The US Department of Energy should build an electron–ion collider (EIC) to investigate the nature of atoms, says a National Academies of Sciences, Engineering, and Medicine committee in a 24 July report. The recommendation backs the aspirations of the US nuclear science community, which in 2015 ranked the project as its top long-range priority for new facility construction. It’s expected to cost in the range of $1 billion.
“The science questions regarding the building blocks of matter are compelling and an EIC is essential to answering these questions,” the committee writes.
The DOE Office of Nuclear Physics will now begin an internal process to certify that no facility with the required capabilities currently exists and that the new device is necessary to advance the agency’s mission. If the agency and Congress approve an EIC, DOE will pick from competing proposals for the device developed at Brookhaven National Laboratory in Upton, New York, and Thomas Jefferson National Accelerator Facility in Newport News, Virginia.
An EIC slams electrons into protons or heavier ions to investigate the quarks and gluons inside the nucleons. A collider with high energy and luminosity—a measure of the rate at which particle collisions occur—would have the fine resolution needed to answer some of the big-picture questions cited by the committee. Those include elucidating the origin of the mass and spin of nucleons, learning how gluons hold nuclei together, and determining whether emergent forms of matter made of dense gluons exist.
Beyond nuclear science, an EIC would benefit astrophysics, high-energy physics, accelerator physics, and theoretical and computational modeling, the committee writes. Further, it is the only high-energy accelerator (excluding light sources) being considered for construction in the nation, and building it would help to maintain US expertise in accelerator and collider science. “An EIC would be a unique facility in the world and would maintain US leadership in nuclear physics,” the report states. Although there is no existing EIC, China is also considering building one.
 |
 |
|
|
In a 2015 long-range plan, the DOE–NSF Nuclear Science Advisory Committee identified the construction of a high-luminosity polarized EIC as the highest priority for new facility construction following completion of the in-progress Facility for Rare Isotope Beams (FRIB) at Michigan State University. The National Academies committee says the 2015 report was “thorough and thoughtful” and had taken into account both science priorities and budgetary realities.
“I’m very pleased to find the National Academies have reached the same conclusion as the nuclear science community that the science is strong and compelling and that this is a must-do program,” says Timothy Hallman, director of the Office of Nuclear Physics at DOE. To maintain its lead in the study of quantum chromodynamics and nuclear interactions, the US “must create this new microscope and look in finer detail so we can see what is going on in these interactions.”
The Brookhaven and Thomas Jefferson (or JLab) facilities have each developed a proposal for an EIC. Brookhaven, which already has the required proton/heavy-ion accelerator in its Relativistic Heavy Ion Collider (RHIC), would build alongside that a new linear accelerator, synchrotron, and storage ring for electrons. JLab, which last year completed a $338 million upgrade to its Continuous Electron Beam Accelerator Facility, proposes constructing a new storage ring for electrons and an ion complex consisting of a linear accelerator, two synchrotron rings, and a storage ring.
In its report, the National Academies committee doesn’t judge the merits of either proposal but says that making use of existing facilities would lower the project’s cost and reduce risks. Both labs’ plans would require additional R&D to minimize design risks and address outstanding accelerator challenges.
It could be several years before an EIC emerges in a DOE budget request. “We won’t be putting any shovels in the ground tomorrow,” Hallman says. Construction will require a new line-item appropriation and will likely take five to ten years to complete.
DOE is currently supplying most of the funding for the $730 million FRIB. That device, due for completion in 2022, is designed to generate large quantities of heavy nuclei and probe the origin of heavy elements.
