Adiabatic Response of Low Density Plasma in AWAKE

A relativistic proton bunch generates a magnetic field that can apply a focusing force to itself when exposed to plasma, which is known as adiabatic focusing. We perform experiments at CERN’s proton-driven plasma wakefield accelerator (AWAKE) to observe the adiabatic focusing response of low density plasma to a relativistic proton bunch. We studied these effects using time-integrated and time-resolves images of the proton bunch as the plasma density was varied in order to determine the effect of the plasma on the dimensions of the bunch. The results of the experiment showed evidence of an increasing focusing response of the bunch to increasing plasma density.