status of thomas jefferson national accelerator facility (jefferson lab)

E ~ E ~ E R Nuclear Physics A623 (1997) 10c-15c

N U C L E A R PHYSICS A

Status of Thomas Jefferson National Accelerator Facility (Jefferson Lab)

Dr. Hermann A. Grunder Director Jefferson Lab, 12000 Jefferson Avenue, Newport News, Virginia, 23606

When first beam was delivered on target in July 1994, the Continuous Electron Beam Accelerator Facility (CEBAF), in Newport News, Virginia realized the return on years of planning and work to create a laboratory devoted to exploration of matter that interacts through the strong force, which holds the quarks inside the proton and binds protons and neutrons into the nucleus. Dedicated this year as the Thomas Jefferson National Accelerator Facility (Jefferson Lab), the completion of construction and beginning of its experimental program has culminated a process that began more than a decade ago with the convening of the Bromley Panel to look at research possibilities for such an electron accelerator.

I . W H Y N O W ?

Just as Quantum Mechanics and Coulomb's Law explained atoms as bound states of electrons and a nucleus, and molecules as bound states of atoms, it is Jefferson Lab's scientific goal to use the theory of Quantum Chromodynamics (QCD) to describe nucleons as bound states of quarks and gluons and nuclei as bound states of nucleons. This machine and its capabilities enables physicists to fill in what are some of the most glaring gaps in our understanding of nature. In the area of atomic physics it is our goal to understand the physical mechanisms and novel features in terms of known basic theory, and answer questions such as "Why do we have nucleons instead of a quark-gluon soup?", "What is the origin of the NN force", and "How do we explain the short distance degrees of freedom?". In the area of atomic physics we hope to probe the basic input to nuclear physics, to help understand the model of physics that has been created. In this area, we seek to understand concepts such as quark confinement, discover where is the glue, and why do we only see quarks in qqq and qq configuration?

What made the time right for a facility such as Jefferson Lab? A combination of key ingredients have come together including the theory of Quantum Chromodynamics, maturity of advanced accelerator technology, advancements in detector technology, and the capability for rapid data acquisition to make it possible for us to answer these questions.

When D. Allan Bromley and his committee met in 1983, they specified what the parameters of the beam for such a machine should be. They called for a machine with an

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energy of 4 GeV that could be upgraded to 6 GeV, a current of 200 I~A, energy spread of A F, JE < 10 -4, emittance of 2 x 10 -8 (geometric at 45 MeV), and a duty factor of 100%, creating a continuous wave accelerator. When paired with the appropriate experimental instrumentation, such a machine would provide a tool of unmatched capability for the world physics community. The Panel wrote as part of their report "We are faced with the tantalizing possibility that quantum chromodynamics (QCD) may provide the theoretical framework for the understanding of the strong nuclear interaction that quantum electrodynamics (QED) has so successfully provided for the purely electromagnetic interaction..."

Figure 1. Aerial view of the accelerator at the Thomas Jefferson National Accelerator Facility

2. M A C H I N E CONFIGURATION AND DESIGN

In planning what Jefferson Lab's accelerator would look like, there was thought given not only to what the physics community wanted now, but what they were likely to want in the future. What was needed was a continuous wave electron accelerator. However, that offered a number of challenges which had to be met. The first was controlling the power cost for such a machine and it was decided that that challenge was best met by utilizing superconducting radiofrequency (SRF) cavities. Though other more mature technologies existed that would allow the necessary specifications, SRF would allow "growth" in the capabilities of the machine since it was a technology at a promising beginning, not a successful end. The next hurdle was limiting the capital expense of such a machine, which was done by using beam recirculation. The final challenge was leaving some room for upgradabilty of the machine.

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This was done through the design of the arcs, with the limitation being synchrotron radiation and resulting degrading beam quality. Thus the CEBAF accelerator was born.

Table 1 Accelerator Requirements: Yesterday, Today and Tomorrow "

Yesterday Today (1995) (1997)

Tomorrow (2000)

Top Energy (GeV) 4

Polarization Non

Beam power 800 kW

Duty factor (DF) (%) 100

Ap/p - 104

4 t o 6 8to 10 possibly more

40% in 1 hall; working towards

80% in 3 halls

80% in 3 halls

800 kW 1 MW

100 declining DF >6 GeV

~10 "~ - 4 x 10 "~

Figure 2. Cryomodules in the south linac secion of the acclerator

The resulting system has 338 SRF cavities in 42 1/4 cryomodules with 340 klystrons in 43 HPAs. In the injector, three independent electron sources allow independent current, independent pulse sequence, and independent polarization to meet the needs of experimenters in each of the three experimental halls. In the extraction region, a single bunch periodic is possible on each recirculation due to rf separators. The entire system is cooled to 2.1K by a

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5000 W central helium liquifier that has been running at 98% availability. The instrumentation and control system has 100,000 i/o points and has been successfully migrated to EPICS, with Jefferson Lab being part of a strong EPICS collaboration. The beam transport system contains 2241 dipole quadrupole and correction magnets in the arcs served by 4.5 km of vacuum lines. Together these systems comprise an accelerator that affords both formidable challenges and rewards.

Numerous milestones and notable successes have marked the way towards the beginning of the scientific program at Jefferson Lab. The machine has performed remarkably well with its cavities performing above specs such that 1 GeV per pass (800 MeV specs) has already been achieved. Accelerator performance has been excellent with 3200 hours of beam delivered for physics at 70% availability. Preliminary data shows that the accelerator is stable enough for serious parity violation experiments.

