Present:
                B. Allongue     CERN
                G. Dumont       CERN
                J. Elias        FERMILAB
                P. Farthouat    CERN
                A. Fucci        CERN
                Z. Hajduk       CERN & CRACOW
                B. Hallgren     CERN
                R. Hammarstrom  CERN
                R. Richter      CERN & MPI
                W. v. Sprolant  CERN
                G. Stefanini    CERN
               (H. v. d. Graaf  NIKHEF)*

      *Harry was not present during the meeting, however,
        I include his preliminary findings on rad-tolerance
        of CCDs and CMOS array devices in the minutes,
        because these results are of general interest for
        the Muon community.
 

Plans for new PROSPERO irradiation:
The next irradiation will probably be scheduled for mid-march 1999 together with the RD49 collaboration (P. Jarron).
 

B. Allongue, W. v. Sprolant: Power supplies irradiated at PROSPERO

Hardware for the test:
A multiplexing system under remote control allowed to test a number of critical parameters of the power supplies during irradiation and record the data online. Apart from voltage and current the ripple on the output voltage could be observed as the voltages were sent to the counting room through a properly matched cable. It was not possible, however, in this first test to observe the operating frequency of the converters, which is expected to be a sensitive measure of the conversion efficiency.
While all PSs were loaded by 80% of the specified current, it was not possible in this setup to create a "step" change on the load and to observe the reaction of the power supply. The time needed to re-establish the nominal output voltage and the shape of the voltage transition (damped, oscillating) would reveal frequency response and transfer characteristics of the internal feedback loop. It would be very useful if later versions of the test system would allow this test mode.

Results:
7 power supplies from different manufactures (2 units of each) were exposed to 2 different doses of neutrons in the irradiation test of sept., 30th. The first dose was 1.8 * 10^11 n/cm^2, the second was 2.3 * 10^12 n/cm^2 (1 MeV equiv.). After the 1.8 * 10^11 run one unit of each type was removed from the hall in order to be available for later rechecking.
The dose of 2*10^11 n/cm^2 is the expected dose (En>100 keV) at the periphery of the Muon detector (location of PS racks) in 10 years of operation (10^8 sec) at full luminosity. A "safty factor" of 4 is already included in this number. This number exceeds the numbers given in table 2 of the document "Atlas Policy on Radiation Tolerant Electronics" for "best location" which means: at large radius. It is important to note that this number is a conservative estimate of the upper limit of the total dose of fast neutrons for electronics racks. If this number, even with the safety factor was not considered reliable, other more crucial and less servicable components of the ATLAS detector would be in serious difficulties (e.g. background in the muon chambers).
The first result of the PROSPERO test w.r.t. power supplies was that:

- all units survived the nominal n-dose as defined above with full   functionality
- units went gradually out of specs beyond 2.5-5 times this nominal n-dose

Nominal doses at periphery of LHC caverns (10 y at full lumi, 10^11 n/cm^2):
ATLAS, barrel and endcap                          2
CMS, barrel                                                0.2
CMS, endcap                                              2

The best performance by far was shown by the CEA unit which had been designed independently of our application to stand gamma irradiation doses up to 1 Mrad.

Plans for further analysis of the irradiated units:
The units will be sent back to the manufacturers for identification  of the faulty components and the exact failure mode. Perhaps components can be optimized and the "lifetime" could be significantly increased at small cost. Most manufacturers showed interest in an in-house analysis of the problem. Unfortunatelly, some of the units still show a remnant activity of up to a factor of 3 above what is the limit for exporting "radioactive devices" to other institutions. (There are different legal limits for handling material inside CERN and for exportation to firms which have no experience with radioactive material.) Main critical isotopes are Antimon 124 (half-life 60
days) and Ta 182 (115 days). We expect clearance for exportation for most units by beginning of february.
 

Z. Hajduk: Results from irrad. of HV caps:

A number of encapsulated HV capacitors (3 kV) for use in the TRT have been irradiated up to 10^13 n/cm^2. No HV was applied during the test. All components survived the test.- Further tests will be necessary under HV and up to 10^14 n/cm^2.
 

B. Hallgren: Future of the TCC2 test beam

Bjoern showed a long list of irrad. tests to be foreseen in the TCC2 testbeam in 1999. Most of the equipment is LHC machine related. The spectra of the irrad. environment in this area are believed to be quite close to the situation in the LHC tunnel. 10^12 n/cm^2 can be accumulated in a few weeks.
The infrastructure of the area has now been improved in order to allow for online measurements. Still access is quite unpredictable, because this is the beam switchyard of the north area.
Bjoern will continue tests of the LMBs (Local Monitor Boards) for DCS in TCC2. Previous tests including the one at PROSPERO have shown that most components of this system survive easily 10^12 n/cm^2. The notable exception was the Siemens Optocoupler IL206A, whose CTR fell to 30% of the initial value. However, as this device is used in a digital application and is uncritical w.r.t. bandwidth the circuit can easily be modified to work down to 10% CTR.
 

G. Stefanini: Plans for HV and LV power supplies in CMS

Giorgio said that present views favour the development of power supply prototypes in collaboration with companies, taking into account the recommandations of the LHC control group. An example is the work with CAEN on HV power supplies. Here the HV will be generated in the (radiation safe) counting room and will be distributed by special control units in the cavern. CAEN has agreed to produce a remote controllable prototype.
A similar program will be followed for LV supplies. While there is a number of competent firms no decision for a manufacturer has yet been taken.
Once prototype units are available a full test of all parameters can be performed at CERN. Resistance to environmental parameters like mag. field and radiation will
also be tested.
 

Harry v.d. Graaf: New preliminary results of the CCD tests:

Today (Nov 12, 1998), I tested the RASNIKs that were irradiated in PROSPERO on September 30, 1998. In PROSPERO we tested two complete RASNIK systems: image source, image sensor and lens were included. The distance between the image source and image sensor was 35 cm; the lens was centered in between.
I found out that the light sources (part of the image source) were giving little or no light. The green indication LEDs were also quite weak.
After replacing the LED cards with non-irradiated cards, the images were perfect: they were even better than those before the irradiation at PROSPERO.
The same damaged light sources were applied earlier in the PETTEN irradiation test: apparently they were damaged to some degree already there.
I must conclude now:
(1) that both the PC18XS (video CCD)and VV5402 (CMOS multi photodiode array) can easily take 91 x 10**11 neutrons/cm2 91 MeV eq.);
(2) that one or more components on LED card, such as the infra-red LEDs, applied in our light sources, can NOT take such a dose.

Concerning (2): Kevan has applied LEDs during his LOWELL test that COULD take such a dose. Furthermore: in ATLAS, the LED cards can be exchanged easely, provided that access is possible. The exchange of LED cards has no influence on the precision or offsets of RASNIK. In the next test at PROSPERO we have the opportunity to test LEDs.
I will soon produce a detailed report about the radiation damage of the PC18XR and VV5402 mentioned above, and, in addition, the VV5404, a second VV5402 and a MARSHALL CMOS device. The latter three image sensors were irradiated in PROSPERO, but not yet tested.
The present conclusions are totally opposite to those of two weeks ago. I apologise for not being more careful when formulating previous conclusions.
 

Robert Richter