FRIB will be the world’s premier rare-isotope beam facility. It will make the majority (about 80 percent) of the isotopes predicted to be bound available for experiments. These isotopes will allow researchers to understand atomic nuclei and their role in the Universe. The tremendous discovery potential of FRIB can be further extended with an energy upgrade of the FRIB linear accelerator to 400 MeV/u for uranium and to higher energies for lighter ions (FRIB400).

The energy upgrade of the FRIB linear accelerator to 400 MeV/u for uranium (FRIB400) will expand the already broad scientific reach of FRIB to encompass the full range of science envisioned by the scientific community and articulated in Nuclear Science Advisory Committee Long Range Plans and studies by the National Academies of Sciences, including:

• Dense nuclear matter can be created and studied up to twice saturation density, critical for multi-messenger astrophysics
• Significant gains in isotope yields will be realized, nearly doubling the reach of FRIB along the neutron dripline and allowing study of extreme, neutron-rich nuclei
• In experiments, thicker targets can be used, increasing the luminosity for measurements of nuclei in key regions of the nuclear chart
• Nuclear reactions can be performed in an energy regime of optimum nuclear transparency, improving their interpretation by reaction theory

The case for the FRIB400 upgrade has been made timely by the dawn of multi-messenger astronomy and the detection of gravitational waves and subsequent follow-up observations of electromagnetic radiation.

The FRIB science community laid out the enormous opportunities in the FRIB400 white paper “The Scientific Case for the 400 MeV/u Energy Upgrade of FRIB,” which was subsequently endorsed at the 2019 Low Energy Community Meeting (LECM2019):

The science case for an energy upgrade of FRIB to 400 MeV/u is extremely compelling and would significantly expand the science opportunities at FRIB, as outlined in the FRIB400 whitepaper

In anticipation of the science potential, as early as in the conceptual design stage of FRIB, space was provided in the FRIB tunnel for an energy upgrade of the accelerator to 400 MeV/u for uranium. The upgrade can be implemented with minimal or no interruption of the FRIB science program.