Dewars, Cryogenics, Cryocoolers
Tristan has built a wide variety of non-magnetic laboratory, field and hand-held liquid helium and liquid nitrogen dewars for use with SQUIDs or any other cryogenic sensor that requires a non-magnetic dewar. Both liquid helium and liquid nitrogen dewars are available configured for use with single or multiple sensors. Our assortment of standard dewar designs include tailed dewars with close access to the sensors (<5 mm), multi-channel dewars, hand-held dewars that operate in any orientation and larger dewars with more than 30-day operating times. Cryogenic inserts are available for all our standard dewars that mount the SQUID sensors rigidly in the dewar and provide any performance features required of the application. Tristan also manufactures a line of cryocooled dewars that eliminate the need for liquid cryogen transfers. Tristan can supply custom dewars for virtually any application. Custom dewars with different size necks, tails, or cryogen reservoirs can be special ordered . For further details including information on Custom Cryogenics, contact Tristan
Liquid Helium Dewars
As mentioned, Tristan liquid helium dewars include features such as adjustable tail dewars for liquid-to-room temperature gaps as small as 2 mm, curved tails to meet a wide variety of applications (e.g., whole head MEG dewars), ultra-low boiloff dewars capable of 90º and/or 180º operation, and coil-in-vacuum technology.
For liquid helium dewars, the first number after the model number usually signifies the liquid helium capacity (e.g., BMD-9 means a 9 liter biomagnetic dewar). Tristan dewars are fabricated from G-10 insulating glass-fiber composites to ensure magnetic transparency. On special order, Tristan will fabricate dewars with metallic outer shells (signified by the letter M following the dewar volume).
Tristan has developed a series of cryocooled LTS SQUID magnetometers using a 1/10th watt Gifford-MacMahon cycle refrigeration. The GM cryocooler first liquefies helium gas and then supplies sufficient refrigeration to keep the helium liquefied during system operation. Depending on the configuration of the detection coils, the design allows measurements to be taken at or near SQUID sensitivity without the cryocooler inducing magnetic or vibrational noise.
For ultra-sensitive measurements, the cryocooler can be turned off. There is sufficient liquid helium ballast to operate the SQUID magnetometer system for more than a day without restarting the cryocooler. This technology is used both in Tristan’s model DRM-300 rock magnetometer (http://www.tristantech.com/pdf/DRM-300datasheetv1.pdf) and a series of OEM susceptometers. For additional information, please contact Tristan.
Liquid Nitrogen Dewars
For HTS SQUIDs or any other application (e.g., NMR) requiring refrigeration to 77 K, Tristan offers a wide variety of liquid nitrogen dewars. They can be supplied as conventional flat bottom or tailed dewars. Curved and adjustable tail dewars are also available. For liquid nitrogen dewars, the first number (first 2 numbers if a 4-digit number) usually signifies outer diameter of the dewar (in inches) and the next number indicates the number of SQUID sensors the dewar typically accommodates (e.g., NLD-530 means a 5″ diameter, three channel nitrogen dewar). Tristan dewars are fabricated from non-magnetic G-10 fiberglass-epoxy composite to ensure magnetic transparency.
Dimensions of NLD-530, NLD-510 and NLD-310 liquid nitrogen dewars, NLD-210 & NMR dewar (4 hour hold time)
For geophysical applications, Tristan offers conventional liquid nitrogen dewars with hold times as long as 2 weeks. Tristan can also supply dewars for borehole and airborne applications. For NDE applications such as magnetic microscopy, Tristan can supply dewars with sensor-to-room temperature gaps as small as 100 mm.
Borehole dewar NLD-530 dewar in tail of Cessna Caravan
Tristan has a long history of designing and building custom cryogenic systems for a wide variety of uses. One recent good example is a set of single item flight certified dewars for airborne use. These liquid helium dewars, currently in use for SQUID measurements of geophysical properties, have passed a stringent set of requirements including loads exceeding 9 g’s. For information in Tristan’s capability in building custom cryogenics, contact Tristan or see http://tristantech.com/rdl for additional information.