Model cavity of an alternating-phase-focused IH-DTL

A compact injector for medical accelerators was designed. The injector consists of a compact Electron-Cyclotron-Resonance Ion Source (ECRIS) and two linacs, which are a Radio-Frequency-Quadrupole (RFQ) linac and an Interdigital H-mode Drift-Tube-Linac (IH-DTL) having the same operating frequency of 200 MHz. For beam focusing of the IH-DTL, the method of Alternating-Phase-Focusing (APF) was applied. Before constructing the compact injector, a model cavity of the IH-DTL was manufactured, and measurements of the electric-field distributions were performed. The gap-voltage distributions, obtained by integrating the measured electric field, were compared with those calculated using a three-dimensional field solver. The accuracy of the calculated field distributions is discussed. Finally, fine adjustments of the gap voltages using inductive tuners are described.