Comprehensive Analysis of Transverse Gradient Undulator for Compact X-Ray FELs based on Laser Plasma Accelerators

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Our capabilities to capture images of atoms and molecules in motion have been revolutionized by X-ray free-electron lasers (FELs) driven by large-scale radio-frequency accelerators. Plasma acceleration is a cutting-edge technique that accelerates electrons more than a thousand times faster than these conventional accelerators. In particular, laser-plasma accelerators are leading the way toward self-contained compact accelerators and light sources. This award will investigate a novel way to produce extreme ultraviolet and X-ray free-electron lasers based on laser-plasma accelerators. The advancement will be used to develop practical applications of laser-plasma accelerators in compact and coherent radiation sources. The award will also support the training of graduate students at Stanford University, engaging them in the development of advanced beam and free-electron lasers theory and simulation tools. Laser-plasma accelerators (LPAs) have shown the abilities to accelerate electron beams from rest up to a few GeV using high-intensity lasers interacting in centimeter-scale plasmas. Although the beams have relatively low emittance and high peak current with only a few femtosecond pulse duration, the beam energy spread is two orders of magnitude larger than the spread from conventional radio-frequency accelerators. Such a large energy spread can make the FEL interaction in a normal undulator very ineffective. A transverse gradient undulator (TGU) can be used to compensate the effects of beam energy spread if the electron energy is correlated with its transverse position in the TGU. Previous theoretical and numerical studies have shown that such a concept may drastically improve the LPA FEL performance. This award will take the concept to practice by studying beam transport and dynamics from a LPA to and inside a TGU with the desired optics properties, and by developing FEL simulation tools that take into account various effects in a TGU. For verification of results, comparisons will be made, where applicable, to TGU experiments through external collaborations.