Charging and ion ejection dynamics of large helium nanodroplets exposed to intense femtosecond soft X-ray pulses

Ion ejection from charged helium nanodroplets exposed to intense femtosecond soft X-ray pulses is studied by single-pulse ion time-of-flight (TOF) spectroscopy in coincidence with small-angle scattering. Scattering images encode the droplet size and absolute photon flux incident on each droplet, while TOF spectra are used determine maximum kinetic energy, $$E_{\text {kin}}$$ , of $$\hbox {He}_{j}^{+}$$ fragments (j = 1–4). Measurements span {He}_N$$ sizes between $$N\sim 10^{7}$$ $$\sim 10^{10}$$ (radii $$R_0$$ 78–578 nm), charges 9\times 10^{-5}$$ 3\times 10^{-3}$$ e/atom. Conditions encompass a wide range ionization expansion regimes, departure all photoelectrons leading pure Coulomb explosion, substantial electron trapping electrostatic potential indicating onset hydrodynamic expansion. The unique combination intensities, sizes, an event-by-event basis reveals detailed picture correlations conditions dynamics ionic fragments. He $$^{+}$$ found be governed repulsion unscreened cations across regimes. impact ion-atom interactions resulting relatively low charge densities increasingly relevant less trapping. findings consistent emergence spherical shell around quasineutral plasma core as degree increases. results demonstrate complex relationship measured that can only disentangled through use coincident scattering data.