A magnetically tapered plasma density for overcoming electron dephasing

One of the main limitations of energy gain in laser wakefield accelerators is the electron dephasing, In order to resolve the dephasing problem, a tapered plasma channel is proposed and tested numerically. The tapered density is created by means of a laser heating, combining an axially increased external magnetic field. The locally strong magnetic field prevents the thermal energy transport crossing the field lines, and leads to a pressure buildup. The pressure gradient expels the plasma radially and tapers the density axially. A tapered plasma with a density contrast of 2.2 within a 6-cm channel is established. Propagating in the tapered plasma channel, the energy of an accelerated electron is expected to be enhanced greatly.