Transport of ps-laser-generated fast electrons under a non-uniform magnetic field produced by a circular coil target is studied by particle-in-cell simulation. The fast electrons can be well-collimated when the coil diameter is about 200 μm for the typical ps laser intensity in the fast ignition or double-cone ignition scheme of laser fusion. The optimized coil diameter results from the competition between the strength enhancement and the non-uniformity growth of the magnetic field as the reduction of the coil diameter. Here the non-uniformity growth can induce the magnetic mirror effect, which causes the reflection of some transporting fast electrons. Particularly, when the coil diameter is larger than 500 μm, the fast electron transport under the produced magnetic field is very close to the case with a uniform magnetic field. The impact of the coil longitudinal position is also analyzed and we find that it can change the electron transport range within the convergent or divergent magnetic field lines, which significantly affects the fast electron transport. This work could not only be applied in fast ignition and double-cone ignition schemes, but also to ion acceleration and radiation sources based on laser-driven fast electrons.

fast electron transport,magnetic field confinement,magnetic mirror effect