Performance of a fast response miniature Adiabatic Demagnetisation Refrigerator using a single crystal tungsten magnetoresistive heat switch

Abstract

a b s t r a c tThe performance of a fast thermal response miniature Adiabatic Demagnetisation Refrigerator (ADR) is presented. The miniature ADR is comprised of a fast thermal response Chromium Potassium Alum (CPA) salt pill, two superconducting magnets and unconventionally, a single crystal tungsten magnetoresistive (MR) heat switch. The development of this ADR is a result of the ongoing development of a continuously operating millikelvin cryocooler (mKCC), which will use only magnetoresistive heat switches. The design and performance of the MR heat switch developed for the mKCC and used in the miniature ADR is presented in this paper; the heat switch has a measured Residual Resistivity Ratio of 32,000 ± 3000 and an estimated switching ratio (on thermal conductivity divided by the off thermal conductivity) of 15,200 at 3.6 K and 38,800 at 0.2 K when using a 3 T magnetic field. The performance of the miniature ADR operating from a 3.6 K bath is presented, demonstrating that a complete cycle (magnetisation, cooling to the bath and demagnetisation) can be accomplished in 82 s. A magnet current step test, conducted when the ADR is cold and fully demagnetised, has shown the thermal response of the ADR to be sub-second. The measured hold times of the ADR with just parasitic heat load are given, ranging from 3 min at 0.2 K with 13.14 lW of parasitics, to 924 min at 3 K with 4.55 lW of parasitics. The cooling power has been measured for operating temperatures in the range 0.25-3 K by applying an additional heat load to the ADR via a heater, in order to reduce the hold time to 3 min (i.e. approximately double the recycle time); the maximum cooling power of the miniature ADR (in addition to parasitic load) when operating at 250 mK is 20 lW, which increases to 45 lW at 300 mK and continues to increase linearly to nearly 1.1 mW at 3 K. To conclude, the predicted performance of a tandem continuous ADR utilising two of the miniature ADRs is presented.

Energy Applications of Magnetocaloric Materials

“…A typical adiabatic demagnetization refrigerator ( Figure 18 ) consists of the full body of a magnetocaloric material placed in the bore of a superconducting magnet. A connection between the magnetocaloric material and the heat sink is established using a thermal switch, which has been extensively researched in several investigations in the past decade . A typical adiabatic demagnetization cycle performs four processes.…”

“…A connection between the magnetocaloric material and the heat sink is established using a thermal switch, [277] which has been extensively researched in several investigations in the past decade. [278,423,424] A typical adiabatic demagnetization cycle performs four processes. 1) The magnetocaloric material in zero field is at the heat-sink temperature with an open heat switch.…”

Single Microwave Photon Detection with a Trapped Electron

“…At 4 K the electron's cyclotron oscillator is typically several quanta above the ground state [5]. In order to cool it further down to the ground state, the Sussex setup is planned to be enhanced with a miniature adiabatic demagnetisation refrigerator (ADR) developed at the Mullard Space Science Laboratory [18]. This device will bring the temperature down to around 80 mK, where the electron's cyclotron oscillator effectively achieves the ground state [5].…”

Solid-State Heating Using the Multicaloric Effect in Multiferroics

“…The purpose of this communication article is to reemphasize the fundamentals of solid-state refrigeration based on the new concept of multicaloric effect in multiferroics A cycle time (path A-B-C in Figure 1d) of the order of seconds is not unrealistic considering the subminute magnetocaloric cycle times presented in Bartlett et al [41] and the relative ease in which an electric field can be generated compared to a magnetic field. When the same heating principle is applied to a suitable multiferroic active element, up to twice the temperature change is expected, leading to even more efficient heating systems.…”