CDC old preamp then and now

This post is a comparison of how our OLD preamplifier behaved more than 4 months ago versus how it (the OLD one) is behaving now. The only conclusion that one can draw is the our OLD preamp bit the dust.

Comparing old and new runs with the old preamp. The pictures below show ADC amplitude histograms for first Fe55 and then tracked and untracked cosmic ray data with 50/50 Ar/CO2 gas mixture (the maximum ADC amplitude for each event contributes one entry for that amplitude in the histogram) and energy spectra obtained by integrating the amplitude histograms. Full ADC range is used.

Its gain has gone up by at least a factor of 4 and there is substantial noise beyond what we used to observe. In the top-right plot below, the peak at channel ~800 is this new noise which is seen as an oddly-shaped 200-mV pulse.

That all said, what it implies is that the comparison measurements that we took (recently) between the old preamplifier and the new one are not meaningful. Because the old one is no longer performing correctly, it makes no sense to compare the new preamplifier with it.

This means that we need to go back to the data that were collected (as input to our paper) to make comparisons. There, we only have Fe-55 at about 2100 V, which was saturating the old preamplifier and would be so off scale in the new one, that no comparison makes sense.

We do have cosmic data at a number of settings with the old preamplifier from before, and all of these show that the gain of the new preamplifier is larger than the old one. We are now undertaking a set of measurements to determine the efficiency curve (vs HV) for the new preamplifier. We already know that it needs to run at least 200V lower than the old one, but we will get the correct operating point and then try to determine if the dynamic range is sufficient for the CDC.

It would also help if there were another old preamplifier that we could use. It would allow us to make the Fe-55 measurements which can be more directly compared. Thus, our request for an old card.

2100V - Fe55 - amplitude, old preamp, 2009 (left) and 2010 (right)