[Jlabsa_gs] Pizza Seminar - Wednesday, June 12 - a message from Lorelei Carlson

Jodi Patient patient at jlab.org
Fri Jun 7 12:23:05 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 COB on June 10, 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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