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[PAST EVENT] Douglas B. Beringer, Physics - Oral Exam for the Ph.D.
Abstract: Superconducting Radio Frequency (SRF) cavities are responsible for the acceleration of charged particles to relativistic velocities in most modern linear accelerators, such as those employed at high-energy research facilities like Thomas Jefferson National Laboratory's CEBAF and the LHC at CERN. Recognizing SRF as primarily a surface phenomenon enables the possibility of applying thin films to the interior surface of SRF cavities, opening a formidable tool chest of opportunities by combining and designing materials that offer greater benefit. Thus, while improvements in radio frequency cavity design and refinements in cavity processing techniques have improved accelerator performance and efficiency -- 1.5 GHz bulk niobium SRF cavities have achieved accelerating gradients in excess of 35 MV/m -- there exist fundamental material bounds in bulk superconductors limiting the maximally sustained accelerating field gradient (approximately 45 MV/m for Niobium) where inevitable thermodynamic breakdown occurs. With state of the art niobium based cavity design fast approaching these theoretical limits, novel material innovations must be sought in order to realize next generation SRF cavities. One proposed method to improve SRF performance is to utilize thin film superconducting-insulating superconducting (SIS) multilayer structures to effectively magnetically screen a bulk superconducting layer such that it can operate at higher field gradients before suffering critically detrimental SRF losses. This dissertation focuses on the production and characterization of thin film superconductors for such SIS layers for radio-frequency applications.
Bio : Douglas Beringer was born and raised in Billings, Montana where he spent his early life studying music performance in piano and orchestral percussion. From 2000-2004 he attended Reed College in Portland, Oregon where he earned a B.A. in physics. Following several beautiful and bizarre years in the greater Portland metropolitan area, he entered the College of William and Mary in 2007 to pursue his PhD. In 2010, he joined Ale Lukaszew's research group where he works with the growth and characterization of thin film superconductors.