Heavy-Ion Beam Acceleration of Two-Charge States from an Ecr Ion Source

TL;DR

This paper presents a design for a superconducting ion linac front end capable of simultaneously accelerating two charge states of uranium, effectively doubling the beam current for heavy-ion applications.

Contribution

It introduces a novel design that enables the acceleration of two charge states simultaneously, with detailed 3D simulations demonstrating its feasibility and performance.

Findings

Successful acceleration of two charge states with minimal emittance growth

Effective bunching and velocity matching for both charge states

Simulation results show tolerable emittance growth under various errors

Abstract

This paper describes a design for the front end of a superconducting (SC) ion linac which can accept and simultaneously accelerate two charge states of uranium from an ECR ion source. This mode of operation increases the beam current available for the heaviest ions by a factor of two. We discuss the 12 MeV/u prestripper section of the Rare Isotope Accelerator (RIA) driver linac including the LEBT, RFQ, MEBT and SC sections, with a total voltage of 112 MV. The LEBT consists of two bunchers and electrostatic quadrupoles. The fundamental frequency of both bunchers is half of the RFQ frequency. The first buncher is a multiharmonic buncher, designed to accept more than 80% of each charge state and to form bunches of extremely low longitudinal emittance (rms emittance is lower than 0.2 keV/u nsec) at the output of the RFQ. The second buncher is located directly in front of the RFQ and matches the velocity of each charge-state bunch to the design input velocity of the RFQ. We present full 3D simulations of a two-charge-state uranium beam including space charge forces in the LEBT and RFQ, realistic distributions of all electric and magnetic fields along the whole prestripper linac, and the effects of errors, evaluated for several design options for the prestripper linac. The results indicate that it is possible to accelerate two charge states while keeping emittance growth within tolerable limits.