CMS FPIX Reinstallation/Commissioning

Lorenzo Uplegger

4/20/09 1

ScheduleMonday Tuesday Wed. Thursday Friday Saturday Sunday

2-8 Mar +Z extraction and transportation

9-15 Mar + Z: Tubes / AOH / Rear foot / Baseline check / Full re-test

16-22 Mar

– Z extraction and transportation

23-29 Mar

– Z: Repair / Tubes / AOH / Rear foot / Baseline check / Full re-test+ Z Re-test / Survey

30 Mar 5 Apr

+Z packing / transport

+ Z insertion (2 days) -Z Re-test / Survey – Z

packing / transport

6-12 Apr – Z insertion (2 days) Detector CheckOut Easter brake!!!

13-19 Apr

Last CO day! CMS +Z START CLOSING!

Very tight schedule ( a little bit more than 4 weeks!!!!) to extract, cross a border, repair, improve, recheck a detector!4/20/09 2

Motivations

Silicone tubes have been used inside the forward pixel detector to make the connection between the Aluminum pipes and the Half-Disk hose barbs

They needed to be replaced with more robust tubes

•Old Silicone tubes are rated up to 1.7 bars•New Silicone tubes are rated up to 10 bars the limit will be set by something else. We will be able to run at 2.4 barg instead of 1.9 barg (big difference in terms of effectiveness of establishing flow)

1. Replace the Silicone tubes with new tubes rated up to 10 bars

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Motivations2. Fix 6% of the detector which broke during operations at P5

• During the July transportation/insertion 1 high voltage wire-bond was broken and we lost immediately one module with 8 Read-Out Chips (ROCs) (<1%)

• After 1 week that the detector was inserted last July a short developed on a power lineinside the half cylinder making impossible to operate 1 petal of the detector whichhas 135 ROCs (~3%)

• After 1 month from the insertion we had another short on a high voltage line which involved 93 ROCs (~2%)

• A little bit later the last incident another module started to give a low signal on theoutput line making it impossible to operate 24 ROCs (~0.5%)

We were eager to understand what was going on and especially we wanted to knowas soon as possible if there was a design flaw that could lead to many more problems!

Unfortunately, all these problems happened on the –Z side (the +Z side was still perfect)and the schedule forced us to extract the +Z side first, giving us little time to interveneon both sides in case all these problems could be the sign of something major. Luckily, that was not the case!4/20/09 4

5

• We wanted to put a “Cold Finger” to perform a thermal contact between the optical laser diodes and the cooling pipes in order to better stabilize the

temperature and thus the analog output signal during operations.

• The humidity reading at P5 has been difficult to interpret !We convinced ourselves that when the magnetic field was turned on, due to some movement caused by the field, the pixel volume was not sealed anymore. This would prevent us to run the detector below -8 on +Z-side and below +2 on the –Z-side. This problem will be addressed by the CERN experts but, to make sure we understand correctly the humidity in the pixel volume, we wanted to replace the humidity sensors and place them in a different position to have more reliable dew point measurements.

Motivations3. Operational stability and humidity monitor improvements

Replacing the silicone pipes, understand and repair the problems with the detector,improve the humidity reading and the stability of the output signal

HAD TO BE DONE IN 1 MONTH!No mistakes were allowed and a careful planning had to be done!!!4/20/09

Extraction

Pixel platform

Pixel table

Base frame

The pixel system has been designed toallow extraction in case it needs to be repaired during the shutdowns!

The concept worked really well!

We also practiced procedures and methodsfor future removal when the detector willbe irradiated and time constraints will beimportant to minimize the exposure to radiation!

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Repair/Commissioning

1. The first 10 days we worked on the +Z side. The silicone tubes were substitute,the cold fingers were placed and the humidity sensors where changed.Both half cylinders were then re-commissioned and almost ready to go back to P5, in the mean time everybody was waiting for the –Z side to understand what was going on there…

2. As soon as the –Z side was back at CERN we all wanted to know what were the problems andwe found out that the power cable in the damaged half cylinder were damaged under

Damagedwires

a heat shrinking plastic placed to keep togetherthe cables of each petals!We removed all the heat shrinking plastic from all the wires, check them to see if there wereany other wires damaged, measured the resistance of all the cables and re-made theones that were not passing a very tight resistance criteria and then re-test them all!

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Repair/Commissioning

3. We then re-tested the +Z side after the cables checkout to have it ready for the P5 reinsertion, while in the mean time we were still working on the –Z side!

4. We realized that the high voltage problem was due to a wire that was pinchedby a board inside the half cylinder that with time developed in a short and we fixed it!

5. We substituted the module with the broken wire-bond.

5. Finally we tried to tackle the last problem of the module that had a very low output signal.Unfortunately this problem appear only in a certain temperature range ( very strange! ) andsince the module is in a delicate position we decided to leave it as it is (~0.5%of the detector).It should work when we’ll go to low temperature!

7. We shipped and reinserted the +Z side while we were still re-commissioning the –Z side.

8. Finally we shipped and reinserted also the –Z side 2 days before Easter brake!

9. During the final commissioning at P5 we had our last emergency. In fact one of the coolingtube, outside the detector, had a small hole caused probably by a mishandling!In one day the CERN team was able to do a fantastic job and fixed it, allowing us to finishthe detector checkout just few minutes before Easter brake!!

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Conclusions

• In the last few months the pixel community made a huge effort to improve significantlythe safety of the detector and to repair and make it more stable after the operational experience at P5 from July to December.

• We carefully planned in January and February all details to make this delicate repairoperation a success.

• In March and April we then executed the plan methodically in a professional way.

• Now the detector is safely back in place and in much better shape (>99.5% efficient)!

• We feel much more confident in operating the detector now that we know why we had all those problems!

• We are ready now to take some data as soon as the beam will be available!

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Added … from P5 to CERN

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