The NSCL laboratory and the FRIB facility

• Prof. Alexandra Gade, National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824-1321, USA

• Prof. C. Konrad Gelbke, National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824-1321, USA

Figure 1: NSCL building complex on the campus of Michigan State University

NSCL (National Superconducting Cyclotron Laboratory) at Michigan State University (MSU) is the largest campus-based nuclear science facility in the US. The laboratory, shown in Figure 1, is funded by the National Science Foundation (NSF) for operating a national user facility and for conducting research in nuclear physics, nuclear astrophysics and accelerator physics. NSCL and the FRIB project have over 500 employees, including more than 30 faculty members with joint appointments in MSU’s Departments of Physics and Astronomy, Chemistry, and Electrical and Computer Engineering. Presently, more than 140 students – approximately half of them doctoral students – are employed and educated at the laboratory.

NSCL

The NSCL user group has recently merged into the FRIB User Organization (FRIBUO) that has over 1250 members and approximately 20 working groups. The laboratory maintains and operates two coupled superconducting cyclotrons, a high-acceptance superconducting fragment separator and a diverse set of experimental end stations. The facility is capable of delivering a broad range of primary beams from hydrogen to uranium that are used for the in-flight production of secondary, rare isotope beams with energies up to nearly 170 MeV per nucleon. Figure 2 gives an overview of the rare isotope beams produced at the Coupled Cyclotron Facility (CCF) so far (2012). The in-flight technique entails accelerating heavy ions to intermediate energies and producing fast moving (v~0.4c) secondary ion beams of short-lived “exotic” nuclei by projectile fragmentation or fission. This method allows for sub-microsecond isotope separation in a chemistry-independent way with short beam development times of a few hours to one day. The high beam energies provide efficient access to nuclei very close to the driplines, both because thick targets can be used and because ions in mixed beams (“cocktail beams”) can be identified on an event-by-event basis. At NSCL, rare isotopes produced with this technique have been stopped in and extracted from a He gas cell to be used in precision ion trap experiments. The capability to reaccelerate the stopped exotic nuclei to energies of several MeV per nucleon is presently being implemented.

Rare isotopes at NSCL are predominantly produced via projectile fragmentation. At high projectile energies, a transmission target is used to remove “participant” nucleons from the projectile nuclei while the non-interacting “spectator” part of the projectile proceeds at essentially beam velocity and close to 0° with narrow longitudinal and transversal momentum distributions. The isotopes of interest are then separated in a fragment separator and transported to the experimental end station. A related technique, in-flight projectile fission, is presently being implemented at NSCL as a production mechanism for heavy neutron-rich nuclei. Other facilities employing projectile fragmentation or fission for the production of rare-isotope beams include GSI/FAIR (Germany), RIBF/RIKEN (Japan) and GANIL (France). Another important technique for the production of exotic nuclei is the so-called isotope separation online (ISOL), where radioactive nuclei are produced and thermalized in very thick targets or target-catcher combinations and extracted for subsequent ionization and re-acceleration. This approach is used, for example, at ISAC/TRIUMF (Canada), ISOLDE/CERN (Switzerland), and SPIRAL/GANIL (France).

Figure 2: Rare isotope beams produced (green) and delivered for experiments (red) at NSCL’s Coupled Cyclotron Facility. Rare isotopes observed at other laboratories, but not yet produced at NSCL are shown in blue. In the vicinity of the proton dripline, many nuclei on the rp (rapid proton capture) process path (blue line) have been reached; on the neutron-rich side of the nuclear chart, lighter r-process (rapid neutron capture) nuclei (dark brown line) have been accessed at NSCL (see JINA).

