1. 1 Proposal on Monitoring depletion voltage (V dep ) of the SCT sensors T. Kondo (KEK) R. Tanaka (Okayama) K. Hanagaki (Osaka) D R A F T

2. 2 Integrated luminosity expected From ATLAS-INDET-98-203 Assuming 100 days/year 10 33 cm -2 s -1 for first 3 years and then 10 34 cm -2 s -1

3. 3 Depletion voltage dependence From ATLAS-INDET-98-203 T cool = -10 ℃ T cool = -15 ℃ beam at T cool 2 weeks at T room

4. 4 Changes of V dep are expected to be quite non-uniform in SCT Full depletion voltage V dep depends on integrated Radiation dose  big r dependence history of Temperature of the bulk, not only during the irradiation, but also during beam off periods.  keep the sesnors at T cool all the time. Actual bulk temperature varies largely on the z location of the modules as well as the part of the sensor.

5. 5  >10 ℃ difference between the coldest and hottest part of sensor From ATLAS-INDET-98-202

6. 6  Possible several ℃ difference between inlet and outlet sides From B. Andree 16 June 2006

7. 7 After bulk-type inversion Applied HV must be greater that V dep because the bulk depletion starts from the non-readout side. n type p type depleted type inversion (2 – 4 years later) Detection efficiency may drop significantly if V apply < V dep

8. 8 Therefore it is important to measure V dep frequently and keep V apply > V dep for efficient SCT operation. It is noted that V dep can be obtained by measuring the noise occupancy !! V noise occupancy V dep