Strong-focusing in tandem accelerator with alternating voltage gradient

A new method to obtain low-energy high-intensity beams from a tandem accelerator of a high design-voltage is presented. In this method, the beam undergoes repeated actions of acceleration and deceleration from alternating voltage gradient along the beam axis, so that the beam divergence is minimized. The practical test was carried out at the 10 MV tandem accelerator at Kyushu University, and the beam transmission efficiency at a low operation voltage of 1 MV was found to be an order of magnitude increased. The method also enables the accelerator to stand a high beam load. The necessary changes in the accelerator configuration are quite simple and easily achievable at a low cost.