The NSCL hosts advanced detection systems and experimental end stations, e.g. the large acceptance high-resolution S800 Spectrograph and the high-field Sweeper Magnet, the high-resolution array HiRA for charged-particle detection, high-resolution and high-efficiency γ-ray detection systems (the Segmented Germanium Array SeGA and the Caesium Iodide Array CAESAR, respectively), neutron detection arrays suited for various energies (Modular Neutron Array – MoNA and its extension LISA, Neutron Emission Ration Observer – NERO, Low-Energy Neutron Detector Array – LENDA and the Neutron Walls), the Beta Counting System (BCS) as well as beta NMR/NQR setups, diamond timing detectors, and the low-energy beam and ion (Penning) trap facility LEBIT. An active-target time projection chamber (AT-TPC), a laser spectroscopy setup, various gas and liquid targets and the SEparator for CApture Reactions (SECAR) are currently under construction. The advanced γ-ray tracking array GRETINA and the Array for Nuclear Astrophysics Studies with Exotic Nuclei (ANASEN) will be hosted for experimental campaigns at NSCL. More detailed descriptions of the existing NSCL instruments can be found online. A broad arsenal of experimental approaches and techniques – event-by-event implantation and decay spectroscopy, inelastic scattering, nucleon knockout, transfer and charge-exchange reactions, central nucleus-nucleus collisions as well as Penning-trap and time-of-flight mass measurements – utilizes these experimental devices to unravel ground- and excited-state properties of short-lived nuclei and their reaction dynamics. Recent research highlights include the discovery of 17 new isotopes by O.B. Tarasov et al. and T. Baumann et al. – among others ⁴⁰Mg and ⁴²Al, β-decay half-life measurements of ⁹⁶Cd, ⁹⁸Ir and ¹⁰⁰Sn, the precision mass measurements of ^68,70Se and ⁷¹Br, the first spectroscopy of bound and unbound nuclear states in the very neutron-rich nuclei ⁴⁶S, ⁶⁰Ti and ²⁴O, ²⁶O, respectively, pioneering conversion-electron spectroscopy of a shape-coexisting 0⁺ state in ⁶⁸Ni, novel time-of-flight mass measurements of ^48,49Ar, the first direct double β-decay Q-value measurement for ⁸²Se, evidence for the di-neutron decay of ¹⁶Be and two-neutron radioactivity of ²⁶O, the pioneering measurements of ⁵⁶Ni and ⁴⁶Sc Gamow Teller distributions, and the first determination of collectivity in ^47,48Ar and of higher-excited states in ⁷²Kr. See the NSCL Front page news and NSCL publications for more highlights. Much of the work at NSCL is relevant for nuclear astrophysics and recent highlights include the development of a new method to constrain the r process, the determination of key properties of ⁵⁸Zn and ²⁶Al, and new insight into the cooling of the neutron star crust.

Figure 3: Schematic layout of the NSCL facility. The experimental area utilizing reaccelerated beams is schematic with the final layout driven by user demand (see text for the status of equipment).

Beam time is approved by the NSCL director who is advised by a Program Advisory Committee (PAC) consisting of several internationally accomplished experts from other institutions. The PAC meets twice per year to evaluate and rank written proposals for beam time according to scientific merit and feasibility. Most research addresses important questions in basic nuclear physics, nuclear astrophysics, accelerator physics, and associated instrumentation research and development. About 5−10% of the beam time is allocated to cross-disciplinary and applied research using, for example, NSCL's Single-Event Effects (SEE) beam line.

More details about NSCL can be found at [http://www.nscl.msu.edu ]

Historical Evolution of NSCL – Past, present and future

The MSU nuclear physics program began in 1958 as an initiative of the Department of Physics. In 1961, the U.S. National Science Foundation (NSF) funded construction of the K50 cyclotron, which became the world’s first high-resolution isochronous cyclotron using new single-turn extraction techniques developed at MSU. During the next two decades, the MSU faculty established an international reputation for its high-quality nuclear science research and instrumentation development program. University researchers achieved unprecedented resolution for charged-particle spectroscopy experiments that combined the advantages of single-turn extraction, dispersion matching, and an Enge magnetic spectrograph. High-resolution neutron spectroscopy experiments were made possible over a wide range of angles by means of an innovative “swinger” magnet. This magnet allowed for variation of the incident beam-direction and measurement of angular distributions of neutrons with a fixed neutron detector and a very long flight path.

