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MSE Seminar: Heterogeneous Deformation and its Influence on Magnetic Flux Trapping in Superconducting Radio Frequency Cavities for Particle Accelerators

Friday, September 20, 2019, 11:00 AM - 12:00 PM
Nedderman Hall 106

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Thomas Bieler, Ph.D.
Professor, Materials Science and Engineering, Michigan State University


Superconducting Radio Frequency cavities for particle accelerators are multi-functional structures; they must hold their precise shape under pressure, yet their ultimate purpose is a functional material that keeps it cool in very strong electromagnetic fields (literally).  As metallurgical defects are a potential cause of local heating centers, it is important to understand their origin and to develop ways to anticipate and minimize them.  Recent magneto optical imaging experiments have shown that grain boundaries and dislocation substructure are correlated with trapped magnetic flux, which oscillates and dissipates energy.  Precipitation of non-superconducting niobium hydride also generates dislocations.  Thus, strategic ways to minimize dislocation content could lead to improvements in cavity performance.  As recrystallization is an efficient way to remove defects, this provides the motivation for exploring the physical and mechanical metallurgy underlying recrystallization, such that a good recrystallization heat treatment during the last heat treatment that a cavity sees before it is put into service may significantly increase the consistency of cavity performance. 


Thomas BielerThomas R. Bieler earned a B.A. in Applied Mechanics at the University of California at San Diego in 1978 and an M.S. in Ceramic Engineering at the University of Washington in 1980. He worked at Sandia National Laboratory in Livermore for five years on high rate deformation. He completed his Ph.D. in Materials Science (with a minor in continuum mechanics) at the University of California at Davis in 1989 and has been at Michigan State University thereafter. His research focuses on characterization of mesoscale deformation mechanisms and plasticity modeling in titanium-based alloys, tin in the context of lead-free solder joints, and high purity niobium used in superconducting particle accelerator cavities. With colleagues, he has published over 320 papers, with more than 6,300 citations and an h-index (ISI) of 42. He is active in ABET Engineering Accreditation, and he is an organizer or co-organizer of many recent symposia involving heterogeneous deformation related to grain or phase boundaries. He is a fellow of TMS.

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