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Re: cost estimates - more questions
Dear ElKe and George,
I have been folowing this exchange of mails and my colleagues and I would
be very interested in participating in the read-out workshop since we have
spend quite few months thinking and working on it.
By simulations of the shower profiles, which were performed in Athens as
well, we concluded in a Document submitted few months ago that 210
channels for the outer section are more than enough (Doc 731-v1) and
moreover we recommended for these the use of finemesh PMT's.
I have the feeling that if we go for SiPM's in the inner layer .it is
reasonable to use conventional PM's at the outer.And from the B-field
measurements,I find that fine-mesh are far more superior in their
(non)-sensitivity than Planacons.
Please keep this document and the relative option in the loop.
Cheers,
Christine
> On Wed, 4 Apr 2007, Elke-Caroline Aschenauer wrote:
>
> Dear George,
>
> sorry more questions, hopefully not to stupid ones.
>
> But first the good news removing discriminators and tds from the outer
> calorimeter saves 240000k$
>
> I know you are planning for a test stand for the sipmt-arrays.
> If we go with the LV distribution version ala ILC, to apply the correct
> resistor for each sipmt-array we need to know the bias corresponding to
> certian gain like 1*10^6 befeore building the distribution chain.
> Have you been planning on measuring the gain vs bias for the arrays in
> your test stand. This can be quite an effort.
>
> Even if we put the gain correction factors in the flash, we might want to
> start from a rougly equal distribution to not loose to much dynamik range
> of the fadc, so it would be good to have the measurement.
>
> For the rest we can actually nicely monitor gain changes with time with
> the response for minimum ionizing particles and can account for them in
> the fadc
> to have a good trigger input.
>
> Go this route we will safe 600000 k$ on HV-boards, of course building the
> distribution system cost something and the test stand to measure gains vs
> bias voltage.
>
> Tell me what you think about my thoughts, I hope they are not to st.....
>
> Cheers elke
>
>
>
>
>
>
>
>
>
>> Date: Wed, 4 Apr 2007 19:01:25 -0400 (EDT)
>> From: Elke-Caroline Aschenauer <elke@jlab.org>
>> To: George Lolos <George.Lolos@uregina.ca>
>> Cc: halld-cal@jlab.org, Eugene Chudakov <gen@jlab.org>,
>> "zisis@uregina.ca" <zisis@uregina.ca>
>> Subject: Re: cost estimates
>>
>> On Wed, 4 Apr 2007, George Lolos wrote:
>>
>>
>> Hi George,
>>
>> thanks for the quick answers, they help me quite a bit. I have some
>> remarks below.
>>
>> >
>> > Hi Elke:
>> >
>> > I will try to address the questions individually, below:
>> >
>> >
>> > Elke-Caroline Aschenauer wrote:
>> >
>> > >Dear George and Zisis,
>> > >
>> > >by trying to come up with the final numbers for the budget, we over
>> run by
>> > >2M$ in procurement and an other 1.5M$ worse of manpower some
>> questions
>> > >came up.
>> > >
>> > >And please don't count any of my questions as an attack against
>> SiPMTs or
>> > >the bcal or ....
>> > >I only try to get numbers straight and answers to unpleasant
>> questions
>> > >which will come.
>> > >
>> > >
>> > Come now Elke, it's only money and it's other people's money :-)
>> ........
>> >
>>
>> hmhm, my tax money goes somehow in, but it is good spent on a FADC for
>> the
>> bcal, so indeed I don't worry to much about it. :)
>>
>>
>> > >1. do we really need CFDs for the outer barrel, what is the advantage
>> for
>> > > the TOF
>> > >
>> > >
>> >
>> > Not at all. In fact, in my logic that I had expressed in a couple of
>> > reports earlier, was that CFD's only make sense for the first few
>> inner
>> > layers where charged particle and critical photon reconstruction
>> > information is derived from. It makes no sense, whatsoever, to
>> > instrument all channels with CFD's. If we go with flash ADC's, all
>> the
>> > other channels past the first 5 layers don't even need TDC's.
