Experimental study of a radial plasma source Available to Purchase

A radially outward acceleration of plasma in cylindrical geometry along an applied electric field and across an axial magnetic field is studied. The configuration, coined a radial plasma source, consists of two ceramic disks positioned parallel to each other, between which a cylindrical molybdenum anode is mounted. The electric field is generated by applying a voltage between the anode and a heated cathode neutralizer that is located away from the ceramic disks. The plasma diagnostic system includes Langmuir probes, an emissive probe, and a balance force meter. The discharge voltage is found to increase when the magnetic field is increased or when the mass flow rate (and the pressure) is decreased. For a discharge current of 1.4 A, the discharge voltage increases from 55 to 120 V when the magnetic field is increased from 0 to 186 G. The azimuthal uniformity of the plasma flow is found to decrease with the increase in gas pressure. The force exerted on the balance force meter is found to be larger than the force exerted by the plasma flow. This disparity indicates that a considerable part of the force is exerted by the neutral gas, which has gained momentum from the plasma via ion-neutral collisions. The force is increased because the momentum delivered for a given deposited power is larger if the energy is deposited in a larger mass, as happens here through plasma collisions. We estimate theoretically the expected force at the collisionless and the collisional limits and find that the measured force is between the expected forces at the two limits.