Test of the Electron Hose Instability in the E157 Experiment*

The E157 experiment is designed to demonstrate highgradient Plasma Wake Field Acceleration over a significant length. It has been suggested that the electron hose instability of the drive beam will degrade the performance of this experiment because the hosing tailelectrons will not fully sample the highest acceleration field. In this paper a parasitic experiment designed to test the extent of the hosing instability is described. In particular, we discuss how the initial beam conditions are determined so that the extent to which any transverse perturbations grow due to hosing can be determined. . 1 DETERMINATION OF THE INITIAL CONDITIONS FOR ELECTRON HOSE INSTABILITY EXPERIMENT In this paper we discuss how we determine the transverse offsets of the various longitudinal beam slices before the beam enters the plasma source in the E157 experiment. Such a well characterized beam is then sent through the plasma that is roughly 1.4 m long with a maximum density of about 2 × 10 cm to see if there is any growth of the transverse offsets of the beam slices due to hosing. 2 MOTIVATION The electron hose instability [1] of the drive beam is of some concern to the plasma wake field accelerator concept because it can lead to the growth of transverse perturbations on the beam due to the nonlinear coupling of the beam electrons to the plasma electrons that are at the edge of the plasma channel through which the beam propagates. The instability is described by two coupled wave equations: