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The time for stationary plasma to recover its original state after a wake is excited determines repetition rate and luminosity of plasma-based colliders. Recent measurements at DESY [1] showed that an argon plasma of density ne≈$10^{16}$cm$^{−3}$ in which a 0.5J(0.5nC,1GeV) e-bunch excited a first wake supported excitation of a second wake at the same location with indistinguishable beam properties within 60ns; in [2] a similar study was carried out in hydrogen plasmas. We report 2024 results at SLAC's FACET-II facility where 20J(2nC,10GeV) e-bunches excited meter-long nonlinear wakes in stationary lithium, hydrogen, and argon plasmas of density ne≈10$^{16}$cm$^{−3}$. Shallow angle optical probing (~100fs, ~1˚) was used to study wakefield remnants at delays 1ns≲∆t≲10$\mu$s. In lithium plasma, probe scatter remained visible out to ∆t≈2$\mu$s. Probe signal persisted up to ∆t≈100ns and ∆t≈300 ns, in hydrogen and argon plasmas, respectively. Bessel beam interferometry revealed nonzero phase shift out to (and possibly beyond) ∆t≈10$\mu$s in argon wakes. The results will be discussed considering findings of experiment E-224 [3], which showed that ion motion dominated energy transport out of the beam-excited region for ∆t≳0.3ns.
[1]R.D’Arcy et al., Nature 603, 58-62(2022).
[2]R.Pompili et al., Commun Phys 7, 241(2024).
[3]R.Zgadzaj et al., Nat Commun 11, 4753(2020).
