Dr. John Verboncoeur
Michigan State University
High-voltage breakdown: from surface multipactor to ionization discharge
High-voltage breakdown in the vicinity of a dielectric or conducting surface is examined across a wide range of conditions using theoretical and experimental treatments. Both DC and RF power sources are considered, across a wide pressure range. DC multipactor along an insulating surface can lead to local heating-driven gas desorption and ultimately to gaseous breakdown. In microwave driven systems, at low pressure, a single-surface multipactor absorbs about 2% of the microwave energy and has a mean energy of hundreds of eV. At 10-50 Torr for L-band radiation, a transition occurs from a single surface multipactor to a detached ionization discharge. Above 50 Torr, the multipactor disappears and the discharge forms a typical sheath, with mean electron energy below 10 eV. Simple scaling laws fit results in the low and high pressure regimes for several gases. Experimental results demonstrate a variable long statistical delay time, followed by a rapid breakdown. UV illumination of the dielectric surface reduces the statistical delay time, making onset of breakdown more consistent. Experiments recently demonstrated arrays of plasma filaments aligned along electric field lines, spaced ≤ ¼ wavelengths at low pressure, with filaments coalescing into more continuous diffuse plasmas at higher pressure. A 1D drift-diffusion fluid model combined with an analytic model for EM wave propagation though plasma slabs of arbitrary profile was able to demonstrate the propagation and spacing mechanisms, including decreasing spacing with increasing microwave power, as well as the diffuse plasma transition at higher pressure.
Plasma Physics Computer Laboratory
The Plasma Theory and Simulation Group (PTSG) at Michigan State University (formerly at the University of California – Berkeley) has developed a set of general purpose plasma codes. This includes particle-in-cell (PIC) codes in multiple dimensions and geometries, designed for basic science and a broad range of applications. We will provide an introduction to the particle in cell simulation method, and a real time tutorial applying them to textbook problems. The code suite, including source code, is available free from the PTSG web site: https://ptsg.egr.msu.edu/.
John P. Verboncoeur received a B.S. (1986) in Engineering Science from the University of Florida, M.S. (1987) and Ph.D. (1992) in Nuclear Engineering from the University of California-Berkeley (UCB), holding the DOE Magnetic Fusion Energy Technology Fellowship. After serving as a joint postdoc at Lawrence Livermore National Laboratory and UCB in Electrical Engineering and Computer Science (EECS), he was appointed Associate Research Engineer in UCB-EECS, and to the UCB Nuclear Engineering faculty in 2001, attaining full Professor in 2008. He served as the Chair of the Computational Engineering Science Program at UCB from 2001-2010. In 2011, he was appointed Professor of Electrical and Computer Engineering at Michigan State University, and added an appointment as Professor of Computational Mathematics, Science, and Engineering in 2015. His teaching includes electromagnetics, plasma physics, neutronics, engineering analysis, and computation. His research interests are in theoretical and computational plasma physics, with a broad range of applications spanning low temperature plasmas for lighting, thrusters and materials processing to hot plasmas for fusion, from ultra-cold plasmas to particle accelerators, from beams to pulsed power, from intense kinetic nonequilibrium plasmas to high power microwaves. He is the author/coauthor of the MSU (formerly Berkeley) suite of particle-in-cell Monte Carlo (PIC-MC) codes, including XPDP1 and XOOPIC, used by over 1000 researchers worldwide with over 350 journal publications in the last decade. He has authored/coauthored over 350 journal articles and conference papers, with over 3500 citations, and has taught 13 international workshops and mini-courses on plasma simulation. He is currently an Associate Editor for Physics of Plasmas, and has served as a guest editor and/or frequent reviewer for IEEE Transactions on Plasma Science, IEEE Transactions on Electron Devices, as well as a number of other plasma and computational journals. He is Past President of the IEEE Nuclear and Plasma Sciences Society, and a member of the IEEE TAB Management Committee. Appointed Associate Dean for Research in the College of Engineering in 2014, he oversees college research activities and strategy. He has also run a number of technology startup companies, including development of one of the big three consumer credit reports, work on the hardware and software of the US Postal Service Mail Forwarding System, command and control software in the defense sector, computerized exercise equipment, and a pioneering cloud based health care management system. He is a fellow of the IEEE.