Charge range on tracking chambers

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

Hall D Electronics:

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