Rare Isotope Accelerator Research Articles

Modest but uneven R&D increases proposed for FY 2013

Uncertainty created by the Budget Control Act of 2011 clouds the outlook for federal science and technologyfunding. Some Department of Energyphysics programs face significant cuts.

Refractory nanoporous materials fabricated using tungsten atomic layer deposition on silica aerogels

We report an approach for preparing refractory nanoporous materials using high surface area silica aerogels as templates for the growth of conformal tungsten (W) coatings by atomic layer deposition (ALD). Nanoporous silica aerogel monoliths were prepared with a variety of initial pore sizes and initial densities in the range of 0.3–0.5g/cc using porogen extraction methods. Next, W ALD using Si2H6 and WF6 reactants at 200°C was employed to coat the inner surfaces of the silica aerogels. After coating, scanning electron microscopy revealed a microstructure in which the ALD W completely encapsulated the silica aerogel micro-cells. The porosity of the aerogels was preserved during the first 10 W ALD cycles allowing the density to be controlled by adjusting the number of W ALD cycles to achieve densities as high as 5g/cc. Nitrogen adsorption surface area measurements revealed a gradual decrease in the surface area of the silica aerogels with increasing numbers of W ALD cycles, consistent with a partial filling of the aerogel voids. The high density nanoporous tungsten monoliths survived high temperature vacuum heating (1500°C) making them promising candidates for solid rare-isotope catchers that can be used in the production of short-lived radioactive isotope beams in facilities such as the facility for rare isotope beams (FRIB).

Low energy beam transport for facility for rare isotope beams driver linear particle accelerator

The driver linac for the facility for rare isotope beams (FRIB) will provide a wide range of primary ion beams for nuclear physics research. The linac will be capable of accelerating a uranium beam to an energy of up to 200 Mev∕u and delivering it to a fragmentation target with a maximum power of 400 kW. Stable ion beams will be produced by a high performance electron cyclotron resonance ion source operating at 28 GHz. The ion source will be located on a high voltage platform to reach an initial beam energy of 12 keV∕u. After extraction, the ion beam will be transported vertically down to the linac tunnel in a low energy beam transport (LEBT) system and injected into a radio frequency quadrupole (RFQ) operating at a frequency of 80.5 MHz. To meet the beam power requirements, simultaneous acceleration of two-charge states will be used for heavier ions (≥Xe). This paper presents the layout of the FRIB LEBT and the beam dynamics in the LEBT. In particular, simulation and design of the beam line section before charge state selection will be detailed. The need to use an achromatic design for the charge state selection system and the advantage of an ion beam collimation system to limit the emittance of the beam injected into the RFQ will be discussed in this paper.

Recent progress on the superconducting ion source VENUS

The 28 GHz Ion Source VENUS (versatile ECR for nuclear science) is back in operation after the superconducting sextupole leads were repaired and a fourth cryocooler was added. VENUS serves as an R&D device to explore the limits of electron cyclotron resonance source performance at 28 GHz with its 10 kW gryotron and optimum magnetic fields and as an ion source to increase the capabilities of the 88-Inch Cyclotron both for nuclear physics research and applications. The development and testing of ovens and sputtering techniques cover a wide range of applications. Recent experiments on bismuth demonstrated stable operation at 300 eμA of Bi(31+), which is in the intensity range of interest for high performance heavy-ion drivers such as FRIB (Facility for Rare Isotope Beams). In addition, the space radiation effects testing program at the cyclotron relies on the production of a cocktail beam with many species produced simultaneously in the ion source and this can be done with a combination of gases, sputter probes, and an oven. These capabilities are being developed with VENUS by adding a low temperature oven, sputter probes, as well as studying the RF coupling into the source.

