Development of a momentum vector measurement instrument in steady-state plasmas

Momentum vector measurement instrument yielding individual and simultaneous identification of local fluxes of momentum components in two different directions, i.e., vector-resolved force, is developed for understanding momentum transport in plasmas and the thrust generation mechanisms of a helicon plasma thruster. A detector plate is attached to a rotational arm connected to a pivot, which has a structure accessible to the inside of the thruster and is mounted on an axially movable balance structure. Simultaneous measurements of displacements of the rotational arm and the axially movable balance give the fluxes of the two different components of the momentum flowing into the detector surface, respectively, e.g., the radial and axial components. The detailed calibration results and the displacement signals induced by applying known forces in a bench test are shown. The results show that the presently developed technique gives resolutions of about 10 μN in the two different directions independently.