Experiments and Simulations of Positron Beam Propagation Through Meter Long Plasma Channels

In the plasma wakefield accelerator (PWFA) acceleration is achieved by wakes induced by a charged particle beam as it traverses the plasma. The wake induced by a positron drive beam in a hollow plasma channel is thought to be have certain advantageous characteristics (larger longitudinal fields and zero transverse field) compared to wakes induced by the same beam in a uniform plasma. We have carried out first experiments on the propagation of a GeV class, kA positron beam through meter-scale plasma channels at SLAC. The partially filled plasma channel is created by photo-ionization of Li vapor using an annular ArF ionizing laser beam. As a result of a low density plasma inside the channel the beam is seen to focus. The positron beam is also seen to be guided by the plasma channel as its injection angle is varied. The energy loss per unit length in the channel is greater than in a similar density radially uniform plasma. 2D, PIC simulations of the experiment are carried out using the codes OSIRIS and QUICKPIC.