Modeling of tungsten filament in gas discharge in H^- ion source

Sources of negative ions such as H^- are essential elements of proton accelerators and tokamaks. They have limited lifetime. The replacement of an ion source is a costly process causing delays in the operation of the entire machine. The hot tungsten filament is the key element that limits the lifetime of the H^- ion source at the Los Alamos Neutron Science Center (LANSCE) facility. An accurate model, which describes the filament physics and provides a reliable estimate on its lifetime, may significantly improve the operation of the facility. Here, we describe such a model, including a comprehensive list of relevant physical processes from first principles. The model can be used to describe different regimes of operation using diagnostics data as input parameters. It has been benchmarked against the data collected during the production cycle at LANSCE and shows good agreement with experimental data.