>> >
>> perfect, so I asume no cfds and tdcs for the outer barrel.
>>
>> >
>> >
>> > >2. currently we instrument the bcal with 4224 channels SiPMTs 1920 in
>> the
>> > > inner and 2304 in the outer,
>> > > we say we combine 2 channels in the other for the electronics so
>> we
>> > > have
>> > > 1920 + 1152 channels of CFD (100$/ch), F1TDC(100$/ch) and FADC
>> (250$/ch)
>> > > of course combining things even more in the outer BCAL, will safe
>> > > money, but of course and I know we don't have a good answer yet
>> what is
>> > > possible.
>> > >
>> > >
>> >
>> > The number of 1920 corresponds to five inner layers. I feel
>> > uncomfortable if we base all our photon trajectory reconstruction on
>> > five layers only. Maybe I am overly conservative but perhaps adding a
>> > sixth layer to bring us to a 12 cm individually instrumented depth, is
>> > something we may wish to consider. This is a minor point and we will
>> > need serious MC simulations to see what we lose or gain, if any.
>> >
>> > As one can see from the energy deposition profiles we have simulated
>> for
>> > the BCAL, even for a 1 GeV photon entering perpendicular to the BCAL
>> (a
>> > situation as limiting as it gets) the number of photons collected past
>> > 15 cm depth is much smaller than what has been collected between 4-12
>> > cm. If we combine every two read-out cells in the outer layers we
>> will
>> > certainly not lose trajectory information because most photons of some
>> > energy to penetrate that deeply will also come at forward angles,
>> > predominantly. In fact, past 16 cm depth or so, in other words past
>> > the eighth cell from the inner face, even four cells combined will
>> most
>> > likely not degrade us at all. When we meet for the SiPM workshop, I
>> > will show all these profiles and I will also send them to you by the
>> end
>> > of the week, I hope, so we can discuss this with more info in front of
>> > all of us.
>> >
>> > The bottom line is that combinations of two and/or four can be done
>> and
>> > should be pursued not only for cost savings but for simplicity of data
>> > handling as well. For the layers past 15 cm, there will be so few
>> > photons per cell most of the time, we are wise to combine outputs of
>> > four cells.
>>
>>
>> okay, lets stick with for the moment until we have more simulations,
>> with
>> excha channel a Fadc in the outer and combine 2 for the inner.
>>
>> >
>> >
>> > >3. now the LV for the SiPMTs, we need bias voltage LV<50V and 10-20
>> nuA/ch
>> > > the questions to answer are do we need in individual bias for each
>> > > SiPMT array?
>> > > if no how many can we combine, are there measurements which show
>> gain
>> > > for several individual SiPMTs?
>> > > If we could combine LV-channels what is the granularity? do we
>> need
>> > > a resistor change to correct for different bias voltages needed,
>> do the
>> > > gains change with time, so we have to adjust the adjustments.
>> > >
>> > >---> I know that are a lot of questions and I appreciate answers are
>> very
>> > > difficult to give but the LV is worse 4224*150=634k$
>> > >
>> > I had answered this question already to Fernardo, I think. The answer
>> > is we don't need to control the voltage to each array. The process
>> > developed by SensL is such that the variations in breakdown voltage
>> > between different batches of Si wafers is less than 1 V and the real
>> > range of variation is closer to 0.1- 0.2 V. So, the idea is that we
>> > select arrays with breakdown voltage within that small tolerance level
>> > and we control them with a common supply voltage. I suspect that we
>> > will have a large number of arrays, each requiring the same voltage,
>> but
>> > we clearly have to limit the number per P/S for other reasons. Each
>> P/S
>> > will be identical to all the rest with only a very small adjustment
>> > range of say 2V. How may we will need? I think this is a question of
>> > the electronics guys to tell us based on current and stability
>> > requirements. The ILC group at DESY has developed such systems for
>> the
>> > thousands of 1 mm2 SiPM's they use and with much greater voltage
>> > adjustment requirements, can't we get some info from them on their
>> design?
