Numerical simulation of the creation of a tapered plasma channel by a nonuniform large magnetic field

In order to resolve the dephasing problem in laser wakefield acceleration, a tapered plasma guiding channel (TPGC) is proposed which is verified through magnetohydrodynamic (MHD) simulation. TPGC is created by means of laser heating combining an axially increasing external magnetic field. MHD simulation shows that a locally strong magnetic field prevents the thermal energy transport crossing the field lines, which consequently leads to a pressure buildup. The pressure gradient expels the plasma radially and tapers the density axially. A tapered plasma with a density variation from 2 x 10(18) to 8 x 10(17) cm(-3) within a 6 cm channel is established. Propagating in the tapered plasma channel, the energy of an accelerated electron is expected to be significantly enhanced.