Jason Brooks Final Defense

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$\sim$$10^{16}$cm$^{-3}$ in which a 0.5J(0.5nC,1GeV) e-bunch excited a 
first wake supported excitation of a second wake at the same location with indistinguishable beam 
properties within 60ns; in [2] a similar study was carried out in Hydrogen plasmas. We report 2024 
results at the SLAC FACET-II facility where 20J(2nC,10GeV) e-bunches excited meter-long nonlinear 
wakes in stationary lithium, hydrogen, and argon plasmas of density ne$\sim$10$^{16}$cm$^{-3}$. 
Shallow angle optical probing ($\sim$100fs, $\sim$1$\deg$) was used to study wakefield remnants at 
delays 1ns$\leq$$\Delta$t$\leq$10$\mu$s. In lithium plasma, probe scatter remained visible out to $
\Delta$t$\sim$2 microseconds. Probe signal persisted up to $\Delta$t$\sim$100ns and $\Delta$t$\sim$300 ns, 
in hydrogen and argon plasmas, respectively. Bessel beam interferometry revealed nonzero phase shift 
out to $\Delta t\sim10\mu$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 $\Delta t$$\geq$0.3ns.

References:

[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).