Hollow plasma has been introduced into the proton-driven plasma wakefield accelerator to overcome the issue of beam quality degradation caused by the nonlinear transverse wakefields varying in radius and in time in uniform plasma. It has been demonstrated that the electrons can be accelerated to the energy frontier with a well-preserved beam quality in a long hollow plasma channel. However, this scheme requires the driver bunch in perfect alignment with the hollow channel, otherwise asymmetric and possibly strong transverse wakefields come into play, which could significantly deflect the beam and deteriorate the beam quality. In this paper, we examine these detrimental effects from theoretical and numerical aspects. We demonstrate that the proton driver is less sensitive to the misalignment due to the strong focusing field formed within the hollow channel. However, the induced transverse fields cause significant particle loss of the witness beam. Fortunately, by adopting a near-hollow plasma channel which maintains a small number of ions within the channel, we create a deep potential well to confine the witness beam. Eventually, the beam quality is well conserved.
|Working group||Theory and computation|