Simulation and Measurement of Helicon Waves at 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 an understanding of wave propagation and power deposition is essential. To this end we have developed a finite element model in Comsol that solves for the quasi 3D wavefields for a given temperature, density and neutral distribution. To do so the antenna currents are decomposed into discrete azimuthal modes and the 3D fields are reconstructed from solutions of the 2D axisymmetric problem for each dominant mode. We present simulation results for measured plasma profiles that reproduce experimentally seen effects such as m=1 mode dominance and asymmetric power deposition. Further we show the current development status of wavefield measuring diagnostics aiming to verify the simulations.