Noise studies: hardware tests and preliminary results Anna, Anton, Giovanni, Pigi, Silvia, A. Boiano, A. Vanzanella

2 Outlook Hardware tests done Cable shield modification First results Future check and tests

3 LV Test done We tested all the 960 LV channels finding 3 different kind of malfunctioning: –A “wrong” impedance between the common “reference ground” of the board and the negative of the LV channel. –A noise at 150 KHz (switching frequency) of about mV, higher than the typical ripple of about mV. –An expected noise at 15 KHz (primary freq. ?) of about 100 mV 8 LV boards have been fixed by the CAEN at CERN in one day (short found) The HV modules are OK.

4 LV Test done The noise at 150 KHz have been measured on the board between the negative/positive pole and the reference ground of the board  NOTE: not between the 2 poles. The same noise has been measured on the LV cable (chamber side) A custom filter was able to reduce both the components of the LV ripple but did not reduce the measured noise on the chamber.

5 Noise Tests on the chamber Then we focused our work on the selected chamber equipped with the following instrumentation: –Scope with a differential probe connected to the output of a FEB channel. –Noise generator with clamp (max PP voltage of 10 Volts) –Lamp to generate external noise (frequency and amplitude not defined) We measured the noise on 3 different points: –between the chamber chassis and the magnet iron (chassis). –between the chamber chassis and the LV negative pole (LV). –looking (differential probe) at the LVDS signal coming out from the FEB (FEB).

6 Noise Tests on the chamber Correlation between the lamp and the FEB output LV ripple on the chamber side

7 Tests with clamp Noise signals generated with a clamp is seen by the cable reduced of a about factor 10 (number of spirals of the clamp) and so 1 Volts was less than 100 mV and 10 Volts about 300 mV. Square wave (freq. 15 KHz) has been used to have a large set of frequencies. The signal is seen by the cable as a fast rise time signal The inductance (nH) of a cable junction depends on the length (mm) and the diameter (mm). The inductance of the junction goes from 255 nH to 16 nH reducing the length from 200 cm to 2 cm, showing a very big improvements in the ground connection of the shield. It is also possible to calculate the lifetime t (nsec) of the signal considering the estimated impedance of the cable R (ohm) and the inductance of the junction H (nH). The lifetime goes from 4,25 nsec to 270 psec reducing the length from 200 cm to 2 cm.

8 Rate with the new chamber config.

9 Chamber restyling All the RB1 and RB4 of the wheels W+2 and W- 2 have been modified from the 16 to the 27 of May. Just few chambers shown a unusual noise in the few monitor runs taken before the 16 th. A clear improvement has been seen in two noisy chambers, but the statistic in not enough and the sparking noise is not easy to reproduce and detect. Unfortunately the runs have been taken in different conditions (HV ON and during the day) and without a clear strategy. We can do more.

10 To be done LV trigger board test (this week) Take monitor data during the night and with HV OFF. Answer to 2 important questions coordinating data tacking and results: 1.Do we have sparkling noise during the data tacking ? 2.Does the chamber ground restyling useful ? LV filter studies. RB3 tests in Sofia.

11 Conclusions The ripple at 150 KHz of the LV power supply (max 200 mV) has seen on the chamber side and it is almost evident that it is not able to generate noise on the FEB (any event has been detected). A LV filter on the chamber side can easly reduce it. The external noise (lamp or clamp) is picked up at the chamber level (cable and strip) and not by the LVDS cable or Link Board. –The mechanism is under studies but is almost clear that the noise clamp type produce an oscillation in the FEB ground that generates FEB output signals. The spark/lamp noise type should be captured by the strips and his strength depend on how far the noise generator is from the chamber. A much better connection of the chamber to the ground and of the cable shield to the ground can be easly obtained reducing as much as we can the length of the junction. The restyling done on the W-2 Sect10 RB4 chamber was able to mask the chamber up to a noise of 10 Volts generated with the clamp on the cable (before it was around 3-4 volts).

12 Conclusions The noise was much higher until 16:00 Most of the tests have been done after 16:00 in order to compare the results. After the 16:00 we have not observed any spark unless the one generated by ourselves with the lamp. Noise generated with the clamp on the HV cable was not able to trigger FEBs. The noise measurements in real time was not easy to do (software should be improved)