==> Next meeting: tuesday,   sept., 1st, 1998, 9:00 h

Present:
                G. Bianchetti   CERN
                J. Buytaert     CERN
                G. Dumont       CERN
                P. Farthouat    CERN
                A. Fucci        CERN
                Z. Hajduk       CERN & CRACOW
                B. Hallgren     CERN
                M.A. Joux       CERN
                H. Reithler     CERN & AACHEN
                R. Richter      CERN & MPI
                W. v. Sprolant  CERN
                G. Stefanini    CERN
 

R. R.: Practical aspects and constraints for n-irrad. at PROSPERO

Philippe Farthouat and R.R. have visited the PROSPERO-site on june, 23rd. We agreed on the following time schedule for the first irrad. on sept. 30th
(a second irrad. is foreseen for nov., 18th):
    Sept., 29th: installation of test-equipment in hall, cabling to control room, pre-rad tests.
    Sept., 30th: irrad. (see below)
Working time at the site is 8:30h to 16:30h; it is not possible to work outside working hours.
 
All material will be controlled for activation after the irradiation. Depending on dose and material's mass and composition, a cool-down of up to
a few days may be necessary. Cleared material will be sent to CERN by mail. TIS says that military safty limits exceed CERN's so there will be no
problem for CERN rad-safety.

Cabling between hall and lab:
There is a patch-panel available with 13 BNC and 15 type C connectors between hall and lab which can be used. There are also 2 DEUTCH connectors
with 37 pins. Length=24 m.

User-made cables:
Length: about 7 m in hall, 5 m in lab and 25 m in-between, therefore 35-40 m should be foreseen.
Diameter: ALL user-made cables have to go through a tube of 50 mm inner diameter and about 3 m length (passage between hall and basement).
Flat-pack multi-twisted pair cables are most unlikely to pass WITH connector, therefore tools for putting connectors on AFTER passage should
be brought along, the same for LV-DC supply cables.

Power cables:
there is a sufficient number of power plugs (220 V) on the wall of the hall. Remember swiss (CERN) plugs are incompatible with french plugs!

Dimensions of hall:
width 8m, length 10 m; reactor at 2.40 m from wall in longitudinal direction, leaving 7.60 m to other wall. In other coordinate reactor is at
4.2 m from wall.  Maximum practical distance from reactor is about 6 m, corresponding to 2*10^11 n/cm^2/h at 100% reactor power.

Irrad. will proceed as follows:

1) 1 hour @ 10% reactor power, giving about 2*10^10 n/cm^2 at 6 m and    about 2*10^11 n/cm^2 at 1.5 m
2) pause of about 30 min for cool down and access for about 15 min to    remove low-dose irrad. material
3) 1 hour @100%, giving 2*10^12 n/cm^2 at 1.5 m
4) pause of 1 hour for cool down and short access
5) 3 hours @100% for high dose irrad.

So the total duration is about 7 hours (9h to 16h).

Users can, of course, tune the dose by selecting the appropriate distance.

No access will be allowed during 2) and 4) for people without a MEDICAL EXAMINATION (blood test), so please do your routine check at CERN soon!

General remarks:

People from the LHC community, who want to participate in this run should give notice and specify requirements of space and doses. It is understood that every user has to prepare all equipment (cabling, power supplies, R/O) for his test on his own. Also installation at the reactor and monitoring during the irrad. are the responsibility of the user.- Passive material can be placed by us, if delivered in time. Please label clearly: owner, kind of sample (material), required radiation dose. Please pack in transparent plastic bags.

People who want to participate in the test, must send their personal coordinates plus a copy of there passport to the center in the first days of september in order to get clearance for the site. I propose to send it to Philippe or R.R. by FAX before sept. 3rd.

The site is located about 30 km north of Dijon and can be reached from Geneva in about 3 hours by car.
 

W. v. Sprolant: Tests of power supplies in magn. field

In DC-DC converters there are several components sensitive to magnetic field: 50 Hz AC/DC transformer, high-freq. DC/DC transformer and induction coils used in voltage filtering at input and output. In these tests the whole DC/DC converter was placed in a magn. field. Output voltage, current and voltage ripple were observed as a function of B and direction of B relative to the axis of the DC/DC converter.

