P.N. Ostroumov

Design of a post accelerator for the Rare Isotope Accelerator Facility

The proposed Rare Isotope Accelerator (RIA) Facility includes a post-accelerator for rare isotopes (RIB linac) which must produce high-quality beams of radioactive ions over the full mass range, including uranium, at energies above the coulomb barrier, and with high transmission and efficiency. The latter requires the RIB linac to accept at injection ions in the 1+ charge state. A concept for such a post accelerator suitable for ions up to mass 132 has been previously presented. This paper presents a modified concept which extends the mass range to uranium. The RIB linac will utilize existing superconducting heavy-ion linac technology for all but a small portion of the accelerator system. The exceptional piece, a very-low-charge-state injector section needed for just the first few MV of the RIB accelerator, consists of a pre-buncher followed by several sections of cw, normally conducting RFQ. Two stages of charge stripping are provided: He gas stripping at energies of a few keV/u, and additional foil stripping at /spl sim/600 keV/u for the heavier ions. In extending the mass range to uranium, however, for best efficiency the helium gas stripping must be performed at different energies for different mass ions. We present numerical simulations of beam dynamics for a design for the complete RIB linac which provides for several stripping options and uses cost-effective solenoid focusing elements in the drift-tube linac.

Application of a new procedure for design of 325 MHZ RFQ.

A new procedure for designing Radio Frequency Quadrupole (RFQ) accelerators has been developed. We present an integrated RFQ design procedure, which is based on modern three-dimensional field map calculations and beam dynamics simulations. The design procedure was integrated with the beam dynamics design and simulation codes DESRFQ & TRACK and applied to the development of a 325 MHz RFQ capable of delivering a 2.5 MeV H− beam with 40 mA peak current for the proton driver (PD) at Fermi National Accelerator Laboratory (FNAL).

Beam test of a grid-less multi-harmonic buncher

The Argonne Tandem Linear Accelerator System (ATLAS) is the first superconducting heavy-ion linac in the world. Currently ATLAS is being upgraded with the Californium Rare Ion Breeder Upgrade (CARIBU). The latter is a funded project to expand the range of shortlived, neutron-rich rare isotope beams available for nuclear physics research at ATLAS. To avoid beam losses associated with the existing gridded multi-harmonic buncher (MHB), we have developed and built a grid-less four-harmonic buncher with fundamental frequency of 12.125 MHz. In this paper, we report the results of the MHB commissioning and ATLAS beam performance with the new buncher.

ASSEMBLY, INSTALLATION, AND COMMISSIONING OF THE ATLAS UPGRADE CRYOMODULE

A new cryomodule containing seven low‐beta superconducting radio frequency (SRF) cavities has been added to the ATLAS heavy ion linac, providing an additional 15 MV accelerating potential to the existing accelerator. We describe the final stages of cryomodule assembly, commissioning, and installation in the ATLAS accelerator. The clean techniques used to achieve low‐particulate rf surfaces are presented, as are the module design features which enable clean assembly and reliable high‐gradient operation. The thermal performance of the cryomodule is described, along with performance data for the SRF cavities. Details on subsystem performance including helium and nitrogen systems, vacuum systems, thermal and magnetic shields, slow and fast tuners, and survey/alignment systems are given.

Accelerators for the advanced exotic beam facility in the U.S.

The Office of Science of the Department of Energy is currently considering options for an advanced radioactive beam facility in the U.S which is a reduced scale version of the Rare Isotope Accelerator (RIA) project [1,2]. This facility will have unique capabilities compared with others both existing and planned elsewhere. As envisioned at ANL, the facility, called the Advanced Exotic Beam Laboratory (AEBL), would consist of a heavy-ion driver linac, a post-accelerator and experimental areas. Secondary beams of rare isotopes will be available as high quality reaccelerated or stopped beams from a gas catcher and high power ISOL targets, as well as, high energy beams following in-flight fragmentation or fission of heavy ions. The proposed design of the AEBL driver linac is a cw, fully superconducting, 833 MV linac capable of accelerating uranium ions up to 200 MeV/u and protons to 580 MeV with 400 kW beam power. An extensive research and development effort has resolved many technical issues related to the construction of the driver linac and other systems required for AEBL. This paper presents the status of planning, some options for such a facility, as well as, progress in related R&D.

