TITLE: Development of a High Average Current Thermionic Injector for an Energy Recovery Linac
DATE: 9:30am, August 3, 2017.
ADDRESS: The 705 meeting room of Building 1
SPEAKER: Steven H. Gold Professor.
Steven H. Gold retired in early 2015 from his position as Senior Scientist for Radiation Generation Physics in the Beam Physics Branch of the Plasma Physics Division at the Naval Research Laboratory (NRL), where he had worked since he obtained his Ph.D. in physics from the University of Maryland in 1978. He is currently a consultant in the areas of plasma science and accelerator R&D. His research interests include high-power microwave sources and applications, advanced accelerator research and development, and free-electron lasers. He has published 70 journal articles and 115 proceedings papers and holds 6 US Patents and 2 Statutory Invention Registrations. He is an elected member of the Administrative Committee of the IEEE Nuclear and Plasma Sciences Society, Chair of the NPSS Chapters and Local Activities Committee, and Secretary of the NPSS Plasma Science and Applications Committee. He is a Life Member and Fellow of the American Physical Society and a Life Fellow of the IEEE, and received the 2008 IEEE Richard F. Shea Distinguished Member Award “for outstanding contributions to the IEEE Nuclear and Plasma Sciences Society and its Plasma Science and Applications Technical Committee.”
ABSTRACT:
High power free-electron lasers (FELs) require the production of high energy electron beams with excellent beam quality and high average current, in order to generate high frequency electromagnetic radiation through the interaction with a periodic transverse wiggler magnetic field. The intrinsic efficiency of the FEL interaction is fairly low. Therefore, to improve the overall device efficiency, the electron beam can be generated by an energy recovery linac (ERL), which uses rf cavities to accelerate the electron bunches produced by an electron injector up to the energy required for the FEL interaction, and then, following the interaction, circulates the electron beam through the same rf cavities to decelerate the electron bunches in order to recover most of the energy of the spent electron beam. The injector is a critical component of the ERL system, since it must deliver the average beam current required by the linac, and since its performance is also critical to the properties of the high energy electron beam that is produced by the linac. Most FEL systems use injectors based on laser-excited photocathodes to produce the high electron beam quality and short electron bunch length that are required, but the technology is complicated and expensive, and also imposes limits on the average current of the electron beam. An alternative is to develop injectors based on thermionic electron gun technology, which is robust, has a long lifetime, and can readily generate very high beam currents. Such thermionic injectors may have significant advantages for high power FELs at infrared wavelengths, provided that they can satisfy the bunch length and beam quality constraints imposed by the application. This lecture will present a brief introduction to ERL-based FEL systems, and discuss some of the basic principles of rf acceleration and thermionic electron gun design. Following this, it will focus on a recent program to develop a high-current electron injector operating at 714 MHz based on a gridded thermionic electron gun.
