1. Noise on chambers M1R4
N.Bondar

2. Chamber M1A4D
Noisy and good channels
RMS 19.15
RMS 3.76
45 ru
18 ru
Total we have noisy chambers 32 on A-side and 18 on C-side

3. The noise origin on chambers M1R4
Electrical circuit of the chamber (simplified)
Internal HV filter
SPB
+HV
RET
GND
100K
8Ohm
0.1K
2.2N
680pF
HV signal by oscilloscope
20ns
Amplitude 50mV
Any HV level
5us
Parasitic signal is produced by switching DC-DC convertor .
There are two options for understanding why we have noise only for some chambers:
- Different level of parasitic signal due to parameters variation
- Wrong filter inside the chamber or poor connected

4. The noise on chambers M1R4
Proposed solution to fix the problem –
additional filter on the output of the power module.
Each filter has 4 identical channels .
The filter prototype has R1=R2 = 470K, C1=1nF R1 R2
+HV
RET
GND C1 J1
Jumper J1 I used to understand where capacitors C1 should be connected.

5. The noise on chambers M1R4
The filter prototype used for tests.
Resistors hidden inside the shrinkable tubes

6. The noise on chambers M1R4
Result of testing filter installed on the CAEN HV module .
Chamber M1R4D FEB 0
RMS results under different conditions
I2C 1 DIALOG 0
Ch Thres Rate(KHz) Mean RMS 1 2 3 4 6 5
RMS
3.2
4.61
2.39
3.45
2.34
3.23
2.3
3.16
2.6
3.46
3.21
3.48
3.76
3.03
RMS
3.18
4.91
2.33
3.76
2.58
3.19
2.59
3.47
3.45
2.64
3.17
3.75 3
RMS
3.55
4.91
2.75
3.76
2.58
3.2
2.59
3.47
3.45
2.63
3.17
3.75
3.46
2.99
RMS
3.54
4.91
2.91
3.75
2.59
3.76
3.47
2.58
3.77
2.64
3.52
4.05
4.33
3.17
RMS
3.55
5.19
2.9
4.03
2.58
3.76
2.59
3.47
3.77
2.63
3.75
4.05
4.33

7. The noise on chambers M1R4
Conditions:
No filter
Filter installed on chamber, Return and GND connected together on chamber
HV on M1 filter on CAEN .Return and GND connected together
HV on M1 filter on CAEN . Return and GND separated. Capacitors connected to GND
HV on M1 filter on CAEN . Return and GND separated. Capacitors connected to Return
6 HV on M1 filter on CAEN . Return and GND separated. Capacitors connected to Return

8. HV-training Oleg 150 CMBs to be trained in WS
~40% done – work on A-side now
CMBs on M5R3-M5R4 are seriously polluted after LS1:
- current at negative polarity appears even below 1kV sometimes
- removing takes up to few weeks