Stopped and reaccelerated beams at NSCL

NSCL’s new ReA3 reaccelerated beam facility is now under construction. We invite future users to begin planning for experiments. The letters of intent submitted by users to the NSCL PAC33 and PAC34 (that met in April 2009 and January 2010, respectively) have helped us get started on identifying users' needs and the particular beams of interest and plan accordingly.

ReA3 will provide world-unique low energy rare isotope beams produced by stopping fast, separated rare isotopes in a gas-stopper, and then reaccelerating them in a Linear Accelerator. It will make available reaccelerated beams of elements that are typically difficult to produce at ISOL facilities.

The ReA3 reaccelerator will open up a range of new experiments in nuclear astrophysics and nuclear structure. In nuclear astrophysics, the possibility will emerge to measure unstudied key reactions directly at near-stellar energies. Nuclear reactions such as Coulomb excitation, nucleon transfer, or fusion can be used at ReA3 to provide new information on nuclear structure.

With this project, NSCL will provide pioneering beams for research in one of the pillars of the next-generation rare isotope facility FRIB. This will allow the user community to develop programs and techniques in reaccelerated beams years before FRIB will come into operation.

Beginning in the EBIT charge breeder, beams from ReA3 will range in energy from 0.3 to 6 MeV/u. The maximum energy is 3 MeV/u for heavy nuclei such as uranium, and 6 MeV/u for ions with A<50. All rare isotope beams that can be produced by fragmentation or in-flight fission with sufficient intensity can be reaccelerated. The look-up table gives the minimum energy, maximum energy, and estimated yield for the reaccelerated beams. Note that, given the absence of operational experience, the estimated yields given by the look-up table is uncertain by up to an order of magnitude. The beam will have a 80 MHz microstructure. Expected beam properties include a transverse normalized emittance of 0.6 π mm mrad and a longitudinal emittance of 0.29 πkeV ns for 90% of the beam at 0.6 MeV/u. The beam will have an energy spread on target of 1 keV/u and a bunch length of 1 ns. The time and energy spread are tunable by a rebuncher in the beam transport system.

A new experimental hall is being constructed with an area of 9,100 sq ft. This will offer ample space for flexible experimental stations as well as for some larger permanent installations of equipment. We envisage building three beam lines.

Scientific equipment that will be used with ReA3 beams includes ANASEN, SuN, JENSA and the Active Target Time Projection Chamber (AT-TPC), among others.

The Array for Nuclear Astrophysics Studies with Exotic Nuclei (ANASEN) is a charged-particle detector array being developed by Louisiana State University and Florida State University and it consists of silicon-strip detectors backed with CsI scintillators arranged in a barrel configuration, and an annular Si detector enclosing the downstream end of the barrel. It will initially be used for proton scattering, (,p), (p,) and (d,p) reaction studies.

The Summing NaI(Tl) SuN detector is a barrel shaped scintillator detector that will be used to study of (p,γ) and (α,γ) reactions. The detector makes use of the summing technique by the large-volume detector surrounding the target covering almost 4π solid angle.

The AT-TPC is being built by a collaboration of researchers from MSU, University of Notre Dame, Western Michigan University, LLNL, LBNL, and St. Mary’s University. The time projection chamber detector will be placed inside a large solenoid so once the beam particles enter the gas chamber, they can interact with the active target. The resulting products will be tracked within the gas vessel of the time projection chamber. It is planned to be used, among other things, for the indirect study of reactions of astrophysical interest either by (d,p) or (3He,d) transfer reactions.

The Jet Gas Target JENSA is a high-density gas-jet target for nuclear astrophysics and reactions studies with rare isotope beams. It is being built by a collaboration from MSU, Colorado school of Mines, Louisiana State University and ORNL. The target is designed for use with large arrays of silicon strip detectors surrounding the jet, as well as external gamma ray detectors to study transfer, (p, ) and (,p) reactions.

The Separator for Capture Reactions (SECAR) is a highly specialized device also planned to be used in ReA3. This recoil separator will be used for the direct measurement of (p,) reactions at astrophysically relevant energies. Although the focus will be on X-ray bursts and novae, it will also address reactions relevant for late burning stages and explosive nucleosynthesis in supernovae.

Among the scientific equipment under construction for experiments with ReA3 beams are:

  • A Si-barrel detector array for nuclear astrophysics studies with exotic nuclei (ANASEN), whose funding has been approved by the NSF/MRI program for a collaboration led by Louisiana State University and Florida State University; and
  • An active target time projection chamber (AT-TPC), funded through the NSF MRI program and being built by a collaboration of researchers from MSU, University of Notre Dame, Western Michigan University, LLNL, LBNL, and St. Mary's University (Canada).

Among the scientific equipment under construction for experiments with stopped beams are:

  • A low energy beam and ion trap facility (LEBIT) for precision mass measurements; and
  • A beam cooler and laser spectroscopy endstation (BECOLA) for laser spectroscopy and beta-NMR studies.