On 7 May, the newly upgraded Continuous Electron Beam Accelerator Facility (CEBAF) delivered the first electron beams to its new experimental complex at the US Department of Energy’s (DOE’s) Jefferson Lab. The success capped a string of accelerator commissioning milestones that were needed for approval to restart experimental operations following CEBAF’s first major upgrade.
CEBAF is an electron-accelerator facility that employs superconducting radiofrequency (SRF) technology to investigate the quark structure of the nucleus. The first large-scale application of SRF technology in the US, it was originally built to circulate electrons through 1–5 passes to provide 4 GeV electron beams. As a result of the operators’ experience in running the machine at its peak potential, the original installation eventually achieved operational energies of 6 GeV (CERN Courier October 2000 p9).
In May 2012, the accelerator was shut down for its 12 GeV upgrade (CERN Courier November 2012 p30). This $338-million project, which will double CEBAF’s maximum energy, includes the construction of a fourth experimental hall (Hall D), as well as upgrades to equipment in three existing halls (Halls A, B and C) (CERN Courier April 2009 p15).
Accelerator operators began the painstaking task of bringing the accelerator back online last December. By 5 February, they had achieved the full upgrade-energy acceleration of 2.2 GeV in one pass through the machine. Then on 1 April, the operators exceeded CEBAF’s previous maximum energy. The accelerator delivered three-pass, 6.11-GeV electron beams with 2 nA average current onto a target in Hall A, and recorded the first data of the 12-GeV era, holding the pattern for more than an hour.
The operators continued to push the upgraded machine, and early on 7 May the energy was increased to 10.5 GeV through the entire 5.5 passes. In the last minutes of the day, 10.5 GeV beam was delivered into the new Hall D complex. Having met all of the major milestones in the 12-GeV project for the DOE approval step, Critical Decision-4A (Accelerator Project Completion and Start of Operations), staff and users are now looking forward to demonstration of 12-GeV energy and beam delivery to Jefferson Lab’s experimental halls for commissioning and the start of experiments.