Modeling neutral beam transport in fusion experiments: Studying the effects of reionisation and deflection

A crucial component for any Neutral Beam Injection system is the beam duct, which connects the beam sources to the fusion reactor. There are two types of losses in the duct: geometrical losses due to scraping of the beam on beamline components, and reionisation losses due to interaction of the beam with background gas. A suite of modeling tools has been created to get insight in the magnitude of the losses and power deposition on beamline components: a molecular flow code taking into account the full 3D geometry to calculate background gas densities, FEM calculations in ANSYS to calculate magnetic fields, particle tracking through the magnetic field while interacting with the background gas via a Monte-Carlo scheme to calculate beam losses and resulting power loads. To illustrate the potential of the suite of models, the NBI beamline 2 of the ASDEX Upgrade tokamak is studied, which recently underwent an upgrade of the box exit scraper. Gas densities and magnetic fields are calculated and compared with measurements. Calculated heat loads are benchmarked with the calorimetry on the residual ion dumps. Power deposition in the duct is calculated before and after the installation of the new NBI box exit scraper to assess the impact of this upgrade.