Hose Instability and Wake Generation by an Intense Electron Beam in a Self-Ionized Gas

The propagation of an intense relativistic electron beam through a gas that is self-ionized by the beam’s space charge and wakefields is examined analytically and with 3D particle-in-cell simulations. Instability arises from the coupling between a beam and the offset plasma channel it creates when it is perturbed. The traditional electron hose instability in a preformed plasma is replaced with this slower growth instability depending on the radius of the ionization channel compared to the electron blowout radius. A new regime for hose stable plasma wakefield acceleration is suggested.

Figure 1

Mechanism of ionization hosing instability: (a) illustration of offset ion column formed by ionization of neutral gas by a tilted beam; (b) particle-in-cell simulation of total charge density ionized by tilted beam (center of charge is shown by a solid line; center of beam by dots); (c) lineout from simulation of beam centroid (dashed line), center of resulting charge density in the self-ionized case (solid line), and a preformed case (dotted line); (d) lineout from simulation of beam centroid (dashed line) and center of resulting charge density (solid line) at a later time ($s=0.35\mathrm{m}$). Simulations are in the above threshold regime.

Figure 2

Comparison of analytic and numerical solutions to Eq. (1, 2)—beam centroid growth vs propagation distance at position $\xi =10.08\mathrm{mm}$ in the beam.

Figure 3

Particle-in-cell simulation results showing centroid of beam vs propagation distance (top), beam real space at 1.4 m (middle), and plasma electron density (bottom) for (a) preformed plasma, (b) near threshold, and (c) above threshold. Also shown on (c) is the unscaled numerical solution (dotted line) of the ionization hosing model Eqs. (3, 4) with $t=0.5c/{\omega }_{\mathrm{pb}}–3c/{\omega }_p$. The traditional hosing theory result (dashed line) is scaled by a factor of 500 to fit on the graph.

Figure 4

Particle-in-cell simulation comparisons of wakes in preformed plasma (left) and self-ionized plasma near threshold (right). (a) and (b) Real space of plasma electrons; (c) and (d) wake electric field $E_z$ on axis. Note that the blowout radius in (a) is clearly larger than the ionization radius in (b). $N_{\mathrm{beam}}=2\times {10}^{10}$, $n_0=5\times {10}^{15}$, $\gamma =60000$.