Multi-Messenger Observations of Neutron Rich Matter

At very high densities, electrons react with protons to form neutron rich matter. This material is central to many fundamental questions in nuclear physics and astrophysics. Moreover, neutron rich matter is being studied with an extraordinary variety of new tools such as the Facility for Rare Isotope Beams (FRIB) and the Laser Interferometer Gravitational Wave Observatory (LIGO). We describe the Lead Radius Experiment (PREX) that uses parity violating electron scattering to measure the neutron radius in $^{208}$Pb. This has important implications for neutron stars and their crusts. We discuss X-ray observations of neutron star radii. These also have important implications for neutron rich matter. Gravitational waves (GW) open a new window on neutron rich matter. They come from sources such as neutron star mergers, rotating neutron star mountains, and collective r-mode oscillations. Using large scale molecular dynamics simulations, we find neutron star crust to be very strong. It can support mountains on rotating neutron stars large enough to generate detectable gravitational waves. We believe that combing astronomical observations using photons, GW, and neutrinos, with laboratory experiments on nuclei, heavy ion collisions, and radioactive beams will fundamentally advance our knowledge of compact objects in the heavens, the dense phases of QCD, the origin of the elements, and of neutron rich matter.

Characteristics of rare isotope beams in the KoRIA facility

The Korea Rare Isotope Accelerator (KoRIA) facility plans to provide neutron-rich rare isotopes (RIs) and stable heavy ion beams for research in the fields of basic and applied sciences. In the facility, both the isotope separator on-line (ISOL) and the in-flight fragmentation (IFF) methods are employed for RI production by 238U fission, which is effective for producing neutron-rich RI beams. These ISOL and IFF systems are designed to obtain world-class RI beam intensity, which allows exotic nuclei near the neutron drip line in the nuclear chart, which have not yet been explored, to be studied. In this paper, the uniqueness of the KoRIA facility under consideration, compared to other facilities, is described, and we present the characteristics of the RI beams that will be available at KoRIA.

BigRIPS separator and ZeroDegree spectrometer at RIKEN RI Beam Factory

The BigRIPS in-flight separator, which became operational in March 2007 at the RI Beam Factory (RIBF) at RIKEN Nishina Center, has been used to produce a variety of rare-isotope (RI) beams by using in-flight fission as well as projectile fragmentation. Its major features are large ion-optical acceptances and two-stage structure. Excellent performance in particle identification is also an important feature. Efficient RI-beam production based on the in-flight scheme has been made possible by these features of the BigRIPS separator, allowing us to greatly expand the accessible region of exotic nuclei. An RI-beam delivery line following the BigRIPS separator is designed to work as a forward spectrometer, called ZeroDegree. As a major experimental device at RIBF, the ZeroDegree spectrometer has been used for a variety of reaction studies with RI beams. In this paper, we present an overview of the BigRIPS separator and the ZeroDegree spectrometer, emphasizing the capability and potential of the new-generation RI beam facility, RIBF.

Current Activities in the Korean Accelerator Community

Since 1988 when Pohang Light Source (PLS) started its construction, the Korean accelerator community has grown very fast and has expanded from electrons to protons and to rare isotopes. At this moment, there are four major activities: the Proton Engineering Frontier Project (PEFP) in Gyeongju, the Korea Rare Isotope Accelerator (KoRIA), the PLS-II, which is an upgrade of the current PLS, and the X-ray Free Electron Laser (XFEL). Besides these major activities, there are several industrial accelerators and medical ones. In this report, the details of these activities are summarized.

