The SEparator for CApture Reactions (SECAR) is a next-generation recoil separator system under construction in the ReA3 Hall at the National Superconducting Cyclotron Laboratory and Facility for Rare Isotope Beams (FRIB) at Michigan State University. Click on the image to see the entire system. SECAR is optimized for the direct measurement of capture reactions on unstable nuclei that drive some stars to explode and synthesize crucial nuclei that make up our bodies and our world. The SECAR Project includes work to design, procure, install, and commission this unique system at ReA3. The project was completed on schedule in 2021, and the SECAR Collaboration and other researchers are now planning measurements to improve our understanding of novae, X-ray bursts, supernovae, and other explosive and exotic astrophysical environments.
A Code of Conduct for the SECAR Collaboration has been adopted and is available to view by clicking here.
A SECAR Collaboration Workshop was held on Monday, August 8, 2022, as a satellite workshop at the 2022 Low Energy Community Meeting. A program for the Workshop is available by clicking here.
The SECAR Project, which began on March 1, 2015, was completed on schedule and on budget in September 2021. The entire system has been commissioned and the key performance parameters have been met. The SECAR Project Team is very grateful for all the assistance from DOE, NSF, MSU, FRIB, the review panels, and our scientific collaborators, their students, and their home institutions. Extended commissioning work is ongoing, as are preparations for a series of upcoming measurements.
The first measurements of the 20Ne(alpha,n) reaction were made with SECAR at the end of August 2021, successfully observing the 23Mg recoils at the final focal plane. Measurements were performed near 2.2MeV/u for several recoil charge states. The image below shows recoils from one measurement, demonstrating excellent rejection of leaky beam. This is an important achievement in SECAR commissioning and an important step towards using SECAR as a tool to measure the cross sections of (alpha,n) reactions that are important for astrophysics.
SECAR performed the first capture reaction measurement to test system performance by measuring a known resonance strength in the 16O(alpha,gamma)20Ne capture reaction. The goals of the experiment are to determine the transmission of 20Ne recoils through SECAR, to measure a known resonance strength, to determine the rejection of "leaky beam" by the separator system alone, and then to determine the "leaky beam" rejection of the combination of the separator and the focal plane detection system. The image below shows the identification of 20Ne recoils in the focal plane detector system; the group of particles below the recoils are "leaky" beam particles that are completely removed when a time coincidence is required between the focal plane signal and the BGO gamma array surrounding the JENSA 4He gas jet target.
The commissioning of the entire SECAR system is proceeding well. A major milestone was reached by the first detection of capture reaction recoils at the SECAR final focal plane detector system. We bombarded 4He nuclei in the JENSA gas jet target system with a beam of 16O from ReA3, and measured 20Ne recoils from the 16O(alpha,gamma)20Ne capture reaction. Particle identification of recoils was made at the final focal plane by using the ionization chamber to measure energy loss and using a silicon strip detector to measure particle energy. The system clearly separated 20Ne recoils from 16O "leaky beam" particles which had undergone multiple scattering off system components to make their way to the final focus plan. beam for an energy measurement. The array of BGO detectors at the target location were also successfully operated, and clearly measured the three expected gamma-ray lines from the 20Ne deexcitation cascade. Furthermore, gamma rays were measured in time coincidence with recoils at the focal plane. This work demonstrated, for the first time, that all SECAR components are functioning: the gas target, target scattering monitors, BGO array, stripper foil, magnets and Velocity filters, beam diagnostics, and focal plane detection systems. This work also demonstrated the successful development of beam tuning procedures that align the incoming beam with the SECAR ion optical axis and the JENSA windowless gas target apertures, as well as our approach to determine the beam energy using the previously calibrated first two dipoles of the SECAR system. The data from this run is under analysis, and subsequent runs will be made as the "SECAR Project Completion Experiment."
The installation of Velocity Filter 2 was completed, and was subsequently conditioned up to +/- 130KV. Commissioning runs of the system continued, for the first time included all magnets, Velocity Filters, diagnostics, and focal plane detectors. Velocity Filter 2 was operated at a total gap voltage of 186 kV in commissioning runs with a 20Ne beam, and the beam was successfully transmitted to the final focal plane. Position spectra of the transmitted beam particles were collected in the ionization chamber, and the MCP, ion counter, and DSSD detectors at the focal plane were all operated successfully.
Work will continue on the SECAR "completion experiment"
to measure a known resonance strength in the
capture reaction. The experiment will also
determine the transmission of 20Ne recoils
through SECAR, and determine the rejection
of "leaky beam" particles both by the separator and
by the combination of the
separator and the focal plane detection system.
The dates of measurements are subject to change based on the facility status. Please check the SECAR Calendar for the latest updates. If using a mobile device, please check the Agenda view shown on the SECAR Mobile Calendar.
"Design of SECAR: a Recoil Mass Separator for Astrophysical
Capture Reactions with Radioactive Beams" by G. Berg, M. Couder,
M.T. Moran, K. Smith, M. Wiescher, H. Schatz, U. Hager, C. Wrede,
F. Montes, G. Perdikakis, X. Wu, A. Zeller, M.S. Smith, D.W. Bardayan,
K.A. Chipps, S.D. Pain, J. Blackmon, U. Greife, K.E. Rehm, and R.V.F. Janssens,
Nuclear Instruments and & Methods A 877, (2018) 87-103.
