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European Laboratory for Particle Physics |
The winter shutdown of the large CERN accelerators began on November 10 for LEP and on November 14 for the SPS. The ring survey of the SPS was carried out on 14 November, 30 hours after the machine was stopped. The levels of induced activity are somewhat higher that in the equivalent period of 1996. This is due to the fact that, following the fire of 13 May, the lead ion run which usually takes place at the end of the physics period (because it uses lower intensity beams and therefore ensures a better "cooling down" of the machine before major maintenance works) was cancelled.
The ring survey in the SPS was repeated on 3 December. At that date the dose rate has decreased to the same values as of 1996. The survey will be repeated in the first week of January, when the major maintenance intervention will start (until now work is only carried out in the "coolest" sextants, i.e. 3, 4 and 5).
The survey in LEP was carried out in points 1 (injection region, where some induced activity at some well localized positions is produced by beam losses during injection), in the four straight sections centered at points 2, 4, 6 and 8, where the superconducting RF cavities are installed, and at points 3 and 7, around the polarization wigglers. Only a few, well localized "hot spots" are found around the RF cavities, with a maximum around 0.8 mSv/h at 10 cm distance from one cavity end. Typical values are much lower, usually not exceeding 10-20 microSv/h. In the injection region, the maximum measured was 60 microSv/h, lower than in the past. In the wiggler regions the dose rate is very low, of the order of 1 microSv/h. The survey will be repeated early in January, as it is known that a few weeks ensure a substantial decrease in the levels of induced activity.
The major intervention carried out in LEP during this winter shutdown will be the dismantlement of several copper cavities at point 6, to leave room for the installation of eight superconducting modules (each consisting of four cavities), which will allow us to increase the LEP energy from 92 GeV to 96 GeV in 1998.
In the experimental areas of LEP accessible during machine operation (ALEPH, DELPHI and OPAL) the integrated doses during the physics period (approximately five months) are of the order of 0.3 mSv on top of a background of 0.1 mSv. Remember the radiation level from natural radiation 80 m underground is only one half of that on the surface due to the nearly perfect shielding against cosmic radiation. In the rooms occupied by physicists they are even lower, about 0.25 mSv. (MS end)
I (MH) would like to inform you about the latest developments in CERN's relation with the outside world. Two addenda were written of the Rapport de Surete in the framework of the Installations Nuclear de Base (INB) as far is LEP is concerned. This was necessary in spite of the fact that LEP will cease operation in 2000 to make room for the LHC.
Technical planning for the LHC proceeds normally. With the civil engineering frozen the shielding requirements for the underground areas are defined. In 1998 the provisional INB report for the LHC should be finished addressing all safety aspects of the future installation. In the meantime the pressure of antinuclear groups in Geneva against the new project increases. CERN management has agreed to organize a public debate in the beginning of the new year on the topic "What CERN does and where it will go" to let some steam blow off (or further heat up the atmosphere?). Also in France some animated discussions are expected before the Declaration de l'utilite public (DUP) will be delivered as the prerequisite before any construction work can start. An interesting year comes to an end and there is an interesting year in perspective.
So quite naturally I come to the end wishing all colleagues and readers of the IARPE Newsletter in the name of my group a Merry Christmas and a successful and healthy New Year,
Manfred Hoefert
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