Speaker
Description
Plasma-based accelerators can sustain multi-GV/m accelerating fields, but the strong focusing forces within the plasma channel can amplify small initial offsets into severe transverse instabilities known as beam break up (BBU) instability. Lebedev et al. [1] established a universal efficiency-instability relation for the blowout regime, asserting that the beam energy spread required to suppress BBU via BNS damping becomes incompatible with collider-quality beams as power-transfer efficiency increases. In this work, we address this trade-off by proposing a theoretical framework on the wake potential to precisely determine the transverse force experienced by a beam loaded trailing bunch. By isolating the self-wake of the witness bunch through its scalar potential, we derive an exact analytical transverse wake function that inherently accounts for the structure of the loaded plasma bubble.
To investigate these dynamics in a high-efficiency regime that preserves beam quality (low emittance and low energy spread), we employ a specifically shaped trapezoidal trailing bunch designed to flatten the longitudinal accelerating field. Our theoretical model is rigorously validated against three-dimensional HiPACE++ Particle-in-Cell (PIC) simulations, demonstrating remarkable agreement and improved accuracy over previous transverse wake function models [1]. Utilizing our analytical framework, we perform a comprehensive parametric study for a 10 GeV plasma stage, mapping efficiency limits against stability thresholds as functions of the plasma bubble radius, the loaded field, and the bunch length. High-fidelity Particle-in-Cell (PIC) simulations within the identified high-efficiency, low-instability regimes show strong agreement with our theoretical predictions for both centroid oscillation and emittance evolution. These results identify a stable operating region in which the energy-transfer efficiency can approach 40%, while emittance growth remains modest and the relative energy spread stays near 1%. By providing a model to map these stable, high-efficiency operating points, this work offers a clearer path toward designing accelerators that maximize energy transfer while maintaining beam stability, contributing to the theoretical foundation required for future compact particle colliders.
References
[1] Lebedev, Valeri, Alexey Burov, and Sergei Nagaitsev. "Efficiency versus instability in plasma accelerators." Physical Review Accelerators and Beams 20, no. 12 (2017): 121301.
Acknowledgements
We acknowledge the support by U.S. Department of Energy, Office of Science under Award No. DE-SC-0014043, DE-SC-0024277 and resources of NERSC facility operated under Contract No. DE-AC02-5CH11231.
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