**room 2219 Engineering Building** Multipactor in the Presence of Higher-Order Modes: A Numerical Study

Scott Rice, FRIB
Tuesday, Aug 08, 1:00 PM - Ph.D. Oral Exam
TBA

Abstract:  Resonant electromagnetic structures are vitally important in engineering and scientific applications, ranging from devices as ubiquitous as antennas and microwave ovens, to devices as demanding as high-power microwave sources and particle accelerator components. As we push the limits on the design and operation of such structures, one of the physical limitations that we must contend with is electrical breakdown, which becomes increasingly likely as we increase field strength and reduce structure sizes. Multipactor is a type of breakdown in which electromagnetic fields accelerate free electrons into a material, which then ejects secondary electrons which are re-accelerated back into the material, and which sustains or grows the breakdown current over time. We are interested in understanding multipactor better because it is one of the common design constraints for high-power resonant structures around microwave frequencies, such as klystrons, couplers, waveguides, and accelerating cavities used in particle accelerators. Besides being a design constraint, we could also potentially employ the non-linear nature of multipactor to intentionally bleed off random harmful power levels which may affect certain sensitive equipment, such as the protection of front-end electronics on radio receivers in space-borne applications. This dissertation details the results of numerical study of two-surface multipactor driven by time-harmonic fields, with a specific focus upon how secondary electron emission models can affect the resulting multipactor predictions, and how multipactor susceptibility and trajectories can be affected by the presence of additional modes within a resonant structure. The primary focus is on multipactor occurring between the inner and outer conductors of coaxial geometries, but some parallel-plate geometries are also considered. The scope of investigation is limited to the multipactor regime in which space charge effects can be neglected. In practice this means the early-time evolution of multipactor, since it takes some time before space charge effects become significant. Despite this simplifying assumption not being applicable to the late-time behavior of multipactor, this approach still allows for much practical benefit in the understanding of multipactor genesis and controllability, which is frequently the most significant concern of engineering interest. Journal papers: Scott Rice and John Verboncoeur, "Migration of Multipactor Trajectories Via Higher-Order Mode Perturbation." accepted for publication in an upcoming issue of IEEE Transactions on Plasma Science, 2017 Scott Rice and John Verboncoeur, "A Comparison of Multipactor Predictions Using Two Popular Secondary Electron Models." IEEE Transactions on Plasma Science, Vol. 42, (no 6), June 2014 Conference proceedings Scott Rice and John Verboncoeur, "Quasi-Analytical Derivation of Parallel-Plate Multipactor Trajectories in the Presence of Higher-Order Mode Perturbations." 2016 IEEE International Power Modulator and High Voltage Conference (2016 IPMHVC), San Francisco, CA, July 5-9, 2016 Scott Rice and John Verboncoeur, "Migration of Multipactor Trajectories Via Higher-Order Mode Perturbation." 43rd IEEE International Conference on Plasma Science (ICOPS 2015), Calgary, Alberta, Canada, June 19-23, 2016 Scott Rice and John Verboncoeur, "Multipactor Breakdown Modelling Using an Averaged Version of Furman's SEY Model." 42nd IEEE International Conference on Plasma Science (ICOPS 2015), Belek, Analya, Turkey, May 24-28, 2015 Scott Rice and John Verboncoeur, "Multipactor Current Growth Modelling Using an Averaged Version of Furman's SEY Model." International Particle Accelerator Conference (IPAC'15), Richmond, VA, May 3-8, 2015 Scott Rice and Lee Harle, "Distinguishing Localized and Non-Localized Scattering for Improved Near Field-to-Far Field Transformations." Antenna Measurement Techniques Association 2014 Annual Conference (AMTA 2014), Tucson, AZ, October 13-16, 2014 Scott Rice and John Verboncoeur, Multipactor Estimation Using an Averaged Version of Furman's SEY Model." 2014 IEEE International Power Modulator and High Voltage Conference (2014 IPMHVC), Santa Fe, NM, June 1-5, 2014 Scott Rice and John Verboncoeur, "Multipactor Current Modelling Using an Averaged Version of Furman's SEY Model." 41st IEEE International Conference on Plasma Science (ICOPS 2014), Washington, DC, May 25-29, 2014 Scott Rice and John Verboncoeur, "Initial Studies of Multipactor Suppression Via TE and TM Modes." North American Particle Accelerator Conference (NA-PAC'13), Pasadena, CA, September 29 - October 4, 2013. Scott Rice and John Verboncoeur, "A Comparison of Multipactor Predictions Using Two Popular Secondary Electron Models." North American Particle Accelerator Conference (NA-PAC'13), Pasadena, CA, September 29 - October 4, 2013