Closed cycle ³He evaporation coolers

As well as our standard designs, we are able to design and manufacture coolers to customers' own individual requirements. Links to our standard range are below:

 

Coolers defined as "Wet" indicates they are suitable to go into a 'wet' cryostat, i.e. one that uses liquid cryogens.

 

Coolers defined as "Dry" means suitable to bolt onto a mechanical cooler, i.e. a pre-cooling device that requires no liquid cryogens, and reaches a low (3 or 4 K) temperature by means of a heat engine, such as a Pulse-Tube cooler or Joule-Thomson cooler.

 

Sample Product links:
	He-10 'Wet' coolers
	He-10 'Dry' coolers

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RULES OF THUMB ON HOW TO SELECT A CHASE RESEARCH COOLER

 

• Do you have a wet dewar or a mechanical cooler?

 

Mechanical coolers are simple to use, as the need for liquid cryogens is avoided, but they have lower cooling capacity than wet dewars. Therefore, a different design is required to obtain optimal operation with a mechanical cooler. Mechanical coolers may also produce troublesome mechanical vibrations.

 

• Do you want to pump on your main dewar or not? If the answer is NO, you should select a fridge with an internal ⁴He bath (He7 or He10).

 

A fridge with no internal ⁴He bath needs a base temperature below 3K to liquefy the ³He charge, so you need to pump on the dewar main bath during the liquefaction phase to achieve this. Operation of the fridge is easier if you do not pump on the main dewar, and also less wasteful of L⁴He (you will pump away almost half of your L⁴He in merely cooling the reservoir).

 

• What temperature do you want to achieve?

 

If you are happy to work at 300 mK or above, one ³He stage will be sufficient. If you need to get below 300 mK you will need either to have a buffer stage, i.e. two ³He stages in all, or to pump on your main bath. Pumping on your main bath during the run will decrease the operating temperature, both by reducing the thermal loads on the fridge, and by reducing the operating temperature of the pumps, thus making them work harder. On the other hand, pumping is troublesome, wasteful of L⁴He, and can introduce vibrations. You need a good reason before choosing to pump!

 

 

It is possible to achieve base temperatures as low as 220mK (no load) with either a He6 fridge running from a pumped main bath, or a He10 fridge running from an unpumped main bath. Base temperatures of between 210mK (no load, He10) and 290mK (no load, He7) may be attained with fridges running from suitable mechanical coolers. These figures assume that suitable radiation shielding is in place, of course. Actual operational temperatures under thermal load will depend upon the loading.

 

• What load and run time do you require?

 

These factors determine the capacity of the fridge. As a rule of thumb, if you want to run the fridge for a day, each 10 microwatts of load will consume 1 STP litre of ³He. An additional allowance must be made for parasitic loads, depending on the fridge design, but in general this allowance is smaller for fridges with a large applied load. Therefore for example, you would need a 3 litre fridge for a 10 to 15 µW load and a day of run time, but need about a 10 litre fridge for 100 µW of load and a day of run time. Also, for large thermal loads, Chase Research incorporates a heat exchanger into the fridge design. This can be used to sink a fairly large heat load at about 1.5 to 2K, thus reducing the load that is applied to the cold head itself, resulting in lower running temperatures and longer run times than would otherwise be possible.

 

• Do you have any special requirements, for example you want to tilt the fridge more than 30 degrees from vertical, or have particular interfacing needs?

 

Then you may need a bespoke design. One of Chase Research Cryogenics’ unique selling points is its ability to design and manufacture bespoke fridges to individual customer requirements. Contact us to discuss your requirements in full.

 

Indicative prices of standard Chase Research Cryogenics Coolers in 2008

 

Priced in UK£:

He3: from £10,000
He6: from £15,000
He7: from £15,000
He10: from £20,000

 

Prices include diode thermometry and wiring to a micro-D connector. Cold head thermometry
(either a Germanium or RuO2 RTD) can also be supplied at an additional cost, or customer
supplied sensors may be fitted free of charge.

 

Prices may be negotiable in some instances, e.g. for multiple orders.

 

 

We have supplied standard and bespoke coolers to a wide range of clients. The following
diagram illustrates just a few examples of our products.