[Jlabsa_gs] **Reminder** Pizza Seminar - Wednesday, June 12, 2019 - a message from Lorelei Carlson
Jodi Patient
patient at jlab.org
Tue Jun 11 09:59:31 EDT 2019
All we ask is that you please RSVP, as we have limited space and want to order
enough food for all attendees.
Please RSVP to: patient at jlab.org by noon on June 11, 2019
For the summer lecture series and other summer events, take a look at the
Jefferson Lab's Graduate Student and Post-Doc Association Wiki:
https://gspda.jlab.org/wiki/index.php/Main_Page
Wednesday, June 12, 2019
***L102***
12:00-1:00 pm
"Growth and properties of vapor diffused Nb3Sn coatings for SRF applications"
Uttar Pudasaini
The College of William & Mary
Abstract:
The critical temperature (≈ 18 K) and superheating field (≈ 425 mT) of Nb3Sn are almost
twice that of niobium, thereby promising the higher quality factor and accelerating
gradient at any given temperature compared to traditional SRF cavities made of niobium.
It can enable higher temperature for cavity operation (4 K Vs 2 K), resulting in significant
reduction in both capital and operating cost for SRF accelerators. The most promising path
toward deployment is by tin vapor diffusion coating of niobium cavity interiors via a two
steps nucleation-then-growth sequence. Understanding of Nb3Sn nucleation and growth is
essential to the progress with Nb3Sn vapor diffusion coatings of SRF cavities. Samples
representing different stages of Nb3Sn formation have been produced and examined to elicit
the effects of nucleation, growth, process conditions, and impurities. Broadly, nucleation
deposits ultra-thin tin film and near-micron sized particles as well, resembling Stranski-Krastanov
growth. Tin diffuses via grain boundaries to the Nb3Sn-Nb interface, where the formation of
Nb3Sn into the niobium bulk takes place during the growth stage. RF measurements of coated
cavities combined with material studies of samples were continuously employed to update the
coating process to coat SRF cavities. Following an updated coating process, we were able to
produce Nb3Sn single-cell cavity with quality factor 2×1010 for accelerating gradient up to
15 MV/m at 4 K, without any significant Q-slope. In this presentation, the genesis of the Nb3Sn
coating in a typical tin vapor diffusion process, effect of different coating parameter variation on
material properties of Nb3Sn, and their consequences to the coating of SRF cavities will be discussed.
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