The accelerator divisions has set up a Radiation-Working Group (chaired by Raymond Rausch SL/CO) with the mandate to test components and complete assemblies in a LHC like accelerator environment. (The group is not concerned with the radiation issues of the LHC detectors). One of the tasks is to test the CERN recommended field-buses. ATLAS DCS has been invited to participate in this work because of our CANbus hardware development.
1. Description of the radiation tests area.
The target area TCC2 has been chosen as the suitable test place. It is there the beams for the North Experimental hall EHN1 (ATLAS and CMS test beams) and the EHN2 hall NA48, NA50 experiments are made, for more information. The place is only accessable for short period of time. There are strict procedures established for the access to the area and the handling of the components after the tests, see the document PRP17 from TIS-RP. The samples become radioactive, and must be treated in accordance with the rules laid down in the CERN Radio Protection Manual.
An estimate about the TCC2 dose rate: about 50 Gy and 5. 1010 neutrons cm-2 can be accumulated in a 6 week running period of SPS. In one year depending on how the accelerators are operating, this gives 3x1011 neutrons cm-2 . It is obvoiusly rather difficult to predict what is the radiation dose beforehand.
As a comparison results from the NIKHEF test see
NIKHEF
. The amount of radiation the NIKHEF CRYSTAL-CAN module received (one day)
was in thermal neutrons:
2.5.1012 neutrons cm-2 and epithermal
neutrons: 5.0.1010 neutrons cm-2 .
It has been estimated that the ATLAS Cavern (in one year) (at distance
of R (cm) > 4m) has a equivalent dose of less
than 1 Gy/year and 5.1010 neutrons cm
-2 The 'hottest' spot in the ATLAS Muon Spectrometer would
receive a dose of 3.1012 neutrons cm-2 of
thermal neutrons (in 10 years) taking into account
a safety factor of 5 (according to ATLAS documentation [
ATLAS radhard
).
2. LMB Measurement program for 1998.
The tests started in April 98. Among them the ATLAS DCS CANbus slave module the Local Monitor Box (LMB). In addition some integrated cicuits, which are used in the LMB, have been tested as separate components. A component testbox has been built to test the components before and after each radiation test, see schematics . For this year it has not been possible to install cables to monitor the systems on-line. All systems and components are therfore non-powered during the irradiations. The components have an inventory number and one referenece sample of each type is kept non-irradiatied. The measurements results of the components before irradiation is available here: radtst1.html
2.1 Results from the first irradiation.
The first irradiation period lasted from 29/4 to 13/5 1998. The dose rate
was between about 20Gy (14 to 22 Gy) and neutrons (equiv. 1 MeV
Si) about 1 1011 neutrons cm-2 .
The following are the results:
1) All five tested optocouplers IL206A
were effected. Their current transfer ratios changed about 70%. One
of the optocoulers is out of specification and one is very close to
the specification limits.
2) In one of the four tested microcontrollers AT90S1200,
one EEPROM memory location was erased. It changed contents from 15H
to FFH. Five bits were erased.
The LMB and all other components had neglible changes due to this radiation test. The detailed measurements results after the first irradiation is available in: radtst2.html
2.2 Results from the second irradiation.
The second irradiation period lasted from 17/6 to 8/7 1998. The dose rate was about 50 Gy and neutrons (equiv. 1 MeV Si) about 1 1012 neutrons cm-2.
1) All but one optocouplers stopped working in the AC test. The current
transfer ratios are now about 30% of the orginal values.
2) The output voltage of the reference circuit AD680 changed a few mV.
3) An additional EEPROM address changed in another AT90S100 microcontroller.
4) The communication to the ADC LMB module using optocouplers ceased to work,
while the CAN controller still works.
2.3 Results from the third period of irradiation.
The third period lasted from 5/8 to 21/9 1998.
The dose rate was about 100 Gy.
1) Optocouplers: . The current transfer ratios are now about 3% of
the orginal values. However they are still functional if the gain in the
circuit is changed by changing the load resistor of the output transistor
from 2.2kohms to 35kohms.
2) The output voltage of the reference circuit AD680 changed a little still
but is still well within the specifactions.
The detailed measurements results after all 1998 irradiation is available in: radtst3.html
Other information is available in :
CERN-TIS-TE-IR-98-11 ; CERN-SL-CO-98-057 ; CERN-SL-98-057-CO
. (CERN-TIS-98-011-TE-IR) . Radiation test programme on cots components needed
for the Large
Hadron Collider at CERN . by Rausch, R ; Tavlet,
M ; (23 p) . 1998 . Publ. Ref.: . 5th European Conference on Radiation Effects
on Components and Systems - RADECS '98
Oxford, UK ; 14 - 15 Sep 1998 .
See CERN-SL-CO-98-057-CO