Design of a 7-MeV APF DTL with robust considerations

A design principle with robust considerations has been applied to design a new alternating phase focused (APF) drift tube linear accelerator (linac) for particle beam therapy. By assuming a sinusoidal synchronous phase formula and a linearly increasing electrode voltage scheme, the structure of the APF linac is automatically optimized with a cost function including robustness using the nonlinear correlated stacking optimization method (CSM). The design procedure includes the radio frequency quadrupole (RFQ) to drift tube linac (DTL) matching, and an end-to-end simulation of the APF acceleration beam dynamics. Moreover, the stability of the solution obtained is analyzed with respect to various independent errors as well as a number of joint errors. The designed APF DTL linac together with an already established RFQ is planned to replace the existing Alvarez-type permanent magnet focused DTL linac aiming at easier manufacturing and cost reduction.