Present:
B. Allongue
CERN
J. Bohm
CERN/Prague Acad. of Sci.
I. Crotty
CERN/RS California
W. Dabrowski
CRACOW
F. Faccio
CERN
P. Farthouat
CERN
A. Fucci
CERN
B. Hallgren
CERN
R. Hammarstrom CERN
P. Jarron
CERN
H. Kurashige
Univ. Kobe
M. Letheren
CERN
E. Lorfevre
CERN/Univ. Montpellier
R. Richter
MPI Munich
W. v. Sprolant CERN
G. Stefanini
CERN
Date of next PROSPERO irradiation: April, 28th, 1999 .
1. J. Bohm: Status of ATLAS-SCT power supplies
Jan described the overall power needs of the ATLAS Semiconductor Tracker
SCT). The total system (barrel and forward) consists of 4088 Modules
of four Silicon strip detectors each. Each Module has a separate ground
and hence a separate power supply, which has to supply 5 voltages between
3.5 and 10V at currents of a few mA up to about 1 A. Total nominal power
per supply (delivered to the module) is 5 W, which gives a total of about
20 kW consumed by the whole system. To this number cable losses of about
5 kW have to be added. About of this amount is dissipated inside the Inner
Detector, where thin aluminium cables have to be used, the rest outside,
where thick copper cables can be used.- Because of considerable voltage
drop on the supply cables (up to 2 V) remote sensing is foreseen for precise
voltage definition at the modules.
The voltage supply system of the Silicon Strip detectors, which also
includes HV of up to 400 V for detector depletion, is controlled by DCS
and interlocked by hardware to a temperature monitoring system. The
HV supplies are developed by Cracow. Presently 4 LV channels, respectively
8 HV channels will go on a 6U card, which allows 48 SCT-Modules to be served
by one crate (12 LV and 6 HV cards) and therefore 86 crates are needed
for the whole system.- Prototype units, containing the full functionality
will be tested in summer 99.
Up to now the power supplies were foreseen to operate in USA15, well
sheltered from radiation, but at considerable extra cost because of long
cables. Recently it appeared that fire safety rules at CERN will impose
additional protective material, which will increase cable diameters and
cost.- Under this circumstances the location of the PSs will be reviewed
in the light of the relatively favorable results on rad-tolerance of power
supplies obtained in the PROSPERO run. Jan plans to perform similar tests
of the SCT power supply system during the PROSPERO run in april.
The question of tolerance to magnetic field will also have to be addressed
(see discussion below).
The total cost forseen for the LV supply system is 300 CHF/module,
including crates.
2. B. Allongue: Status of post-PROSPERO tests of irrad. power supplies
Bruno briefly summarized the results of the PROSPERO run of september,
30th, 98, where seven different power supply types had been tested, one
unit of each up to about 2 * 10^11 n/cm^2 (nominal ATLAS dose in 10 years,
including a safety factor of 4) and another one up to 2.3 * 10^12 n/cm^2.
All units with the lower dose survived and operated inside specs. The
other ones started to fail beyond 6 * 10^11 n/cm^2. Only one unit, made
by CEA, survived up to the end (see prev. minutes for details).
For further analysis of the damaged units four power supply types could
now be sent to the manufacturer, two are still waiting for clearance by
rad. safety. Results from SYCO and LAMBDA are expected soon. The CEA DC/DC
converter, which was irradiated to 2.3 * 10^12 n/cm^2 (equivalent to about
100 years of ATLAS operation) has been analysed by the manufacturer.
Though the unit had apparently operated correctly throughout the irradiation,
later analysis had revealed a drift of the output voltage by
60 mV w.r.t. the situation before irradiation. The drift has now been
traced back to the failure of the voltage reference circuit. After
replacing this circuit the nominal output voltage was restored.
Discussion:
Q (W.Dabrowski): The fact that all six power supply types tested at
PROSPERO only failed beyond 6 * 10^11 n/cm^2 (equivalent to 30 years of
ATLAS operation) is quite encouraging, yet this is a very low "statistics".
