Dear Mike, following Francoise proposal and having a long weekend without beam, we started to perform a kicker grading measurement. However, our findings are surprising and yet puzzling to us, so we thought it might be a good time to ask for your opinion and advice. We setup the measurement as similar as possible like it has been performed last year before te MuLan run. The oscilloscope settings were restored, the HV probe is the same and grounded with the same cable and at the same position inside the kicker. In the attachment you'll find an example of one card from last year (2005-hv2-dn-01.png) and one from our recent measurement (up_01.png). The subtracted signal between the drain and the source is the orange M1. In general, we observed that the spikes at the transitions are much larger than last year. While then they had been around 7-15mV with spikes up to 30-40mV for the worse cards, we now have spikes usually in the order of 30-60mV with some cards even higher than that. The shown example is one of the worst. In addition we observe that the amplitude of the wiggles at the beginning of each transition are much more pronounced than last year. They have a frequency in the order of 50MHz. Furthermore, the baseline of our measurement is in general noisier than last year. We had a longer phone call with Francoise to ensure that we're in principal doing the same like last year. There is one major difference, namely that we ave one pump connected to the kicker tank which is pumping. We want to repeat the measurements without the pump but the strong correlation of the wiggles with the transition and the high frequency might indicate that this is not the source of this. The major question arising is, if what we see is related to the MOSFET cards and if that's a bad sign? And why is the amplitude so much stronger? In other words, are these big spikes really induced on the card itself or is this something connected with our way of measuring. Because in case of the latter these large spikes could be just an artefact of that. We already see the wiggles with the probe being inside a cabinet but not touching any card. When we close the cabinet having the probe outside we do not pickup this signal anymore. I should also mention that we already reseated all cards and optic fibres of the cabinet HV1 without any improvement. Francoise idea was to exchange one optic fibre completely to see if tht makes a huge change. We hope that you can give us some new ideas. You also might judge if this current results are consistent with the cards or optic fibres becoming worse (hopefully not) or if this rather points to some problems with our measurement. Looking forward to your answer greetings from PSI Peter
Attachment:
2005-hv2-dn-01.png
Description: 2005-hv2-dn-01.png
Attachment:
up_01.png
Description: up_01.png
