Impurity beam-trapping instability in tokamaks

The sensitivity of neutron energy production to the trapping by impurities by injected neutral beams is considered. The beam-trapping process is affected by inherent low-Z contamination of the tritium plasma, by the species composition of the neutral beam, and by the entrance angle of the beam. The sensitivities of the process are compared to these variables and to the variation with wall material. One finds that use of a low-Z, low sputtering material could retard a possible beam trapping instability