Speaker
Description
Attosecond-level ultrafast electron diffraction (UED) experiments in the MeV regime increasingly rely on electron guns that act not only as injectors but also as well-defined longitudinal dispersive optical elements. Building on the concept of multi-dimensional phase-space manipulation, we investigate a class of “dispersion-engineered” RF electron guns whose internal dynamics are tailored such that the RF phase of maximum energy gain nearly coincides with the phase of minimum time of flight. Within a general transfer-map formalism we derive design conditions on frequency, effective cell number and cell lengths that yield a controllable gun longitudinal dispersion together with a strongly reduced first-order sensitivity of the exit time to RF phase and amplitude fluctuations. The framework is applicable to S-, C- and X-band structures with various non-integer cell configurations (e.g. 1.4-, 2.33-cell), and is intended as a theoretical guideline for future electron-gun designs dedicated to attosecond UED. As an illustrative example, we analyse a 2.33-cell S-band electron gun whose dispersion can be matched to downstream THz or magnetic compressors, enabling few-femtosecond, potentially attosecond-level bunches with intrinsically stabilized arrival time at the sample. The study outlines how RF electron guns can be systematically engineered as special-purpose electron guns optimized for attosecond UED facilities.
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