Ion detachment in the helicon double-layer thruster exhaust beam

This study is devoted to simulating the orbits of the ions in the supersonic beam observed experimentally in the laboratory development of the helicon double-layer thruster. Given the cylindrical symmetry of the problem, the particle orbits are generated in cylindrical coordinates (r, phi, z), thereby enabling the analysis of magnetic detachment (in which the particles free themselves from the magnetic field of the source) to be confined to the analysis of the curvature of trajectories on the (r, z) plane. Because the trajectory of a magnetized particle in space is helical, detachment can be established if the curvature of r(z) on the (r, z) plane asymptotically approaches zero. The simulation shows that the detachment surface is a paraboloid opening in the direction of the expanding magnetic field, with its base along the radial (r) axis oscillating around the axial value z approximate to 0.38 m. The radius of the ion-beam detachment surface is in agreement with laboratory measurements of the beam density profile in the detachment region.