Measurement of the impulse from a magnetic nozzle for the model experiment of laser fusion rocket

Abstract

Magnetic nozzle is a component of a propulsion system which obtain thrust from a plasma in a magnetic field. Previous works have investigated the plasma behavior and thrust performance of the magnetic nozzle through experiment and simulation. A thrust stand with a pendulum has been used to experimentally evaluate the impulse bit generated by magnetic nozzle. A direct method, which measures the impulse bit on the magnet by putting it on the pendulum, may be difficult to measure the displacement because of the vibration. An indirect (target) method, which measures the impulse of the plasma accelerated by the magnetic nozzle, can be applied for large pulsed-electromagnets, but may be difficult to measure all of the impulse because of the limited detectable area. Here, we performed two impulse bit measurements with pendulum methods for the same magnetic nozzle. Also, we measured ion current at the same position of the target measurement to investigate the ion extraction from the nozzle. Although the obtained impulse bits are different, the target measurement reproduced the similar energy dependence as the simulation results. In addition, the spatial distribution of ions discharged downstream of the magnetic nozzle could be obtained by ion measurement. Combining these results suggests the possibility of evaluating impulses by target measurement in the future.