Vacuum problems in JETFunded under: FP2-FUSION 10C
JET has a fully metallic, completely welded vacuum vessel which can be heated up to 500 C. The internal surface is approximately 1000m2, the volume 200 m3, and the installed pumping speed for hydrogen 8500 l/s. The base pressure (mainly hydrogen) is normally smaller than 2x1.0 E-7 mbar at the operating temperature of 300 C. The total pressure for impurities can be as low as 5x1.0 E-10 mbar, depending on conditioning methods applied and the wall materials used. The operation of JET has demonstrated the need to protect the metallic walls of the vessel against damage by energetic electrons. Initially fine grain, high purity graphite was used, later beryllium layers of a total thickness of about 1 micron were evaporated onto the graphite and then massive beryllium was employed as the material in contact with the plasma. This paper briefly describes the principle of tokamak experiments and discusses the role of plasma contamination by impurities generated at the walls of the vacuum vessel, the design of the JET vaccuum vessel, the wall conditioning techniques employed and the experience gained with different wall materials.
Bibliographic Reference: Report: JET-P(90)24 EN (1990) 11 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199011478 / Last updated on: 1994-12-02
Original language: fr
Available languages: fr