A Novel Thrust Measurement Method For Plasma Rockets with Magnetic Nozzles Using B-field Measurements


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A Novel Thrust Measurement Method For Plasma Rockets with Magnetic Nozzles Using B-field Measurements


Abstract

A novel thrust measurement method for plasma rockets that employ magnetic coils is presented. The validity and feasibility of the thrust measurement method is analyzed using an analytic model of plasma flow through a magnetic coil as well as an experiment where the interaction between a nozzle coil and an induced plasma current is examined with two magnetic coils. First, the thrust on a coil is shown to result from the interaction between diamagnetic currents in the expanding plasma and the coil, and is found to be proportional to the induced radial field B_ind,r in the vicinity of the coil. Next, the scaling of thrust with plasma thruster parameters is derived, indicating that the typical magnitude of B_ind,r at the nozzle coil lies between 10-3 G - 1 G. Magnetic probes with the required sensitivity and dynamic range are described. Third, the error in the B_r measurement method due to the necessary vertical offset in probe position is examined with an analytical model of plasma flow through a magnetic coil, and is found to lie between 1%-10%, depending on the initial radius of the plasma flow. Lastly, empirical thrust estimates from the B_r method and trusted thrust stand method are found to be highly correlated in a two-loop approximation, with the percent error between them largely attributed to probe positioning error in the Br method. Also included are the calibration procedure for the B_r thrust measurement method and predictions for the future experiment with a plasma thruster that will further investigate the validity of the B_r method.