Demonstration of feedback control regulation process for microwave discharge ion thruster in space gravitational wave detection

High thrust noise limits the application of microwave discharge ion thruster (MDIT) on space gravitational waves (GWs) detection, which needs to be suppressed by a feedback control system. A feedback control experimental platform is established for MDIT choosing microwave power and ion beam current respectively as controlled variable and feedback parameter. Experiments show the feedback control system adjusts screen grid (SG) current by regulating microwave power to compensate for fluctuations of acceleration grid (AG) current, which is mainly because the ability of microwave power to adjust SG current is dramatically stronger than that to adjust AG current. Faced with fluctuations of decreasing flow rate, the feedback control system boosts microwave power to stabilize ion beam current. However, the AG current shows diametrically opposed characteristics for operations with different interception rates under regulation of a feedback control system. Further study shows this phenomenon is the macroscopic reflection of ion trajectories variations on AG current under the function of specific electric field when feedback control system changes the proportions of primary ions and charge exchange (CEX) ions by influencing CEX reaction intensity in the grid system and its downstream region. Analysis of mean free path shows the CEX reaction intensity in the grid system is stronger than that downstream from AG. Therefore, the physical process in the grid system dominates variations of AG current.