Counting down to 2 Kelvin – the clock is ticking...

This article depicts the fastest way to reach a sample temperature of 2 K or -271°C with the Quantum Design DynaCool. We start at 302 K, which is about normal ambient temperature. The DynaCool, or, more precisely, the PPMS-DynaCool, is a system for measuring physical properties at high magnetic fields and low temperatures. Depending on the available options, measured parameters can be magnetic, electric or thermal behavior. The system is operated by a sequence in the professional Windows software, where the user can manually determine the order of the executable commands. Coding knowledge is not necessary. The sequence is shown in the figure.
This is how we proceed: We start a logfile for the data that interests us and, above all, the temperature and temperature status. After that, DynaCool starts controlling the temperature. The maximum possible value is 50 K/min, which we do not fully achieve. Our highest speed is around 30 K/min. After approx. 29 minutes, we fall below a sample temperature of 10 K, which means we have operated at an average speed of about 10 Kelvin per minute. Once the temperature drops below 10 K, the DynaCool temp control automatically switches the cooling mode to the so-called “Low Temperature Flow”.  The system’s cooling is now slower, but cooler. To achieve this, the system software changes the flow rate or the two capillaries which are the core of the temperature control. Below 10 Kelvin, the base temperature of 1.85 K must be reached and stabilized. The system can remain at 1.85 K for an unlimited period of time.
With 2 Kelvin, our goal is a bit higher. All in all, it hasn’t even taken 45 minutes to reach 2 Kelvin. The temperature stabilizes quickly. No variations, no oscillations and the noise stays in the mili-Kelvin range. The full temperature curve is depicted in the figure. The temperature is plotted on a logarithmic scale.
According to our sequence, DynaCool stays at 2 Kelvin for 5 minutes and then heats up to 300 Kelvin again.

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