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Cryogenics and Fluids Branch

A Brief Cycle Description, Advanced Adiabatic Demagnetization Refrigerator

The Parts of the Advanced Adiabatic Demagnetization Refrigerator

The Advanced Adiabatic Demagnetization Refrigerator consists of 3 simple Adiabatic Demagnetization Refrigerators in a row. Each of the 3 refrigerators contains these parts:

• The Salt Pill: The salt pill is a block of a paramagnetic substance which can absorb heat. We can make it dump that heat by means of the next item on the list:
• The Magnet: We can increase the magnetic field of the magnet in order to increase the temperature of the salt pill and allow us to dump the heat to a higher temperature heat sink. To get to that heat sink, the heat must pass through the next item on the list:
• The Heat Switch: We're all familiar with electrical switches. When we turn them on, electricity flows. When we turn them off, electricity can't flow. A heat switch does the same thing for heat. Turn it on, heat can flow. Turn it off, heat can't flow.

The Advanced Adiabatic Demagnetization Refrigerator in the schematic diagram has 3 stages, each stage a simple Adiabatic Demagnetization Refrigerator. I've labelled these stages (in order) the Cold End Stage, the Mid Stage, and the Hot End Stage. Each stage is connected to the next one through its heat switch. The jobs of the stages are:

• The Cold End Stage: Stays at a constant low temperature, absorbing heat from the payload to keep it cold.
• The Mid Stage: Collect accumulated heat from the Cold End Stage, dump it to the Hot End Stage.
• The Hot End Stage: Accept heat from the Mid Stage, dump it to the warm heat sink (which may be a mechanical refrigerator or a coolant bath.)

The Cycle

• We start the cycle with all the heat switches turned off. The Cold End Stage has been absorbing heat from the payload. It needs to dump some of the accumulated heat.
• The Mid Stage has cooled to slightly colder than the Cold End Stage. The switch connecting the Mid and Cold End Stages turns on. Heat flows from the Cold End Stage to the slightly cooler Mid Stage. When enough heat has transferred, the heat switch turns off.
• We now must warm up the Mid Stage so it can dump the transferred heat to the Hot End Stage. We do this by increasing the magnetic field produced by the Mid Stage Magnet. The Mid Stage Salt Pill heats up.
• The heat switch connecting the Mid and Warm End Stages turns on. Heat flows from the Mid Stage to the Hot End Stage.
• When enough heat has transferred, the heat switch turns off. The magnetic field drops.
• We now must warm up the Hot End Stage so that it can dump the transferred heat to the heat sink. So, we turn up the field of the Hot End Stage Magnet. The Hot End Stage Salt Pill warms up.
• The heat switch connecting the Hot End Stage to the heat sink turns on. Heat flows from the Hot End Stage to the heat sink. When enough heat has flowed, the heat switch turns off. The magnetic field drops. The cycle can begin again.

• Cycle Animation
• Advanced ADR page

Curator: Mark O. Kimball NASA Official: Eric A. Silk Last Updated: 09/11/2014