The 12 GeV Upgrade Project: Doubling CEBAF's Energy
Upgrading the accelerator will be a relatively straightforward process. An experimental hall, Hall D, will be added to the site. The accelerator will receive additional accelerating cryomodules in the linacs. The Central Helium Liquefier will be upgraded. Stronger magnets will be installed in the nine recirculation arc beam lines to handle a higher-energy electron beam, and a beam line will be added to allow electrons to make an extra pass through one linac before being delivered to Hall D.
Though originally designed to deliver a 4 GeV beam, CEBAF is now capable of producing an electron beam of about 6 GeV, exceeding design specifications by 50%. This success has opened up the possibility of a relatively simple and inexpensive upgrade of CEBAF's top energy. The higher energy will be attained by adding 10 new cryomodules, which accelerate, or pump energy into, the electrons in the electron beam.
Cryomodule development teams at Jefferson Lab are now working to produce a seven-cell SRF cavity cryomodule that will fit into the same space as the original units. These new cryomodules will be built to exceed the original CEBAF specification by a factor of five (a cryomodule four times better than original specs has already been demonstrated by these teams). Five of the seven-cell SRF cavity cryomodules will be installed in already available space in each linac.
The Central Helium Liquefier, which provides the helium necessary for superconductivity, will be upgraded to support the additional cryomodules. Stronger magnets for recirculating electron beams between the linacs for five full acceleration passes will be installed. DC power supplies and spreader/recombiners in the machine will be updated or replaced and the radiofrequency system will be modified. In addition, an extra beamline leading to a sixth pass through just the north linac will be added. That pass will yield a 12 GeV electron beam for the new end station, Hall D. The present halls (A, B and C) will receive electrons with energies up to 11 GeV.