Late on April 1, the crown jewel of the Department of Energy's Thomas Jefferson National Accelerator Facility (“Jefferson Lab”) sparkled its way into a new era. Following an upgrade of the Continuous Electron Beam Accelerator Facility, the CEBAF accelerator delivered the highest-energy electron beams it has ever produced into a target in an experimental hall, recording the first data of the 12 GeV era. The machine sent electrons around the racetrack three times (known as “3-pass” beam), resulting in 6.11 GeV electrons at 2 nanoAmps average current for more than an hour.

"This achievement is a major milestone in the commissioning of the upgraded CEBAF," said Hugh Montgomery, Jefferson Lab director. "Although it's early yet as far as delivering beam for experiments, we are beginning to see the flowers that will become the fruits of our labors from this upgrade."

The CEBAF accelerator is a superconducting accelerator that had been designed to circulate electrons through one to five passes through the machine to deliver electron beams with maximum energies of 4 GeV, or 4 billion electron-volts. These beams were then delivered into one of the lab's three experimental areas, called halls, where they were directed into the nuclei of target materials for nuclear physics experiments. The original CEBAF provided its first electron beams to a target in an experimental hall in 1994. Due to efficiencies in the original design and experience gained by the operators in running the machine at its maximum potential, the original machine eventually achieved operating energies of 6 GeV.

In 2008, construction began for doubling the energy of the accelerator to 12 GeV. The 12 GeV Upgrade is a $338 million project that, in addition to doubling the maximum energy of the electron beams in Jefferson Lab's accelerator, also includes the construction of a fourth experimental hall and upgrades to equipment in the existing halls.

Since the accelerator was shut down for 18 months to complete the machine upgrade, it was anticipated that baby steps would be required to optimize the settings of hundreds of components in order to deliver the higher energy beam. The first electron beams at 6 GeV for 12 GeV commissioning were delivered into Experimental Hall A on April 1 at 4 p.m. for just over 11 minutes.

The run satisfied the requirement for 12 GeV Upgrade Project Level 2 Milestone (2-09) "Hall A Beam Commissioning Complete". The milestone is defined as "events recorded from beam-target interactions using the Hall A spectrometer detector systems with 3-pass > 6 GeV beam energy and at least 2 nA average beam current."

Source: Jefferson Lab