ADVANCED BEAM-DYNAMICS SIMULATION TOOLS FOR RIA* R. W. Garnett, T. P. Wangler, J. H. Billen, LANL, Los Alamos, NM, USA; J. Qiang, R. Ryne, LBNL, Berkeley, CA, USA; K. R. Crandall, Tech Source, Santa Fe, NM, USA; P. Ostroumov, ANL, Argonne, IL, USA; R. C. York, Q. Zhao, Michigan State University, East Lansing, MI, USA Abstract We are developing multi-particle beam-dynamics simulation codes for RIA driver-linac simulations extending from the low-energy beam transport (LEBT) line to the end of the linac. These codes run on the NERSC parallel supercomputing platforms at LBNL, which allow us to run simulations with large numbers of macroparticles. The codes have the physics capabilities needed for RIA, including transport and acceleration of multiple-charge-state beams, beam-line elements such as high-voltage platforms within the linac, interdigital accelerating structures, charge-stripper foils, and capabilities for handling the effects of machine errors and other off-normal conditions. This year will mark the end of our project. In this paper we present the status of the work, describe some recent additions to the codes, and show some preliminary simulation results. * INTRODUCTION The present concept for the Rare Isotope Accelerator (RIA) project [1] includes a 1.4-GV CW superconducting driver linac. The driver linac is designed for multicharge- state acceleration [2] of all stable species, including protons to >900 MeV and uranium to 400 MeV/u. In conventional heavy-ion linacs, a single charge-state beam of suitably high intensity from an electron-cyclotron resonance (ECR) ion source is injected into the linac. The linac typically contains one or more strippers at higher energies to further increase the beam charge states and improve acceleration efficiency. However, the limitation to a single charge state from the ion source and from each stripper significantly reduces the beam intensity. This disadvantage is addressed in the RIA driver-linac design concept by the innovative approach of simultaneous acceleration of multiple charge states of a given ion species, which results in high-power beams of several hundred kilowatts for all beams ranging from protons to uranium. Initial beam-dynamics studies [2], supported by experimental confirmation at the Argonne ATLAS facility [3], have demonstrated the feasibility of this new approach. The high-power beam associated with multiple charge- state acceleration introduces a new design constraint to control beam losses that can cause radio-activation of the driver linac [4]. Radio-activation of the linac beam line components will hinder routine maintenance and result in reduced availability of the facility. Therefore, it will be important for the RIA project to produce a robust beam- dynamics design of the driver linac that minimizes the * This work is supported by the U. S. Department of Energy Contract W-7405-ENG-36 threat of beam losses. As an important consequence of this design requirement, we have been developing a computer-simulation code with the capability of accurately modeling the beam dynamics throughout the linac and computing the beam losses. The driver linac is made up of three sections. The first is the pre-stripper accelerator section consisting of an ECR ion source, and a low-energy beam transport (LEBT) line, which includes a mass and charge-state- selection system, and an external multi-harmonic buncher system. The pre-stripper section continues with the initial linac stage consisting of a room-temperature RFQ linac, a medium-energy beam transport (MEBT) line, and the low-velocity (low-β) superconducting accelerating structures. The pre-stripper section, accelerates the beam, consisting of two charge states for uranium, to an energy of about 10 MeV/u, where the beam passes through the first stripper and new charge states are produced. The second section of the linac uses medium-β superconducting structures to accelerate the multicharge- state beam from the first to the second stripper at an energy of about 85 MeV/u. This medium-β section accelerates about five charge states for uranium. This is followed by the third and final section of the linac, which uses high-β superconducting structures to accelerate typically four charge-states for uranium to a final energy of 400 MeV/u. The overall performance of the driver linac is crucially dependent on the performance of the LEBT and RFQ. The LEBT is designed to focus, bunch, and inject two charge states for uranium into alternate longitudinal buckets of the RFQ. The LEBT RF buncher system consists of two main components. The first RF buncher cavity system (multi-harmonic buncher) uses up to four harmonics and is designed to capture 80% of each charge state within the longitudinal acceptance of the RFQ. A second RF buncher cavity matches the velocity of each charge state to the design velocity of the RFQ. To avoid problems from beam-induced radio- activation, beam losses must be limited to less than about 1 watt per meter [5],[6],[7] particularly in the high-energy part of the accelerator. This low beam-loss requirement imposes a challenge for controlling emittance growth throughout the driver-linac, especially because of the complication of multiple charge-state beams. In addition to increasing the intensity, acceleration of multiple charge-state beams produces a larger total longitudinal emittance, increasing the threat of beam loss. For any proposed design it is imperative to compute the high- energy beam losses with sufficient accuracy to ensure that the beam-loss requirements are satisfied. Such a computation normally requires the use of simulation Proceedings of 2005 Particle Accelerator Conference, Knoxville, Tennessee 0-7803-8859-3/05/$20.00 c 2005 IEEE 4218