| 摘要 |
When it is desired to change the magnetic field levels in a superconducting magnet, it is conventional practice to employ electrical leads. One end of the leads is maintained at cryogenic temperatures while the other is at ambient temperature. In some cases, it is desirable to remove the leads when they are not being used, in order to reduce thermal losses. In that case, it is conventional practice to make and break the contact at the cryogenic temperature. However, repeated make and break contacts with such lead can produce worn contact surfaces that eventually exhibit a higher resistance than is desired. This high resistance will give rise to heating of the cryogenic components. In order to alleviate this problem, an excitation lead system is provided which is removable from the cryostat. Furthermore, thermal insulation means are provided so that the external connection is relatively warm when the leads are connected, but is maintained at relatively cold temperatures during normal operation of the superconducting device. The fact that the contact is relatively warm when the lead is in use relaxes the requirement for a low resistance contact.
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