5.2 Key components Ë 123Fig. 5.2:Schematic of the columnar liquid nitrogen vessel with thin bottom. (1) Flange. (2) Vacuum.
(3) Super-insulation [15].
Fig. 5.3:Photograph of the cylindrical liquid nitrogen vessel with thin
bottom.inside diameters of the vessel are 200 and 150 mm, and the height is 250 mm. The
liquid nitrogen vessel can operate continuously for over 16 hours, and can hold 7
YBCO samples of 30 mm in diameter. After 14 years the liquid nitrogen vessel still has
excellent constant temperature performance. The vessel has been used successfully
to measure the levitation forces of YBCO bulk over the PMGs. During the experiment,
the YBCO is fixed to the bottom of the columnar liquid nitrogen vessel. It also provides
experience for the development of the on-board rectangular liquid nitrogen vessel
with a thin bottom and large size.
In order to avoid a collision between the vessel’s bottom surface and the upper
surface of the PMG, there is a gap of 1.5 mm when the vessel moves down to the lowest
point. Thus, the minimum distance between the sample and the PMG surface is 5 mm.
The YBCO is cooled in a zero magnetic field with liquid nitrogen, and it can move up
and down at different velocities.