Magnetic Dipole Inflation with Cascaded Arc and Applications to Mini-Magnetospheric Plasma Propulsion

Mini-Magnetospheric Plasma Propulsion (M2P2) seeks to create a plasma-inflated magnetic bubble capable of intercepting significant thrust from the solar wind for the purposes of high speed, high efficiency spacecraft propulsion. Previous laboratory experiments into the M2P2 concept have primarily used helicon plasma sources to inflate the dipole magnetic field. The work presented here uses an alternative plasma source, the cascaded arc, in a geometry similar to that used in previous helicon experiments. Time resolved measurements of the equatorial plasma density have been conducted and the results are discussed. The equatorial plasma density transitions from an initially asymmetric configuration early in the shot to a quasisymmetric configuration during plasma production, and then returns to an asymmetric configuration when the source is shut off. The exact reasons for these changes in configuration are unknown, but convection of the loaded flux tube is suspected. The diffusion time was found to be an order of magnitude longer than the Bohm diffusion time for the period of time after the plasma source was shut off. The data collected indicate the plasma has an electron temperature of approximately 11eV, an order of magnitude hotter than plasmas generated by cascaded arcs operating under different conditions. In addition, indirect evidence suggests that the plasma has a β of order unity in the source region. As an alternative, Mini-Magnetospheric Plasma Propulsion (M2P2) seeks to create a plasma-inflated magnetic bubble capable of intercepting significant thrust from the solar wind. One of the critical factors for plasma-inflation is the creation of high β plasma. β is the ratio of plasma pressure (proportional to density×temperature) to magnetic field pressure (proportional to the square of the magnetic field strength). In theory, a high β plasma with a large Magnetic Reynolds number injected into a modest (~1 m, 0.1 T) magnetic dipole will carry the magnetic field outward (“inflate”) as the plasma expands. The condition of a large Magnetic Reynolds number indicates that the plasma pushes the magnetic field outward faster than the magnetic field can diffuse inward through the plasma. The resulting magnetic field scales as a current sheet (B scales with 1/r), and it then becomes possible to produce the required magnetic field at the required distances to yield thrusts ~1N. The M2P2 system can thus be used as a high ∆V, high efficiency propulsion system for a modest (100s of kg) interplanetary spacecraft, using reasonable amounts of onboard power (few 10s of kW) and consumables.