First Thomson Scattering Results in the Helicon Plasma Source for Awake

A critical component of the Advanced Wakefield (AWAKE) experiment [1] for proton-driven plasma wakefield acceleration is the source that provides the suitable plasma environment. The stringent requirements: scalable in length (~100 m in future experiments) [2] , high electron density (n e ) (2 x 10 20 m -3 – 7 x 10 20 m -3 ) with a longitudinal homogeneity at the 0.25% level [3] , and tunnel compatibility, pose a major physical and engineering challenge to the plasma source and the corresponding diagnostics.