Abstract
Premodulated comblike electron bunch trains are used in a wide range of research fields, such as for wakefield-based particle acceleration and tunable radiation sources. We propose an optimized compression scheme for bunch trains in which a traveling wave accelerator tube and a downstream drift segment are together used as a compressor. When the phase injected into the accelerator tube for the bunch train is set to $\ensuremath{\ll}\ensuremath{-}100\ifmmode^\circ\else\textdegree\fi{}$, velocity bunching occurs in a deep overcompression mode, which reverses the phase space and maintains a velocity difference within the injected beam, thereby giving rise to a compressed comblike electron bunch train after a few-meter-long drift segment; we call this the deep overcompression scheme. The main benefits of this scheme are the relatively large phase acceptance and the uniformity of compression for the bunch train. The comblike bunch train generated via this scheme is widely tunable: For the two-bunch case, the energy and time spacings can be continuously adjusted from $+1$ to $\ensuremath{-}1\text{ }\text{ }\mathrm{MeV}$ and from 13 to 3 ps, respectively, by varying the injected phase of the bunch train from $\ensuremath{-}220\ifmmode^\circ\else\textdegree\fi{}$ to $\ensuremath{-}140\ifmmode^\circ\else\textdegree\fi{}$. Both theoretical analysis and beam dynamics simulations are presented to study the properties of the deep overcompression scheme.
Highlights
The application ranges of free electron lasers (FELs), wakefield-based accelerators, and tunable radiation sources can be greatly extended by driving them with a train of short electron microbunches rather than with a single bunch [1,2,3,4,5,6,7,8,9]
A bunch train with a subpicosecond bunch length and a repetition rate of a few terahertz can be quite useful in the coherent excitation of plasma waves in plasma wakefield accelerators [19,20] and in the generation of frequencytunable narrow-band terahertz radiation [7,21,22] as well as in other beam dynamics applications [5,23,24,25]
From both theoretical predictions and beam dynamics simulations, we find that, when the phase of the traveling wave accelerator (TWA) tube is varied over a large range of values of ≪ −100°, the generated laser-comb bunch train is widely tunable in both energy and bunch interval after a few meters of drift
Summary
The application ranges of free electron lasers (FELs), wakefield-based accelerators, and tunable radiation sources can be greatly extended by driving them with a train of short electron microbunches rather than with a single bunch [1,2,3,4,5,6,7,8,9]. From both theoretical predictions and beam dynamics simulations, we find that, when the phase of the TWA tube is varied over a large range of values of ≪ −100°, the generated laser-comb bunch train is widely tunable in both energy and bunch interval after a few meters of drift In this scheme, the TWA tube overcompresses the beam, reversing the phase space of the bunch train while maintaining a velocity difference (or energy chirp) within the bunch train at the TWA exit; the long drift segment gives rise to gentle and uniform compression of the bunch train. The key results for four bunches under deep overcompression are presented for both the low-charge case and the high-charge case; these results demonstrate the applicability of the optimized compression scheme for generating comblike beams
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