Thermal Magnetoconductivity of Tungsten Below 6 K: Combining the Zero-, Low- and High-Field Cases

Hills, MJ; Hepburn, I. D.; Bartlett, J.; Hardy, Gareth

doi:10.1007/s10909-014-1220-7

Cited by 10 publications

(2 citation statements)

References 28 publications

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“…They are naturally in the high thermally conducting (on) state and are switched off by the application of a magnetic field perpendicular to the direction of heat flow, which suppresses the electronic conduction; the heat conducted due to the electrons decreases with increasing magnetic field, with the thermal conductivity ultimately being dominated by phonons. For detailed MR theory, refer to Hills et al [8].…”

Section: Magnetoresistive Heat Switchesmentioning

confidence: 99%

“…However, based on experiments and research conducted at MSSL on a range of tungsten heat switches, the thermal conductivity has been estimated. In Hills et al [8], an equation is derived which allows the thermal conductivity (j) below 6 K to be calculated as a function of magnetic field (B) and temperature (T) (see Eq. (1)).…”

Section: Single Crystal Tungsten Mr Heat Switch For the Millikelvin Cmentioning

confidence: 99%

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

Bartlett¹,

Hardy²,

Hepburn³

2015

Cryogenics

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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.

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Section: Magnetoresistive Heat Switchesmentioning

confidence: 99%

Section: Single Crystal Tungsten Mr Heat Switch For the Millikelvin Cmentioning

confidence: 99%