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Re: cost estimates - more questions
On Wed, 4 Apr 2007, George Lolos wrote:
Dear George,
I think we can continue this discussion during our BCAL readout
workshop end of the month like under the headline
testing and calibration of SiPMTs.
We should also list requirements for the FADC to be 100% sure all we need,
like zero suppression and so on is foreseen.
Happy easter
elke
> Date: Wed, 04 Apr 2007 22:13:15 -0600
> From: George Lolos <George.Lolos@uregina.ca>
> To: elke@jlab.org
> Cc: gen@jlab.org, halld-cal@jlab.org,
> Zisis Papandreou <Zisis.Papandreou@uregina.ca>
> Subject: Re: cost estimates - more questions
>
> Hi Elke:
>
> I should have started charging for my time...:-)
>
> Replies below, as usual:
>
> >>> Elke-Caroline Aschenauer <elke@jlab.org> 04/04/07 5:44 PM >>>
> 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$
>
>
> This is good news, indeed. Any finder's fees for me? :-)
>
>
>
> >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.
>
> The idea is that first SensL will test the arrays and verify breakdown
> voltage. They must do this to certify that the SiPM array acts as a
> limited Geiger avalanche PD and every unit will have its breakdown
> voltage recorded just like PMT manufacturers record the data sheet for
> every PMT they ship out. Therefore, we will select arrays with
> identical breakdown voltages to test and verify operation and with the
> equipment we plan to buy we can measure the gain vs V. Once the testing
> equipment is set up, like Carl has done at JLab, testing the arrays is
> neither involved nor difficult and we expect deliveries to take over a
> year or two so it's a process we can handle if we're set up.
>
>
> >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.
>
> We agree. I suspect that the gain of the SiPM arrays for a given value
> above breakdown voltage will be far more fixed than we're used from
> conventional PMT's because of the very linear avalanche multiplication
> in such small gaps. I am more concerned with FADC dynamic range due to
> the huge range in number of photons reaching the sensors as a result of
> physics processes rear to front, a fact we saw during the test beam run
> with conventional PMT's.
>
>
> >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.
>
> Sounds reasonable. In fact, thresholds can also be checked and
> established with MIP's as a fraction of energy deposition of a MIP.
> Just as a point of comparison, one P.E. in the SiPM corresponds to
> something like 26 keV energy deposited in the SciFi in the center of the
> BCAL. Since the DR of the SiPM's is essentially at the one P.E. level,
> we can easily establish a comfortable way to eliminate cells with no
> energy collection. By the way, we have simulated how many a one GeV
> muon delivers to the end of the BCAL and if I recal correctly the mean
> is around 250 photons.
>
>
> >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.
>
> I am glad to see how much we save because in my mind the cost of the
> SiPM option needs to be considered in terms of all associated costs vs a
> more conventional option, not just the cost of the sensors alone.
>
>
> >Tell me what you think about my thoughts, I hope they are not to
> st.....
>
> I'll keep silent on this one.... :-)
>
> Cheers,
>
> George
>
>
>
>
>
>
>
> > 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
> > >
> > >
> > >
> > >
> >
> > ( `,_' )+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=
> > ) `\ -
> > / '. | +
> > | `, Elke-Caroline Aschenauer =
> > \,_ `-/ -
> > ,&&&&&V Jefferson Lab +
> > ,&&&&&&&&: HALL-D 12C / F381 121-A Atlantic Avenue =
> > ,&&&&&&&&&&; Mailstop: 12H5 Hampton, VA 23664 -
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> > | | ;--' | Mail: elke@jlab.org Mobil: 001-757-256-5224 -
> > '--' `-.--. | +
> > \_ | |---' Tel.: 001-757-269-5352
> =
> > `-._\__/ Fax.: 001-757-269-6248
> -
> >
> +=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+
> >
> >
>
> ( `,_' )+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=
> ) `\ -
> / '. | +
> | `, 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 -
>
> +=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+
>
>
>
( `,_' )+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=
) `\ -
/ '. | +
| `, 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 -
+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+