In 1975, NSF approved construction of a prototype superconducting magnet that later became the main magnet for NSCL’s K500 cyclotron, the world’s first operational superconducting cyclotron. Designing and constructing this magnet laid the foundation for the laboratory’s leadership in applications of superconductivity to nuclear physics accelerators and beam transport and analysis systems. In 1978, the NSF/DOE Nuclear Science Advisory Committee (NSAC) recommended construction of NSCL as a national user facility, involving construction of a superconducting K1200 cyclotron, at that time the world highest-energy continuous wave accelerator. In 1982, the first beam was extracted from the K500 cyclotron and the K500 nuclear science program was initiated with a modest array of equipment, largely carried over from the K50. In 1988, the first beam was extracted from the K1200 cyclotron, and an interim research program was initiated with a new 92-inch scattering chamber and a partially completed 4π charged-particle array installed in series on a temporary beam line. Concurrently, the remaining superconducting beam transport system was completed.

In October 1990, the full experimental program began after an eight-month shutdown to install the superconducting beam transport system and the superconducting A1200 fragment separator/beam-analysis system, the world’s first superconducting fragment separator. The K1200 cyclotron was injected by newly developed Electron Cyclotron Resonance (ECR) ion sources. During the next nine years, a variety of new devices for research in nuclear science were developed and brought on-line, and the K1200 cyclotron was operated in support of a user program in experimental heavy-ion science that attracted scientists from around the world. Rare, short-lived isotopes produced via projectile fragmentation of the K1200 cyclotron beam and then separated in flight with the A1200 fragment separator/beam-analysis system became a staple for the experimental program. The NSCL was the first laboratory in the world that allowed transport of these rare-isotope beams to all its beam lines.

In 1993, the NSF approved construction of the S800, a high-resolution large-solid-angle superconducting magnetic spectrograph that was completed in 1996. To this date (2010) the S800 remains a state-of-the art instrument with a maximum rigidity of 1.2 GeV/c, an energy resolution of 10⁴, an energy range of 10%, and a large angular acceptance: Δθ = 10° and Δφ = 7°. The S800 has been used in many pioneering experiments and continues to play a crucial role in NSCL’s rare-isotope research program.

In 1994, the NSCL proposed a major capability upgrade by refurbishing and coupling its two superconducting cyclotrons (the K500 and the K1200) and by building a novel high-acceptance superconducting fragment separator (the A1900). The technology developed for the A1900 was used for the fragment separator design at the next generation rare isotope facility RIBF at RIKEN.

In 1995, NSAC developed the priorities for a new long range plan for nuclear science and recommended an immediate NSCL upgrade to the proposed coupled cyclotron facility (CCF). NSF approved the funding for construction of the CCF in 1996. Stand-alone operations of the K1200 cyclotron for research continued until the end of June 1999. From July 1999 through May 2001, operation of NSCL as a user facility was suspended to allow installation of the coupling line and the A1900 fragment separator and other needed reconfigurations of the high bay experimental areas. The CCF was completed in time and within budget and began operations for rare-isotope research in July 2001.

In recent years, the NSCL has designed, built, and implemented a large and versatile array of state-of-the-art experiment apparatus, much of it unique at the time of conception. Examples include various advanced charged-particle, γ-ray, and neutron detection arrays; high-speed tracking detectors; a highly granular β-detection system suitable for use with cocktail beams; a superconducting sweeper magnet to allow for neutron coincidence experiments around zero degrees; a helium-gas cell followed by a low energy beam transport and ion trap system (LEBIT) for precision mass measurements; a new Radio Frequency Fragment Separator (RFFS) for background suppression with neutron-deficient beams; and a digital data-acquisition system (DDAS) for improved γ-ray tracking. Starting in 2006, the experimental areas underwent significant reconfiguration to remove equipment no longer used, to allow more efficient utilization of existing or new equipment, to meet newly emerging user needs, and to shorten the time needed to tune and deliver rare-isotope beams to experimenters.

Currently, NSCL is commissioning two improved momentum-compression beam-lines that will accommodate novel high-performance gas stoppers (designed and built by Argonne National Laboratory and MSU) for stopping rare-isotope beams. After extraction from these gas stoppers, the rare-isotope beams can be transported into a new stopped-beam experimental area currently under construction, which will house experimental apparatus for ion trapping and laser spectroscopy experiments. Alternatively, the stopped rare isotopes can be transported to an Electron Beam Ion Trap (EBIT) charge breeder where they are ionized into a high charge state suitable for efficient reacceleration in a 3.2 MeV/nucleon superconducting linac (dubbed ReA3) completed in 2014. A new experimental hall for experiments with reaccelerated beams was completed in 2009 and is being equipped with beam lines and experimental apparatus at present.

