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NEWS | Jan. 5, 2010

Dr. Kevin Jensen Elected Fellow of the American Physical Society

By Amanda Bowie

Kevin Jensen, a research physicist in the Vacuum Electronics Branch, Electronic Science and Technology Division, at the Naval Research Laboratory has been elected as a Fellow of the American Physical Society, Division of Physics of Beams. His work has been cited for fundamental contributions to the theory and modeling of electron emission sources for particle accelerators and microwave tubes.

According to the APS, members of the society are eligible for nomination by four or more Fellows. The nomination is then evaluated by a Fellowship committee of the appropriate APS division. Election is limited to 0.5% of the membership, and is therefore recognition by one's peers of outstanding contributions to physics.

Dr. Jensen has a record of achievement spanning two decades in the physics of electron sources for rf vacuum electronic devices (otherwise known as gridded tubes, conventional microwave power tubes, gyrodevices, and free-electron lasers). Historically, thermionic cathodes have been the mainstay, but the quest for intense beams or very short bunches means other electron sources have been considered, such as field emitters, secondary emitters, and photocathodes. Dr. Jensen's most distinctive contributions have therefore been in understanding of the physics of electron emission in these areas.

His most significant achievements include: a theoretical model unifying thermal, field, and photoemission, such that each of the most familiar emission equations are limiting cases; extension of field emission models to include field enhancement, emission variation, and statistical changes in performance as a consequence of degradation; models of dark current and emission-induced breakdown in particle accelerators; and a photoemission theory incorporating material and laser parameters, coatings, optical and surface properties, scattering mechanisms, emission probability for the prediction of quantum efficiency and emittance (a measure of how much an electron beam spreads as it propagates). The photoemission theory's analysis of alkali metals on metal surfaces, published in the Journal of Applied Physics, was honored by the Berman Research Publication Award in 2007.

His models for quantum efficiency (QE) and dark current / field emission were incorporated into NRL's advanced Particle-In-Cell (PIC) simulation code MICHELLE (winner of the 44th Annual R&D Award in 2006), and was the first time that a beam code used accurate materials-based models to treat surface non-uniformity and emission variation and their impact on emittance. As electron sources are one of the two major components requiring further development for the realization of the Innovative Naval Prototype (INP) megawatt-class free electron laser (FEL) for ship defense (see Scientific Assessment Of High-power Free-Electron Laser Technology (National Academies Press, Washington, DC, 2009)), accurately modeling emission is strikingly important.

Dr. Jensen received a B.S. degree in applied physics in 1981 from Columbia University, and MS and PhD degrees in physics from New York University. He came to NRL in 1987 as a National Research Council post-doc. In 1990, he joined the theory section of the Vacuum Electronics Branch. After 1994, he served as a program manager for the Vacuum Microelectronics and Advanced Emitter Technology efforts within the branch. In 2003, he became a member of the Joint Technology Office's Technical Area Working Group (TAWG) for free electron lasers.

Dr. Jensen has given invited talks at the Int'l Vacuum Nanoelectronics Conference, Int'l Field Emission Symposium, Int'l Vacuum Electron Sources Conference, and at workshops on photocathodes and electron sources. He has chaired / co-chaired sessions at the Int'l Conference on Plasma Science, the Materials Research Society (MRS), and the Electrochemical Society (ECS). For MRS and ECS, he has co-edited three books containing the conference proceedings of those sessions. He serves on committees for the IVNC and IVESC and others. He was a Guest Editor for the Special Issue on Vacuum Microelectronics in Solid State Electronics, and has since served on its editorial committee. He is co-author on several encyclopedia and book chapters such as Noise and Fluctuations Control in Electronic Devices (American Scientific Publishers, 2002), Micropropulsion for Small Spacecraft (AIAA, 2000) and others. He is the author of the theory chapter in Vacuum Microelectronics, (Wiley, 2001), and most recently of the book Electron Emission Physics (Advances in Imaging and Electron Physics, Volume 149, Academic Press, 2007). He has authored or co-authored over 95 journal articles and conference proceedings on thermal, field, secondary and photoemission, and devices based upon these processes.

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