Study of Electron-Beam Propagation through Preionized Dense Foam Plasmas

The transport of an intense electron-beam produced by the Vulcan petawatt laser through dense plasmas has been studied by imaging with high resolution the optical emission due to electron transit through the rear side of coated foam targets. It is observed that the MeV-electron beam undergoes strong filamentation and the filaments organize themselves in a ringlike structure. This behavior has been modeled using particle-in-cell simulations of the laser-plasma interaction as well as of the transport of the electron beam through the preionized plasma. In the simulations the filamentary structures are reproduced and attributed to the Weibel instability.

Figure 1

Setup and target layout.

Figure 2

Electron spectra measured for different foam target conditions and spectrum obtained from the simulation for similar target and laser conditions (total number per MeV).

Figure 3

Optical emission data obtained using a $250\mu \mathrm{m}$ foam target. The image shows the reprocessed data obtained from both cameras with different gray filters by overlying in order to show the substructure of the inner circle as well as the filaments in the outer region. The positions of the inner filaments are indicated with a circle with $50\mu \mathrm{m}$ in diameter, whereas the spot including the filaments in the outer region has a diameter up to $100\mu \mathrm{m}$.

Figure 4

Simulation of electron density of hot electrons after 10, 20, and $100\mu \mathrm{m}$ propagation [(a),(c),(e)] and $x$ component of the magnetic field surrounding the filaments [(b),(d),(f)].