Beam-dynamics design of a 2 MeV/u heavy-ion IH-DTL with electromagnetic quadrupole structure

Abstract

The interdigital H-mode (IH) drift tube linac (DTL) with an electromagnetic quadrupole (EMQ) structure combines an IH-DTL acceleration structure with a quadrupole focusing–defocusing (FD) lattice and can achieve a high acceptance when high shunt impedance is ensured. Between the radio frequency quadrupole (RFQ) and IH-DTL, the IH-EMQ dynamics allows only one quadrupole magnet to match the two structures directly, which is different from KONUS (Kombinierte Null Grad Struktur, combined zero-degree structure) and alternating-phase focusing (APF) dynamics. To match KONUS or APF DTL with the RFQ, at least three quadrupole magnets are required. This paper describes the design process of the IH-EMQ beam dynamics and applies and verifies the method by applying it to design a 2MeV/u heavy-ion IH-DTL with the help of detailed simulation and analysis. With the input energy of 400keV/u, the DTL accelerates particles with a charge-to-mass ratio as low as 1/6.5. The normalized root mean square emittance increases by 7%. The IH-DTL with the IH-EMQ dynamics design offers a normalized transverse acceptance (99% particles) of 3.89(x)/3.56(y)πmm⋅mrad while preserving an effective shunt impedance of 87MΩ/m.