Present: M. Atac, M. Bosteels, A. Cararro, K. Gabathuler, G. Gobbi, S.
Grohmann, G. Hallewell, R. Hammarstrom, A. Hervé, S. Ilie, J. Inigo-Golfin, P.
Petagna, B. Pirollet, A. Placci and A. Smith.

L. Feld, J. Godlewski, H. Postema and A. Onnela were unable to attend the meeting.

1. First Results from the Irradiation Tests

Sorin presented his preliminary results on C6F14 irradiated by neutrons and
gammas at PSI.  The neutron activation results would be compared with
predictions from simulations.
Irradiation of samples with 6 Mrad of Co60 gammas produced destruction of
about 1% of the C6F14. In addition to pure samples, 10% hexane  had been added
to other samples to simulate unsaturated production of C6F14. There was no
change in viscosity in either type of sample at this received dosage. Some
absorbtion at the UV end of the spectrum was observed but most of this was
removed by passing the samples through filters of activated charcoal or active
Al. Microscopic examination of the surface of st. steel bars which had been in
contact with the liquid during irradiation of the samples showed that some
material had been deposited on the surfaces and cracks had been formed on some
of the deposits. Aluminium surfaces were tested similarly and the sample with
added hexane showed the most damage. Sorin believed the deposits were polymers
as they appeared to be insulating.
M. Atac said that he was planning to carry out irradiation tests in which he
would weigh the exposed materials before and after irradiation to show whether
deposition or erosion had taken place. R. Hammarstrom wondered whether the
deposits would be liable to break off on cooling to -20C but this was not
thought to be likely.

2. Latest Reults from Phase I Tests

Greg summarised the tests carried out at Marseilles and CERN on C4F10
evaporative cooling. The flow rate per stave was typically 0.5 g/sec at 20C to
achieve the -5C temperature required on the staves. Studies would start later
on the use of capillaries to replace the ruby injectors, some of which had
blocked on the University of Geneva’s test set-up. There was some discussion
of the problem of liquid forming on the return part of the cooling circuit and
the effect of switching on power  (heating) if liquid were present.  Worry was
expressed that this could lead to almost explosive type pressure rises.  Greg
reported that the pixel and SCT groups were going to provide many structures
to test.
Greg reported, on behalf of Antti and Jan, that vibration tests had been
carried out on an aluminium cantilever beam using the CMS liquid recirculator.
The natural frequency of the beam had first been measured. Fluid flow had
produced a movement of 2.5 micron amplitude at the first harmonic of the
pumping frequency. The tests showed that care must be taken to avoid having
support structures with natural frequencies which could be excited by the
freequency of the pumps used.

3. CMS Phase II Liquid circulator Layout

Robert presented his proposed layout for the -20C liquid coolant tests in
B186. The cooling unit would be on the floor of the building with the CMS test
structures being centred around a height of 5.5 m above the floor. The return
coolant would be taken up to a height of 11.5 m to simulate the real height in
CMS before descending to pass through a structure which would model the use of
the return coolant for removing heat from power cables. Copies of this layout
will be sent to contacts for the other experiments. Others may request copies
from A. Smith.

4. Review of the capabilities of ILK Dresden

Steffen introduced the ILK project at CERN which is supported half by CERN and
half by the German government and ILK. ILK is a non-profit making R&D company
covering air conditioning and refrigeration technologies. They also have the
capacity to do lubrication and chemical studies. The aim of the project is to
carry out studies, designs and experimental tests of cooling systems, and in
particular to study the integration of cooling into ATLAS and CMS. ILK have
lots of software available and a library of the properties of refrigerants. He
would add C3F8, C4F10, C6F14 and CF3I to this library. He mentioned C3F7H
(R222ea) as a possible refrigerant, it having a boiling point at atmospheric
pressure of -15.6C, a vapour pressure of 1.29 bar at -10C, and a higher heat
capacity than either  C3F8 or C4F10.
Steffen was still looking for a project for himself at CERN and he believed he
could contribute to the design of the ATLAS cooling circuits and arrange for
tests with oil free compressors on the new refrigerants. In addition, he could
do real scale prototype tests for CMS. He will coordinate between ILK and CERN
and provide general support but ideally he would like also to be involved in a
couple of projects.
Both ATLAS and CMS expressed interest in using his capabilities.

5. Heat shields

Alain explained that CMS had a study underway on the -10C to +20C heat
shields, and he introduced Andrea Carraro who has been carrying out the
calculations and performing insulation tests in the TA1 area. Michel added
that RAL had a similar study programme in progress. Paolo Petagna was starting
to look at feed throughs and expected to begin tests next year.
Greg added that ATLAS had two separate studies going for two different heat
shields. One recent complication had arisen from a suggesation that the beam
pipe should only have a bellows at one end which implied that its wire support
could move by about 2 cms. There was a short discussion of the problems of
bake-out in situ.

6.  Coolants

CMS foresees using C6F14 or a similar special liquid for cooling the full
tracker, including MSGC’s, and the pre-shower detector. All other detectors
will be water cooled.
ATLAS plans to use evaporative cooling for the silicon trackers and to use
C6F14 elsewhere, with water only being used to cool electronics racks.

7. Next Meeting

The date of the next meeting will be decided shortly and communicated to you.

 
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