A passive switch has an internal absorber and operates automatically; it turns ON and remains fully ON while the hot end temperature is greater than around 15-20K. In the ON state the thermal conductivity is large (around 100mW/K at 4K). When the hot end temperature drops below around 10K the switch will start to turn OFF though it will not be fully OFF until the hot end temperature is ~4K. When the switch is OFF it has a residual thermal conductance dictated by the material properties and dimensions of the shell.
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