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

Bao, Shiran; Guo, Wei

doi:10.1103/physrevapplied.11.044003

Cited by 11 publications

(5 citation statements)

References 53 publications

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“…As shown in our early work [12], heat transfer of He II in non-homogeneous geometries (such as from cylindrical or spherical heaters) can exhibit new features. Understanding the behavior of the peak heat flux in these geometries could benefit research work such as quenchspot detection on He II cooled superconducting accelerator cavities [40,41] and the heat and mass transfer processes due to a vacuum failure in He II cooled accelerator beamline tubes [42][43][44][45].…”

Section: Discussionmentioning

confidence: 99%

Boiling and cavitation caused by transient heat transfer in superfluid helium-4

Sanavandi,

Hulse,

Bao

et al. 2022

Preprint

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Superfluid helium-4 (He II) has been widely utilized as a coolant in various scientific and engineering applications due to its superior heat transfer capability. An important parameter required in the design of many He II based cooling systems is the peak heat flux q * , which refers to the threshold heat flux above which boiling spontaneously occurs in He II. Past experimental and numerical studies showed that q * increases when the heating time t h is reduced, which leads to an intuitive expectation that very high q * may be achievable at sufficiently small t h . Knowledge on how q * actually behaves at small t h is important for applications such as laser ablation in He II. Here we present a numerical study on the evolution of the thermodynamic state of the He II in front of a planar heater by solving the He II two-fluid equations of motion. For an applied heat flux, we determine the heating time beyond which the He II near the heater transits to the vapor phase. As such, a curve correlating q * and t h can be obtained, which nicely reproduces some relevant experimental data. Surprisingly, we find that there exists a critical peak heat flux q * c , above which boiling occurs nearly instantaneously regardless of t h . We reveal that the boiling in this regime is essentially cavitation caused by the combined effects of the first-sound and the second-sound waves in He II. Based on this physical picture, an analytical model for q * c is developed, which reproduces the simulated q * c values at various He II bath temperatures and hydrostatic head pressures. This work represents a major progress in our understanding of transient heat transfer in He II.

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Section: Discussionmentioning

confidence: 99%

Boiling and cavitation caused by transient heat transfer in superfluid helium-4

Sanavandi,

Hulse,

Bao

et al. 2022

Preprint

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“…When the heat flux exceeds a small critical value, quantized vortices are nucleated spontaneously in the superfluid, which can impede the counterflow and increase the temperature gradient [21]. Our lab has done extensive characterization work on both steady-state [22][23][24][25][26][27][28][29] and transient counterflow [30][31][32] in bulk He II.…”

Section: He II Heat Transfer Modelingmentioning

confidence: 99%

Heat and mass transfer during a sudden loss of vacuum in a liquid helium cooled tube -- Part III

Garceau¹,

Bao²,

Guo³

2021

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A sudden loss of vacuum can be catastrophic for particle accelerators. In such an event, air leaks into the liquid-helium-cooled accelerator beamline tube and condenses on its inner surface, causing rapid boiling of the helium and dangerous pressure build-up. Understanding the coupled heat and mass transfer processes is important for the design of beamline cryogenic systems. Our past experimental study on nitrogen gas propagating in a copper tube cooled by normal liquid helium (He I) has revealed a nearly exponential slowing down of the gas front. A theoretical model that accounts for the interplay of the gas dynamics and the condensation was developed, which successfully reproduced various key observations. However, since many accelerator beamlines are actually cooled by the superfluid phase of helium (He II) in which the heat transfer is via a non-classical thermal-counterflow mode, we need to extend our work to the He II cooled tube. This paper reports our systematic measurements using He II and the numerical simulations based on a modified model that accounts for the He II heat-transfer characteristics. By tuning the He II peak heat-flux parameter in our model, we have reproduced the observed gas dynamics in all experimental runs. The fine-tuned model is then utilized to reliably evaluate the heat deposition in He II. This work not only advances our understanding of condensing gas dynamics but also has practical implications to the design codes for beamline safety.

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“…Locating these surface hot spots for subsequent defect removal is the key for improving the cavity performance. Our team has recently developed an innovative molecular tagging technique for locating surface hot spots via tracking thin lines of He * 2 molecular tracers [25,26]. These tracers move with the normal fluid [27][28][29][30], and therefore the transient radial heat transfer from a hot spot can lead to line deformations that contain accurate information about the spot location.…”

Section: Introductionmentioning

confidence: 99%

“…These tracers move with the normal fluid [27][28][29][30], and therefore the transient radial heat transfer from a hot spot can lead to line deformations that contain accurate information about the spot location. In order to extract this information, it is critical to understand how the heat energy is partitioned between the thermal layer and the second-sound pulse [25]. However, despite some limited studies on steady-state vortex distribution near a spherical heater [31,32], the transient behaviors of the thermal layer and its interaction with the second sound in this geometry have remained largely unexplored [18].…”

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

Cited by 11 publications

References 53 publications

Boiling and cavitation caused by transient heat transfer in superfluid helium-4

Boiling and cavitation caused by transient heat transfer in superfluid helium-4

Heat and mass transfer during a sudden loss of vacuum in a liquid helium cooled tube -- Part III

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

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