FRIB

The Facility for Rare Isotope Beams (FRIB) is a new scientific user facility supporting the mission of the Office of Nuclear Physics in the U.S. Department of Energy Office of Science. FRIB is funded by the Department of Energy Office of Science (DOE-SC), Michigan State University (MSU), and the State of Michigan. Located on campus and operated by MSU, FRIB will provide researchers with the technical capabilities to study the properties of rare isotopes and to put this knowledge to use in various applications, including in materials science, nuclear medicine, and the fundamental understanding of nuclear material important to nuclear weapons stockpile stewardship. Examples of important research areas include:

• Nuclear Structure – What is the nature of the nuclear force that binds protons and neutrons into stable nuclei and rare isotopes? What are the limits of nuclear existence?
• Nuclear Astrophysics – What is the nature of neutron stars and dense nuclear matter? What is the origin of elements heavier than iron in the cosmos? What are the nuclear reactions that drive stars and stellar explosions?
• Tests of Fundamental Symmetries – Why is there now more matter than antimatter in the universe?
• Application of Isotopes to Society - What are the potential uses in medicine, energy, material sciences, and national security?

Figure 4: Preliminary design layout for the Facility for Rare Isotope Beams (FRIB).

FRIB will afford users research opportunities with fast, stopped, and reaccelerated beams of rare isotopes. Features of FRIB design include:

• State-of-the-art superconducting-RF driver linear accelerator that provides 400 kW for all beams with uranium accelerated to 200 MeV/nucleon and lighter ions to higher energies (protons up to 600 MeV)
• Space in the linac tunnel and shielding in the production area to allow upgrading the driver linac energy to 400 MeV/nucleon for uranium and 1 GeV for protons without significant interruption of the future science program
• High-power in-flight production target and three-stage high-acceptance high-resolution fragment separator to produce and deliver rare isotopes with high rates and high purity
• Provisions in the fragment separator for future implementation of isotope harvesting and for adding (limited) multi-user capability
• Space available and provisions in the facility design for adding a second target facility, for example for ISOL beam production with protons or light ions up to 400 kW, expanding science opportunities and enhancing (providing full) multi-user capability in the future
• Three beam stopping stations – two gas stopping stations and one solid stopper – to provide “stopped” beams with highest efficiency for precision experiments and for reacceleration
• A superconducting-RF reaccelerator with upgrade possibilities to provide beams up to 12 MeV/nucleon (uranium) and higher energies for lighter beams (e.g., 21 MeV/nucleon for ⁴⁸Cr)
• Experimental areas (47,000 sq ft) for science with stopped beams, reaccelerated beams, and fast beams. Space available to double the size of experimental areas or for housing additional rare isotope research facilities
• A full set of well-tested experimental equipment in place for research in all FRIB science areas
• Opportunity for a pre-FRIB science program using the existing in-flight separated beams from the Coupled Cyclotron Facility and the ReA3 reaccelerator. Users will be able to mount and test equipment and techniques and do science with beams at all energies in-situ so that they are immediately ready for experiments when FRIB is complete; this will allow for a continually evolving science program during the time FRIB is under construction, which will seamlessly merge into the research program at FRIB
• A User Relations Office during establishment of the FRIB facility to support development of user programs and experimental equipment
• Venues for community input through an FRIB Users Organization (for individual users) and the Rare Isotope Research and Education Board (for institutions)
• Strong governance through the MSU President’s Project Advisory Committee, Science Advisory Committee, Project Management Advisory Committee, Accelerator Systems Advisory Committee, and Experimental Systems Advisory Committee

For more information, see the FRIB webpage.

Current status

Figure 5: Photograph of the Facility for Rare Isotope Beams (FRIB) site at Michigan State University (March 2017). Construction of the FRIB conventional facilities—the tunnel for the linear accelerator and support buildings on the surface—began in early spring 2014. In March 2017, FRIB achieved beneficial occupancy of civil construction, and technical installation activities escalated as a result.

