Instrumentation for localized superconducting cavity diagnostics

Conway, Zachary; Ge, Mingqi; Iwashita, Yoshihisa

doi:10.1088/1361-6668/30/3/034002

Cited by 10 publications

(12 citation statements)

References 27 publications

(40 reference statements)

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“…Besides the cylindrical geometry, transient heat transfer of He II in spherical geometry is also relevant to practical applications. In particular, it has been known that superconducting accelerator cavities cooled by He II can quench due to transient heating from tiny surface defects [24]. Locating these surface hot spots for subsequent defect removal is the key for improving the cavity performance.…”

Section: Introductionmentioning

confidence: 99%

Transient heat transfer of superfluid $^4$He in nonhomogeneous geometries -- Part I: Second sound, rarefaction, and thermal layer

Bao,

Guo

2021

Preprint

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Transient heat transfer in superfluid 4 He (He II) is a complex process that involves the interplay of the unique counterflow heattransfer mode, the emission of second-sound waves, and the creation of quantized vortices. Many past researches focused on homogeneous heat transfer of He II in a uniform channel driven by a planar heater. In this paper, we report our systematic study of He II transient heat transfer in nonhomogeneous geometries that are pertinent to emergent applications. By solving the He II two-fluid equation of motion coupled with the Vinen's equation for vortex-density evolution, we examine and compare the characteristics of transient heat transfer from planar, cylindrical, and spherical heaters in He II. Our results show that as the heater turns on, an outgoing second-sound pulse emerges, in which the vortex density grows rapidly. These vortices attenuate the second sound and result in a heated He II layer in front of the heater, i.e., the thermal layer. In the planar case where the vortices are created throughout the space, the second-sound pulse is continuously attenuated, leading to a strong thermal layer that diffusively spreads following the heat pulse. On the contrary, in the cylindrical and the spherical heater cases, vortices are created mainly in a thin thermal layer near the heater surface. As the heat pulse ends, a rarefaction tail develops following the second-sound pulse, in which the temperature drops. This rarefaction tail can promptly suppress the thermal layer and take away all the thermal energy deposited in it. The effects of the heater size, heat flux, pulse duration, and temperature on the thermal-layer dynamics are discussed. We also show how the peak heat flux for the onset of boiling in He II can be studied in our model.

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Section: Introductionmentioning

confidence: 99%

Transient heat transfer of superfluid $^4$He in nonhomogeneous geometries -- Part I: Second sound, rarefaction, and thermal layer

Bao,

Guo

2021

Preprint

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“…The maximum accelerating gradient of SRF cavities can be improved by removing the surface defects via mechanical grinding, tumbling the cavity, and electron or laser re-melting [4][5][6]. In order to locate the surface defects, a multi-channel temperature mapping (T-mapping) method was first developed [7,8].…”

Section: Introductionmentioning

confidence: 99%

“…Despite the usefulness of T-mapping, the spatial resolution is limited by the spacing between sensors (i.e., of order 1 cm). Furthermore, the installation of the large amount of sensors makes the application of this method an extremely laborious task [6]. An alternative way to apply T-mapping is to scan the cavity surface using a rotating arm with just a few sensors arranged in a stripe.…”

Section: Introductionmentioning

confidence: 99%

Quench-Spot Detection for Superconducting Accelerator Cavities Via Flow Visualization in Superfluid Helium-4

Bao

Guo

2019

Phys. Rev. Applied

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Superconducting ratio-frequency (SRF) cavities, cooled by superfluid helium-4 (He II), are key components in modern particle accelerators. Quenches in SRF cavities caused by Joule heating from local surface defects can severely limit the maximum achievable accelerating field. Existing methods for quench spot detection include temperature mapping and second-sound triangulation. These methods are useful but all have known limitations. Here we describe a new method for surface quench spot detection by visualizing the heat transfer in He II via tracking He * 2 molecular tracer lines. A proof-of-concept experiment has been conducted, in which a miniature heater mounted on a plate was pulsed on to simulate a surface quench spot. A He * 2 tracer line created nearby the heater deforms due to the counterflow heat transfer in He II. By analyzing the tracer-line deformation, we can well reproduce the heater location within a few hundred microns, which clearly demonstrates the feasibility of this new technology. Our analysis also reveals that the heat content transported in He II is only a small fraction of the total input heat energy. We show that the remaining energy is essentially consumed in the formation of a cavitation zone near the heater. By estimating the size of this cavitation zone, we discuss how the existence of the cavitation zone may explain a decades-long puzzle observed in many second-sound triangulation experiments.

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“…We introduce two quench localization systems, temperature mapping system and second sound system, that are widely used in laboratories. Many other diagnostic techniques exist, such as X-ray radiation mapping [24] and optical inspection, and we refer to [2] and the references therein for more information. The temperature mapping system (T-mapping) [2] is a traditional approach for locating a quench position by measuring small temperature increases on the exterior of SRF cavities in liquid helium bath.…”

Section: Introductionmentioning

confidence: 99%