屏栅边缘小孔孔径对离子推力器性能的影响

Influence of screen gird aperture diameter in outer region on performance of dual-mode ion thruster

提出并实验验证了一种通过减小屏栅边缘小孔孔径消除双模式离子推力器中束流离子对三栅极系统减速栅边缘小孔溅射刻蚀的方法.基于30 cm双模式离子推力器,在小推力高比冲和大推力高功率两种工作模式下实验对比研究了屏栅边缘小孔孔径对推力器放电损耗、束流平直度和减速栅边缘小孔刻蚀速率和刻蚀范围的影响.当束流半径95%外的屏栅小孔孔径缩小26%后, 30 cm双模式离子推力器在小推力高比冲模式和大推力高功率模式下放电损耗分别减小10%和21%;束流平直度分别下降3%和10%;减速栅边缘小孔存在离子溅射刻蚀的小孔排数由边缘5排减小到最边缘1排,刻蚀速率明显减小,并且当工作900 h后最边缘小孔刻蚀现象也消失.实验结果表明:减小屏栅边缘小孔孔径是一种解决双模式离子推力器小推力高比冲模式下束流离子对三栅极系统减速栅边缘小孔溅射刻蚀的有效方法,而且不会降低推力器效率,但是会造成束流均匀性变差.

To eliminate the erosion in the apertures at the edge of the decelerate grid of a dual-mode ion thruster three-grid optical system,a new method of reducing the diameter of the apertures in the outer region of the screen grid is proposed.In order to investigate the method of influencing the discharge loss and the uniformity of the beam current density and also reducing the aperture erosion region and erosion rate of the decelerate grid,two kinds of three-grid optical systems are designed and fabricated with the same material and physical parameters except the diameter of the apertures in the outer region of the screen grid.The first kind is that the diameter of the aperture in the outer region of the screen grid is equal to that in middle region of the screen grid,it is designated as the same aperture diameter grid optical system.The second kind of three-grid optical system is that the diameter of screen apertures whose center distance from the center of grid is larger than 0.95 times the beam radius,is reduced by 26%and therefore the physical transparency of optical system is reduced by 8.8%,it is designated as the small aperture diameter grid optical system.The comparison between the same aperture diameter grid optical system and small aperture diameter grid optical system is performed by assembling them into a 30-cm-diameter dual-mode ion thruster,and the ion thruster performance test,beam flatness test and 600-h-endurance test are conducted in the two typical operation modes,namely the low thrusthigh specific impulse mode and large thrust-high power mode.A comparison of small aperture diameter grid optical system with the same aperture diameter grid optical system shows that the discharge loss of the 30-cm dual-mode ion thruster in the low thrust-high specific impulse mode and large thrust-high power mode are reduced by 10%and 21%respectively,the beam flatness is decreased by 3%and 10%respectively,the number of rows of the apertures which are sputtered by beam ions at the edge of the decelerate grid is reduced from 5 to 1.In addition,the erosion rate is significantly reduced and the erosion phenomenon disappears after 900-hlong-duration operation.These results signify that reducing the screen grid aperture diameter in the outer region is an effective method to eliminate aperture erosion at the edge of the decelerate grid of a dual-mode ion thruster three-grid optical system and that this method will not reduce the efficiency of the thruster,but cause the beam current uniformity to worsen.