E→ × B→ radial plasma acceleration

A radially outward acceleration of plasma in cylindrical geometry along an applied voltage and across an axial magnetic field is studied. The configuration, coined a radial plasma accelerator (RPA), consists of two ceramic discs, each of a 8 cm diameter, which are positioned parallel to each other at a distance of 5 mm. Between the discs a cylindrical molybdenum anode of 4 cm diameter and 5 mm height is mounted. A magnetic field circuit generates an axial magnetic field. A heated cathode neutralizer is located 4 cm from ceramic discs. An argon gas is ionized, accelerated radially by the applied electric field across the axial magnetic field. All the measurements are taken for a discharge current of 1.4 A, a magnetic field up to 0.02 T, a mass flow rate through the cathode of 4 sccm. The mass flow rate through the anode is varied from 17.5 sccm to 50 sccm and, consequently, the pressure varied from 2.5 mTorr to 6.6 mTorr, and the applied anode-cathode voltage varied from 130 V to50 V. The plasma diagnostic system included a Langmuir probe, a heat flux probe and a pendulum thrust meter, all located 8 cm from the center of the disks. The heat flux is deduced from measurements of the temperature variation of the heat flux probe1. The azimuthal uniformity of the plasma flow is found to decrease with the increase of gas pressure. The thrust delivered to the thrust meter is found to be comparable to the thrust delivered to the plasma by the magnetic field pressure. However, the plasma momentum at the thrust meter turns out to be considerably smaller, indicating that the neutral gas gains through collisions with the plasma ions a large fraction of the momentum and delivers this momentum to the thrust meter.