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.
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 πkeV 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 starting with two beam lines.
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:
