NASA's Jet Propulsion Laboratory has developed a Hall thruster with a variable-area discharge chamber that improves the performance and lifetime of the thruster. Conventional Hall thrusters have poor ionization efficiency, which limits the thrust-to-power ratio that can be achieved with the thruster. JPL's novel Hall thruster has a variable-area discharge chamber that conforms to the curvature of the local magnetic field and optimizes the ionization efficiency of the thruster and, therefore, significantly improves the power-to-thrust ratio that can be achieved. This innovative device decreases spacecraft costs and enables fast, efficient orbit transfers.
The discharge chamber of a Hall thruster includes an ionization zone, a transition region, and an acceleration region. With the variable-area discharge chamber, the channel is wider through the acceleration region than through the ionization zone, effectively forming a diverging nozzle. This enables high thrust-to-power ratio at relatively low discharge voltages because the high-density ionization zone increases ionization efficiency, the low-density acceleration region increases efficiency and decreases wall losses, and the transition region smoothly connects the two. Note that the location of this transition region is important for proper operation of the device. Choosing the downstream boundary of the transition region such that the magnetic field has reached about 80% of the maximum centerline magnetic field strength ensures that the benefits of the narrow-area portion of the channel are realized.
During operation, a magnetic field forms within the discharge chamber having a converging plasma lens configuration such that the field lines are concave and symmetric across the discharge chamber. This configuration improves performance and thermal margin, decreases plume divergence, and increases lifetime because it decreases the plasma flux to the wall while focusing the ions such that their radial velocity is minimized.
The discharge chamber can be used in aerospace applications such as station-keeping, orbit transfers, and interplanetary missions; and in semiconductor applications such as materials processing, thin films, and implantation.