• a TOF between MCP (start)-Anode (Stop). Here, the typical temporal resolution is around 450 ps FWHM. I wrote a "self calibration program" which determines the center of the TOF (with gaussian model) for each channel. From this one could expect to achieve 300-200 ps in real experiment.
• the distribution of the hit on the DS16. The purple dots are for the regular lines and the red for the mirror image lines: A->B, C->D, E->F,G->H. The strong irregularities are mostly due to a to high discriminator threshold or too low gain on the MCP.
• the hit distribution in pixels underline this assumption. Since I cannot go higher than 2200V through the plate without noise 100Hz, it is hard so far to do anything better...
• the resulting image

As we can see, one main problem is that many DS16 channels are never answering. Thus this morning I checked the termniation of the DS16 (50 Ohm). Most of the channels are around 51.4+/- 0.3 Ohm, some at 49 and have been marked with a yellow tape. Unfortunatelly, the card A present a lot of channels with 80 Ohm. After a final test with the pulser, this card stoped to work !! Damned....

During the afternoon, I did some double checked the data of friday with little different voltage configuration:

• front MCP - 2100 V
• rear MCP +200 V
• anode +250->700 V

I cannot use the gage on since it just localized all the hits in the center of the detector, and does not give an average effeciency. At 550V a second peak (wings) with 5 pixels start to appear, the time of flight is pretty symmetric a small step at short time of flight. At 600 V, the time of flight is perfectly symmetric, but the MCPs behaved very strange, up to 10 kHz noise, then went down to a few Hz...mmm… Back to 550V and I increased rear MCP.

At higher MCP voltage the picture got more homogeneous … For a strange reason the count rate is stable around 30 Hz, but the acquisition program is unstable ? memory leak … While I was checking the code, the signal of the oscilloscope has started to behave strangely much too large, and many mutli-hits. However, the count rate was stable somewhat a little lower: 10-20Hz. Since, I suspected something really abnormal, I checked everything and found that the current went up to 80-90 micro amp, again ! Why do these bloody MCPs not work normally, I cannot reach more than 2.25 kV through the plate ?

When I tried to increase step by step (100 V per 100 V) the voltage up to 2200 V through the plate (the ion gage is always off when I ramp up) , the dark count rate started to increase up to 1kHz or more… I quickly went down to 1800 V, but the current was twice higher. This meant that there was a drop in resistance down to 20 MOhm. It may be due to current leak through the plates ?.... Anyway I let it on for a while at 1800V until everything was normal...I ramp up again, and point out a limit (see arrow in the picture) where the problem started and I took a picture of the pulse shape. I continued to work for a while close to this limit at least to check the signal on the anode.

There was a terrible noise when the acquisition system started. The acquisition system was frozen around 1kHz or less. After one or two hours to understand where the noise was coming from, it turned out that it was necessary to avoid the NIM-bin as much as possible and to feed directly the MCP signal into the DS16. Hence, we directly got in ECL format the MCP signal and we used the level translator to have a trigger. Doing so, it seemed to avoid ground loup or antena effetcts and we could get the acquisition system working up to 25 kHz. A short study of the image with the gage on, as a function of the MCP voltage is done. In the table we give the number of events as a function of the MCPs voltage. At 2300 V the gain is enough for the MCP signal, but on the anode we still get a better hit distribution 3 pixels at 2400 V (around 2200 V through the plates).

One should try to user a little higher voltage but there was a software bug… memory allocation problem due to some FIFO full??? In any case the distribution of the hits on the DS16 looked the same than yesterday. The signal on the cards A, B, E, F, G, H was about the same intensity which is much better but the distribution was still very chaotic… In the rush before leaving, I checked with a pulse generator whether some DS16 channels were dead. Hopefully everything is fine, but I should double check !! Is it a real physical signal ?.... It could be because A & B looked mirror image as well as E-F & G-H