>> >
>> > If we can control 16 arrays per P/S, then the number drops down to 264
>> > and I believe we should eb able to drive 16 arrays for each, right?
>> By
>> > the way, the SensL arrays are more in the 30 V range not as high as 50
>> V.
>> >
>>
>> I know that the breakdown voltage is only around 30V, but 50V as max
>> will
>> not make a difference in the cost and is a nice number.
>> But let me ask some more questions. I know you said the breakdown
>> voltage is very similiar for sipmts with production process sensl wants
>> to use. No problem I can accept this, but if you use this to combine HV
>> channels you make the implicit assumption that there is a 100% direct
>> connection betwen the breakdown voltage and the gain of a SiPMT. Do we
>> know this as a fact. I know you are aware of this but we cannot
>> tolerate to big differences in gain because of the trigger. Or we put a
>> gain correction factor in the FPGA of the FADC, to apply a gain
>> correction
>> before the summing.
>>
>> I can ask chris this is an option.
>> I agree with you that you can build a distribution system which takes
>> care about small channel to channel variations, and if we can apply gain
>> factors in FADC even different time constants in ageing are to relevant.
>> The only open question would be the effect on the TOF performance.
>>
>> I will ask at DESY to see what their experience is also they have
>> studied
>> the variation in gain for different SiPMTs with the same bias voltage.
>> I keep you in formed, what I find.
>>
>> > >
>> > >4. there is also the question where to but the cfds and where to do
>> the
>> > > summing. Cables are also an issue.
>> > > If we would but the CFDs next to the SiPMTs we need double the
>> amount
>> > > of cables 8000 instead of 4000, I think that is not an option,
>> summing
>> > > the outer BCAL channels by 2 directly next to the SiPMTs will only
>> safe
>> > > 1000 cables.
>> > > ----> so I think we have to put the CFDs after the cables
>> > > ----> comments
>> > >
>> > >
>> > With the outer layer SiPM arrays combined in two's and/or four's, we
>> > don't even want to use CFD's but we certainly want to discriminate
>> them
>> > since most of the cells will add zero signal but will contribute DR
>> > P.E.'s. This discrimination can happen after their combination at
>> some
>> > level, say 10 P.E.'s (about 260 keV in energy deposition). For the
>> > inner layers is there such a problem with cables? If yes, then we can
>> > indeed discriminate them when the analog signal cable reaches the
>> > electronics racks.
>> >
>>
>> ups, here you lost me. If I don't use the outer bcal for tof, I also
>> need
>> any discriminator on it or do I miss something. The FADC of course would
>> is untouched.
>>
>>
>> I will implement the changes for the cfd's and also the f1tdc.
>> For the LV I would like to see what they say at DESY.
>>
>>
>> Cheers elke
>>
>>
>> > I hope I have answered most of them in an informative way,
>> >
>> > Cheers,
>> >
>> > George
>> >
>> >
>> >
>> >
>>
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>> | `, Elke-Caroline Aschenauer =
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>
> ( `,_' )+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=
> ) `\ -
> / '. | +
> | `, Elke-Caroline Aschenauer =
> \,_ `-/ -
> ,&&&&&V Jefferson Lab +
> ,&&&&&&&&: HALL-D 12C / F381 121-A Atlantic Avenue =
> ,&&&&&&&&&&; Mailstop: 12H5 Hampton, VA 23664 -
> | |&&&&&&&;\ 12000 Jefferson Ave +
> | | :_) _ Newport News, VA 23606 Tel.: 001-757-224-1216 =
> | | ;--' | Mail: elke@jlab.org Mobil: 001-757-256-5224 -
> '--' `-.--. | +
> \_ | |---' Tel.: 001-757-269-5352 =
> `-._\__/ Fax.: 001-757-269-6248 -
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