M. Doleans

Status report on the NSCL RF fragment separator

The Radio Frequency Fragment Separator (RFFS) proposed in [1] is now operational at the National Superconducting Cyclotron Laboratory (NSCL). The RFFS is an additional purification system for secondary beams at the NSCL after the existing A1900 fragment separator and will primarily be used to purify beams of rare neutron deficient isotopes. A similar device is already in use at RIKEN [2]. The RFFS uses an rf kicker to angularly separate unwanted particles from the desired ion beam, a pi/2 phase advance cell to rotate the beam in phase space before the beam reaches a collimating aperture for purification, and a final pi phase advance cell to transport the desired beam to the experiment. The final design for the rf kicker and the focusing system is presented and a status report on the building and commissioning effort is given.

Beam dynamics studies for the reacceleration of low energy ribs at the NSCL

Rare Isotope Beams (RIBs) are created at the National Superconducting Cyclotron Laboratory (NSCL) by the in-flight particle fragmentation method. A novel system that stops the RIBs in helium gas and reaccelerates them is proposed to provide opportunities for an experimental program ranging from low energy Coulomb excitation to transfer reaction studies of astrophysical reactions. The beam from the gas stopper [1] will first be brought into a Electron Beam Ion Trap (EBIT) charge breeder [2] on a high voltage platform to increase its charge state, and then accelerated up to about 3 MeV/u by a system consisting of an external multi-harmonic buncher and a radio frequency quadrupole (RFQ) followed by a superconducting linac. The superconducting linac will use quarter-wave resonators with optimum acceleration for particle velocities as a fraction of the speed of light (betaopt) of 0.041 and 0.085 for acceleration and superconducting solenoid magnets for transverse focusing. The accelerator system design and the end-to-end beam dynamics simulations are presented.

RF-Kicker System for Secondary Beams at the NSCL

The design and construction of a radio frequency fragment separator (RFFS) kicker system at the National Superconducting Cyclotron Laboratory (NSCL) of Michigan State University (MSU) has been proposed. This RFFS will be used to further purify secondary beams of rare isotopes after the exiting the A1900 Fragment Separator and will open a wide range of possibilities for new experiments at the forefront of nuclear science. The proposed system is studied as an efficient alternative to the traditional approach using a Wien filter. Rare neutron deficient secondary beams are challenging to purify because of the presence of intense contaminants that cannot be removed by the traditional energy loss method. However, velocity differences resulting in time-of-flight (TOF) differences can be used for the effective separation of the beams transversely using the time-varying electromagnetic fields of the RF kicker. Its technical design is presented together with the beam dynamics analysis of a secondary beam in realistic 3D electromagnetic fields. The expected purification improvement of the exotic beams for the foreseen nuclear physics experiments is shown in detail.

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.

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.

End-to-end beam dynamics simulations of the isf driver linac

The proposed Isotope Science Facility (ISF) is a major upgrade of the coupled cyclotron facility at the National Superconducting Cyclotron Laboratory (NSCL) that will provide the nuclear science community with world-class beams of rare isotopes. The ISF driver linac will consist of a front-end and three acceleration segments of superconducting cavities separated by two charge-stripping sections, and will be capable of delivering primary beams ranging from protons to uranium with variable energies of >200 MeV/nucleon. The end-to-end beam simulation studies including beam element misalignments, dynamic RF amplitude and phase errors, and variations in the stripping foil thickness, have been performed to evaluate the driver linac performance. The beam simulation effort was focused on the most challenging uranium beam with multiple charge states using the newly-developed RIAPMTQ/IMPACT codes. This paper describes the ISF, discusses the beam dynamics issues, and presents the end-to-end beam simulation results.

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.

Simulations of Solenoid and Electrostatic Quadrupole Focusing of High Intensity Beams from ECR Ion Source

Because of its axisymmetric property and reasonable effectiveness, solenoids have been widely used to focus beams at various injectors. For a multi-component beam with solenoidal focusing, beam quality can be significantly deteriorated due to the magnetic focusing strength dependence on the beam charge-to-mass ratio. Electrostatic quadrupole focusing has been explored as an alternative option at the National Superconducting Cyclotron Laboratory (NSCL) for the injection line of the superconducting cyclotrons. We present the results of simulations for both systems.