Speaker
Description
At FACET-II, laser heater (LH) optimization, encompassing power, alignment, and timing, is employed to suppress microbunching instabilities and customize longitudinal current profiles. Analogous techniques at LCLS have demonstrated that temporally shaped LH pulses can imprint programmable slice energy spreads that, after bunch compression, convert into controlled current modulations, enabling attosecond lasing, bunch trains, and caustic suppression [1]. At FACET-II, we extend this paradigm toward plasma wakefield acceleration: tailored LH imprinting via short Gaussian modulations, combined with RF linac phase tuning, enables the controlled generation of multi-spike current profiles optimized for resonant plasma wakefield excitation, where the inter-spike spacing is matched to the local plasma period. Driving plasma wakefields resonantly with a current spike train enables coherent wakefield superposition and amplitude growth along the train, simultaneously increasing the accelerating gradient and the transformer ratio beyond the symmetric-driver limit, as recently demonstrated experimentally in the linear regime and proposed for extension to the nonlinear regime at FACET-II [2,3].
In this contribution, start-to-end simulations and machine-learning-guided scans over the joint LH power, LH profile, and RF linac phase space identify operating points producing well-separated, high-current spikes at the FACET-II plasma injector entrance [4], made experimentally accessible by a newly commissioned LH pulse stacker. We present simulation results alongside preliminary experimental characterization, establishing the laser heater as a flexible, shot-by-shot instrument for active longitudinal beam shaping at FACET-II.
[1] D. César and A. Marinelli, Phys. Rev. Accel. Beams 24, 110703 (2021)
[2] L. Verra et al., Phys. Rev. E 112, 045205 (2025)
[3] C. Emma et al., Phys. Rev. Lett. 134, 085001 (2025)
[4] N. Sudar and Y. Ding, arXiv:2208.03973 (2022)
| Working group | WG5 |
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