| 摘要 |
<p>An improved cryostat for the superconducting magnet (50) of an NMR spectrometer comprises a nested structure of isothermal shells (112,114,116) surrounding a thermally conductive central reservoir (110) of substantially spherical shape containing liquid helium in which the superconducting solenoid remains operational when only partially immersed. A radiation shield (112) surrounding the central reservoir is cooled by the boil-off of escaping helium vapor. The radiation shield is enclosed within an isothermal shell (114) maintained at the temperature of liquid nitrogen by thermal contact with a liquid nitrogen reservoir (114') disposed above the region of the central reservoir and shielded therefrom by a wall of the isothermal shell. An outer radiation shield (116) surrounds the liquid nitrogen reservoir and associated isothermal shell and the outer radiation shield is maintained at a constant temperature. A hermetically sealed containment vessel (118) forms the outer wall of the cryostat and provides a port for evacuating to a very low common pressure all the interior spaces between adjacent nested structures. <IMAGE></p> |
