Dilution Refrigerator Measurement Systems

The cooldown time of any system is highly dependent on the amount of added mass, how well it is thermalized, and the quality of copper parts. Because every experiment is different, the added mass varies too much to offer a generalized fully loaded cooldown specification.

You can find performance graphs on our Dilution Refrigerator Measurement System pages that give example cooldown times for different system configurations.

Yes, each Bluefors DR and Helium system (SD, LD, XLD450sl, XLD1000sl) comes with our Gas Handling System and the required amount of helium-4 (60 L, 90 L, 180 L). Both are included in the system cost.

The He-3/He-4 ratios of Bluefors Dilution Refrigerators are:

• SD: 12L/60L
• LD350/LD450/XLD450/LH: 18 L/90 L or 20 L/90 L (for improved cooling power),
• XLD1000: 40 L/180 L

The optimal He-3/He-4 ratio for the XLD1000sl system is 40 L/180 L. There is no reason to add more He-3, as it won’t result in increased cooling power.

To further increase XLD1000sl cooling power we recommend upgrading the pulse tubes to PT310 & PT425 which increase the MXC cooling power by 10-15%

Yes, cooling power can be increased by using a 20 L/90 L He-3/He-4 ratio instead of 18 L/90 L. We do not guarantee an exact value, but we have observed higher cooling power using a 20 L/90 L ratio than the guaranteed values for 18 L/90 L.

To further increase the LD450 cooling power we recommend upgrading the pulse tube to PT310 which increases the MXC cooling power by 15-20%.

The LD system can be shipped with He-4 (90 L) only, but He-3 needs to be transferred during installation. The minimum amount of He-3 is 18 L. For the transfer, the container can be connected to either the KF16 or KF25 port on the gas handling system.

Old mixtures can be used, but the concentration must be known. Our system does not include equipment to analyze the isotopic composition in advance. It is also challenging to extract isotopes selectively once they are mixed.

The 18 L minimum amount of He-3 corresponds to about 17% concentration. This is the minimum concentration your mixtures must have to allow the system to function (in this case all He-4 would be pumped away, and the tank filled with the old mixture).

It is likely that old mixtures would be more concentrated. In this case, some He-4 can be left in the tanks and enough mixture to provide 18-24 L of He-3 would be transferred .

Mixtures should also be clean. We strongly recommend running the mixtures though at least an LN2 trap , and preferably also through an LHe-trap prior to the installation. If the mixtures come from an old dilution refrigerator with oil pumps, they can contain impurities which the LN-trap does not catch and may cause clogging of the system.

Note: For an XLD1000 system, the mixture amounts should be adjusted to 180L (He-4) and minimum 40L (He-3), corresponding to an 18% He-3 concentration.

No, the He-3 gas used does not need to be purchased from Bluefors. If a customer has their own He-3 gas, it is possible to use that. In those cases, the system is delivered with He-4 gas only and the He-3 can be transferred into the gas handling system through KF16 or KF25 port during installation.

The He-3 gas should have N3 (99.9%) purity, and the bottle should have a CGA 580 valve with 600 PSIG (depending on how many liters are in the bottle).

The minimum required amount of He-3 depends on the system type:

• SD: 12 L
• LD350/LD450/XLD450/LH: 18 L
• XLD1000: 40 L
• Helium systems: 0 or 7 L