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Amrit, Jay; François, M.X.

doi:10.1023/a:1016341826786

Cited by 14 publications

(8 citation statements)

References 8 publications

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“…In sum- mary, R K constitutes the major impedance for heat evacuation from monocrystalline cavities. On a more fundamental aspect of the Kapitza resistance, previous studies [4,5] on polycrystalline niobium have shown that R K systematically decreases as the surface roughness is increased. Results of the present study, as seen in Fig.…”

Section: B Kapitza Resistancementioning

confidence: 98%

“…K between the outer cavity wall and the surrounding superfluid helium coolant. The thermal conductivity of niobium is generally monitored by controlling parameters like (i) the chemical purity [residual-resistivity ratio (RRR)] [4,5], (ii) the grain size anisotropy and thermal resistance at boundaries between grains [6] in the case of polycrystals, especially in the vicinity of the welding of two half cells, and (iii) the deformation the niobium samples have been subjected to [7] and the dislocation density in Nb.…”

Section: Introductionmentioning

confidence: 99%

“…This transmission is (as we shall see later) barely due to acoustic properties of the bulk niobium and the superfluid, unlike for solid/solid interfaces. Experiments carried out on clean well-characterized surfaces have shown [12] that the major factors which contribute to the transmission arise from the solid/liquid He interface morphology at microscales/nanoscales, with the exact dependence on surface chemical purity and surface roughness yet to be established in a general theory. Hence, R K has to be measured for each sample.…”

Section: Introductionmentioning

confidence: 99%

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

Amrit

Antoine

2010

Phys. Rev. ST Accel. Beams

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The use of large grains or single crystal niobium to improve the Q factor of superconducting rf cavities for particle accelerators, is presently under study. Heat extraction which plays a decisive role in the thermomagnetic stability of these devices depends on the thermal conductivity of niobium K and the thermal boundary (Kapitza) resistance R K at the niobium/superfluid helium interface. Here we present the first measurements of R K performed between 1.5-2.1 K with single crystal (111) niobium, having two different surface morphologies, namely, a surface with a damage layer and a chemically polished surface. The thermal conductivity of the single crystal Nb samples is also simultaneously determined. For monocrystalline niobium we demonstrate that R K is an increasing primary limiting factor with temperature, contrary to the behavior found for polycrystalline cavities. The present investigation reveals for the first time that the presence of impurities (metallic particles and oxygen) within the damage layer leads to a stronger R K , although the effective heat exchange area to the superfluid is increased. We further show the importance of dislocations in the thermal conductivity of monocrystalline niobium.

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Section: B Kapitza Resistancementioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Amrit

Antoine

2010

Phys. Rev. ST Accel. Beams

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“…Several studies reveal that nanometer length scale surface roughness plays an important role in affecting the Kapitza conductance [8,9]. At a macroscopic level, larger scale roughness carries more number of smaller scale roughness superimposed onto them.…”

Section: Kapitza Conductance Measurementsmentioning

confidence: 99%

Thermal design studies in superconducting rf cavities: Phonon peak and Kapitza conductance

Aizaz

Grimm

Wright

2010

Phys. Rev. ST Accel. Beams

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Thermal design studies of superconducting radio frequency (SRF) cavities involve two thermal parameters, namely the temperature dependent thermal conductivity of Nb at low temperatures and the heat transfer coefficient at the Nb-He II interface, commonly known as the Kapitza conductance. During the fabrication process of the SRF cavities, Nb sheet is plastically deformed through a deep drawing process to obtain the desired shape. The effect of plastic deformation on low temperature thermal conductivity as well as Kapitza conductance has been studied experimentally. Strain induced during the plastic deformation process reduces the thermal conductivity in its phonon transmission regime (disappearance of phonon peak) by 80%, which may explain the performance limitations of the defect-free SRF cavities during their high field operations. Low temperature annealing of the deformed Nb sample could not recover the phonon peak. However, moderate temperature annealing during the titanification process recovered the phonon peak in the thermal conductivity curve. Kapitza conductance measurements for the Nb-He II interface for various surface topologies have also been carried out before and after the annealing. These measurements reveal consistently increased Kapitza conductance after the annealing process was carried out in the two temperature regimes.

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“…The details of the experiments are described in [10]. Our experiments were done on pure single crystal silicon disks (2 mm in thickness and 2 cm in diameter).…”

Section: Comparison With Experimentsmentioning

confidence: 99%