High-Density Helicon Studies on the Madison AWAKE Prototype

The AWAKE project at CERN opens up the frontier of next generation electron colliders using beam-plasma wakefield acceleration. Acceleration gradients exceeding 1 GV/m have been demonstrated using a laser-ionized plasma. However a full scale accelerator will need a reliable, high-density plasma source that scales to kilometer lengths with a high degree of axial density uniformity. The Madison AWAKE Prototype (MAP) is utilizing 30 kW of RF power to generate a helicon plasma with expected densities reaching 10²⁰ m^-3 in a multi-antenna setup. In order to optimize the density profile in MAP, an understanding of wave propagation and power deposition is essential. To this end we have developed a finite element model that solves for the quasi-3D wavefields and power deposition for a given temperature, density and neutral distribution. Using this model alongside experimental measurements and analytics we have for the first time revealed the mechanism responsible for the directionality of helicon discharges and the preference of right- over left-handed whistler modes. In addition to this discovery, we will further present current results for measured plasma density and ion temperature along with our progress towards enabling high-power steady-state operation.