MULTI-MESSENGER OBSERVATIONS OF NEUTRON-RICH MATTER

At very high densities, electrons react with protons to form neutron-rich matter. This material is central to many fundamental questions in nuclear physics and astrophysics. Moreover, neutron-rich matter is being studied with an extraordinary variety of new tools such as Facility for Rare Isotope Beams (FRIB) and the Laser Interferometer Gravitational Wave Observatory (LIGO). We describe the Lead Radius Experiment (PREX) that uses parity violating electron scattering to measure the neutron radius in 208Pb. This has important implications for neutron stars and their crusts. We discuss X-ray observations of neutron star radii. These also have important implications for neutron-rich matter. Gravitational waves (GW) open a new window on neutron-rich matter. They come from sources such as neutron star mergers, rotating neutron star mountains, and collective r-mode oscillations. Using large scale molecular dynamics simulations, we find neutron star crust to be very strong. It can support mountains on rotating neutron stars large enough to generate detectable gravitational waves. Finally, neutrinos from core collapse supernovae (SN) provide another, qualitatively different probe of neutron-rich matter. Neutrinos escape from the surface of last scattering known as the neutrino-sphere. This is a low density warm gas of neutron-rich matter. Neutrino-sphere conditions can be simulated in the laboratory with heavy ion collisions. Observations of neutrinos can probe nucleosyntheses in SN. Simulations of SN depend on the equation of state (EOS) of neutron-rich matter. We discuss a new EOS based on virial and relativistic mean field calculations. We believe that combing astronomical observations using photons, GW, and neutrinos, with laboratory experiments on nuclei, heavy ion collisions, and radioactive beams will fundamentally advance our knowledge of compact objects in the heavens, the dense phases of QCD, the origin of the elements, and of neutron-rich matter.

Neutron rich matter, neutron stars, and their crusts

Neutron rich matter is at the heart of many fundamental questions in Nuclear Physics and Astrophysics. What are the high density phases of QCD? Where did the chemical elements come from? What is the structure of many compact and energetic objects in the heavens, and what determines their electromagnetic, neutrino, and gravitational-wave radiations? Moreover, neutron rich matter is being studied with an extraordinary variety of new tools such as Facility for Rare Isotope Beams (FRIB) and the Laser Interferometer Gravitational Wave Observatory (LIGO). We describe the Lead Radius Experiment (PREX) that is using parity violation to measure the neutron radius in 208Pb. This has important implications for neutron stars and their crusts. Using large scale molecular dynamics, we model the formation of solids in both white dwarfs and neutron stars. We find neutron star crust to be the strongest material known, some 10 billion times stronger than steel. It can support mountains on rotating neutron stars large enough to generate detectable gravitational waves. Finally, we describe a new equation of state for supernova and neutron star merger simulations based on the Virial expansion at low densities, and large scale relativistic mean field calculations.

The SPIRAL2 Project and experiments with high-intensity rare isotope beams

The SPIRAL2 facility at GANIL, which entered recently in the construction phase consists of a new superconducting linear accelerator delivering high intensity, up to 40 MeV, light (proton, deuteron, 3-4He) beams as well as a large variety of 14.5 MeV/nucleon heavy-ion beams and the associated Rare Isotope Beam facility. Using a dedicated converter and the 5 mA deuteron beam, a neutron-induced fission rate is expected to approach 1014 fissions/s for high-density UCx target. The energies of accelerated RIBs will reach 5-10 MeV/nucleon for fission fragments and 20 MeV/nucleon for neutron-deficient nuclei. The physics case of SPIRAL2 is based on the use of high intensity RIBs & stable-ion beams and on possibilities to perform several experiments simultaneously. A use of these beams at a new low-energy ISOL facility (DESIR) and their acceleration to several MeV/nucleon will open new possibilities in nuclear structure physics, nuclear astrophysics and reaction dynamics studies. The high intensities (up to 1011pps) and a high cost of RIBs impose a use of the most efficient and innovative detection systems like ACTAR, FAZIA, GASPARD, HELIOS, NEDA, PARIS and a new separator/spectrometer S3.

