Abstract Knowledge of radiative heat transfer between bodies at various temperatures is essential for efficient design of cryogenic devices. Radiative far-field heat transfer is commonly taken into account. Nevertheless, when the distance d between components of a device becomes small, smaller than the characteristic wavelength of Planck’s far field thermal radiation, an additional heat transfer caused by thermal electromagnetic near-field starts to play a role. At cryogenic temperatures and micrometric distances, this near field heat transfer can exceed the far-field one by orders of magnitude. We report experimental results on near-field and far-field heat fluxes q transferred across a plane parallel vacuum gap d between pair of identical copper (RRR=10) and tungsten (RRR=1.5) samples. The heat flux q was measured over the distances d =1–100 μm and for various temperatures T2 =15 – 80 K of the hot sample and the temperature T1 down to 5 K of the cold one. We compare the copper and tungsten data with previously published results for normal metals Nb and NbN. For each pair of identical samples, the measured values of near-field thermal conductivity of vacuum gap, KT=q/(T2-T1), collapse into nearly a single dependence on the gap size d. Thus for specific metallic surfaces, this relation enables estimate the near field heat flux at cryogenic temperatures over micrometric distances.

中文翻译：

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低温下宏观金属表面之间的近场辐射传热

摘要 了解不同温度下物体之间的辐射传热对于低温设备的有效设计至关重要。通常考虑辐射远场传热。然而，当器件组件之间的距离 d 变小时，小于普朗克远场热辐射的特征波长时，热电磁近场引起的额外热传递开始起作用。在低温和微米距离下，这种近场传热可以超过远场传热几个数量级。我们报告了在一对相同的铜 (RRR=10) 和钨 (RRR=1.5) 样品之间通过平面平行真空间隙 d 传递的近场和远场热通量 q 的实验结果。在距离 d =1–100 μm 上测量热通量 q，并且对于热样品的各种温度 T2 =15 – 80 K 和温度 T1 下降到冷样品的 5 K。我们将铜和钨数据与之前公布的普通金属 Nb 和 NbN 的结果进行比较。对于每对相同的样品，真空间隙近场热导率的测量值 KT=q/(T2-T1) 几乎完全依赖于间隙尺寸 d。因此，对于特定的金属表面，这种关系能够估计低温下微米距离上的近场热通量。真空间隙近场热导率的测量值 KT=q/(T2-T1) 几乎完全依赖于间隙尺寸 d。因此，对于特定的金属表面，这种关系能够估计低温下微米距离上的近场热通量。真空间隙近场热导率的测量值 KT=q/(T2-T1) 几乎完全依赖于间隙尺寸 d。因此，对于特定的金属表面，这种关系能够估计低温下微米距离上的近场热通量。