Generation of Phase-controlled Accelerating Structures in Plasma∗

A novel mechanism for generating large (> 1 GeV/m) accelerating wakes in a plasma is considered. We employ two slightly detuned counter-propagating laser beams, an ultra-short timing pulse and a long pump, which exchange photons and deposit the recoil momentum into the plasma electrons. A rapidly rising electron current is thereby generated, inducing an plasma wake with phase velocity equal to the group velocity of the short pulse, which can be used for particle acceleration. It turns out that, by modulating the amplitude and frequency of the pump, one can generate periodic phase-controlled accelerating structures in the plasma (“plasma linac”). By the judicious choice of the duration of each segment of the pumping beam, acceleration unlimited by the dephasing can be realized. The amount of transverse focusing can be also adjusted. The important advantage of this type of plasma accelerator over the conventional laser wakefield accelerator is that it requires modest laser intensities I 10W/cm.