Conference Agenda

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Session Overview
Location: Ballroom EF
Date: Monday, 20/June/2022
8:30am - 9:30amIPMHVC Plenary Lecture - J. Verboncoeur
Location: Ballroom EF
Session Chair: Nicholas M Jordan, University of Michigan
8:30am - 9:30am

From Multipactor to Ionization Breakdown: Review and Recent Advances

J. P. Verboncoeur1, D.-Q. Wen1, A. Iqbal1, Y. Fu2, P. Wong1, P. Zhang1

1Michigan State University; 2Tsinghua University

Multipactor and its transition to gaseous ionization breakdown remain persistent limitations in RF device operation, particularly at high power. Nonlinear effects can couple multiple carrier frequencies, cause instabilities and dispersion, and result in temporary failure as well as permanent damage. These phenomena are relevant to conducting and dielectric surfaces, in devices ranging from communications to high power microwave sources, to accelerators and even high gradient microwave circuits and devices.

We update this ongoing work, carried out over the past decade, examining the process of initial multipactor growth, surface heating and gas desorption, and subsequent evolution to ionization breakdown. We look at a variety of mitigation schemes, from spatio-temporal signal modulation and wave mode configuration to surface morphology and materials properties. Both single-surface dielectric multipactor and two-surface conductive electrode multipactor are considered.

This work is part of a larger effort which includes development of standardized platforms in planar, coaxial, and stripline configurations, with both computational and experimental analogs to enable validation and develop analytic and predictive capability integrated with well-tested experiments. The test cells enable study of multipactor susceptibility and transition to ionization breakdown, as well as novel material, geometric, and electrical mitigation schemes in isolation or as a system. Test cell designs allow variations in gap spacing, driving frequency, waveform shape, ambient and desorbed gas, surface morphology, and many other key parameters. The cells will motivate integration and development of novel diagnostics, such as direct multipactor electron detection, optical/VUV emission spectroscopy, and X-ray imaging, at ns timescales and sub-mm- spatial scales.

The test cells and corresponding models will be published in detail and made available to the community as standard reference platforms on which repeatable basic physics results can be studied, validated, benchmarked, and openly published.

*This work was supported by AFOSR MURI Grant No. FA9550-18-1-0062 and AFOSR BAA Grant FA9550-21-1-0367. The contributions of the entire MURI team are gratefully acknowledged: Texas Tech University (led by A.A. Neuber), University of Michigan (led by R.M. Gilgenbach), University of New Mexico (led by E. Schamiloglu), and University of Wisconsin led by J.H. Booske).

Date: Tuesday, 21/June/2022
8:00am - 8:30amIPMHVC Magna Stangenese Memorial
Location: Ballroom EF
Date: Wednesday, 22/June/2022
1:30pm - 3:00pmIPMHVC Plenary Lecture - R. Joshi
Location: Ballroom EF
Session Chair: Allen Garner, Purdue University
1:30pm - 2:30pm

Modeling electric-field driven nonequilibrium phenomena for applications to pulsed power, electron beam generation, transport in materials, and electromanipulation for biomedicine

R. P. Joshi, M. Brown, W. Milestone, M. Sanati, J. Mankowski, J. Dickens, A. Neuber

Texas Tech University, United States of America

This talk will briefly touch upon the many innovative applications involving nonequilibrium and ultrafast processes in areas of pulsed power and high power microwaves driven by high electric fields. Many applications either involve the use of high electric fields to help enhance system currents or power generation (as in high power microwave systems), or to take advantage of non- equilibrium transient phenomena which can produce larger responses (e.g., the transient drift velocity overshoots in photoconductive switches), or be used to curtail the role of slower processes (such as dynamic shielding based on charge transport that typically require longer times), or help attain high internal electric fields in a targeted manner through robust displacement currents (e.g., the field penetration into sub-cellular organelles in biomedical applications). It is, therefore, possible that somewhat different system responses and outcomes can be achieved due to the ultrashort temporal regimes, or under the influence of high local electric fields. This operating domain can often trigger novel physics, or lead to effects dominated by nonequilibrium processes, or simply bring certain mechanisms to the forefront that might otherwise have remained negligible under near-equilibrium conditions.

This presentation will focus on our efforts at modeling and simulations of phenomena dominated by high electric fields, with inclusion of the transient processes. The goal is towards a better understanding for successful and more efficient applications to pulsed power, high power microwave generation, and biomedicine. The talk would include aspects of electron emission, outgassing in high power machines, operation of ultrafast photoconductive switches, materials engineering to curtail deleterious effects, electrochemotherapy and possible nerve stimulation, etc. The connection between engineering and the underlying science will also be discussed that can then lead to optimization.


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