This paper investigates whether biased electrodes can improve the performance of a microwave-discharge water ion thruster, which has been proposed as a propulsion system for CubeSats. Previously, for several microwave ion sources, the beam currents have been increased by mounting a biased electrode in the discharge chamber. The effect of a biased electrode on a water ion thruster was unclear because its magnetic field profile and characteristic length compared with the microwave wavelength are different from those used in previous studies. To investigate the effect, a thruster was divided into three parts: magnets, a microwave antenna, and a discharge chamber, which is comprised of an electrically conductive sidewall and a screen grid. The parts were isolated electrically. Bias voltages from $-$44 to ＋ 44 V were applied to the microwave antenna or magnets by an additional power supply. These bias voltages were applied with respect to the screen grid and sidewall voltage. A maximum screen current of 12.7 mA was obtained for an antenna bias voltage of 38.2 V. This is 2.3 times larger than the current without a bias voltage. This increase could be caused by a combination of an increase of plasma density and ion extraction efficiency. The plasma density could increase with the gain of the total absorbed power. The ion extraction efficiency could increase due to the change in the plasma potential distribution. Overall, the mass utilization efficiency of the water ion thruster increased from 3.3% to 7.9% and the discharge loss decreased from 280 to 150 W/A at the antenna bias of 38 V. The performance with water electron source was evaluated. The thrust force, specific impulse, thrust-to-power ratio, thrust efficiency were 190 $\mathrm{\mu }$N, 350 s, 5.9 $\mathrm{\mu }$N/W, and 1.0%, respectively at the antenna bias of 25 V.

本文研究了偏置电极是否可以提高微波放电水离子推进器的性能，该推进器已被提议作为立方体卫星的推进系统。以前，对于几个微波离子源，通过在放电室中安装偏置电极来增加束流。偏压电极对水离子推进器的影响尚不清楚，因为与微波波长相比，其磁场剖面和特征长度与以前研究中使用的不同。为了研究这种效果，推进器分为三个部分：磁铁、微波天线和放电室，放电室由导电侧壁和屏幕网格组成。这些部件是电气隔离的。偏置电压来自$-$ 通过附加电源向微波天线或磁铁施加44 至 + 44 V。这些偏置电压是相对于屏栅和侧壁电压施加的。天线偏置电压为 38.2  V时获得的最大屏幕电流为 12.7 mA 。这是没有偏置电压时电流的 2.3 倍。这种增加可能是由等离子体密度和离子提取效率的增加共同引起的。等离子体密度会随着总吸收功率的增加而增加。由于等离子体电位分布的变化，离子提取效率会增加。总体而言，水离子推进器的质量利用效率从 3.3% 提高到 7.9%，放电损耗从 280  W/A降低到 150 W/A，天线偏置为 38 五、水电子源性能评价。推力、比冲、推力比、推力效率为190 $\mathrm{\mu }$N，350 秒，5.9 $\mathrm{\mu }$N/W 和 1.0%，分别在天线偏置为 25  V 时。