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High Efficiency X-ray (HEX) Production


OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Weapons OBJECTIVE: Design and develop high efficiency targets for the conversion of electrons to x-rays with performance beyond that of typical high atomic number bremsstrahlung converters. DESCRIPTION: This topic area will explore new materials and physics for higher efficiency electron to x-ray conversion. High energy electrons, up to 10 MeV, can be produced for irradiation applications, but have limited penetration (~several centimeters) or are deleterious to the organoleptic characteristics of some types of food, such as meat proteins. High energy x-rays up to 7.5 MeV have improved penetration and do not change the desired organoleptic characteristics. However, the conversion of electrons to x-rays is an inefficient process, with conversion efficiencies of < ~10%. Slowing electrons down through the bremsstrahlung process is typically used to create x-rays from an electron beam striking a high atomic number target (such as tungsten or tantalum). This STTR will focus on the use of advanced materials and new approaches to more efficiently convert electrons to photons and demonstrate performance in a food irradiation application. Approaches could include nanostructure engineered crystalline targets making use of electron and x-ray diffraction, nano-channel targets, energy recycling, or direct beam-wave interactions. Advances could make a significant impact for many applications beyond food irradiation such as medical device sterilization and non-destructive test and evaluation. PHASE I: Phase I will demonstrate feasibility of high efficiency electron to x-ray conversion through modeling and preliminary experiments. Specifically, efficient conversion of x-rays is sought at 5 MeV to 7.5 MeV energies corresponding to upper regulatory limits for food irradiation applications. Successful performers will achieve a minimum of > 20% conversion efficiency, and work to reach the objective performance goal of > 50% conversion efficiency. Such efficiencies would substantially advance the state of the art and potentially allow for lower cost systems with lower size, weight, and power for a range of applications. Beam forming is a secondary goal of the program, with interest in pencil or fan-beams. Phase I will also include preliminary manufacturability studies and economic analysis activities indicating the suitability of the approach for cost-sensitive applications such as food irradiation. Schedule/Milestones/Deliverables Phase I fixed milestones for this program must include: • Month 1: Initial report detailing proposed conversion system supported with preliminary modeling and empirical data, including anticipated x-ray energy distributions • Month 3: Report on the conversion system’s likelihood of achieving program efficiency goals, supported by experimental, simulated or modeled data • Month 5: Interim report describing efficiency performance, manufacturability, and cost of proposed target system • Month 7: Update to interim report: Given this report needs to support the Phase II proposal, it should provide compelling evidence the conversion system can achieve overall program efficiency (threshold 20%, objective 50%) and suitability goals (operation in high energy, high current environments) • Month 8: Final Phase I report summarizing technical approach and status in achieving Phase I goals and plans to achieve program goals by the end of Phase II; this should be a culmination of the Phase 1 effort, demonstrating a viable technical path supported by empirical and modeling data to achieving overall program goals, with risks and mitigation strategies fully detailed Monthly written technical progress reports (see template under SBIR/STTR BAA DOCUMENTS at All proposals must include the following meetings in the proposed schedule and costs: • Virtual kickoff for Phase I • Regular monthly teleconference meetings with the Government team for progress reporting as well as problem identification and mitigation; proposers typically prepare a slide deck to aid in the discussion PHASE II: Phase II will further develop and refine proof-of-concept conversion systems, culminating with the demonstration of performance goals under high current conditions. Phase II will evaluate conversion systems under realistic conditions for food treatment with continuous beam powers ranging from 2 kW to 10 kW. The conversion systems will demonstrate maintaining x-ray production efficiency goals while addressing practical engineering issues such as mechanical stress and thermal management. Proposers should outline specific metrics and conditions for test that align with their commercialization strategy. The Phase II option will develop a strategy to integrate the conversion system with the DARPA SBIR Safe Food for Everyone (SaFE) program electron accelerator. Additionally, the option period will explore producing usable quantities of the optimized conversion systems with low-cost techniques, support demonstrations meeting program goals, and define a minimum viable product for food irradiation applications. Schedule/Milestones/Deliverables. Phase II fixed milestones for this program must include: • Month 1: Phase II Kickoff. Slide deck summarizing technical approach to meet overall goals, risks, and risk mitigations and quantified milestone schedule • Month 6: Preliminary Design Review • Month 9: Conversion system characterization: Report characterizing the performance of the conversion system, including efficiency and preliminary thermal handling and mechanical properties • Month 12: Critical Design Review. Report capturing the final conversion system that when realized credibly achieves overall performance and suitability goals • Month 15: Integration Report: Report describing results integrating the conversion system into electron accelerators and results supporting demonstrations of interest • Month 18: Final Report: End of base period report that summarizes performance and suitability and results of initial practical demonstrations Option Schedule/Milestones/Deliverables • Month 21: Option Period Performance Report: Updated performance results, manufacturing studies, cost analysis, market analysis, and design refinements supporting a minimum viable product • Month 24: Final Phase II Report. Summary of overall performance, testing, production, and demonstrations meeting program goals and full definition of minimum viable product; delivery of conversion system to SaFE performers. Monthly written technical progress reports (see template under SBIR/STTR BAA DOCUMENTS at PHASE III DUAL USE APPLICATIONS: The resultant conversion system could be commercialized as a component technology during Phase III by working with various commercial vendors of high-power accelerator systems to provide an improved converter for food irradiation applications. Alternately, x-ray systems have broad applications such as medical, inspection, and security industries where such a converter could offer significant value. Market analysis, economic analysis, and minimum viable product definition could be undertaken for these and other applications. REFERENCES: 1. Technology Perspectives Factual Document for the Basic Research Needs Workshop on CompactAccelerators for Security and Medicine, DoE Office of Science, May 2019 2. Basic Research Needs Workshop on Compact Accelerators for Security and Medicine Tools for the 21st Century, May 6-8, 2019 KEYWORDS: Food irradiation, cold pasteurization, medical sterilization, x-rays, linear accelerators, radiation dose
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