Une expérience d'application de la télédétection spatiale à l'anthropologie : l'étude des peuplements anciens du Diamaré (Cameroun septentrional)

A partir de l'observation d'une relation entre les vestiges archéologiques et les sols "hardé" au Nord du Cameroun on a recherché par la télédétection spatiale à identifier ces sols grâce à leur haute réflectance qui est fonction de leur aspect de surface. L'expérience montre d'abord que cet aspect de surface est le fruit de divers facteurs, pédologiques, topographiques, climatiques et anthropologiques agissant dans le temps peut-être du Néolithique à l'Actuel, ensuite que les résultats cartographiés peuvent préciser la prospection. (Résumé d'auteur

Layout and Design of the Auxiliary Bus-Bar Line for the LHC Arc Main Cryostat

The superconducting multipole magnets housed in the cold mass of the LHC arc short straight sections, together with the arc dispersion suppressor and matching section quadrupole magnets, will be electrically fed along the 3 km arcs via 600 A and 6 kA superconducting flexible cables. These will be routed into a tube running parallel to the cold masses, placed inside their cryostat [1], from power converters located at each of the 16 arc extremities. The superconducting 53.5 m cable segments will be inserted in the pipeline at machine installation time in the tunnel, thus limiting the number of useless electrical interconnections to the minimum necessary. Cryogenically connected to the 1.9 K superfluid helium vessel of the cold masses at each main quadrupole location, this so-called auxiliary bus-bar tube (EAB) will be thermally and mechanically separated from the magnet main stream. The general layout of the pipeline, its thermo mechanical functional specification and the tight cryogenic, mechanical, electrical, interface and geometrical constraints imposed by the LHC arc cryostat are presented, together with its detailed design

The Interconnections of the LHC Cryomagnets

The main components of the LHC, the next world-class facility in high-energy physics, are the twin-aperture high-field superconducting cryomagnets to be installed in the existing 26.7-km long tunnel. After installation and alignment, the cryomagnets have to be interconnected. The interconnections must ensure the continuity of several functions: vacuum enclosures, beam pipe image currents (RF contacts), cryogenic circuits, electrical power supply, and thermal insulation. In the machine, about 1700 interconnections between cryomagnets are necessary. The interconnections constitute a unique system that is nearly entirely assembled in the tunnel. For each of them, various operations must be done: TIG welding of cryogenic channels (~ 50 000 welds), induction soldering of main superconducting cables (~ 10 000 joints), ultrasonic welding of auxiliary superconducting cables (~ 20 000 welds), mechanical assembly of various elements, and installation of the multi-layer insulation (~ 200 000 m2). Defective junctions could be very difficult and expensive to detect and repair. Reproducible and reliable processes must be implemented together with a strict quality control. The interconnection activities are optimized taking into account several constraints: limited space availability, tight installation schedule, high level of quality, high reliability and economical aspects. In this paper, the functions to be fulfilled by the interconnections and the various technologies selected are presented. Quality control at different levels (component/ interconnect, subsystem, system) is also described. The interconnection assembly sequences are summarized. Finally, the validation of the interconnection procedures is presented, based in particular on the LHC prototype cell assembly (STRING2)

Thermal Design and Performance of the Electrical Distribution Feed Box of the LHC prototype cell

The Electrical Distribution Feed Box (DFBS) is a 4.5 K saturated liquid helium cryostat constructed for the Large Hadron Collider (LHC) Prototype Cell (String 2). The thermal design of the DFBS is presented, with emphasis on the modelling of the cooling of the current lead chimneys via the helium bath boil-off gas and on the design of the lambda plate. The expected performance is compared to measurements done during the first operation phase of the LHC prototype cell

Cryogenic and vacuum sectorisation of the LHC arcs

Following the recommendation of the LHC TC of June 20th, 1995 to introduce a separate cryogenic distribution line (QRL), which opened the possibility to have a finer cryogenic and vacuum sectorisation of the LHC machine than the original 8 arcs scheme, a working group was set up to study the implications: technical feasibility, advantages and drawbacks as well as cost of such a sectorisation (DG/DI/LE/dl, 26 July 1995). This report presents the conclusions of the Working Group. In the LHC Conceptual Design Report, ref. CERN/AC/95-05 (LHC), 20 October 1995, the so-called "Yellow Book", a complete cryostat arc (~ 2.9 km) would have to be warmed up in order to replace a defective cryomagnet. Even by coupling the two large refrigerators feeding adjacent arcs at even points to speed up the warm-up and cool down of one arc, the minimum down-time of the machine needed to replace a cryomagnet would be more than a full month (and even 52 days with only one cryoplant). Cryogenic and vacuum sectorisation of an arc into smaller sectors is technically feasible and would allow to reduce the down-times considerably (by one to three weeks with four sectors of 750 m in length, with respectively two or one cryoplants). In addition, sectorisation of the arcs may permit a more flexible quality control and commissioning of the main machine systems, including cold testing of small magnet strings. Sectorisation, described in detail in the following paragraphs, consists essentially of installing several additional cryogenic and vacuum valves as well as some insulation vacuum barriers. Additional cryogenic valves are needed in the return lines of the circuits feeding each half-cell in order to complete the isolation of the cryoline QRL from the machine, allowing intervention (i.e. venting to atmospheric pressure) on machine sectors without affecting the rest of an arc. Secondly, and for the same purpose, special vacuum and cryogenic valves must be installed, at the boundaries of machine sectors, for the circuits not passing through the cryoline QRL. Finally, some additional vacuum barriers must be installed around the magnet cold masses to divide the insulation vacuum of the magnet cryostats into independent sub-sectors, permitting to keep under insulating vacuum the cryogenically floating cold masses, while a sector (or part of it) is warmed up and opened to atmosphere. A reasonable scenario of sectorisation, namely with four 650-750 m long sectors per arc, and each consisting of 3 or 4 insulation vacuum sub-sectors with two to four half-cells, would represent an additional total cost of about 6.6 MCHF for the machine. It is estimated that this capital investment would be paid off by time savings in less than three long unscheduled interventions such as the change of a cryomagnet

Update of the LHC Arc Cryostat Systems Layouts and Integration

Since the LHC Conceptual Design report's publication in October 1995 [1], and subsequent evolutions [2], the LHC Arc Cryostat System has undergone recently a number of significant changes, dictated by the natural evolution of the project. Most noteworthy are the recent decisions to route the large number of auxiliary circuits feeding the arc corrector magnets in a separate tube placed inside the cryostat with connections to the magnets every half-cell. Further decisions concern simplification of the baseline vacuum and cryogenic sectorization, the finalization of the design of the arc cryogenic modules and the layout of the arc electrical distribution feedboxes. The most recent features of the highly intricate cryogenics, magnetic, vacuum and electrical distribution systems of the LHC are presente