12 GeV Upgrade Technical Scope
Schematic layout of the required facility modifications to realize the 12 GeV Upgrade.
The 12 GeV Upgrade is highly cost effective due to existing features of the Continuous Electron Beam Accelerator Facility (CEBAF). The superconducting radiofrequency linear accelerators contain superconducting niobium cavities operating, on average, at 50 percent above their design specifications in accelerating gradient and Q. The success of this technology opens up the possibility of a relatively simple, inexpensive upgrade of CEBAF's top energy. This goal is also made possible due to the CEBAF tunnel "footprint," which was designed so that the magnetic arcs could accommodate an electron beam of up to 24 GeV.
The latent voltage of the installed superconducting cavities has brought CEBAF's accelerating performance to nearly 6 GeV and superconducting radiofrequency (SRF) development successes have led to two cryomodules that are a factor of two more powerful than the original design. A cryomodule development program has yielded a final design that exceeds the original design specification by a factor of five. The cryomodules to be used for the 12 GeV Upgrade use higher performing seven cell cavities while maintaining the overall length of the original cryomodule design. Using space already available in the accelerator tunnels, 10 final design higher performance cryomodules will be installed at a modest cost.
The new experimental Hall D will use the electron beam to produce a coherent bremsstrahlung beam and house a solenoid detector to carry out a program in gluonic spectroscopy to experimentally test current understanding of quark confinement. All three existing halls will be upgraded to receive the new Five-pass, 11 GeV beam. The additional experimental equipment proposed for Halls A, B and C take full advantage of currently installed apparatus.
Accelerator
The accelerator portion of the upgrade will be constructed on the framework of the existing CEBAF accelerator. A 12 GeV beam to Hall D and up to an 11 GeV beam is needed for Halls A, B, and C. To achieve this, the accelerator will be upgraded to 2.2 GeV/pass (1.1 GeV/linac) and the beam transport system upgraded and expanded. These upgrades will be made:
- Ten new higher-voltage cryomodules, i.e., superconducting radio-frequency (SRF) accelerating elements (five per Linac).
- Ten new RF stations to power the 10 new cryomodules.
- Approximately double the refrigeration capacity.
- Modifications to the magnets in the recirculation arcs and their power supplies to keep the higher energy beam confined to the existing beam path.
- Modifications to the extraction system to support the higher energy beams.
- A tenth arc-beamline to provide an extra pass through the North Linac. This additional acceleration pass will bring the beam up to the 12 GeV required to accommodate the experimental program in the new hall (Hall D).
- A new beamline connecting Hall D to the baseline accelerator.
The beam transport system will carry 12 GeV beam to Hall D as well as beam at energies up to 11 GeV to Halls A, B, and C. The choreography required to accomplish these tasks is complicated and will require increasing the strength of the bending and focusing magnets. Modifications to the system of magnets, which separates the beams into their proper paths through the recirculation arcs and them recombines them for the pass through the acceleration sections, also will be completed.
Technical Scope for Experimental Equipment
Technical scope for the experimental equipment is described in the following Design Solution Documents (DSDs):
Hall D
 Architect's rendering of Hall D complex
| The Hall D sub-project consists of building a new large acceptance detector for photon beam experiments located in a new experimental hall at the northeast corner of the CEBAF accelerator. |
Proposed Hall A, B, & C
Upgrades to the three existing halls include:
 Hall A - High Resolution Spectrometer (HRS) Pair, and specialized large installation experiments | Hall A - Upgrade the beamline to achieve the capability of delivering the maximum energy five-pass beam. Continued use with existing spectrometer pair and for special set-up experiments. |
 CLAS12 - CLAS upgraded to higher (1035) luminosity and coverage | Hall B - Upgrade the existing CLAS detector with new magnets and detectors to capture the more forward-focused reaction products at the increased luminosity. |
 Super High Momentum Spectrometer (SHMS) at high luminosity and forward angles | Hall C - Install a new spectrometer system called the Super High Momentum Spectrometer or SHMS (central momentum up to 11 GeV/c) enabling measurements of particles scattered at up to full beam momentum. This will be used together with the existing High Momentum Spectrometer (HMS). |
Civil Construction
The Civil Construction subproject consists of modifications to existing buildings and utility systems to support the 12 GeV accelerator operations, an addition to the Central Helium Liquefier (CHL), including substations and cooling towers, and construction of a new experimental hall (Hall D) complex with utilities. The majority of the conventional facilities to support the 12 GeV accelerator operations are the utility upgrades of low-conductivity water (LCW) and power. The existing CHL Building will be expanded to house compressors for CHL #2. The mechanical and electrical systems serving CHL #2 will be similar to the existing system serving CHL #1. The Hall D complex consists of an experimental hall to house GlueX experimental equipment, an extension of the tunnel to house the new beam transport line and tagger magnet, a counting house, tagger building, beam dumps, cryogenics plant and service buildings. Utilities include water, sewer, electricity, telecommunications, chilled water, LCW and cryogenic distribution.
