Modeling the time variation of beam–grid fusion reaction rates in an Inertial Electrostatic Confinement device driven by a ring-shaped magnetron ion source

Abstract

We use the two-dimensional analysis code KUAD2 to simulate trajectories in an Inertial Electrostatic Confinement (IEC) device driven by a ring-shaped magnetron ion source (RS-MIS). This aims to maximize the path length λCX for ion-gas charge exchange by operating at just units of mPa D2 gas pressures; however, under these conditions simulations reveal a surprisingly small path length for ion loss to the (Mo) cathode grid λgrid ∼ 30 cm ≪ λCX. By developing an ad hoc model relating the time variation of cathode temperature and absorbed D2 surface density, we use the simulated flux Γgrid of ions striking the cathode grid to obtain the neutron production rate (NPR) arising from ‘beam-grid’ reactions. Results indicate that at units of mPa pressures, beam-grid NPR may dominate over the ‘beam-gas’ and ‘beam-beam reactions,’ providing a qualitative explanation for earlier experimental observations of time-varying NPR-dependence on cathode grid current and gas pressure.