A driver linac for the advanced eotic beam laboratory: Physics design and beam dynamics simulations

The Advanced Exotic Beam Laboratory (AEBL) being developed at ANL consists of an 833 MV heavy-ion driver linac capable of producing uranium ions up to 200 MeV/u and protons to 580 MeV with 400 kW beam power. We have designed all accelerator components including a two charge state LEBT, an RFQ, a MEBT, a superconducting linac, a stripper station and chicane. We present the results of an optimized linac design and end-to-end simulations including machine errors and detailed beam loss analysis.

Experimental results on multi-charge-state lebt approach

A multi-charge-state injector for a high-intensity heavy-ion linac is being developed at ANL. The injector consists of an all-permanent magnet ECR ion source [1], a 100 kV platform and a Low Energy Beam Transport (LEBT). The latter comprises two 60-degree bending magnets, electrostatic triplets and beam diagnostics stations. At present the injector system allows us to accelerate all ion species up to qtimes100 keV total kinetic energy, where q is the charge state of an ion. In the current installation, the accelerating tube is followed by a 90deg magnet and a beam measurement station [2]. Recently we studied the production of metal ion beams using an oven technique and high intensity light ion beams from the ECR ion. A pepper pot emittance meter based on a scintillator screen has been developed and tested with various CW ion beams. It was found that a Csl (Tl) crystal has a high sensitivity for a variety of ion species from protons to heavy ions with the current densities even below 1 muA/cm2.

Heavy-Ion Beam Dynamics in the RIA Post-Accelerator

The RIA post-accelerator (RIB) includes three main sections: a room temperature injector with design ion charge-to-mass ratio 1/240 and output energy of ∼ 93 keV/u, a superconducting (SC) linac for ions with charge-to-mass ratio 1/66 or higher up to an energy of ∼ 1 MeV/u and a higher energy SC linac including existing ATLAS to produce 10 MeV/u beams up to uranium. Two strippers are installed between the sections. Extensive accelerator design studies and end-to-end beam dynamics simulations have been performed to minimize the cost of the linac while providing high-quality and high-intensity radioactive beams. Specifically, we have found that cost-effective acceleration in the front end can be provided by several hybrid RFQs proposed and developed for acceleration of low-velocity heavy ions. For beam focusing in the second section it is appropriate to use electrostatic lenses and SC quadrupoles inside common cryostats with the resonators.

Parallelization of track for large scale beam dynamics simulation in linear accelerators

Large scale beam dynamics simulations are important to support the design and operations of an accelerator. From the beginning, the beam dynamics code TRACK was developed to make it useful in the three stages of a hadron (proton and heavy-ion) linac project, namely the design, commissioning and operation of the machine. In order to combine the unique features of TRACK with large scale and fast parallel computing we have recently developed a parallel version of the code. We have successfully benchmarked the parallel TRACK on different platforms: BG/L and Jazz at ANL, Iceberg at ARSC, Lemieux at PSC and Seaborg at NERSC. We have performed large scale end-to-end simulations of the FNAL proton driver where 108 particles were tracked. The actual parallel version has the potential of simulating 10 particles on 10 racks with 20,480 processors of BG/L at ANL, which will be available next year. After a brief description of the parallel TRACK, we will present results from highlight applications.

Review of a Spoke-Cavity Design Option for the RIA Driver Linac

A design option for the 1.4 GV, multiple-charge-state driver linac required for the U.S. Rare Isotope Accelerator Project based on 345 MHz, 3-cell spoke-loaded cavities has been previously discussed [1]. This paper updates consideration of design options for the RIA driver, including recent results from numerically-modeling the multi-charge-state beam dynamics and also cold test results for prototype superconducting niobium three-spoke-loaded cavities.