Drive Systems for Photonic Bandgap (PBG) Accelerators

As high energy physics facilities get bigger and more costly, the DOE HEP program seeks to develop advanced technologies that can be used to reduce the overall machine size and cost. Incom Inc. and the Stanford Linear Accelerator Center (SLAC) are co-developing photonic band-gap (PBG) microstructures to enable compact, high-gradient ( & gt; 1GeV/m), inexpensive particle accelerators. To date, this collaboration has succeeded in developing 2D PBG structures with a strong TM01-like accelerating mode at =2.1 micron. These PBG structures are manufactured using proprietary glass forming, capillary draw, and finishing technology. Current prototypes are based on Borosilicate glass, with 2 to 4 microns capillary diameters. Ultimately these PBG structures will be powered by lasers operating in the 1 to 2.5 micron wavelength range. This on-going work is funded by DOE award no. DE-SC0000893. Our work points to a number of challenges that are beyond the scope of current funding, and which must be resolved before these PBG structures can be practically deployed as accelerators. The critical path development and primary objective of this Phase I application is the design, modeling, construction and bench testing of effective PBG laser coupling structures which enable optical energy and electrons to simultaneously be coupled into the accelerator sections. The integrated photonic band gap accelerator (PBG) is comprised of both coupling and accelerating sections. Methods will also be developed to modify and tune the as built PBG structure to optimize laser coupling and to dynamically alter performance. Other objectives include optimizing fabrication methods using fused silica glass, reducing PBG capillary dimensions to 1.5-2 microns and enhancing control of critical separations between defect capillary and the surrounding matrix. Manufacturing methods that insure the surface finish, flatness and thickness of the PBG must be further refined. These PBG structures will provide an order of magnitude improvement in accelerating gradient over conventional RF systems. SLAC will do extensive modeling work to explore options for laser coupling into these structures. Since these PBG structures are quite different from those used in telecom, any coupling scenario must be developed from first principles. Preliminary modeling work suggests solutions for end coupling but also points to side coupling as a simpler and better way to proceed. In addition to this critical modeling, SLAC will also perform calculations with SLAC software to convert prototype structural parameters for use in simulations. Incom will develop optimized PBG and coupling structures meeting the 1.5-2.0 micron capillary diameter, 100 micron thick, using borosilicate and fused silica glass, and will deliver large area ( & gt;15mm diameter) wafers to facilitate easy handling, for SLAC testing. Incom will explore advanced wafer finishing methods intended to insure surface finish, and flatness, including CMP (chemical-mechanical-planarization) and fluid jet polishing methods to fabricate ultra-thin (100-microns), ultra-flat wafers, as dictated by the SLAC modeling. Incom will also demonstrate methods to tune or modify as built PBG structures to control, or bias their performance. Chemical etch and material doping strategies will be employed to accomplish this. Commercial Application and Other Benefits: Successful development of PGB accelerators will provide an accessible low cost source of high energy electrons, and possibly low energy, polarized neutron beams and will result in a new class of small powerful low-cost accelerators that will replace current source technology in applications such as e-beam lithography, scanning and transmission electron microscopy, and Auger spectroscopy. These small accelerators will have applications throughout industrial fabrication, structural analysis, diagnostics, and instrumentation. Potential medical benefits are profound e.g. by supplying systems with local radiation delivery and reduced tissue damage. The ultimate beneficiaries of this technology will be the public as served by the commercialization of reliable flexible low-cost accelerators and innovative devices that result from this research effort.