1. Humidity effects in SSD Mino for SSD 1 WRC meeting - 1/3/2011

2. ITS Ventilation machine  On Feb 19 th at 22:00 the ITS ventilation machine has been switched off for SDD injector tests  Concurrent increase of outside humidity  Effects on SSD: 5 HV trips in the following 8h (5 ladders off) Increased bias current on 20 “high current” ladders Increased noise on Sintef modules (P-sides)  On Feb 21 st at 1200 the ventilation is back Fast recovery of the ladders Mino for SSD 2 WRC meeting - 1/3/2011

3. Treated-air route ALICE Cavern CR5 Mino for SSD 3 WRC meeting - 1/3/2011 ITS Ventilation Machine ITS SSD-C sensor SSD-A sensor Pre-treated air A sideC side = RH sensors

4. Ventilation OFF: effects on humidity 4 STOPSTART  C-SIDE  Relative Humidity in the manifold before SSD  23%  38% in ~12h  A-SIDE  Relative Humidity inside the SSD barrel on the opposite side (outlet)  17%  25% in ~36h Mino for SSD WRC meeting - 1/3/2011

5. Effect of increased humidity on SSD bias current 5 A601 bias current 110uA → 280uA in 12h 280uA → 110uA in 5h ● high current on all the problematic ladders ● 5 current trips STOPSTART  C-SIDE  Relative Humidity in the manifold before SSD  23%  38% in ~12h Mino for SSD WRC meeting - 1/3/2011

6. Current-Humidity correlation Mino for SSD WRC meeting - 1/3/2011 6 Similar behaviour for all the “Sintef ladders” (~20 out of 144)

7. Mino for SSD 7 bias current and humidity seen in all normal Sintef ladders SSD meeting March’10 WRC meeting - 1/3/2011

8. Humidity Effects: on global noise ● firstly spotted in the average Noise evolution: global average Noise suppressed when Rel. Humidity < 15% ● average noise on Sintef correlated with the R.H. ● due to de-insulation effects on irradiated Sintef sensors Relative Humidity (<15% 10-18/02) P noise N noise 10feb 18feb 3 4 5 6 15 10 5 20 25 R.H. [%] noise [rms ADC] N noise P noise 4 3 2 1 5 6 noise [rms ADC] 10 3015 20 25 Relative Humdity [%] Mino for SSD 8 WRC meeting - 1/3/2011 SSD meeting March’10

9. Humidity Effects: Sintef Vs R.H. ● Noise averaged over all (active) Sintef ladders ● global noise: ~1 ADC channel gained at low humidity ● single module noise: ● @16%: P-noise down to acceptable values in many cases ● both sides generally decreasing Mino for SSD 9 WRC meeting - 1/3/2011 SSD meeting March’10

10. Conclusions Mino for SSD WRC meeting - 1/3/2011 10  Rather dramatic influence of humidity on current  Affects mostly high-current ladders (“Sintef ladders”)  Non-Sintef ladders are not affected  Keeping the humidity low (15 % on SSD-A sensor):  is beneficial for Sintef current  allows to recover ~30 modules (low noise)