D. Gorelov

Improvement of the Longitudinal Beam Dynamics Tuning Procedure for the MSU RIA Driver Linac

The Rare Isotope Accelerator (RIA) driver linac will use a superconducting, cw linac with independently phased superconducting rf cavities for acceleration and utilize beams of multiple-charge-states (multi-q) for the heavier ions. Given the acceleration of multi-q beams and a stringent beam loss requirement in the RIA driver linac, a new beam dynamics code capable of simulating nonlinearities of the multi-q beam envelopes in the longitudinal phase space was developed. Using optimization routines, the code is able to maximize the linearity of the longitudinal phase space motion and thereby to minimize beam loss by optimizing values for the amplitude and phase of the cavities for a given accelerating lattice. Relative motion of the multi-q beams is also taken into account so that superposition of the beam centroids and matching of their Twiss parameters are automatically controlled. The new tuning procedure and its benefit on the performance of the beam dynamics in the longitudinal plane are discussed in the paper.

Failure Modes Analysis for the MSU RIA Driver Linac

Previous end-to-end beam dynamics simulation studies [1] using experimentally-based input beam parameters [2], including alignment and rf errors and variation in charge-stripping foil thickness have indicated that the Rare Isotope Accelerator (RIA) driver linac proposed by Michigan State University (MSU) has transverse and longitudinal acceptances more than adequate to accelerate light and heavy ions to final energies ≥ 400 MeV/u with beam powers of 100 to 400 kW. Further beam dynamics studies [3] were carried out using a new beam envelope code recently developed at MSU to optimize the setting of the rf phase and amplitude of the cavities throughout the linac. During linac operation, equipment loss due to, for example, cavity contamination, problems with cryogenic systems, or failure of rf or power supply systems, can lead to, at least, a temporary loss of some of cavities and focusing elements. To achieve high facility availability, each segment of the linac should be capable of adequate performance even with some failed elements. In order to prove the flexibility and robustness of the driver linac lattice design, beam dynamics studies were performed to evaluate the linac performance under various scenarios of failed cavities and focusing elements with proper correction schemes. The result of these beam dynamics studies is presented in this paper.

The beam dynamics studies of combined misalignments and RF errors for RIA

The National Superconducting Cyclotron Laboratory (NSCL) design for the Rare Isotope Accelerator (RIA) driver linac uses superconducting quarter-wave, half-wave and 6-cell elliptical cavities with rf frequencies ranging from 80.5 MHz to 805 MHz with two charge-stripping chicanes. The driver linac requirements include acceleration of light and heavy ions to final beam energies of /spl ges/400 MeV/nucleon with final beam powers of 100 to 400 kW. The impact of simultaneous misalignment and rf errors for the full RIA driver linac, including the charge-stripping chicanes, on the 6-dimensional beam emittance was evaluated by simulation. Beam loss and large-amplitude beam behaviors were also studied.

Analysis of a multi-spoke option for the RIA driver linac

Beam dynamics simulations of the proposed Rare Isotope Accelerator (RIA) driver linac have been done. The RIA driver linac is designed to accelerate stable ion beams from proton to uranium to final energies of 400 MeV/u for the heaviest and about 900 MeV/u for the lightest ions with beam powers of 100 to 400 kW. Two stripping sections are used to increase the charge state of heavy ions and minimize the total accelerating voltage required. To achieve the final beam power and to reduce the ion source requirements, multi-charge state beam acceleration is used. Multi-spoke structures in the high-energy part of the driver linac have been proposed as an alternative to the baseline design of 6-cell elliptical structures. A comparative analysis of this alternative is explored including beam dynamics, error constraints, and manufacturing issues.

Design study of a superconducting linac for RIA

The proposed Rare Isotope Accelerator Facility (RIA) requires a heavy-ion driver linac capable of accelerating uranium to 400 MeV/u with the beam powers of 100 to 400 kW. The beam power requirement will be met for very heavy ions by simultaneous acceleration of multiple charge states because of ion source limitations. To minimize the number of accelerating structures, two charge stripping stations have been proposed for nuclei heavier than Kr. The intensity loss due to multiple stripping is minimal by the multiple charge acceleration. However, the technical challenges and concomitant risks of the stripping stations for the proposed beam powers are significant particularly at the lowest energy. As a consequence, an alternative layout with only one stripping station at a point about twice the energy of the lowest energy of the two-station scenario is proposed. This scheme removes one stripping system, but increases the installed accelerator requirement by about 10%. The beam dynamics of the driver linac has been studied using a newly written single particle tracking program as well as other extant programs.

Beam Simulation Studies of the LEBT for RIA Driver Linac

The low energy beam transport (LEBT) system in the front‐end of the Rare Isotope Accelerator (RIA) uses a 70 kV platform to pre‐accelerate the ion beam from a 30 kV Electron Cyclotron Resonance (ECR) ion source, followed by an achromatic charge selection system. The selected beam is then pre‐bunched and matched into the entrance of a Radio Frequency Quadrupole (RFQ) with a multi‐harmonic buncher. To meet the beam power requirements for heavy ions, high current (several mA), multi‐species beams will be extracted from the ECR. Therefore, it is crucial to control space charge effects in order to obtain the low emittance beam required for RIA. The PARMELA code is used to perform the LEBT simulations for the multi‐species beams with 3D space charge calculations. The results of the beam dynamics simulations are presented, and the key issues of emittance growth in the LEBT and its possible compensation are discussed.

The riapmtq/impact beam-dynamics simulation package

The Fortran 90 RIAPMTQ/IMPACT code package is a pair of linked beam-dynamics simulation codes that have been developed for end-to-end computer simulations of multiple-charge state heavy-ion linacs for future exotic-beam facilities. The simulations can extend from the low-energy beam-transport line after the ECR ion source to the end of the linac. The work has been performed by a collaboration including LANL, LBNL, ANL, and MSU. The code RIAPMTQ simulates the linac front end including the LEBT, RFQ, and MEBT, and the code IMPACT simulates the main superconducting linac. The codes have been benchmarked for rms beam properties against previously existing codes at ANL and MSU. The codes allow high-statistics runs on parallel supercomputing platforms, such as NERSC at LBNL for studies of beam losses. The codes also run on desktop PC computers for low-statistics design work. We show results from 10-million-particle simulations at NERSC of designs by ANL and MSU for the Rare-Isotope Accelerator.

An injector for a multi ion beam driver linac

An advanced facility for the production of exotic shortlived isotopes far from stability (RIA) could use as the driver a high power cw superconducting linac. Due to the wide range of particle velocities (/spl beta/=0.019-0.81), different cavity types are required. This paper describes a possible design for the injector portion (up to /spl beta/=0.1) of the driver linac. The proposed injector design consists of a multi-harmonic buncher, an RFQ (f=57.5 MHz), 4-gap fork resonators (f=57.5 MHz), and finally, 2-gap quarter wave resonators (f=86.25 MHz). The results of numerical simulations and a comparison different possible RFQ designs (4-vane, IH) are presented.