Description

Overview: X-ray free-electron lasers (XFELs) depend on multi-GeV electron beams produced by large accelerators of which just a few exist at national labs due to their large scale and cost. Demand for access to XFELs vastly outstrips availability, limiting their scientific impact. Compact sources of coherent x-rays would break this bottleneck and make their remarkable x-ray science much more widely accessible. XFELs currently work by self-amplification of spontaneous emission (SASE), which leads to periodic density modulations (bunching) in the electron beam that produces powerful coherent x-ray output. We are pursuing a novel method to produce bunching and coherent x-rays at much lower electron beam energy that will also overcome the noise properties inherent to the SASE process.
Understanding production of electron beam density modulations in lower energy x ray accelerator beams is of critical importance. We combine methods of electron microscopy and state-of-the-art accelerators to close major knowledge gaps Can a periodic electron density modulation at nm scale be generated by diffraction of an electron beam with high peak current and MeV energy? Can the period of the density modulation in the nanopatterned beam be continously varied over a wide range? What limits are set by lens aberrations and space charge forces? Can the pattern be demagnified to approach hard x-ray wavelengths? Can the beam be accelerated and reimaged at even smaller demagnifications? What aberrations are introduced by RF acceleration?
Our nanopatterned electron beam research results will have broad significance in the design of next generation compact XFELs. Our research aims to test a disruptive hypothesis that modestly relativistic electron beams can generate and sustain density modulations at x-ray scale. We assert that XFELs can shrink dramatically in size and cost, and that the remarkable science they produce can be accessed by a much broader portion of the scientific community.
We will test this hypothesis using a combination of electron diffraction and beam transport studies at SLAC and ASU. We aim to: (1) develop foundational understanding of diffraction of relativistic beams through experiments with thin slab Si crystals in SLACs ultrafast electron diffraction facility and to create a dynamical beam stop that extinguishes the forward beam; (2) determine the dependence of diffraction parameters on electron beam properties (charge, current, emittance) using experiment and simulation derived from first principles; (3) demonstrate that diffraction can result in a nanopatterned beam where Si grating structures and imaging optics are used to establish the density modulation in the patterned beam; (4) demonstrate that our nanopatterned beam retains its density modulation through acceleration with tunable period using our new state-of-the-art ASU accelerator facility.
Intellectual Merit: For the first time, critical insights will be attained into electron density modulations at x-ray scale in modestly relativistic beams. The interplay of experiment with theory will expand our knowledge in key areas of electron beam dynamics by combining electron diffraction with relativistic beam transport to explore the limits of electron trajectory control at the nanometer scale. Significant investments have been made in alternative accelerator technologies that to date have not yielded significantly smaller or less expensive x-ray light sources. Our approach will succeed where others have failed because risk is managed by our novel integration of proven conventional technologies leading to multiple orders of magnitude reductions in the size and cost of brilliant x-ray sources.
Broader Impact: Addressing a critical national need, we will mentor and train the next generation of x-ray and accelerator scientists and engineers in our new world class accelerator R&D and x-ray science facility. Dissemination with global reach will be achieved through our Nanopatterned Electron Beams Discovery Mission website, which will host training modules that fortify our hands on instructional classroom outreach programs to middle- and high-school students and through our K 12 Science is Fun program at ASU. Our research will provide the postdoctoral fellow and a number of graduate and undergraduate students with national and international exposure.
StatusFinished
Effective start/end date8/15/167/31/19

Funding

  • National Science Foundation (NSF): $526,938.00

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coherent radiation
electron beams
radiation
x rays
accelerators
modulation
free electron lasers
electron diffraction
bunching
costs
diffraction
students
spontaneous emission
aberration
trajectory control
websites
electron trajectories
x ray sources
relativistic electron beams
electron states