Thermo-mechanical behaviour of a single slice test device for the FRIB high power target

One of the major challenges of the FRIB project (Facility for Rare Isotope Beams) at Michigan State University is the design and integration of the production target to produce rare isotope beams via fragmentation reaction. In the most extreme case, a 400kW uranium beam of 200MeV/u will be focused in a 1mm diameter spot, leading to a power density of 60MW/cm3 for a C target. Up to 200kW may be dissipated in the target.A rotating solid carbon disk concept has been selected as the target design approach for all primary beams up to uranium to provide high-power operation. A high rotational speed is necessary to compensate for the high power density. A multi-slice approach allows the evacuation of the large amount of heat deposited by the increase of the radiating area. In the present design study, the multi-slice target device has a diameter of about 30cm and rotates at about 5000RPM (revolutions per minute). The first step of the R&D strategy consists in the development and test of a 20kW single-slice target prototype. This single disk device is designed to accept the same fraction of power as each disk of the final multi-slice target. Critical information on thermal-mechanical properties can be obtained thus at a lower power level than the one of the full device. Different carbon materials were tested. An electron beam of ∼20keV was used for the thermal tests. Simulations were performed using the ANSYS code for the thermo-mechanical behaviour of the target, the resulting deformation and the stress profiles of heated graphite disks. Results of the simulations were compared with experimental data.

Second Generation HTS Quadrupole for FRIB

Quadrupoles in the fragment separator region of the Facility for Rare Isotope Beams (FRIB) will be subjected to very large heat loads (over 200 Watts) and an intense level of radiation (~10 MGy per year) into the coils of just the first magnet. Magnets made with High Temperature Superconductors (HTS) are advantageous over conventional superconducting magnets since they can remove these heat loads more efficiently at higher temperatures. The proposed design is based on second generation (2G) HTS which allows operation at ~50 K. 2G has been found to be highly radiation tolerant. The latest test results are summarized. The goal of this R&D program is to evaluate the viability of HTS in a real machine with magnets in a challenging environment where HTS offers a unique solution.

Radiation Resistant Superferric Quadrupole Magnets With Warm Iron

The Facility for Rare Isotope Beams to be built at Michigan State University will be capable of providing beams of any element at energies of at least 200 MeV/u at beam powers of 400 kW. The fragment production target is in close proximity to the superconducting quadrupole magnets. These magnets have to operate in the high-radiation environment, with calculated radiation doses of more than 10 MGy per year. The design of a large bore, superferric quadrupole magnet that provides high field gradient of 15 T/m and effective length of 0.6 m is presented. The current design is “warm-iron” with a nominal yoke length of 520 mm and a pole radius of 135 mm. A coil design based on spinel insulated cable-in-conduit conductor that provides ample current margin provides significant long lifetime against radiation damage. The major challenges are the tight geometry, high forces and remote handling of an irradiated magnet. This paper presents the magnet design including coil forces and coil restraint system. In addition, coil properties, conductor stability and full mechanical details are also presented.

The UNEDF Project

A new era has dawned for nuclear structure and reaction theory. Renewed interest in the physics of nuclei is fueled by experiments at rare isotope beam facilities, which explore new regions of exotic nuclei; by astrophysical observations and simulations, which require controlled extra-polations of the nuclear equation of state; by the use of nuclei in experiments on fundamental symmetries, which rely on robust nuclear structure information; and by nuclear energy and security needs, which include predictions of reaction cross-sections and fission fragment properties. The UNEDF collaboration of nuclear theorists, applied mathematicians, and computer scientists is addressing this broad spectrum of physics through a comprehensive study of all nuclei, based on the most accurate knowledge of the strong nuclear interaction, the most reliable theoretical approaches, the most advanced algorithms, and extensive computational resources.

