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Advanced ADR Cycle

This page describes the cycling of a simple 3-stage advanced Adiabatic Demagnetization Refrigerator (ADR). For an animated schematic depiction of the cycle, see the Animated Advanced ADR. (This animation uses JavaScript.)

This page assumes that you know how the ADR works. For a review, see our ADR Primer. For a less technical view, see the Introduction to ADR's.

Main Parts of the Simple Advanced ADR

A real advanced ADR would contain other parts, such as support structure and magnetic shielding. However, those parts are not important for a simplified discussion of the cycle.

Follow the Heat

Political reporters are often advised to "follow the money". But we, as students of the advanced ADR, will follow the heat flow from one end to the other of the device.

Where the Heat Comes From

Heat is constantly leaking into the advanced ADR from warmer surroundings. It can come in through the physical supports. It can also come in as infrared radiation -- perhaps the radiation that is being studied by the astronomical sensor that the advanced ADR is cooling. Also, the electronics in the astronomical sensors might create a small amount of heat.

Into the Cold End Salt Pill

The purpose of the cold end salt pill is to absorb this heat, so that the astronomers' sensors can stay at their best operating temperature. To hold the cold end temperature steady while the heat is flowing in, the ADR operators must slowly reduce the magnetic field produced by the magnet at the cold end pill. (For an explanation of how the magnetic field change allows the salt pill to absorb heat, see our ADR Primer. For a less technical view, see the Introduction to ADR's.)

The operators must remove the stored energy from the cold end salt pill before they ramp the magnetic field all the way down to zero. For that step, they send the heat:

From the Cold End Salt Pill to the Middle Salt Pill

The middle salt pill is designed so that it can be cooled to a temperature slightly colder than that of the cold end salt pill. That's just what the operators do when they're ready to dump the heat from the cold end to middle pill. (They cool the middle salt pill down by reducing the magnetic field produced by the magnet that surrounds it.) Then they activate the heat switch that connects the middle and cold end salt pills. This allows heat to flow from the cold end pill to the (now slightly colder) middle pill.

As heat flows from the cold end salt pill, operators must increase the magnetic field produced by the magnet that surrounds the cold end pill. If they left the field constant, the temperature of the salt pill would drop as the heat flowed out. When they have transferred as much heat, and ramped up the cold end magnetic field, as much as they want, the operators stop ramping up the magnetic field. The then turn the heat switch off, to block any flow of heat back from the middle pill to the cold end pill.

The operators must also start slowly decreasing the field of the cold end salt pill's magnet, to keep the temperature in the cold end pill constant.

From the Middle Salt Pill to the Hot End Salt Pill

Before they can transfer heat from the middle pill to the hot end pill, operators must bring the middle pill up to the top of its temperature range and bring the hot end pill to the bottom of its temperature range. They do this by ramping up the magnetic field of the middle salt pill magnet and ramping down the field of the hot end salt pill magnet. When the middle salt pill's temperature is higher than the hot end pill's, operators turn on the heat switch that connects the 2 pills. Heat now flows from the middle pill to the slightly colder hot end pill.

When the heat has been transferred, the operators turn off the mid to hot end heat switch.

From the Hot End Salt Pill to the Heat Sink

Operators now heat up the hot end salt pill (by ramping up the magnetic field of the hot end magnet.) They then activate the heat switch that connects the hot end salt pill to the heat sink. The sink might be a liquid helium bath (in which case operators can dump the heat quickly) or a mechanical cryocooler (in which case operators must dump the heat more slowly.)

All the time that the middle and hot end salt pills have been transferring the heat out, the cold end salt pill has been absorbing heat, preparing to start the cycle over again.

Return to Advanced ADR Page.
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Curator: Mark O. Kimball
NASA Official: Eric A. Silk
Last Updated: 09/11/2014