Kapitza resistance cooling of single crystal (111) niobium for superconducting rf cavities

Amrit, Jay; Antoine, C.

doi:10.1103/physrevstab.13.023201

Cited by 7 publications

(9 citation statements)

References 20 publications

(33 reference statements)

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“…The results from direct measurements of the thermal resistance of the SRF Nb cavities presented in this article showed a weak dependence from treatments such as sand blasting, BCP and anodization applied to the outer surface. The temperature dependence and the values of thermal resistance we have measured are consistent with the results of Kapitza resistance measurements on small, flat samples [6,7,8] and of thermal resistance obtained from rf measurement of cavities [9]. The small variations of thermal resistance with outer surface treatments can be related to the thermal conductivity of the Nb being the dominant term.…”

Section: Discussionsupporting

confidence: 86%

“…Previously, thermal resistance measurements on SRF niobium samples were carried out in an experimental cell and supplemental measurements of the thermal conductivity allowed extracting Kapitza resistance [6,7,8]. Palmieri et al, [9] measured the thermal boundary resistance via the rf surface resistance measurement in SRF cavities and reported a decrease in thermal boundary resistance after anodizing the outer surface of the cavity.…”

Section: A Thermal Resistance Measurementmentioning

confidence: 99%

“…In our present study, we have estimated the thermal resistance of SRF cavity using the method similar to that used to characterize Nb samples in refs. [6,7]. The schematic representation of the experimental set up is shown in figure 1.…”

Section: A Thermal Resistance Measurementmentioning

confidence: 99%

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Role of thermal resistance on the performance of superconducting radio frequency cavities

Dhakal

Ciovati

Myneni

2017

Phys. Rev. Accel. Beams

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Thermal stability is an important parameter for the operation of the superconducting radio frequency (SRF) cavities used in particle accelerators. The rf power dissipated on the inner surface of the cavities is conducted to the helium bath cooling the outer cavity surface and the equilibrium temperature of the inner surface depends on the thermal resistance. In this manuscript, we present the results of direct measurements of thermal resistance on 1.3 GHz single cell SRF cavities made from high purity large grain and fine grain niobium as well as their rf performance for different treatments applied to outer cavity surface in order to investigate the role of the Kapitza resistance to the overall thermal resistance and to the SRF cavity performance. The results show no significant impact of the thermal resistance to the SRF cavity performance after chemical polishing, mechanical polishing or anodization of the outer cavity surface. Temperature maps taken during the rf test show non-uniform heating of the surface at medium rf fields. Calculations of Q 0 (B p ) curves using the thermal feedback model show good agreement with experimental data at 2 K and 1.8 K when a pair-braking term is included in the calculation of the BCS surface resistance. These results indicate local intrinsic non-linearities of the surface resistance, rather than purely thermal effects, to be the main cause for the observed field dependence of Q 0 (B p ).

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Section: Discussionsupporting

confidence: 86%

Section: A Thermal Resistance Measurementmentioning

confidence: 99%

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Role of thermal resistance on the performance of superconducting radio frequency cavities

Dhakal

Ciovati

Myneni

2017

Phys. Rev. Accel. Beams

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“…It is believed that large grain material tends to exhibit a slightly higher medium field Q value than fine grain material [24,[65][66][67], because it has less GB. However large grain also exhibits very high quality grain substructure as can be inferred from the high phonon peak observed from thermal conductivity measurements [68,69], and crystalline substructure can as well explain the experimental observations.…”

Section: B Grain Boundariessupporting

confidence: 59%

Influence of crystalline structure on rf dissipation in superconducting niobium

Antoine

2019

Phys. Rev. Accel. Beams

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Bulk niobium is the most common material used in the fabrication of rf superconducting cavities for accelerators. Predicting and reducing the rf surface dissipation in these cavity structures is mandatory, since it has a tremendous cost impact on the large accelerator projects. In this paper the author hopes to demonstrate that sources of dissipation usually attributed to external causes (mainly flux trapping during cooldown and hydrides precipitates) are related to the same type of crystalline defects that affect the local superconducting properties and can be at the source of early vortex penetration at the surface. We also want to show how these types of defects can explain some of the discrepancies observed from other laboratories in niobium cavity doping experiments. Understanding the origin and the role of these defects could provide direction for improving material specifications as well as improving fabrication control from sheet material to completed cavity. In particular, we will demonstrate that dislocation entanglements, due to the fabrication damage layer, have the strongest impact for the pinning behavior of trapped flux, as well as hydrogen segregation in cavity niobium. The author wishes to present to the superconducting radio frequency (SRF) accelerator community the synthesis of experimental results scattered in the literature, completed with some personal results. The results of this effort provide a new perspective on recently published work in the domain of SRF cavity doping and sensitivity to trapped flux during cooldown. I will also try to draw whenever possible, some conclusions about other types of superconductors used for SRF applications including Nb=Cu thin films and to discuss their possible change of behavior with field or frequency. I will concentrate on surface and material science aspects since the experimental results on rf cavities have already been treated elsewhere.

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“…The convenient availability of large Nb crystals has enabled a more precise characterization of the Kapitza resistance at the niobium/superfluid helium interface [128].…”

Section: Medium-field Q-slopementioning

confidence: 99%

Superconducting Radio-Frequency Technology R&D for Future Accelerator Applications

Reece¹,

Ciovati²

2013

Reviews of Accelerator Science and Technology

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Superconducting rf technology (SRF) is evolving rapidly as are its applications. While there is active exploitation of what one may term the current state-of-the-practice, there is also rapid progress expanding in several dimensions the accessible and useful parameter space. While state-of-the-art performance sometimes outpaces thorough understanding, the improving scientific understanding from active SRF research is clarifying routes to obtain optimum performance from present materials and opening avenues beyond the standard bulk niobium. The improving technical basis understanding is enabling process engineering to both improve performance confidence and reliability and also unit implementation costs. Increasing confidence in the technology enables the engineering of new creative application designs. We attempt to survey this landscape to highlight the potential for future accelerator applications.

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Kapitza resistance cooling of single crystal (111) niobium for superconducting rf cavities

Cited by 7 publications

References 20 publications

Role of thermal resistance on the performance of superconducting radio frequency cavities

Role of thermal resistance on the performance of superconducting radio frequency cavities

Influence of crystalline structure on rf dissipation in superconducting niobium

Superconducting Radio-Frequency Technology R&D for Future Accelerator Applications

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