Status of the FRIB project with a new fragment separator

The surprising variation of the cross sections for the production of the most neutron-rich nuclei by the fragmentation of 48Ca and 76Ge beams at Michigan State University (MSU) continues to show the importance of determining the properties of exotic nuclei. Future detailed studies of such exotic nuclei are being assured through the establishment of the Facility for Rare Isotope Beams (FRIB), a cutting-edge research facility to advance understanding of rare nuclear isotopes and the evolution of the cosmos, by the US Department of Energy at MSU. The new facility is expected to take something less than a decade to design and build and will provide a broad range of research opportunities for an international community. The facility is based on a superconducting-RF driver linear accelerator that will provide a maximum beam power of 400 kW for all beams ranging from uranium accelerated to 200 MeV/u, to lighter ions with increasing energy, down to protons at 600 MeV/nucleon. Rare isotope beam production at a beam power of 400 kW has never been done and presents a number of large challenges. The heart of the FRIB facility will be a next-generation three-stage projectile fragment separator specifically designed to handle the very intense primary and secondary beams.

Fragment separator momentum compression schemes

We present a scheme to use a fragment separator and profiled energy degraders to transfer longitudinal phase space into transverse phase space while maintaining achromatic beam transport. The first order beam optics theory of the method is presented and the consequent enlargement of the transverse phase space is discussed. An interesting consequence of the technique is that the first order mass resolving power of the system is determined by the first dispersive section up to the energy degrader, independent of whether or not momentum compression is used. The fragment separator at the Facility for Rare Isotope Beams is a specific application of this technique and is described along with simulations by the code COSY INFINITY.

EBIS/T charge breeding for intense rare isotope beams at MSU

Experiments with reaccelerated beams are an essential component of the science program of existing and future rare isotope beam facilities. NSCL is currently constructing ReA3, a reaccelerator for rare isotopes that have been produced by projectile fragmentation and in-flight fission and that have been thermalized in a gas stopper. The resulting low-energy beam will be brought to an Electron Beam Ion Source/Trap (EBIS/T) in order to obtain highly charged ions at an energy of 12 keV/u. This charge breeder is followed by a compact linear accelerator with a maximum beam energy of 3 MeV/u for 238U and higher energies for lighter isotopes. Next-generation rare isotope beam facilities like the Facility for Rare Isotope Beams FRIB, but also existing Isotope Separator On-line (ISOL) facilities are expected to provide rare-isotope beam rates in the order of 1011 particles per second for reacceleration. At present the most promising scheme to efficiently start the reacceleration of these intense beams is the use of a next-generation high-current charge-breeder based on an EBIS/T. MSU has formed a collaboration to develop an EBIT for this purpose. A new high-current EBIS/T breeder will be developed and constructed at MSU, where also first tests on achievable beam rate capability will be performed. The EBIT is planned to be installed at the Isotope Separator and Accelerator facility ISAC at TRIUMF laboratory for on-line tests with rare isotope beams and to provide intense energetic reaccelerated radioactive beams. The status of the ReA3-EBIS/T in the NSCL reaccelerator project is given with a brief summary of results, followed by a discussion of plans for the future high-intensity EBIS/T charge breeder.

Plans for the Facility for Rare Isotope Beams

The Facility for Rare Isotope Beams (FRIB) will be a new National User Facility for nuclear science, funded by the Department of Energy (DOE), Office of Nuclear Physics (NP) and operated by Michigan State University (MSU). FRIB will cost approximately $550 million to establish and take about a decade to design and build.

Estimated Limits on Uncontrolled Beam Losses of Heavy Ions for Allowing Hands-On Maintenance at an Exotic Beam Facility Linac

The purpose of the study is to obtain estimates of limits on uncontrolled beam losses of heavy ions for allowing hands-on maintenance at a heavy-ion linac for a rare isotope beam facility. Semiempirical formulas are used to estimate dose equivalent rates from activated accelerator components for 1 W/m uncontrolled losses of protons up to 1 GeV. The estimated dose rates after a 100-day irradiation time, 4-h postshutdown cooling time are compared to a hands-on maintenance limit of 1 mSv/h (100 mrem/h) at 30 cm. The transport codes PHITS and MCNP5 and activation code DCHAIN-SP 2001 are used to verify the estimate for proton losses and to obtain limits on heavy-ion beam losses that will satisfy the hands-on maintenance dose rate limit.