A model experiment of a double-cone target using a gap target

We have conducted preliminary experiments to prove the vacuum-shielding effect using an Al-Cu double-foil (both Al and Cu foils are 1 mm × 1 mm × 10 μmt) target with a vacuum-gap. Particle-in-cell simulation results have shown that the double-cone confines the electrons for hundreds of femtoseconds by the sheath electric field inside the vacuum-gap [T. Nakamura, et al., Phys. Plasmas 14, 103105 (2007)]. Cu-Kα intensity decreased with the vacuum-gap, i.e., the number of fast electrons that reached the Cu foil decreased with the gap. In the stack measurement, the number of electrons detected in the target surface direction increased with the gap. These results indicate that when the double-cone target is used, fast electrons created by an ignition laser can be reflected from the vacuum-gap, move along the cone surface, and be transferred towards the cone tip.