The SECAR Project is funded by the
Office of Nuclear Physics in the
U.S. Department of Energy Office of Science
National Science Foundation.
Contributions were also made by:
SECAR will be used to advance our understanding of stellar explosions including novae, X-ray bursts, and supernovae, as well as other exotic astrophysical sites including supermassive stars, hypernovae, Thorne-Zytkow objects, and the very first stars in the Universe. By facilitating direct measurement of reactions on unstable isotopes, SECAR will establish an empirical foundation for simulations of the element creation and energy generation occurring in these fascinating astrophysical systems. For additional details, please see this document on science with SECAR from the 2014 SECAR pre-Conceptual Design Report.
A major milestone was reached with the SECAR system: the first detection of capture reaction recoils at the final focal plane detector system. We measured 20Ne recoils from the 16O(alpha,gamma)20Ne capture reaction as the "completion experiment" of the SECAR Project. More details are given above in the News section.
The manuscript "Design of SECAR: a Recoil Mass Separator for Astrophysical Capture Reactions with Radioactive Beams" by G. Berg, M. Couder, M.T. Moran, K. Smith, M. Wiescher, H. Schatz, U. Hager, C. Wrede, F. Montes, G. Perdikakis, X. Wu, A. Zeller, M.S. Smith, D.W. Bardayan, K.A. Chipps, S.D. Pain, J. Blackmon, U. Greife, K.E. Rehm, and R.V.F. Janssens was published in Nuclear Instruments and & Methods A 877, (2018) 87-103.
The SECAR system consists of 8 Dipole Magnets (red components in the diagram), 15 Quadrupole Magnets (yellow), 5 Multipole Magnets (light blue), and two Velocity Filters (dark blue). The first set of dipole magnets in SECAR performs a critical charge-state selection of both the recoils and unreacted projectiles that enter the SECAR system. The primary projectile rejection components of SECAR are the two Velocity Filters. These devices, also known as Wien Filters, have a vertical magnet field B and a horizontal electric field E that together serve to deflect the trajectory of any particles with a velocity different than E/B. By appropriately tuning these fields, the unreacted beam particles that enter the system can be deflected away while the reaction products of interest (recoils) are passed through to eventually reach the focal plane. Since the unreacted beam particles have an intensity of 1013 - 1017 higher than the capture reaction recoils of interest, the SECAR design includes two Velocity Filters to obtain the level of projectile rejection needed to enable the identification of capture reaction recoils at the SECAR focal plane, and thereby enable the measurement of critical capture reactions on unstable nuclei that power certain types of stellar explosions. More information on the separator can be found in the this SECAR Project Update presentation by Hendrik Schatz (May 2020).
The SECAR focal plane features two microchannel plate (MCP) detectors followed by a position-sensitive gas ionization counter. The first detectors will determine the ion velocity by their time of flight, and the second detector will determine the ion atomic number Z by measuring their differential energy loss and total energy loss (dE-E) in the detector gas. The focal plane is designed to give an additional factor of 104 separation of scattered projectile background and capture reaction recoils beyond that provided by the separator magnets and velocity filters.
The Jet Experiments for Nuclear Structure and Astrophysics (JENSA) system provides 4mm-wide ultra-dense jets of hydrogen and helium gas that serve as the target for capture reactions measurements with SECAR. The high densities possible with JENSA -- over 1019   atoms/cm2 with He -- and the elimination of reactions off of backing materials commonly found in foil targets, makes this gas jet system ideally suited for our experiments. JENSA also functions as a windowless extended gas target that enables searches for resonances with unknown energies to be carried out. Once located, complimentary, higher-resolution studies can be carried out with the jet target. More information on JENSA can be found in this JENSA update presentation by Kelly Chipps (May 2020). Also, please visit the JENSA web site for more details.
NEWS: A SECAR Collaboration Workshop was held on Monday, August 8, 2022,
as a satellite workshop at the 2022 Low Energy Community Meeting.
A program for the Workshop
is available by clicking here.
The SECAR Collaboration is an open, active collaboration of researchers who are passionate about measuring thermonuclear reactions that drive some stars to explode. Please Join Us if you are interested in contributing to our separator system or by submitting a proposal to enhance our scientific program.
Now that the SECAR Project is complete, we have transitioned the SECAR Collaboration to have a focus on proposing, running, and analyzing experiments. We have now established a SECAR Collaboration Agreement that codifies the activities and organizational structure of the collaboration.
We have also adopted a SECAR Code of Conduct that describes the expectations of the conduct of collaboration members.
Please click here to learn more about the SECAR Collaboration.
Please click here to learn more about submitting a proposal with the SECAR system.
If you are interested
in Joining the SECAR Collaboration and contributing
to the SECAR system and/or to the scientific program
utilizing this system, please contact one of the members
of the SECAR Collaboration Executive Council:
Manoel Couder, Notre Dame Univ -- Chair
Michael Smith, ORNL -- Communications
or you can contact the following SECAR experts:
Kiana Setoodehnia, FRIB -- SECAR Device Physicist
Hendrik Schatz, MSU
Fernando Montes, MSU