Direct Thrust Measurement of a Permanent-Magnets Helicon Plasma Thruster for Space Propulsion

A thrust imparted by a permanent-magnets helicon plasma thruster is directly measured by using a pendulum thrust balance. The source consists of a 6.5-cm-inner diameter glass tube and a magnetic nozzle provided by arrays of permanent magnets. The configuration is designed so as to have maximum field strength of about 100 Gauss near the open end of the source. The flow rate of argon propellant is chosen as 25 sccm and a plasma is produced by 13.56 MHz helicon and/or inductively coupled discharges. The main plasma is guided by the magnetic nozzle and flows out from the source. It is observed that the whole structure of the source attached to the pendulum balance moves only during the plasma production, and its displacement is measured by a laser displacement sensor. The obtained maximum thrust is presently 7.5 mN for 2 kW rf power.