Energen, Inc. has developed and demonstrated a high conductance detachable thermal link for operation at sub-Kelvin temperatures using high force, long stroke cryogenic magnetostrictive actuators. Such mechanical heat switches are an important component for calorimeters and adiabatic demagnetization refrigerators (ADRs) which are increasingly being considered for instrumentation and detector cooling.

This heat switch uses KelvinAll, a magnetostrictive material developed by Energen, as the active element. Unlike other magnetostrictive materials, KelvinAll operates over a broad temperature range. At cryogenic temperatures it delivers a long stroke, allowing a large separation gap between the contacting surfaces when the switch is disengaged. This makes alignment and operation of the heat switch easy.

This heat switch is normally closed to allow fast cooling, and is designed to eliminate any net force between the contacting surfaces. This heat switch is designed so that there is no contact when the power is on, however, the opposite can also be achieved. We have tested our detachable heat switch at cryogenic temperatures, and verified thermal conductance values of 30 mW/K at 4.2 K and 14 mW/K at 1.7 K. Higher conductance is available with stronger mechanical contact between the surfaces.