Development of a prototype superconducting radio-frequency cavity for conduction-cooled accelerators
G. Ciovati, J. Anderson, S. Balachandran, G. Cheng, B. Coriton, E. Daly, P. Dhakal, A. Gurevich, F. Hannon, K. Harding, L. Holland, F. Marhauser, K. McLaughlin,… 展开作者
G. Ciovati, J. Anderson, S. Balachandran, G. Cheng, B. Coriton, E. Daly, P. Dhakal, A. Gurevich, F. Hannon, K. Harding, L. Holland, F. Marhauser, K. McLaughlin, D. Packard, T. Powers, U. Pudasaini, J. Rathke, R. Rimmer, T. Schultheiss, H. Vennekate, D. Vollmer
超导射频（SRF）腔相比常导腔具有更高效率，这使得高能连续波直线加速器（linacs）的发展成为可能。近年来，高质量 Nb$_3$Sn 薄膜涂层制备技术的进步，以及 4 K 温区具有高制冷能力的低温制冷机的出现，使得通过热传导冷却方式运行 SRF 腔并在加速器所需的相关加速梯度下工作成为可行。传导冷却 SRF 直线加速器的一个可能应用场景是环境领域，该应用需要能量为 $1 - 10$ MeV、功率为 1 MW 的电子束。我们为此类应用设计了一台 915 MHz SRF 直线加速器，并研制了一个原型单腔，通过使用低温制冷机在实现 1 MeV 能量增益所需的加速梯度下运行该腔，以验证所提出的设计。该腔体内表面具有约 $3$ $\mu$m 厚的 Nb$_3$Sn 薄膜，沉积在约 $\sim4$ mm 厚的块体 Nb 基底上，外部为约 $\sim7$ mm 厚的块体 Cu 外壳，并带有三个 Cu 连接凸耳。该腔体在 4.3 K 的液氦中测试，峰值表面磁场达到 53 mT。我们设计并建造了一个水平测试低温恒温器，用于测试由三台 Gifford-McMahon 低温制冷机冷却的腔体。在 General Atomics 进行的传导冷却腔体射频测试中，实现了 50 mT 的峰值表面磁场，并且在高达 18.5 W 的射频热负载下仍能稳定运行。由微音效应引起的峰值频率偏移为 23 Hz。这些结果代表了迄今为止传导冷却 SRF 腔所达到的最高峰值表面磁场，并满足 1 MeV 能量增益的要求。
英文摘要：
The higher efficiency of superconducting radio-frequency (SRF) cavities compared to normal-conducting ones enables the development of high-energy continuous-wave linear accelerators (linacs). Recent progress in the development of high-quality Nb$_3$Sn film coatings along with the availability of cryocoolers with high cooling capacity at 4 K makes it feasible to operate SRF cavities cooled by thermal conduction at relevant accelerating gradients for use in accelerators. A possible use of conduction-cooled SRF linacs is for environmental applications, requiring electron beams with energy of $1 - 10$ MeV and 1 MW of power. We have designed a 915 MHz SRF linac for such an application and developed a prototype single-cell cavity to prove the proposed design by operating it with cryocoolers at the accelerating gradient required for 1 MeV energy gain. The cavity has a $\sim 3$ $μ$m thick Nb$_3$Sn film on the inner surface, deposited on a $\sim4$ mm thick bulk Nb substrate and a bulk $\sim7$ mm thick Cu outer shell with three Cu attachment tabs. The cavity was tested up to a peak surface magnetic field of 53 mT in liquid He at 4.3 K. A horizontal test cryostat was designed and built to test the cavity cooled with three Gifford-McMahon cryocoolers. The rf tests of the conduction-cooled cavity, performed at General Atomics, achieved a peak surface magnetic field of 50 mT and stable operation was possible with up to 18.5 W of rf heat load. The peak frequency shift due to microphonics was 23 Hz. These results represent the highest peak surface magnetic field achieved in a conduction-cooled SRF cavity to date and meet the requirements for a 1 MeV energy gain.
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We demonstrate practical accelerating gradients on a superconducting radiofrequency (SRF) accelerator cavity with cryocooler conduction cooling, a cooling technique that does not involve the complexities of the conventional liquid helium bath. A design is first presented that enables conduction cooling an elliptical-cell SRF cavity. Implementing this design, a single cell 650 MHz Nb3Sn cavity coupled using high purity aluminum thermal links to a 4 K pulse tube cryocooler generated accelerating gradients up to 6.6 MV/m at 100% duty cycle. The experiments were carried out with the cavity-cryocoo…
SRF cavities for particle acceleration are conventionally operated immersed in a bath of liquid helium at 4.2 K and below. Although this cooling configuration is practically and economically viable for large scientific accelerator installations, it may not be so for smaller accelerators intended for industrial applications such as the treatment of wastewater, sludge, flue gases, etc. In this paper, we describe a procedure to operate SRF cavities without liquid helium that can be used to construct electron-beam sources for industrial applications of electron irradiation (1-10 MeV electron energ…
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 $μ$m thick layer of Nb$_3$Sn on the inner s…
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The research note presents results of coupled RF and thermal simulation of a cryocooler conduction cooled 650 MHz SRF cavity made of bulk niobium and coated with Nb3Sn on the RF surface. The cavity is part of a particle accelerator design capable of producing 10 MeV, 1000 kW electron beam for application in wastewater treatment. More details of the accelerator design are presented in R.C. Dhuley et al. (2022) Phys. Rev. Accel. Beams 25, 041601.
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