New Science on the Horizon as Upgraded Particle Accelerator Meets Commissioning Milestones

The recently upgraded CEBAF accelerator delivers its highest-energy electron beams into a new experimental complex for the first time.

Image courtesy of Jefferson Lab
The new beamline connecting the Continuous Electron Beam Accelerator Facility accelerator to its newest experimental area, Hall D, was christened with beam on May 7. The beamline rises 5 meters before entering the Hall D tagger complex.

The Science

Originally constructed in the early 1990s, the Continuous Electron Beam Accelerator Facility is in the midst of an upgrade to double the energy of the electrons it can produce for experiments to 12 billion electron-volts (12 GeV). The upgrade includes the construction and installation of 10 new, high-performance superconducting radiofrequency cryomodules with dedicated microwave sources, approximately 80 new and more than 1,000 upgraded steering/focusing magnets with power supplies, more than 700 machine diagnostics, more than 5 km of vacuum lines, and many other items. Brought back online in the fall of 2013, the CEBAF accelerator has met the commissioning goals for >6 GeV beam into a pre-existing experimental hall and now >10 GeV beam into a new experimental area, Hall D.

The Impact

Researchers need very big microscopes to study the very small building blocks of matter. CEBAF's electron accelerator and experimental areas are capable of revealing the building blocks of protons and neutrons, quarks and gluons, in detail never before accessible. Experiments already approved for CEBAF aim to map out the internal structure of protons and neutrons in 3D for the first time, to solve the "missing spin" problem in protons and neutrons, and to finally answer the question: Why can no quark ever be found alone? In addition, the research and development culminating in high-performance superconducting radiofrequency cryomodules benefits future accelerator design and construction worldwide.


The CEBAF accelerator is based on superconducting radiofrequency (SRF) technology and produces a stream of charged electrons. CEBAF was the first large-scale application of SRF technology in the U.S., and it is the world's most advanced particle accelerator for investigating the quark structure of the atom's nucleus. The 12 GeV CEBAF Upgrade is a $338 million DOE project to double the accelerator's maximum operational energy and includes upgrades to equipment in three existing halls, as well as the construction of a fourth experimental hall, Hall D. In the last steps of accelerator systems commissioning before its summer shutdown, the machine delivered its highest-energy beams ever, 10.5 GeV, through the entire accelerator and through the newly installed beamline to the Hall D Tagger Facility, where CEBAF's electron beam is converted into the photons that will be used for studying quark confinement in Hall D. Commissioning will continue in FY2015 in order to achieve the full 12 GeV energy and to send beams to Jefferson Lab's experimental halls for commissioning the new spectrometers and the start of experiments.


Arne Freyberger
Jefferson Lab, Head of Accelerator Operations

Leigh Harwood
Jefferson Lab, 12 GeV CEBAF Upgrade – Associate Project Manager


DOE Office of Science Nuclear Physics Program.

Commonwealth of Virginia.


Jozef Dudek et al., "Physics opportunities with the 12 GeV upgrade at Jefferson Lab." The European Physical Journal A 48, 187 (2012). [DOI: 10.1140/epja/i2012-12187-1]

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