Results:

1) output voltage fell to zero between 150 and 300 Gauss, unless B was perpendicular to the field in the ferrite-coils. While the voltage went to zero, input power minus output power remained roughly constant, i.e. heating of the unit didn't increase significantly and no unit was permanently damaged.

2) unless B was perpendicular to the filter's ferrite-torus, large amplitude noise appeared around 150-300 Gauss. The 50 Hz of the supply was the main component but higher frequencies could also be seen.

Discussion:

Aligning of B to the direction of the ferrites is not a practical option for the experiment, therefore technics of shielding must be studied. Simplest solution would be wrapping of the complete unit in  mu-metal. Transformers and coils could also be shielded individually. The ferrite-components could finally be replaced by such of a higher magnetic strength. These possibilities and their cost-implications should be investigated.
 

W. v. Sprolant: Preparation for irrad. tests of DC-DC-converters in PROSPERO

A number of DC/DC converters has been acquired from different vendors and with different technology. A concept has been worked out to operate and constantly monitor all devices during the irradiation. All devices will supply a load of 75% of the specified maximum. The following parameters will be monitored: voltage, current in and out, voltage ripple. To reduce cabling, a muliplexing system with mechanical relays is foreseen. As the relays are matched to 50 Ohm, voltage ripple can be observed in the control room without significant interference.

For the control of the relays a low-cost commercial system will be used, which includes the interface software to the LabView-DAQ. Data will be recorded automatically and stored for documentation and later analysis.
 

B. Hallgren: Results from 2nd irrad. in TCC2

Bjorn described the TCC2 radiation area in LAB II, where the accelerator division has started to test CERN recommended field-buses. Results of the first irrad. period have been reported in the last meeting.

Bjorn said that the second irradiation period (17/6 to 8/7) had delivered a n-dose of about 2.5 * 10^11 n/cm^2 while the first had delivered 10^11 n/cm^2. A total dose of 5 to 8 krad of gamma irrad. was accumulated during the tests.- The crucial components of the LMB (Local Monitor Board for DCS) have been tested and the results compared to those of the 1st irrad. period. None of the components was powered during the test.

Bjorn pointed out that the measured radiologic activation of the exposed equipment was about 15 mySivert/hour after irrad., 5 mySiv/h after 2 days and 1 mySivert/h after 6 days. Allowed limit is 5 mySiv/h, typical natural activation is 0.1 mySiv/h.

Several components showed no detectable change of el. parameters w.r.t. pre-rad measurements. However, opto-couplers were severely damaged (see below).

No detectable damage:

Philips CAN-bus controller interface PCA82C250

ADM660 switch-capacitor converter to invert the input supply voltage

AD680 bipolar bandgap reference, giving 2.5V output @ 4.5 to 36 V input

ADP3301 high accuracy 100mA linear regulator voltage reference

Detectable damage:

Siemens Optocoupler IL206A, an optically coupled pair with a GaAs LED and a silicon NPN phototransistor.- 5 devices were irradiated, a sixth served as reference. The damage is best characterized by the CTR (current transfer ratio). For all 5 devices the CTR degraded quite homogeneously from about 90% to 60% after the 1st to 30% after the 2nd irradiation. Bjoern remarked that they could therefore be used as a cheap radiation monitor, allowing a simple comparision between different irradiation sites.- For the purpose of the LMB application the circuits were unusable because 30% CTR was not sufficient to trigger logic levels.

The LMB Pt100 temperature sensor (a complete LMB-box with several circuits) didn't respond any more after the 2nd irrad. Probably due to opto-coupler
failure, but this has to be verified, as in-built ADC could also fail.

ATMEL AT90S1200 RISC Processors with flash memory and EEPROM data storage: Among the 5 devices 2 were OK. 2 devices had a changed memory location in
the EEPROM, 1 device was unusable for other reasons.- Important question whether re-programming of EEPROM is possible or whether memory is permanently stuck, has still to be settled.

==> Next meeting: tuesday,   sept., 1st, 1998, 9:00 h

Robert Richter