| A new electrodeless accelerator concept, called Faraday Accelerator with Radio-frequency Assisted Discharge (FARAD), that relies on an RF-assisted discharge to produce a plasma, an applied magnetic field to guide the plasma into the acceleration region, and an induced current sheet to accelerate the plasma, is presented. The presence of a preionized plasma allows for current sheet formation at lower discharge voltages and energies than those found in other pulsed inductive accelerator concepts. A proof-of-concept experiment, supported by optical and probe diagnostics, was constructed and used to demonstrate the main features of the FARAD and to gain physical insight into the low-voltage, low-energy current sheet formation and acceleration processes. Magnetic field data indicate that the peak sheet velocity in this unoptimized configuration operating at a pulse energy of 78.5 J is 12 km/s. It is found that changes in the background gas pressure and applied field affect the initial preionized plasma distribution which, in turn, affects the sheet's initial location, relative magnetic impermeability and subsequent velocity history.; The results of the experimental investigation motivated further theoretical and numerical investigations of pulsed inductive plasma acceleration. A model consisting of a set of coupled circuit equations and a one-dimensional momentum equation was nondimensionalized leading to the identification of several scaling parameters. Numerical analysis revealed the benefits of underdamped current waveforms and led to an efficiency maximization criterion that requires matching the external circuit's natural period to the acceleration timescale. Predictions of the model were compared to experimental measurements and were found to be in good qualitative agreement and reasonable quantitative agreement for most quantities.; A set of design rules aimed at producing a high-performance FARAD thruster are derived using the modeling results and physical insights. The rules concern the optimization of each of the major processes in FARAD: plasma acceleration, current sheet formation, applied field generation, and mass injection and preionization, and are cast as specific prescriptions for the dynamic impedance, inductance change, circuit damping, plasma collisionality (or magnetization), magnetic field strength and topology, and intra-pulse sequencing. |
