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BEAMS, ACCELERATORS, AND COHERENT RADIATION SOURCES 92 5 Beams, Accelerators, and Coherent Radiation Sources INTRODUCTION AND BACKGROUND Consideration of the state and health of plasma science within the grouped disciplines of intense charged-particle beams, accelerators, and coherent radiation sources presents a picture perhaps representative of trends relevant to plasma science in general. Recent history suggests themes, several of which appear in common with other areas impacted directly or indirectly by plasma science. Basic and applied research have been supported indirectly within large Department of Defense (DOD) weapons-driven and DOE energy-driven application programs, such as the directed-energy weapons, nuclear weapon effects testing, and magnetic/inertial confinement fusion. There have been notable scientific and technical accomplishments in this area, along with visible examples of yet to be achieved or inflated expectations. Finally, and perhaps most important, there is concern about future funding availability and the organizational advocacy necessary to sustain, and advance, the underlying intellectual, facility and equipment infrastructure in light of evolving national defense, economic, and social priorities. RECENT ADVANCES AND SCIENCE AND TECHNOLOGY OPPORTUNITIES Intense Charged-Particle Beams The mission for intense charged-particle beams has changed considerably over the last decade. Research and development sponsored by DOD, the Strate
BEAMS, ACCELERATORS, AND COHERENT RADIATION SOURCES 93 gic Defense Initiative Organization (SDIO), and DOE resulted in facilities such as the Advanced Test Accelerator (ATA) at Lawrence Livermore National Laboratory for directed-energy weaponry, low-impedance multi-terawatt pulsed power machines for nuclear weapon effects simulation, and intense beams for fusion plasma heating. Kiloamp-MeV electron beams were developed that support high average power operation in excess of 100 kW with repetition rates approaching 1000 pulses per second (pps). Gyrotrons, devices that utilize a spinning electron beam in an axial magnetic field to produce millimeter waves for electron cyclotron resonance heating, successfully generated several hundred kilowatts in long pulses up to 3 s in duration at frequencies up to 140 GHz. Considering that 10 years ago, 100-ms outputs at 28 GHz and comparable power levels were representative, the technical community is justifiably proud of this technological accomplishment. Similarly, klystron technology has been advanced to higher frequencies (11.4 GHz) and powers (up to 100 MW), and the operation of a gyroklystron amplifier at the 20-MW power level at 11 GHz has been demonstrated. Many of the military mission-oriented efforts have been canceled. However, industrial applications of high-energy electron beams, including bulk sterilization of medical products and food, toxic waste destruction via oxidation, and processing of advanced materials, are in the demonstration stage. Technology transfer from the laboratories to industry is being encouraged actively. Having invested several hundred million dollars over the past decade in developing intense charged-particle-beam systems for military use, the emphasis by federal agencies on technology transfer for industrial applications seems prudent. Charged-particle-beam parameters vary greatly, depending on the application. A NASA concept for beaming power to space requires basic plasma science research addressing such physics issues as low emittance growth (< 20Ï mm-mr), beam breakup modes, and high current beam transport. Similarly, high energy electron-beam systems proposed for toxic waste cleanup, enhanced welding, heat treatment, and material processing generally have less stringent requirements on voltage flatness and emittance, but require reliable generation and maintenance of very high average powers. The interaction of intense charged-particle beams with plasmas, partially ionized gases, and matter offers rich scope for the study of strongly driven collective processes complementary to intense laser-plasma interactions. Electron and ion sources for intense beams have progressed from an empirical art to a developing science. Experiments, simulation, and analytical theory have contributed to this evolution, stimulated by the needs of inertial confinement fusion and other research programs. Intense ion beams also make possible the creation of magnetic field- reversed ion rings in which the self-magnetic field of the circulating ion current exceeds the externally applied magnetic field. Such a ring would be a compact object of high energy density with unique theoretically predicted features, such