Speaker
Description
The final nuclear physics experiments with “6 GeV CEBAF” were conducted in 2012 at which point
the accelerator complex was upgraded to double the beam energy and add a fourth experimental
hall. The accelerator upgrade was split into two periods, a six month period preceding the final 6 GeV
operations and an 18 month period post 6 GeV operations. Following completion of the upgrade work,
the new accelerator was commissioned over a roughly two year period during five distinct runs totaling
36 weeks of operation. Milestones for these commissioning periods focused on achieving incremental
success in different technical areas including learning how to simultaneously operate two cryoplants,
finding optimum operating parameters for new “C100” cryomodules that employ new RF control
systems, commissioning the new Hall D beam transport line, and multi-hall operation at the highest
passes using new 750 MHz separator cavities. During the final commissioning run, the linacs operated at
maximum design energy enabling 12 GeV beam delivery to Hall D and 11 GeV beam delivery to Hall A at
high average current. Fall 2016 saw the official start of the 12 GeV physics program, with nuclear
physics experiments performed at Halls A, B and D during an 11 week run. All of the halls received
polarized beam, although only Hall A required it. Polarization was high (> 80%) at 11 GeV eliminating
concerns that increased levels of synchrotron radiation at the higher passes would serve to dilute beam
polarization. The future holds challenges, notably, improving machine reliability and up-time, and
maintaining linac gradient. This talk presents a summary of the CEBAF 12 GeV Upgrade – successes and
setbacks – and future plans.
