Measurement of ion acceleration characteristics of a laser-electrostatic hybrid microthruster for space propulsion applications

For space propulsion applications, a fundamental study of a laser-electrostatic hybrid thruster was conducted. A new type of thruster, in which a laser-produced plasma was accelerated by an additional electrostatic field, was tested to optimize the ion acceleration process. A time-of-flight measurement by a Faraday cup showed that the average speed of ions was about 15 km/s when only 0.04 mJ of laser impulse was introduced to a copper target. When an accelerator electrode with a 6-mm-diameter hole was placed in front of the laser target, it was observed that the average speed of ions increased. The maximum velocity was 23 km/s, which corresponded to the case where the accelerator grid was biased to +100 V for the target-to-electrode gap of 2 mm. It was found that the positively biased electrode was more effective than the negatively biased electrode for ion acceleration in the thruster.