summary on slide 22 (a back-up slide) of my presentation 
>>>>> for the
>>>>> Hall D Drift Chamber Review of 6-8 March 2007, document 751. Anyway,
>>>>> these numbers have not changed in years....
>>>>>
>>>>> For the CDC, the dynamic range is shown to be 100 fC - 3 pC - a 
>>>>> factor
>>>>> of 30. Because the charge amplifier has a peaking time of about 11 
>>>>> ns,
>>>>> the dynamic range of the preamp would be about 400 fC for point
>>>>> ionization (~13% of total charge). The gain of the preamp would 
>>>>> then be
>>>>> ~ 1000 mV (a reasonable maximum amplitude to expect from a 
>>>>> preamplifier)
>>>>> divided by 400 fC times a factor to allow for some headroom before
>>>>> saturation, say 80%. The result is 2 mV/fC.
>>>>>
>>>>> Similarly for the FDC, the dynamic range for the anodes was 
>>>>> estimated to
>>>>> be 300 fC - 3 pC, a factor of 10. For the preamp, 400 fC for point
>>>>> ionization and 2 mV/fC for gain.
>>>>>
>>>>> For the FDC cathodes, the dynamic range was estimated to be 10 fC - 1
>>>>> pC, a factor of 100. For the preamp, 133 fC for point ionization 
>>>>> and 6
>>>>> mV/fC for gain. Note that here, the estimate presumed a 1/3 of the
>>>>> charge of the anode on the cathode (charge sharing on adjacent 
>>>>> strips).
>>>>> Later, it was decided that this number needed to be changed to 1/5 
>>>>> based
>>>>> on published data. For the preamp, the point ionization was then
>>>>> estimated to be 80 fC and 10 mV/fC for gain.
>>>>>
>>>>> According to these estimates, the CDC and the FDC anodes require the
>>>>> same gain (2 mV/fC) and the FDC cathodes require x5 gain or 10 mV/fC.
>>>>>
>>>>> Obviously, this numbers must be updated to reflect the physics 
>>>>> events in
>>>>> the detectors. I hope this helps.
>>>>>
>>>>> Regards,
>>>>> Fernando
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