1981 Volume 50 Issue 3 Pages 296-302
Heliotron E, which is a large-scaled device of Heliotron series, is in operation in Kyoto University. Target plasma parameters of this machine are as follows; plasma density 1×1020m-3, electron temperature 1 keV, ion temperature 0.8 keV and nτ 1018-1019 sec/m3. Plasma confining magnetic fields are produced by the helical coil current. To assure the accuracy of the helical coils, the high level of accuracy was required to the profile of the vacuum chamber. The vacuum chamber twists around the torus by 9.5 times and its poloidal cross section shows a race-track shape in any toroidal position. Major radius is 2200 mm and minor radius is 215.5 mm. The material is the high-strength non-magnetic steel which has low permeability (μ<1.4), high yield strength (≥40kgf/mm2) and special chemical composition (25Cr-12Ni-0.3N). The thickness of the wall is from 20 to 33 mm.
To make the vacuum chamber, 190 pieces were joined together by EB welding after the hot press forming.
A giant apparatus (6.5 m×6.5 m×3.5 m) was prepared and applied and a special re-focusing coil was used for the long beam welding.
The profile accuracy of the vacuum chamber has been controlled as follows; major radius ±3 mm, minor radius ±4.5-1.5 mm, where minus means the inner side.
X-ray and dye-penetrant quality of all welds was acceptable for ASME pressure vessel code and JIS. The laekage was less than 1.3×10-8 Torr 1/sec. The final pressure is 2×10-8 Torr.
