Abstract
Energy-efficient plasma-wakefield acceleration of particle bunches with low energy spread is a promising path to realizing compact free-electron lasers and particle colliders. High efficiency and low energy spread can be achieved simultaneously by strong beam loading of plasma wakefields when accelerating bunches with carefully tailored current profiles [M. Tzoufras et al., Phys. Rev. Lett. 101, 145002 (2008)PRLTAO0031-900710.1103/PhysRevLett.101.145002]. We experimentally demonstrate such optimal beam loading in a nonlinear electron-driven plasma accelerator. Bunches with an initial energy of 1GeV were accelerated by 45MeV with an energy-transfer efficiency of (42±4)% at a gradient of 1.3 GV/m while preserving per-mille energy spreads with full charge coupling, demonstrating wakefield flattening at the few-percent level.
Highlights
Energy-efficient plasma-wakefield acceleration of particle bunches with low energy spread is a promising path to realizing compact free-electron lasers and particle colliders
Bunches with an initial energy of 1 GeV were accelerated by 45 MeV with an energytransfer efficiency of ð42 Æ 4Þ% at a gradient of 1.3 GV=m while preserving per-mille energy spreads with full charge coupling, demonstrating wakefield flattening at the few-percent level
Plasma wakefields [1] driven by intense particle beams [2,3] can provide accelerating gradients in the multi-GV/m range [4,5,6], promising more compact accelerators for high energy physics and photon science [7,8,9,10]
Summary
Transverse deflection structure quadrupoles Plasma cell Imaging (c) quadrupoles LANEX screen. The electron bunches were diagnosed downstream of the plasma cell with a dipole spectrometer, using five quadrupoles for point-to-point imaging of the beam from the plasma exit to a LANEX screen [Fig. 1(d)]. An object-plane scan was performed with the imaging quadrupoles, verifying the location of the waist and measuring the horizontal divergence to be ð0.23 Æ 0.03Þ mrad in the tail and up to 1 mrad in the head (higher due to coherent-synchrotron-radiation effects [34]). These measurements imply minimum beam sizes of 2–10 μm and normalized slice emittances of 1–20 mm mrad (tail to head, respectively). The longitudinally averaged transformer ratio T is calculated as the mean energy gain of the trailing bunch normalized by the maximum energy loss within the driver [36]; the longitudinally averaged energy-transfer efficiency is calculated as η
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