The physics community has responded with enthusiasm. Currently, Jefferson Lab's user group has about 1100 members. As of PAC 10 1034 days of beam have been approved representing 80 experiments with 596 authors from 116 institutions in 23 countries ( and this is only 1/3 of the time requested!). Italian physicists are collaborators on 32 of the 80 approved experiments with strong participation in both Halls A and B. Jefferson Lab's Italian collaborators have made major contributions to the construction of experimental equipment, providing key parts of the basic equipment for the Cerenkov counter and the "waterfall" target and the septum project in Hall A which will allow us to launch a world-class program in hypemuclear physics. In Hall B, they have contributed to the large angle calorimeters which substantially extend the range of momentum transfer available to electron scattering experiments with the CEBAF Large Angle Spectrometer (CLAS) and facilitates other important measurements. The Jefferson Lab Theory Group has published about 50 papers in the last two years spanning nuclear structure to perturbative QCD, with two papers by DR. Nathan Isgur in the "top ten citations" in nuclear and particle physics. The quality of the initial data taken in hall C has been at or above expectations illustrating that modem detector technology is leveraging the unique capabilities of this machine. The approved experiments reflect these capabilities and are shown in Table 2

Table 2 Totals of Approved Experiments by Physics Topic for Program Advisory Committees (PACs) 4-10

Topic Number

Nucleon and Meson Form Factors and Sum Rules 10 Properties of Nuclei 31 N* and Meson Properties 25 Strange Quarks 14 TOTAL 80

Jefferson Lab offers its user community three experimental halls which can run experiments simultaneously, with complementary capabilities and equipment. Hall C, the first to come on-line is equipped with a High Momentum Spectrometer (HMS) which has a large solid angle, a moderate resolution (10 -3) and a maximum acceptance of 7 GeV/c. The Short Orbit Spectrometer (SOS) has a large momentum acceptance and a very short (7.4m)

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optical path for use in detecting particles having a short lifetime, such as low momentum Jt's and K's. Five experiments have already been completed with two more expected to be final by the end of the calendar year. At the beginning of 1997 the first major experiment installation will begin. Initial experiments include an investigation of the validity of the quark counting rules in the photodisintegration of the deuteron, measurements of the neutron electric form factor, and studies of kaon electro-production. Hall C is also the area envisioned for the installation of specialized detectors designed to investigate specific problems such as hypernuclear physics and parity violation.

Hall A, which has begun commissioning experiments is equipped with two optically identical high resolution (Ap/p = 104) magnetic spectrometers (HRS) having a relatively large solid angle and a maximum momentum of 4 GeV/c. The detector packages have been optimized differently; one for detecting electrons and one for detecting hadrons. The Hall A experimental program will conduct detailed investigations of the structure of nuclei, and look at the elastic, inelastic, weak structure of the nucleon, and the strange quark contributions to the charge and magnetization distributions of the nucleons to provide stringent tests for microscopic models of the nucleon.

tk

Figure 3. The CEBAF Large Acceptance Spectrometer in Hall B

Hall B, scheduled to begin operation in late 1996 (Note: In the time between the Daphne conference and time of publication, Hall B had received first beam) is equipped with a large acceptance detector (CEBAF Large Acceptance Spectrometer, CLAS), designed to carry out experiments which require the detection of several only loosely correlated particles in the hadronic final state, and measurements at limited luminosity. A major focus of the research program in Hall B is the investigation of the quark-gluon structure of the nucleon. The CLAS detector will also be used in a variety of other investigations requiring data on multiparticle final states. Commissioning of the CLAS will begin of March 1997, with first data expected in the summer of 1997.

3. LAB FUTURE PLANS AND OPPORTUNITIES

The highest priority at Jefferson Lab is to run the presently approved experimental program. Efforts are also underway to stretch the upper energy from 4 to 6 GeV for user

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experiments. The next focus will be to upgrade the energy of the machine into the 8-10 GeV region as recommended by a user workshop. This will be accomplished by adding additional cavities and upgrading the performance of those with lower gradients in an evolutionary way.

In addition to the capabilities provided to our world-class nuclear physics program, mastery of SRF technology has led to derivative missions as well. Jefferson Lab has been active in partnership with industry to apply its SRF technology for an accelerator driven free electron laser. There are industrial applications for a cost-effective, high average power sources of coherent infrared and ultraviolet light. These include primarily materials processing that will enable new and value-added products. Industrial partners have identified SRF technology as the quickest most cost-effective route to such a device for industrial processing, and thus an industry-driven alliance, the Laser Processing Consortium, was organized to develop, test and apply high average power FELs. The program plan has three phases; Phase 1 which is an IR demonstration at 1 kw in the 3-6 micron range, Phase 2 which will extend capabilities in the IR to the 1-6 micron range and Phase 3, which is a 1 kw laser in the UV. With funding from the Department of Defense and the Commonwealth of Virginia and support form the Department of Energy, the IR demo is now under construction with first light expected the first part of 1998.

As the nation's newest laboratory, Jefferson Lab has worked hard to become a center of scientific and academic excellence that benefits not only the nation's scientific community but the nation's economic competitiveness as well. With continued sound planning, excellent staffing, and cutting edge technology the phenomenal contributions that can come from such a facility will be realized.