Development of an ADR Refrigerator with Two Continuous Stages

Abstract

We present a magnetic cooling chain designed to have a continuous heat sink below 50 mK. It has been focused on providing a cryogen-free and autonomous operation for the users. The challenge is to provide two levels of continuous cooling in order to control the heat balance on the coldest stage. Designed for scientific research and high sensitivity cryogenic detectors applications, the prototype has been validated with a kinetic inductance detectors array. A completely autonomous operation of the cryogenics system from 300 K down to 100 mK has been validated.

Accurate Prediction of the Magnetic Ordering Temperature of Ultralow-Temperature Magnetic Refrigerants

“…To obtain high resolution, it typically operates at temperatures below 100 mK. − The only cryogenic refrigeration technology that can reach such low temperatures under gravity-free conditions is adiabatic demagnetization refrigeration (ADR). This technology relies on the magnetocaloric effect (MCE), i.e., the magnetic entropy or adiabatic temperature of magnetic refrigerants changes in response to the applied magnetic field. − Therefore, ADR has been intensively investigated by space administrations in the past three decades, such as NASA/Goddard Space Flight Center, JAXA (Japan), and ESA (Europe). − As ADR operates in the temperature range of 100 mK to 4 K and no magnetic refrigerants reported so far exhibit a large magnetic entropy change (−Δ S m ) throughout this temperature range, a cascaded multistage ADR system is adopted to achieve continuous refrigeration. , In the current ADR system, paramagnetic salts are used as magnetic refrigerants below 1 K because they have small −Δ S m at temperatures above 1 K, , while Gd 3 Ga 5 O 12 (GGG) is employed as magnetic refrigerants at 1–4 K. , However, the −Δ S m of GGG, despite being much larger than that of paramagnetic salts, is objectively insufficient, especially under a low magnetic applied field on account of the higher need for the cooling power of recent advances in arraying and multiplexing technologies . Hence, there is an urgent need to seek magnetic refrigerants with large −Δ S m at temperatures of 1–4 K for the increasing requirements.…”

“…8−10 As ADR operates in the temperature range of 100 mK to 4 K and no magnetic refrigerants reported so far exhibit a large magnetic entropy change (−ΔS m ) throughout this temperature range, a cascaded multistage ADR system is adopted to achieve continuous refrigeration. 11,12 In the current ADR system, paramagnetic salts are used as magnetic refrigerants below 1 K because they have small −ΔS m at temperatures above 1 K, 13,14 while Gd 3 Ga 5 O 12 (GGG) is employed as magnetic refrigerants at 1−4 K. 15,16 However, the −ΔS m of GGG, despite being much larger than that of paramagnetic salts, is objectively insufficient, especially under a low magnetic applied field on account of the higher need for the cooling power of recent advances in arraying and multiplexing technologies. 17 Hence, there is an urgent need to seek magnetic refrigerants with large −ΔS m at temperatures of 1−4 K for the increasing requirements.…”