Superconducting Technology Assessment - nitrd

Enclosures and Shields
Enclosures and shields are required to operate SCE:
■ At cold temperatures.
■ Under vacuum.
■ Without magnetic interference, undue radiative heat transfer or vibration.
The vacuum dewar is an integral part of the cryocooler operation and should be designed concurrently. A hard
vacuum is needed to avoid moisture formation in the system during the operation at low temperatures and to
minimize convective heat transfer from the cold to warmer parts. Vibration of the system can translate into
parasitic magnetic currents that may disrupt the operation of SCE circuits. Most of the engineering data such as
magnetic noise levels, vibration levels, materials used and design techniques are trade secrets to various companies
such as NGST, HYPRES and others who developed such systems in the past.
The basic operation of SCE circuits at temperatures as low as 4 K has been demonstrated by several companies as
prototypes or as products. Most of these systems were single rack or single stage standalone systems. A few
examples are shown in the following figures.
As can be seen in these figures, all of them use a circularly symmetrical packaging approach and are of a similar
size, on the order of 20-100 cm. Other rack mounted designs can be envisioned for distributed systems.
Cryo packaging information about non-U.S. applications is scarce. Although several sources, such as NEC, report
on their SCE circuit design and performance, they seldom report on their packaging approach. Reported test results
may be derived from laboratory style apparatus.
Figure 6. A prototype cryo enclosure for operation at 4 K (Ref: NGST).
233