Re: Back of the envelope Dynamic range

[Elton Smith <elton@jlab.org>]

HI Fernando,

Thanks for the plot. We had ignored your Cdet/Camp factor of 0.5. Your
gain for the FDCs should be updated to 8^10^4. We agree that the dynamic
range is fine for the FDCs.

Curtis should comment on 1) operating gain of the CDCs (2x10^4?), and 2)
the required dynamic range. My guesstimate is factor of 10 for dE/dx and a
factor of 3 for Landau fluctuations, giving a total of 30. Linearity of
this entire range is probably not required, as even saturation would
identify slow protons. Clearly the region of linearity is most important
for the FDC cathodes which matches the dynamic range.

Thanks, Elton.




Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton@jlab.org
(757) 269-7625

On Wed, 14 Feb 2007, Fernando J. Barbosa wrote:

> Hi Elton,
>
> I made a slide which I am attaching. Please check the numbers as I show
> what a MIP in the chamber corresponds to the charge into the preamp.
>
> Regards,
> Fernando
>
> Elton Smith wrote:
> > Hi Fernando,
> >
> > Yesterday during your presentation you showed the dynamic range of the
> > preamp to saturate at 400 fC. We are a little confused about the range
> > required. I know that there was quite a bit of discussion at the time the
> > range was decided, but simple estimates give higher numbers and we need to
> > know what we are missing.
> >
> > Fernando was correct in that the induced signal on the wire on the wire
> > coming from the electron signal is only about 20% of the avalanch charge
> > (in the first say 10 ns). Therefore, we obtain the following for a minimum
> > ionizing track:
> >
> > Simon says that the gain of the FDC is about 0.8x10^5.
> >
> > assume: 100 ions, 20% of Qtot, Gain=10^5, e=1.6x10^-19.
> > Signal charge (anode) = 0.2 x 100 x 10^5 x 1.6x10^-19 ~ 300 fC
> > Signal charge (cathode) ~ 300 fC x 1/2 x 1/4 ~ 40 fC.
> >
> > My preliminary (rough) estimate concludes that this should work for the
> > FDC cathodes. The FDC anodes under the nominal design do not use the
> > FADCs, but would likely saturate if they do.
> >
> > For the CDC, the anode signal will also be used for dE/dx, so a factor of
> > at least 30 is needed in dynamic range. These would clearly saturate at a
> > Gain of 10^5, but we might want to run them at lower gain.  At G=10^4
> > gain, and 30 dynamic range, we get a maximum signal of 900 fC, also
> > saturating the preamp.
> >
> > Comments? What am I doing wrong?
> >
> > Thanks, Elton.
> >
> >
> >
> >
> >
> >
> > Elton Smith
> > Jefferson Lab MS 12H5
> > 12000 Jefferson Ave
> > Suite # 16
> > Newport News, VA 23606
> > elton@jlab.org
> > (757) 269-7625
> >
>