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Dewar & Refrigerator Modifications
Dewar and Refrigerator Modifications

Case and radiation shield extensions (increase "B" dimension) The "B" dimension refers to the vertical distance from the cold work surface to the radiation shield. When larger than standard amounts of work space are needed, both the case and radiation shield lengths may be increased.
Custom hole pattern on cold work surface To accommodate special requirements, the standard pattern of tapped holes in the bottom plate may be modified.
Exterior finish The exterior finish of all dewars and refrigerators is anodized aluminum. Gold is the standard color; however, blue, red, green, black and purple are also available.
High altitude / balloon modification When the case of a dewar must be operated at temperatures well below the standard range, indium seals are substituted for the standard butyl o-rings.
Increased LHe and/or LN2 capacities For each vessel diameter the standard length nearly equals the diameter. For additional capacities, without increasing the diameter, the length of the vessel is increased up to a factor of two. For larger increases in capacity and hold time it is better to increase the diameter.
Inverted operation To facilitate direct optical access to the work space from above, a modification may be added that allows the dewar to operate inverted without significant penalty in hold-time. Large windows may be accommodated in this configuration.
LHe cooled radiation shield To provide additional rejection of incident IR backgrounds within the dewar, a shield may be added which attaches directly to the cold work surface. Usually this shield is fitted with a removable bottom plate similar to the standard shield.
Low temperature modification (LHe only) To facilitate pumping the LHe bath to temperatures below 1.4K the neck tube is modified. This modification permits temperatures as low as 1.2K.
Low temperature modification (LN2 only)
To pump liquid nitrogen below the triple point, copper webbing is added to the interior of the cryogen vessel. This increases thermal contact with the solid nitrogen and allows for effective cooling.
Rigid support system Standard dewar supports are designed to provide excellent hold-times. When greater strength is needed to meet special mechanical requirements a more rigid support system is used in place of the standard system.
Split case and radiation shield To provide direct access to the work space, the case and radiation shield are modified by insertion of demountable joints at the proper location.