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Accelerator Seminars


Accelerator Seminar Committee:
  Chair: Carlos Hernandez- Garcia
    Members: Steve Benson, Gianluigi Ciovati, Vasiliy Morozov and Kevin Jordan


 Accelerator Seminars are scheduled weekly on Thursday's from 11:00 a.m. - 12:00 p.m.
If you would like to schedule a seminar, please contact Carlos Hernandez-Garcia for approval.

 

DATE, TIME: March 23, 2017, 11:00 a.m.

LOCATION: CEBAF Center, Room L102

TITLE: Summary from Tesla Technology Collaboration Meeting

SPEAKER: Charlie Reece, SRF Institute, Jefferson Lab

ABSTRACT: The Tesla Technology Collboration (TTC) is the international collaboration of institutions involved with SRF for accelerators. The collaboration meetings provide for shared technical problem-solving and rapid communication of new developments. This year's main TTC meeting was hosted by FRIB. The working groups focused on (1) performance frontier, (2) on-beamline performance degradation, (3) issues encountered in production, and (4) cryomodule design, assembly, and performance. There were 123 registrants. The variety and complexity of SRF implementations continue to grow, simultaneous with both new technological advances and lingering plaguing vulnerabilities. I'll offer extracted highlights from working group summaries that may be of interest to JLab accelerator scientific staff.

 

DATE, TIME: May 8, 2017, 11:00 a.m.

LOCATION: To be determined

TITLE: Exploration of Fundamental Metallurgical Properties, and Superconducting Correlations in SRF Nb Coupons

SPEAKER: Shreyas Balachandran, Florida State University

ABSTRACT:This is an exciting time for SRF Nb technology with the development of impurity doping techniques that have resulted in elevated quality factors, Q0, at low fields and mid and high field anti-Q-slopes in both fine grain and large grain cavities. These advances, however, have been accompanied by reduced quench fields and a susceptibility to trapped flux on cooling the cavities. The factors controlling these properties are not fully understood and at the Applied Superconductivity Center (ASC) we are trying to provide insight into the impact of cavity treatments by applying low cost coupon techniques that evaluate the superconducting properties, and correlate microstructure on coupon SRF Nb samples. The main goals of our work are to provide: a) Characterization/Analysis of current cavity technology, b) Comprehensive microstructural, chemical, and property evaluation of SRF cavity coupons, and c) Correlate metallurgical state and magnetic properties with strategically characterized samples. Our collaboration with Jefferson Lab enables us access to samples processed by new techniques, and cavity cutouts which allows us to characterize coupons directly useful to cavity builders. We will present some of our recent work, with an emphasis on physical metallurgy of Nb. We find that low angle grain boundaries (<10o) are present in large grain SRF Nb sheets, and are very hard to recognize due to the lack of surface relief. However, these structures can lead to premature flux penetration as seen by magneto optical imaging (MOI), and can trap magnetic flux during cool down. By deliberately loading with the Nb surface with hydrogen, we are able to show direct evidence that high temperature nitrogen doping suppresses hydride formation up to 50 µm from the Nb surface. However, there are residual strains remaining around hydrides even after the warmup. These strained regions can still degrade the Nb surface even in the absence of hydrogen, if they are unrecovered after an 800˚C heat treatment. Our latest work on low temperature N doping coupons indicate a consistent increase in Hc3 values with N doping indicating significant surface changes. Hc3 value increases from 620 mT after a standard 800 ˚C/3 h heat treatment to 1100 mT after a 120˚C N doping, and 1040 mT after 160 ˚C N doping low temperature N doping protocol. Increased Hc3, values are consistent with a decrease in mean free path. We also observe orientation dependent nano-structures on low temperature N doped coupons. This coupon testing is in conjunction with the latest cavity tests (Cavity RDL-02) that are being conducted at JLAB. These activities have been largely possible due to seamless collaboration involving FSU, JLAB, and MSU. There is much more to explore.

 

Seminar Archives: [2017]  [2016]  [2015]  [2014]  [2013]  [2012]  [2011]  [2010]  [2009]  [2008]  [2007]  [2006]  [2005]  [2004]  [2003]  [2002]  [2001]