Theoretical analysis and simulation study of the deep overcompression mode of velocity bunching for a comblike electron bunch train

摘要

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 $ensuremath{ll}ensuremath{-}100ifmmode^circelseextdegreei{}$, 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 $ensuremath{-}1ext{ }ext{ }mathrm{MeV}$ and from 13 to 3 ps, respectively, by varying the injected phase of the bunch train from $ensuremath{-}220ifmmode^circelseextdegreei{}$ to $ensuremath{-}140ifmmode^circelseextdegreei{}$. Both theoretical analysis and beam dynamics simulations are presented to study the properties of the deep overcompression scheme.