The Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab is a world-class 4 GeV electron accelerator which serves a 1300-member worldwide nuclear physics user community. Its scientific mission is to explore the transitional regime between the conventional nucleon description of matter and the underlying quark structure of matter.
Jefferson Lab plans to expand the research capabilities of its Continuous Electron Beam Accelerator facility (CEBAF) dramatically by tripling the beam energy to 12 GeV by 2006, and then doubling the energy again by 2015. The increased beam energy, together with a new hermetic 4pi detector, will make new phenomena accessible using the unique properties of CEBAF's high duty factor electron beam to include the spectroscopy of quark-antiquark systems (the mesons) and the search for and study of gluonic excitations. These essential new studies will provide key insights into how hadronic matter is constructed from quarks and gluons, and complement the work already underway at Jefferson Lab to answer this fundamental question via studies of the structure of three-quark systems (the proton and neutron) and of finite nuclei. Such a facility would complement other nuclear physics capabilities, keeping the U.S. nuclear physics program at the cutting edge world-wide.
In addition to opening qualitatively new fields, higher beam energies will expand the capability of the CEBAF accelerator to pursue its ongoing research program by permitting the extension of experiments to substantially higher momentum transfers (providing correspondingly finer spatial resolution) and to higher excitation energies. This combination will provide an even more powerful tool for investigating the transition from the regime in which the "conventional" nucleon description of nuclear matter applies to the regime where the underlying quark degrees of freedom become evident. NSAC has endorsed the proposed energy upgrade, noting in its 1996 Long-Range Plan that "the community looks forward to future increases in CEBAF's energy and to the scientific opportunities that would bring." The upgrade is also supported enthusiastically by our user community, which has held a number of workshops on the subject.
A subsequent doubling of the beam energy (to 24 GeV) will further enhance the physics program, facilitating the program of semi-exclusive reaction studies of the quark sub-structure of the nucleon that are widely viewed as the next logical step in completing our understanding of nucleon structure. Many studies world-wide have identified this capability as defining the next-generation nuclear physics facility.
The budget profile (in FY98$) and timeline for the planned upgrades is as follows:
FY2003-2006
12 GeV
$80M ($7M, $25M, $28M, $20M)
FY2012-2015
24 GeV
$100M
The first stage of the energy upgrade (to 12 GeV) requires that we stay the course detailed in our Institutional Plan, which calls for improving performance of our superconducting radiofrequency (SRF) components from the 20 MV design energy gain per cryomodule to the goal of an 80 MV cryomodule; our most recent production cryomodule operates at 48 MV. Operating at higher energies will require that some recirculating arcs are upgraded, and exploiting the new physics accessible with these energies will require a new, hermetic detector. In order to prepare for the upgrade, we must also carry out detector studies to resolve key design and construction issues and develop a complete design for the upgraded arcs prior to FY2003. The cost of the upgrade will be split roughly equally between the machine and the detector.
Jefferson Lab's user community includes over 1300 scientists; two-thirds of them are working on approved experiments. At any one time, 80-150 of these users are stationed on-site to work on their experiments or on related theory activities.