Heat Switch

Our research is motivated by precision control of heat flow in ultra-low temperature experiments. Specifically, the experiments in our lab are run at temperature of approximately 100 milli-Kelvin. In order to reach the extremely low temperatures, an adiabatic magnetization refrigerator (ADR) must be used. However, in the process of using the ADR, residual heat is generated which must be drawn off to a cold bath.The device used to connect and disconnect the salt pill to the cold bath, in our case a helium bath, is called a heat switch. We developed a mechanical heat switch that is powered by a stepper motor. A stepper motor uses coils of wire to alternate the location of magnetic fields within the motor. This causes a permanent magnet rotor to rotate in small steps, which is why stepper motors are precise control tools that are easily controlled by computer. To control our stepper motor, we used a program usually intended for tuning the motor. We need this motor to run at 4 Kelvin, and the stepper motors used in our experiment needed only slight modifications to do so. Our design uses the stepper motor to control a worm gear assembly to turn a steel rod. The mechanical advantage we gain from the worm gear assembly allows us to use a smaller motor, which also requires less current to operate. This is advantageous because a) we have little space to fit the heat switch and b) the smaller the current, the less heat is generated while operating the motor. The steel rod is connected to copper plates that slide together to create the connection between the salt pill and the helium bath. The copper plates are used because they have a high heat conductance, which allows for a fast transfer of heat. The plates are also gold plated to increase this value further. Both the computer control mechanism and overall heat conductance value require improvement before this device can be considered a viable replacement for the heat switch already in place.

heat switch photo