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August 2, 2012 FDC meeting


  1. Cathode corrosion
  2. Production Construction Tracking (Dave)
  3. Engineering (Bill)
  4. Electronics (Chris, Nick)
  5. Test set-up in 126 (Beni)
  6. Other


Participants: Bill, Eugene, Dave, Nick, Chris, Simon, Beni, Vlad, and Lubomir

Cathode corrosion

- Bill: Olga is doing FTIR (Fourier Transform InfraRed) studies, that give information not only about the elemental composition but also about the bonds between the elements. She's looking at used and unused EPDM samples and there's some difference but the interpretation of the FTIR results is difficult. It will be also interesting to look at the copper samples and also Epoxy samples (Epon and Epolite) if possible with this method. Tim proposed to use pressure paper to look if the EPDM O-ring fills the grove and apply more pressure on the sides of the groove.

- Vlad (also with the help of his dad who's chemist) studied the literature about the copper corrosion. Normally as a first step copper reacts with watter (moisture) CO2 and O2 forming hydrides of Cu2O (copper oxide) that has redish color (Cu2O is good conductor). On the next step due to again water and sulfur (or chlorine) copper salts are formed like CuSO4, CuS and CuO (copper monoxides, mono-sulfides) having black/gray color what we are actually seeing, which are moderate conductors. Especially hydrogen sulfide is dangerous, we can identify it with lead acetate paper that we have ordered. Important is also that carbon serves as catalyst. We see that the EPDM O-ring leaves carbon traces very easily just by pressing it against the copper foil.

- Three testing chambers are being considered: one with production wire frame and cathodes is running under HV for more than a week, it has both EPDM and Viton O-rings inside. Second test is with the small-scale prototype, that will have similar materials inside as explained in the document above: same EPDM, Viton, same wires (deadened already), Epon epoxy. Tomorrow we will have all the O-rings needed and will start that test, as well. Vlad proposed another test using a vacuum chamber (that didn't work to remove the bubbles from the epoxy) and his scheme is linked above. The idea is to increase the temperature (with a lamp) by 10-20degC resulting in 3-6 times speeding up of the corrosion. We will also increase the humidity inside the chamber. The test will be done without HV so far. Also we have a simple test outside of the clean room: we just sandwiched EPDM/Vition O-rings with copper foil between two g10 plates under the weight of one lead brick. After putting in addition some tab water, corrosion spots appeared especially on the EPDM sample.


- Dave showed the latest Construction Tracking file (linked): now refurbishing second package. The plan is to use all the spare cathodes there plus three newly build: all of them using new foils and one spare cathode frame (the only we had), and two refurbished (type-1 and type-2). The refurbished frames came from package #1 by successfully removing the foils. For package #1 we may use some of the cathodes from package #2 that didn't have bad channels (indicated with blue color) and all of the spare foils left after building package #2.

- Roger is trying to contact Allflex to order new foils, but the guy is in vacation, will be back on Monday. Roger will ask Allflex also for new rigid-flexes, even it turned out we can re-use the old ones; in fact not all of the removed flexes can be re-used but we will improve the removal procedure.

- We are trying to repair one of the damaged cathodes from package #1. First, the traces were covered with conductive ink resulting in <10 Ohm resistance. The trick is to shake the pen very well before using it and to apply very thin layer, actually it can be thinned later using ethanol. Next, the trace/O-ring area of one connector was covered with Kapton using Hysol epoxy. We will test it for leakage. The pen we are using, according to TECHSPRAY data sheets has silver, n-Butyl acetate (as solvent), and polymers. Viton O-ring is not compatible with acetate solvents, but first, the solvent evaporates in an hour time frame, second it's covered with Kapton. We discussed using stencils to cover the traces with conductive ink, it will help but we need to make 9, for each connector.

- The refurbishment of the package #2 is delayed not only because of the corrosion problem, but also there was a delay with the delivery of the conductive (thermally) rubber that we use to re-heat the cathode rigid-flex connections. There were resistance problems (10-100 Ohm on the contacts) with the two spare cathodes type-3, the very first cathodes produced, that we want to put now in the second package.

- Vlad on the grounding scheme (linked above): the ground positions shown in degrees starting from North counterclockwise when looking from the upstream of the package. Three types of groundings as shown on the pictures. The clips are supposed to come by August 15, ... procurement forgot to inform the company to go with the full production.


- Bill: Caleb is done with the the colling system design, Bill will do minor modifications. Caleb's report will be linked later.


- Chris: After some e-mail exchanges with the PCB manufacturer, the extra four sets of PCBs are supposed to be shipped on 8/6/12.

Test set-up in 126

- Beni: fADC125 times out and can't be read out with the Linux ROCs. It turned out that there were time-outs also with the Motorola ROC, but it could recover after that and we could use the data. Gerard is working on this problem, it's in the firmware.