If e.g. 100 identical units had been tested it might well
have happend that 20 had failed much earlier. Such a result is not
excluded by the measurements. For the thousands of power supplies used
at
LHC more statistical significance is necessary.
A: This is certainly true. It would be essential to locate the weak
point(s) in the power supplies, like, e.g. op-amps and opto-couplers, and
study their rad-tolerance separately and in larger quantities. Components
of different producers would have to be compared.
3. B. Hallgren: Re-evaluation of LMBs tested in the PROSPERO run
With the exception of the opto-couplers the Local Monitor Boards (LMBs)
had well survived 2.3 * 10^12 n/cm^2, accumulated during the PROSPERO run.
Tests immediately after the run showed that the CAN protocol was still
operating correctly. Four months after irrad. the unit was re-tested: The
AMTEL's EEPROM had changed several memory locations and had to be re-programmed.
This demonstrates the necessity of the LMBs in-circuit programmibility.
Bjoern also reported on some other opto-couplers. There seem to be
indications that older products may be more rad-tol than the latest
devices. This should be tested in another irrad. run.
4. P. Jarron: Status of rad-tol voltage regulators
Prototypes of rad-tol voltage regulators in ST bipolar technology will
only be availabe by end-of-march. Ihere is still hope, they can be tested
in the april PROSPERO run.
There was a discussion with ST on the possibility of producing also
neg. voltage regulators as requested by some users. For the moment the
answer was not very encouraging, as a small demand for those devices is
anticipated.
5. R. Richter: Users and test items for the next n-irradiation:
The next PROSPERO run is foreseen for Wednesday, April, 28th.
The following projects have announced their interest in this run:
1) ATLAS-MDT MPI-Munich S. Schael/R.R. ALMY optical sensors
2) ATLAS-TGC Weizmann N. Lupu temperature sensors
3) ATLAS-SCT Prague J. Bohm power supplies
4) ATLAS Clermont Ph. Rosnet Tile calorimeter
5) CMS-Si-Det CERN G. Stefanini prototypes of LV supplies
6) CMS CERN Ph. Bloch preshower detector
7) RD49 CERN P. Jarron ST voltage regulators
Please send us a mail a.s.a.p. if other projects want to participate.
Typical schedule:
Arriving at PROSPERO site (close to Dijon) in the morning of april,
27th (3 hours by car from CERN). Install and test the
equipment.
april, 28th: irradiation, whole day (9:00h to 16:00h).
6. Discussion on the B-field problem for power supply components:
Measurements done by William v. Sprolant in 1998 have shown that of-the-shelf
transformers may become inefficient at B-fields as low as
300-500 Gauss, which is the range of field strengths expected at the
periphery of the ATLAS and CMS halls. The same is probably true for
inductances in filters. We need a concept to solve this problem a.s.a.p.
Robert Hammarstroem said that commercial transformers are available,
made from higher quality ferrites, which tolerate B-fields like the ones
mentioned above. They are probably not much more expensive.
We are looking for a volunteer to analyse the market of this material
with the help of Robert and order a number of these units. William v. Sprolant
would be ready to test them as soon as they become available.
7. Discussion on rack-cooling in a B-field environment:
William v. Sprolant had also measured the efficiency of air-fans. Theresult
was that the electrical motors stopped working around 500 Gauss. It is
not known, whether electrical motors with better B-filed-hardness are available
on the market. It is probably the same problem of ferrite
quality which we encountered with the transformers. If the magnetic
parts of motors could be modified by using a better material, this would
probably be the easiest solution. However, electrical motors could also
be replaced by pressurized-air or hydraulic-powered motors, which are available
for a wide range of power.
There was some discussion on the general concept of rack cooling. In
typical LEP-racks a water cooled heat exchanger plus fan was located below
each crate as air was streaming serially through all crates and returning
through a duct outside the crates.- However, a parallel air-flow could
also be envisioned, as was pointed out by William. In this case a single
heat-exchange and fan unit (though more powerful) would be necessary as
the cool air would only once pass through a crate.
In both cases, serial or parallel ventilation of the crates, magnetic-field
resistent fan motors are needed. Here again a careful analysis of available
technology on the market would have to be a first step to a solution of
this problem.
Robert Richter