Magnetizing nonlinear plasma wakefields for positron acceleration: mechanism and operating limits
Abstract
Positron acceleration is possible in linear plasma wakes, but the nonlinear electron-driven blowout regime confines simultaneous acceleration and focusing to narrow regions of returning plasma electrons. Here we investigate how an axial magnetic field reorganizes this nonlinear return to open an operating regime for sustained positron acceleration in a uniform plasma. Using quasi-3D and full-3D particle-in-cell simulations, we connect the formation of finite-radius electron columns, or gyro images, to witness transport and its operating limits. The image spacing is governed by the quasi-static invariant, while canonical angular momentum limits the return radius. Modified by the orbit-sampled wake potential, this mechanism yields a positioning law that accurately predicts the density peaks across a wide range of magnetic field strengths. At a plasma density of 1016 cm-3 and a 35 T axial field, the reorganized structure expands the usable accelerating and focusing interval by more than a factor of four compared to the unmagnetized case. A positron witness bunch placed at the settled phase of this band achieves 92% capture over a 60 mm stage, with the normalized emittance saturating at 83 mm mrad. Independent codes confirm sustained transport, yielding energy gains between 99 and 150 MeV, though numerical convergence on the exact energy gain remains an open challenge. Together with beam loading, alignment, and driver-energy scaling tests, these results establish magnetic control of the nonlinear electron return as a route to single-stage positron acceleration. Beam quality preservation, formation-transient control, and solenoid integration define the necessary next development steps.
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BibTeX
@misc{liu2026magnetizing,
title = {{Magnetizing nonlinear plasma wakefields for positron acceleration: mechanism and operating limits}},
author = {Yung-Kun Liu and Pisin Chen and Ching-En Lin and Spencer Gessner and Bernhard Hidding},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.33175},
eprint = {2609.33175},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.33175},
}
RIS
TY - UNPB
TI - Magnetizing nonlinear plasma wakefields for positron acceleration: mechanism and operating limits
AU - Yung-Kun Liu
AU - Pisin Chen
AU - Ching-En Lin
AU - Spencer Gessner
AU - Bernhard Hidding
PY - 2026
DA - 2026/09/27
PB - arXiv
DO - 10.48550/arxiv.2609.33175
UR - https://arxiv.org/abs/2609.33175
AB - Positron acceleration is possible in linear plasma wakes, but the nonlinear electron-driven blowout regime confines simultaneous acceleration and focusing to narrow regions of returning plasma electrons. Here we investigate how an axial magnetic field reorganizes this nonlinear return to open an operating regime for sustained positron acceleration in a uniform plasma. Using quasi-3D and full-3D particle-in-cell simulations, we connect the formation of finite-radius electron columns, or gyro images, to witness transport and its operating limits. The image spacing is governed by the quasi-static invariant, while canonical angular momentum limits the return radius. Modified by the orbit-sampled wake potential, this mechanism yields a positioning law that accurately predicts the density peaks across a wide range of magnetic field strengths. At a plasma density of 10^16 cm^-3 and a 35 T axial field, the reorganized structure expands the usable accelerating and focusing interval by more than a factor of four compared to the unmagnetized case. A positron witness bunch placed at the settled phase of this band achieves 92% capture over a 60 mm stage, with the normalized emittance saturating at 83 mm mrad. Independent codes confirm sustained transport, yielding energy gains between 99 and 150 MeV, though numerical convergence on the exact energy gain remains an open challenge. Together with beam loading, alignment, and driver-energy scaling tests, these results establish magnetic control of the nonlinear electron return as a route to single-stage positron acceleration. Beam quality preservation, formation-transient control, and solenoid integration define the necessary next development steps.
ER -