Present: M. Bosteels , H. Breuker, L. Feld, J. Godlewski, R. Gregory, G. Hallewell, S. Ilie, G. Lenzen, T. Niinikoski, A. Onnela, A. Placci, H. Postema, A. Smith and M. Wilhelmsson.

1. The minutes of the previous meeting were accepted.

2. Monophase cooling update

Lutz Feld presented the results of calculations and cooling tests carried out on CMS MSGC modules at 18C. The measurements were in agreement with calculations. HFE had been used and tests with HFE had also been carried out on silicon at -10C for a barrel module, an end-cap module and a full size disk module. In addition to measuring pressure drop versus flow rate and various temperature gradients, the variation of temperature with heat load had also been measured to check for stability against thermal runaway. HFE was also a candidate fluid for cooling the Pixels but tests had not yet been carried out though there was confidence that its behaviour would be similar to that of the modules already tested.  CMS was satisfied that the proposed cooling system would work for the SST and MSGC’s.
The next steps were to do more work on prototypes and a prototype cooling system, and to decide on the final cooling fluid.

Michel Bosteels then presented the schematic diagram of a possible monophase system, and explained the differences between CMS and ATLAS arising from their service galleries being at different levels. In particular, the drainage of a liquid system is more difficult for ATLAS. He had supplied Geneva University with a small system and expected to have the Phase I system ready within 2 weeks. ATLAS expressed interest in borrowing this system later in the year.

Hans Postema continued with an account of why CMS was in favour of liquid cooling systems. CMS had had an internal debate on this subject. They believed such systems would be less complex and hence more reliable. They did not believe that the advantages to be gained from evaporative cooling in terms of reduction in material were too significant, and felt that the reduced pipe diameters would have to be compensated by additional material to provide sufficient surface for heat transfer.  Greg interjected that ATLAS had considered liquid cooling and had calculated higher pressure drops and larger quantities of material for pipework than presented by CMS and he cast doubt on the figures presented. The origin of these differences could not be resolved in the meeting, and it remains for the members of each collaboration to check their own figures if they reckon they are critical. Greg also pointed out that CMS had not included the additional size of the supply piping with its insulation and it was acknowledged that this had been omitted in the CMS summary.  Hans concluded by saying that CMS considered their monophase tests to be successful so far. What remained to be done was to carry out irradiation analyses of fluorocarbons, and to design the complete cooling loops for the final systems.

3. Results of calculations on fluorocarbons

Tapio had calculated a vast number of parameters for both C3F8 and C4F10, using a pipe diameter of 1.4 mm for the former and 4 mm for the latter. In particular, he had calculated pressure drops along a barrel STC stave for 2 phase flow and had also calculated some temperature gradients. Although there was some inconsistency in the results of the calculations for the phase of the flows for C4F10, he concluded that the heat transfer and temperature gradients were comparable for the two fluorocarbons and that they would not behave very differently, provided the flow regime of C4F10 could be verified to be OK.

4. Irradiation effects in fluorinerts

Sorin Ilie presented a list of the doses, including neutron fluxes, expected in the individual subdetectors. F18   is the longest living isotope with a half life of 109 minutes. He had calculated the activity if C4F10 were to be used in ATLAS, and also for a perfluoro CF compound and had obtained the agreement of TIS that the induced activity could be considered as being zero after 7 hours. The saturation level of radioactivity would be a few thousand Bq/cm3 which would reduce to zero residual activity after 10 hours. Michel pointed out that the induced activity meant that pipes could not pass near zones occupied by people unless they were to be well shielded from the 0.51 MeV gammas coming from positron emission. Leaks of radioactive PFC’s would be dangerous and this problem should be addressed with TIS.
Regarding the chemistry of other compounds produced, Sorin started by indicating that water will produce gaseous oxygen and hydrogen under irradiation. For perfluoroethers, CF’s will be produced and these will form HF on contact with moisture. Perfluorocarbons will have a lower production of HF. PFE’s would be more reactive than PFC’s and would produce more toxic gases. He proposed that tests be carried out on C4F10 in the gaseous phase and C6F14 in liquid phase. The irradiation should be done at room temperature in 10 steps up to 5Mrad. Scould be done with a Co60 or Cs137 source. Measurements should be made to determine :-
 the nature of radiolytic products
 pressure modifications v dose
 viscosity changes v dose
 induced corrosion on stainless steel and aluminium.
Sorin will make a preliminary list of tests to be done and the materials needed, such as containers etc. This list will be circulated to the experiments who should provide feedback with any additional tests they think necessary. Enquiries will have to be made to determine whether payment will be required for irradiation of samples carried out at outside institutes such as PSI, RAL and reactors.

 5.  Status of the Phase I Programme

Greg’s system was in the process of being dismantled in Marseilles prior to it being sent to CERN. Michel expected that all the systems he was producing would be ready in 1 month’s time.
It was announced that ATLAS had appointed a guru to be responsible for the production of structures to be used in the cooling tests.
C6F14 is available from DELPHI via Georg but, after the donation of the initial 10 Kg, further quantities may have to be paid for. ATLAS was planning to buy 25 Kg each of C3F8, C4F10 and C6F14. It was pointed out that special pumps are needed for PFC’s, but DELPHI had managed to acquire suitable pumps which were now comercially available.
Greg presented the results of the latest tests he had carried out at Marseilles on 50 cm long Pixel sectors with a heat load of 36W. A temperature of -18C had been easily maintained. A structure supplied by NIKHEF was also tested and in this case the temperature changes were monitored as the heat load was increased.

6.  A.O.B.

Jan announced that he was starting to look at vibration and proposed that he and Antti give a joint report at the next meeting on how such vibration tests could be carried out, with a list of the necessary equipment either already existing or to be acquired.
There was some discussion of Phase II. Jan believes that monophase tests are necessary and Greg needs evaporative tests. Greg considered it essential that the control systems are tested in Phase II and he believed this was a common problem for all experiments. Alasdair was not sure that the control systems of ATLAS and CMS were sufficiently identical to make all tests on one system and this would have an important bearing on the Phase II budget. As Greg was worried about the lack of definition of this budget, Alasdair would re-open discussions with the technical coordinators/resource managers.
Michel believed that an inventroy of the number of heat exchangers, connectors, Pt100’s, valves etc needed for the final systems should be made and entered into a data base. He was willing to take care of the data base but required input from the groups. A similar exercise had been made by the Gas Club. Jan supported this suggestion and Antti added that it would also be useful for considering which materials should be qualified for use in the different radiation environments.

7.   Next meeting

The next meeting will take place on Tuesday 7th July at 14h00 in B40 R-C10.

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