Superconducting radio-frequency cavities are commonly used in modern particle accelerators for applied and fundamental research. Such cavities are typically made of high-purity, bulk Nb and are cooled by a liquid helium bath at a temperature of ~2 K. The size, cost and complexity of operating a particle accelerator with a liquid helium refrigerator makes the current cavity technology not favorable for use in industrial-type accelerators. We developed a multi-metallic 1.495~GHz elliptical cavity conductively cooled by a cryocooler. The cavity has a ~2 $\mu$m thick layer of Nb$_3$Sn on the inner surface, exposed to the rf field, deposited on a ~3 mm thick bulk Nb shell and a bulk Cu shell, of thickness $\geqslant 5$ mm deposited on the outer surface by electroplating. A bolt-on Cu plate 1.27 cm thick was used to thermally connect the cavity equator to the second stage of a Gifford-McMahon cryocooler with a nominal capacity of 2 W at 4.2 K. The cavity was tested initially in liquid helium at 4.3 K and reached a peak surface magnetic field of ~36 mT with a quality factor of $2\times 10^9$. The cavity cooled by the crycooler achieved a peak surface magnetic field of ~29 mT, equivalent to an accelerating gradient of 6.5 MV/m, and it was able to operate in continuous-wave with as high as 5 W dissipation in the cavity for 1 h without any thermal breakdown. This result represents a paradigm shift in the technology of superconducting accelerator cavities.

中文翻译：

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具有高热稳定性的多金属传导冷却超导射频腔

超导射频腔常用于现代粒子加速器，用于应用和基础研究。此类腔体通常由高纯度、块状 Nb 制成，并通过约 2 K 温度的液氦浴冷却。使用液氦制冷机操作粒子加速器的尺寸、成本和复杂性使得当前的腔体技术无法有利于用于工业型加速器。我们开发了一种由低温冷却器传导冷却的多金属 1.495~GHz 椭圆腔。腔体的内表面有约 2 $\mu$m 厚的 Nb$_3$Sn 层，暴露在射频场中，沉积在约 3 mm 厚的块状 Nb 壳和块状 Cu 壳上，厚度为 $\ geqslant 5$ mm 通过电镀沉积在外表面上。螺栓固定式铜板 1. 27 cm 厚用于将腔赤道热连接到 Gifford-McMahon 低温冷却器的第二级，在 4.2 K 时标称容量为 2 W。腔最初在 4.3 K 的液氦中进行测试，并达到峰值表面磁场约 36 mT，品质因数为 $2\times 10^9$。由低温冷却器冷却的腔体实现了~29 mT 的峰值表面磁场，相当于 6.5 MV/m 的加速梯度，并且它能够在连续波中工作，腔体中的耗散高达 5 W 1 h 没有任何热击穿。这一结果代表了超导加速器腔技术的范式转变。3 K 并达到 ~36 mT 的峰值表面磁场，品质因数为 $2\times 10^9$。由低温冷却器冷却的腔体实现了~29 mT 的峰值表面磁场，相当于 6.5 MV/m 的加速梯度，并且它能够在连续波中工作，腔体中的耗散高达 5 W 1 h 没有任何热击穿。这一结果代表了超导加速器腔技术的范式转变。3 K 并达到 ~36 mT 的峰值表面磁场，品质因数为 $2\times 10^9$。由低温冷却器冷却的腔体实现了~29 mT 的峰值表面磁场，相当于 6.5 MV/m 的加速梯度，并且它能够在连续波中工作，腔体中的耗散高达 5 W 1 h 没有任何热击穿。这一结果代表了超导加速器腔技术的范式转变。