Accelerator Research and Applications Featured at PAC 1995
Monday morning's opening plenary session featured talks by prominent leaders in the particle accelerator community on current research facilities, including CEBAF and Argonne's Advanced Photon Source. Other sessions during the week reported on the status of such facilities as Fermilab's Main Injector Complex and Tevatron collider, Brookhaven's RHIC, and HERA in Germany. The meeting concluded Friday afternoon with a plenary session featuring talks on photon-photon colliders, transmutation and energy production using high-power accelerators, and an update on the Large Hadron Collider, which was approved for construction at CERN last December.
Pulsed and High Intensity Beams. New high average power system designs incorporating thermal management techniques are allowing researchers at Sandia National Laboratories to use high peak power technology in a number of non-thermal industrial application areas, such as materials processing, food processing, stack gas cleanup, and the destruction of organic contaminants. High current pulsed accelerators were developed during the late 1960s through the late 1980s to investigate new effects in high energy density systems. According to E.L. Neau, who spoke on Tuesday morning, the new systems employ semiconductor or saturable magnetic switches to achieve short pulse durations which can then be added to give megavolt accelerating potentials while achieving power levels of several hundred kilowatts.
High Energy Accelerator Beam Dynamics. Researchers at Fermilab have found that a variety of nonlinear wave phenomena can be observed in beams sufficiently close to the linear stability limit, such as nonlinear three-wave coupling and the formation of perturbations resembling solitons. According to P.L. Colestock, these can then be used to diagnose aspects of the beam dynamics and the machine impedance. In addition, a number of new techniques for future linear colliders have been developed and tested at the Stanford Linear Accelerator Center as part of the Final Focus Test Beam experiment, including the ion scattering monitor, the wire-alignment system, and the cam-shaft magnet mover.
Superconducting Magnets. Superconducting magnets have become essential components of hadron colliders and compact electron accelerators, and recent advances in this technology include the development of permanent magnet quadropoles, dipoles, and other multipoles which are used in an increasing number of accelerator applications for transporting and manipulating charged particle beams. Research applications include drift tube linear accelerators; industrial applications encompass accelerators for isotope production, ion implantation accelerators, and neutron generation accelerators.
According to Argonne's Efim Gluskin, who spoke at a Tuesday afternoon session, each of the world's 26 operational synchrotron radiation facilities uses at least one insertion device (ID) as a source of radiation, although a modern facility could employ as many as 25 IDs operating simultaneously. In their ongoing efforts to design the optimal ID device, researchers have developed a number of new devices, including super high field superconducting IDs, extra small gap undulators, and special devices for generating variably polarized radiation.
Microelectronic Applications. Accelerators are increasingly being used for microelectronic applications. For instance, X-ray lithography is being considered as a promising alternative to the optical lithographic methods currently employed in the semiconductor industry to pattern integrated circuits. However, according to Motorola's William Johnson, circuit feature sizes continue to shrink, and optical lithography may not be capable of patterning them with the process latitude and cost effectiveness required in commercial manufacturing.
New X-ray synchrotron storage ring prototypes are currently being developed to produce X rays for research purposes, but these are too large and expensive for commercial use. However, David Yu of DULY Research, Inc., described a new process that uses a high-gradient electron accelerator (HGA) driven by a high-power microwave source combined with superconducting magnet technology. "The high gradient, and hence short injector, would result in substantial reduction in capital equipment, space and shielding costs," he said, adding that using the HGA as a full-energy injector could enhance the intensity of the emitted X rays and reduce the wafer exposure time.
The advent of practical, high-performance gated vacuum field-emitter arrays (FEAs), which are fabricated by lithographic methods, could be used to produce a class of RF sources with distinct advantages in efficiency and compactness. Capable of producing pulsed beams at high frequency with high current density, FEAs are produced by placing an electrode (called the "gate") very close to arrays of sharp tips, such that a low gate-to-emitter voltage can extract electrons from the tips.
Medical Applications. Accelerators also find applications in medicine and the biosciences. For example, more than 16,000 patients in the last 40 years have been treated at accelerator laboratories around the world using radiation therapy with proton and light-ion beams. The beams allow for significantly improved placement of radiation dose in the tumor while sparing normal tissue surrounding it, and the medical community is seeking to expand the number of treatment facilities, with an emphasis on dedicated facilities close to hospital services and resources.
Tunable near-monochromatic X rays in the 14-18 KeV range are now available at the Vanderbilt University Free Electron Laser Facility for medical and materials research. According to Vanderbilt's F.E. Carroll, the beams are particularly useful in the diagnosis of breast cancer and the analysis of lung lesions. Furthermore, their use in chemoradiotherapy allows the selective activation of drugs that have concentrated in tumors, and Carroll reported that pilot projects show promise for synergistic local lethal effects in the treatment of breast, liver and brain tumors. The X rays are also being used to design and test new detectors for diagnostic imaging.
Since becoming available for biomedical research, free electron lasers (FELs) are playing a major role in optimizing laser emission wavelengths while minimizing adverse effects for photoablative and photothermal use, particularly because of their superior tunability. Researchers at Germany's University of Tubingen have developed a model based upon FEL photoablation data suitable for the development of new medical and surgical lasers to study selective interactions with tissue components prior to preclinical investigations.
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