Construction of the FRIB conventional facilities—the tunnel for the linear accelerator and support buildings on the surface—began in early spring 2014. Research and development activities have been successfully completed, with much of the R&D work accomplished in collaboration with national laboratories. Final design of the technical systems—accelerator and experimental equipment—is nearly complete, and technical construction started in October 2014. In March 2017, FRIB achieved beneficial occupancy of civil construction, and technical installation activities escalated as a result, with the 4K cryoplant completed since December 2017 and commissioning of the cryomodules ongoing. Cryomodule production is now at peak capacity, with the project team building twelve cryomodules per year. Project completion is expected in 2022, managing to early completion in 2021.

History

On December 11, 2008, after a rigorous merit review process conducted by a panel of world-renowned experts from universities, national laboratories and federal agencies, the DOE-SC announced that MSU had been selected to design and establish FRIB, a cutting-edge research facility to advance the understanding of rare nuclear isotopes and the evolution of the cosmos. The new facility will provide research opportunities for an international community of approximately 1,000 university and laboratory scientists, postdoctoral associates, and graduate students. Upon completion, FRIB will operate as a scientific user facility supporting the mission of DOE-SC’s Office of Nuclear Physics.

“The Department of Energy’s new Facility for Rare Isotope Beams at Michigan State University promises to vastly expand our understanding of nuclear astrophysics and nuclear structure,” said Acting Associate Director of the Office of Science for Nuclear Physics Eugene Henry in the official DOE press release. “This capability will allow physicists to study the nuclear reactions that power stars and stellar explosions, explore the structure of the nuclei of atoms and the forces that bind them together, test current theories about the fundamental nature of matter, and play a role in developing new nuclear medicines and techniques.”

Figure 6: Progress on the linear accelerator as of December 2017.

There are about 3,000 known isotopes and as one approaches the limits of stability (where nuclei have extreme proton-to-neutron ratios), isotopes become rarer and harder to produce. The main focus of FRIB is to produce such rare isotopes, including many that have never before been produced in the laboratory, study their properties, and use them in applications to address national needs. The FRIB concept has undergone numerous studies and assessments within DOE and by independent parties such as the National Research Council of the National Academy of Sciences. These studies—in addition to the joint DOE/National Science Foundation (NSF) Nuclear Science Advisory Committee (NSAC) 2007 Long Range Plan—concluded that such a facility is a vital part of the U.S. nuclear science portfolio, complements existing and planned international efforts, and will provide capabilities unmatched elsewhere. Thus, the selection announced in December 2008 is the culmination of studies, analyses, and recommendations conducted since the 1996 NSAC Long Range Plan first recommended the development of a next-generation nuclear structure and astrophysics facility as a high priority.

Figure 7: On 11-12 July 2018, the Facility for Rare Isotope Beams accelerated first beam in three of forty-six superconducting cryomodules (painted green). Beam in the warm radio-frequency quadrupole was previously accelerated in September 2017.

Civil construction (Critical Decision 3a) started in March 2014 and technical construction started in October 2014 (CD-3b). The Project was baselined (CD-2) in August 2013 and a preferred alternative was selected in September 2012 (CD-1). In March 2017, FRIB achieved beneficial occupancy of civil construction, and technical installation activities escalated as a result.

In September/October 2017, the front end with the ion source and low-energy beam transport were completed. The FRIB cryogenic plant made its first liquid helium at 4.5 Kelvin (K) in November 2017. Liquid helium makes FRIB’s accelerator cavities superconducting and is needed to operate FRIB’s superconducting linear accelerator. The 4 K cryogenic plant was completed in December 2017, and in July 2018, following two days of commissioning, beams of argon and krypton were accelerated in the first three superconducting cryomodules to the Key Performance Parameters required at project completion. Cryomodule production is now at peak capacity, with the project team building twelve cryomodules per year.

Sponsored by: Dr. Nicolas Alamanos, CEA, IRFU; F-91191 Gif-sur-Yvette, France, France

Reviewed by: Anonymous

Accepted on: 2010-01-15 03:19:35 GMT