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<p>"Growth and properties of vapor diffused Nb3Sn coatings for SRF applications" <br>
</p>
<p><br>
</p>
<p> Uttar Pudasaini <br>
</p>
<p><br>
</p>
<p><br>
</p>
<p> The College of William & Mary
<br>
</p>
<p><br>
</p>
<p>Abstract:<br>
</p>
<p>The critical temperature (¡Ö 18 K) and superheating field (¡Ö 425 mT) of Nb3Sn are almost
<br>
</p>
<p>twice that of niobium, thereby promising the higher quality factor and accelerating
<br>
</p>
<p>gradient at any given temperature compared to traditional SRF cavities made of niobium.
<br>
</p>
<p>It can enable higher temperature for cavity operation (4 K Vs 2 K), resulting in significant
<br>
</p>
<p>reduction in both capital and operating cost for SRF accelerators. The most promising path
<br>
</p>
<p>toward deployment is by tin vapor diffusion coating of niobium cavity interiors via a two
<br>
</p>
<p>steps nucleation-then-growth sequence. Understanding of Nb3Sn nucleation and growth is
<br>
</p>
<p>essential to the progress with Nb3Sn vapor diffusion coatings of SRF cavities. Samples
<br>
</p>
<p>representing different stages of Nb3Sn formation have been produced and examined to elicit
<br>
</p>
<p>the effects of nucleation, growth, process conditions, and impurities. Broadly, nucleation
<br>
</p>
<p>deposits ultra-thin tin film and near-micron sized particles as well, resembling Stranski-Krastanov
<br>
</p>
<p>growth. Tin diffuses via grain boundaries to the Nb3Sn-Nb interface, where the formation of
<br>
</p>
<p>Nb3Sn into the niobium bulk takes place during the growth stage. RF measurements of coated
<br>
</p>
<p>cavities combined with material studies of samples were continuously employed to update the
<br>
</p>
<p>coating process to coat SRF cavities. Following an updated coating process, we were able to
<br>
</p>
<p>produce Nb3Sn single-cell cavity with quality factor 2¡Á1010 for accelerating gradient up to
<br>
</p>
<p>15 MV/m at 4 K, without any significant Q-slope. In this presentation, the genesis of the Nb3Sn
<br>
</p>
<p>coating in a typical tin vapor diffusion process, effect of different coating parameter variation on
<br>
</p>
<p>material properties of Nb3Sn, and their consequences to the coating of SRF cavities will be discussed.</p>
<br>
</div>
<br>
<p></p>
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