[Halld-tracking-hw] New preamp

[Fernando J. Barbosa]

Hi Naomi (and Yves),

Naomi Jarvis wrote:
> Hi Fernando,
>
> I have put some more preamp output (after the shaper) pictures online 
> at http://www.jlab.org/Hall-D/software/wiki/index.php/Preamp_3

The pictures for the new preamp, at 2000V for Fe-55 and cosmics are 
exactly the same - maybe cosmics?

>
> For the gas mixture 50/50 Ar/CO2 with the 55Fe source, the preamp 
> output is saturating before the working voltage of the chamber is 
> reached. At 1900V it looks fine but there is some saturation shown at 
> 2000V and a lot at 2100V. I also looked at this using the old preamp, 
> which did not show any saturation. Yves's earlier work (using the old 
> preamp) determined that the working voltage for that gas mix should be 
> around 2000 to 2100V, so this is causing some anxiety. It looks like 
> the gain of the new preamp is approximately 1/3 of that of the old 
> preamp. The signals are no longer bipolar. (Also I think the later 
> signals after 500 ns are probably due to a delayed avalanche from the 
> cathode following Ar+ recombination.)

The old preamp had a gain of 1.5 mV/fC and a dynamic range of 400 fC; 
the new one is 0.75 mV/fC. The attenuation of 18m of cable is 0.57 and 
the shaper gain is 2.16. Looking at the first set of pictures (1900V), 
the middle picture shows an amplitude of 500 mV or 270fC of input charge 
on the old preamp; the picture on the right shows an amplitude of 300 mV 
or 325 fC of input charge on the new preamp - this is beyond the linear 
dynamic range of the preamp with the nominal settings. If you look at 
GlueX-doc-1364, table 2 shows a linear range of 260 fC for the nominal 
settings (first row). In this case, the preamp is not saturating but it 
is not linear. This may explain, in part, the shape of the pulse.

At 2000V, the new preamp shows a markedly saturated behavior at an 
amplitude of 500 mV (~flat top) or >540 fC of input charge. This is way 
beyond the dynamic range of the preamp. The best dynamic range 
configuration is shown on table 2, second row, with a gain of 0.57 and a 
dynamic range of 380 fC. I can send you another preamp with this 
configuration but it will be saturated at 2000 V also. I suggest you 
determine the plateau with the new preamp for confirmation. You may need 
to change the gas mixture, maybe to 40Ar/60CO2, and get the detector 
within the operating range of the preamp.

>
> When going over the draft of the cable assembly two points caught 
> attention:
> - page 2/6: no color is specified or it is not readable on page 6 for 
> the 5 different cable types. We do not care as long as the CDC is 
> green or pink :-)
> - page 6: on the right side the orientation of cable and connector is 
> indicated and clear but on the left side it is not clear where the 
> conductors need to be soldered to - maybe it is mentioned but on the 
> copy we have all text on page 6 is unreadable.

I have attached another copy of the cable specs and you should be able 
to read the pdf in very fine detail.

Section 3, page 6/17 shows the colors of the labels. Sorry, the CDC has 
no color specified for the label, green is already assigned and I am not 
aware of pink heat shrink. If you insist, I can assign you the green.;-)

On this same page, the connector on the left (3M) has the wire numbers 
shown; the connector on the right (ERNI) only needs the red stripe for 
orientation as this is an IDC connector.

Thanks for the feedback and let me know if you want me to send you 
another preamp configured for wider dynamic range as stated above.

Best regards,
Fernando

>
> Best regards,
>
> Naomi (and Yves).
>
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