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Humidity effects in SSD

During the WRC meeting on March 1, 2011, we discussed the significant impact of humidity on the performance of SSD systems, particularly related to the ITS ventilation machine. After the machine was switched off for injector tests on February 19th, external humidity levels rose, leading to increased bias currents, noise levels, and HV trips. The observed effects included a rise in relative humidity from 23% to 38% in the manifold and a notable increase in bias current of high-current ladders. Keeping humidity low yielded benefits to SSD performance, enabling a recovery in module functionality.

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Humidity effects in SSD

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

  2. ITS Ventilation machine WRC meeting - 1/3/2011 • On Feb 19th 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 21st at 1200 the ventilation is back • Fast recovery of the ladders

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

  4. Ventilation OFF: effects on humidity STOP START • 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 WRC meeting - 1/3/2011

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

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

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

  8. SSD meeting March’10 Humidity Effects: on global noise • firstly spotted in the average Noise evolution: global average Noise suppressed when Rel. Humidity < 15% 6 noise [rms ADC] P noise 25 R.H. [%] Relative Humidity (<15% 10-18/02) 5 20 15 4 10 N noise 3 5 10feb 18feb P noise noise [rms ADC] 6 • average noise on Sintef correlated with the R.H. • due to de-insulation effects on irradiated Sintef sensors 5 4 3 N noise WRC meeting - 1/3/2011 2 1 10 15 30 20 25 Relative Humdity [%]

  9. SSD meeting March’10 Humidity Effects: Sintef <Noise> 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 WRC meeting - 1/3/2011

  10. Conclusions • 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) WRC meeting - 1/3/2011

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