SBIR-STTR Award

This project investigates a new type of high Q resonant structure, which has recently been demonstrated, to develop high gradient, superconducting accelerator cavities. Based on the concept of a Photonic Band Gap (PBG) resonator, these new structures are physically significantly different from the resonant cavities currently used in normal superconducting devices. A resonant mode suitable for accelerating charged particle beams arises from the presence of a defect in a two-dimensional lattice of dielectric obstacles placed between two conducting sheets. PBG resonators have two unique properties that may overcome many of the limitations in the present state of the art: (1) it may be possible to obtain a structure with no higher order modes and with the single resonant frequency energy distributed in a pure monopole mode, thereby reducing beam instabilities and also reducing energy losses; and (2) it is expected that one could achieve Q > 106 at 4K using presently available niobium material, with particular ease, because only flat sheets of superconductor are required, with no joints or bends. In Phase I, optimum configurations of PBG structures for accelerator applications are being established through numerical simulations. Suitable means will be established for coupling fields between adjacent resonators and for coupling radio frequency power into a PBG accelerator structure. The construction of a cryogenic test facility suitable for experimental evaluation of PBG configurations will be specified and its cost anytime requirements planned. This project is evaluating the potential applicability of PBG resonant structures for very high gradient, high energy electron accelerators as well as for high gradient, high current proton and heavy-ion accelerators. The findings will be incorporated in a report on the potential performance and applicability of PBG resonant structures for very high gradient, high Q acceleration structures, including the design of a high power test structure. The Phase II project would build and test a room temperature model to verify design features and would build and test a superconducting version. Anticipated Results/Potential Commercial Applications as described by the awardee: This project should evaluate and demonstrate the benefits of using a new resonant structure based on the concept of a PBG with defect. This structure should allow more efficient, smaller footprint, and higher gradient electron and proton linear accelerators. In addition to being used in government laboratories, this structure has projected commercial applications, including sources for x-ray lithography, production of medical radionuclides, uses in medical proton therapy, and uses in nuclear waste transmutation.

High energy linear accelerators generally utilize a series of suitably phased resonant cavities to effect the transfer of energy from microwave sources to the electron beam. The current design of the cavities is quite complex. This project is concerned with the demonstration of a Photonic Band Gap (PBG) resonator in a configuration suitable for the development of a high gradient (50 Mev/m) superconducting accelerator cavity. PBG resonators have unique properties which may overcome many of the limitations in present state-of-the-art accelerator cavity designs. The resonator is expected to have a very high quality factor (Q), defined as stored energy divided by dissipation per cycle. The very high Q resonance many prevail over a very large frequency range, so that higher order mode Q degradation is no longer a problem. In Phase I, numerical simulations of PBG structures were performed as a function of system parameters, with the purpose of establishing optimum configurations for accelerator applications (such as elimination of higher order modes and maximizing the ratio of the peak surface electric field to the average on-axis accelerating field). Many hundreds of cases were run. Experiments were initiated to develop a suitable means for coupling fields between adjacent resonators and for coupling radio frequency (RF) power into a PBG structure. Planning was completed for design and construction of a cryogenic test facility suitable for experimental evaluation of potential PBG configurations. In Phase II, the design will be finalized for the PBG resonator structure and accelerator cavity configuration. PBG resonators will be constructed. A test stand cryostat will be designed and fabricated, and the first phase of testing PBG resonators singly and in coupled units will be completed. The test system will then be shipped to a high energy test facility to complete the beam tests. Anticipated Results/ Potential Commercial Applications as described by the awardee: The successful demonstration of a high gradient accelerator structure using the Photonic Band Gap resonator concept will have a tremendous impact on the development of future linear colliders and on practical electron linacs for future medical applications. This simple, low-loss structure would allow one to build rather compact, efficient lines for producing synchrotron radiation or high energy photons.