Experimental study of ion beamlet steering by aperture displacement in two-stage accelerator

Abstract

The steering of ion beamlets in a two‐stage accelerator has been measured as functions of both aperture displacement and field intensity ratio between extraction and acceleration regions. Three different types of displacement have been investigated; i.e., displacement of (1) plasma grid, (2) gradient grid, or (3) suppressor grid with respect to the other three grids. In each case, the steering angle is found to be linear with the aperture displacement, and independent of final beam energy and beam current. The variation of steering angle with displacement distance is compared with the value predicted by linear theory using thin lens approximation. It is confirmed that they agree well in the case of (3), while they show appreciable differences in the cases of (1) and (2). This is because the lens effect of the gradient grid is weaker than is predicted by the linear theory. The deterioration of beam optics due to steering has not been observed.