Thomas Jefferson National Accelerator Facility
The Thomas Jefferson National Accelerator Facility (Jefferson Lab) in Newport
News, Virginia, is centered on the Continuous Electron Beam Accelerator
Facility (CEBAF), a 4 GeV continuous wave superconducting recirculating
electron accelerator. It is the world's pioneering large-scale application
of superconducting radio frequency (SRF) technology.
Jefferson Lab's secondary mission, conducted with industry and the
U.S. Navy, is the development of SRF driven high-average-power, wavelength-tunable
free electron lasers (FELs).
Jefferson Lab also reaches out to help increase science literacy in
education programs for students and teachers from elementary schools, middle
schools, and high schools.
The CEBAF Accelerator at Jefferson Lab
The scientific purpose of the CEBAF accelerator is the study of the quark
structure of nuclei. The experiments require electron beams with a unique
combination of characteristics:
High energy, for access to the transition region between the hadron-meson
description of nuclear matter and the quark-gluon description.
High current, for precise measurement of relatively small electromagnetic
High duty factor, for coinciding observation of both the scattered electron
and the nuclear fragments from a given interaction.
High beam quality, for high resolution.
|The simplest accelerator design approach would be simply a single linear
accelerator (linac) of sufficient length to reach the needed 4 GeV energy.
At the 5 NW/m accelerating gradient of CEBAF's SRF cavities, this would
require a linac 800 m long with a prohibitively large cost. Therefore CEBAF's
beam is cycled five times through a pair of antiparallel linacs connected
by recirculation arcs. This approach is made possible by the fact that
electrons move at very nearly the speed of light at quite modest energies.
At only 50 MeV, for instance, the electron velocity is 0.99995c. Once fully
relativistic, an electron's velocity is essentially independent of energy.
Thus beams at different energies can pass together through the linacs,
all maintaining the proper phase relative to the RF field.
||In this five-pass system, five electron beams at five different energies
are simultaneously present in either linac. Each recirculation path - five
at one end of the "racetrack" configuration, and four at the other - is
tuned to accommodate a different energy. The recirculation arc transport
lines are achromatic and isochronous, provide matching in all phase space
coordinates, and have adequate bend radii and strong focusing to minimize
quantum excitation to preserve beam quality.
|Beams are extracted from the accelerator for simultaneous use in three
experimental halls. The three halls house various kinds of spectrometers
to analyze nuclear reaction, covering both the need for high resolution
as well as the need to capture as many of the reaction products as possible.
||The accelerator's 1497 MHz, five-cell superconducting niobium cavities
were originally developed at Cornell University and later adopted for CEBAF.
A waveguide at one end acts as the fundamental RF power input coupler and
as a coupler for extracting some of the higher- order modes generated by
the beam current; at the other end of the cavity, two waveguides perpendicular
to each other and to the beam axis serve as couplers to extract higher-order
modes. The cavities are linked as pairs for operation at 2 Kelvin inside
liquid helium cryostats called cryounits. Four cryounits make up the accelerator's
basic operating unit, the cryomodule. Forty cryomodules with a total of
320 cavities make up the accelerator.
Free Electron Laser Development at Jefferson Lab
Another program at TJNAF is to develop powerful, multipurpose free- electron
lasers (FELs) based on the laboratory's SRF technology. A construction
program is underway in collaboration with the Laser Processing Consortium
(LPC), a growing partnership of high technology manufacturers, start-up
companies, research universities, government, and the U.S. Navy. Under
construction are the first in a planned series of Jefferson Lab FELs and
a user facility for developing FELs and applications. The initial FEL is
to be a highly efficient, kilowatt-level infrared device, the IR Demo FEL.
The machine will constitute a source of intense picosecond infrared light
pulses. It will be used to investigate both the propagation of these pulses
through the atmosphere and the physics of their interaction with solids.
Jefferson Lab has also designed a kilowatt-level ultraviolet (UV) FEL
based on SRF technology. Full scale, cost effective industrial applications
require a 100kW level UV FEL. The LPC has formulated a phased development
plan, starting with the kilowatt machine in Phase 1, and culminating with
a full scale prototype in Phase 2. Examples of applications include modification
of polymer film, fiber, and composite surfaces, the processing of metal
surfaces and electronic materials, the micro machining or surface finishing
of metals, ceramics, semiconductors, and polymers, the evaluation of materials
nondestructively, and the monitoring of manufacturing processes.
Brookhaven National Laboratory -
The Relativistic Heavy Ion Collider
Under normal conditions, quarks and gluons are confined within protons
and neutrons; it is impossible to find a "free and unattached" quark or
gluon. However, theory predicts that at very high temperatures and pressures,
quarks and gluons will be free to move independently over relatively large
distances, forming a "quark-gluon plasma."
||Creating a quark-gluon plasma is the goal of another new facility,
the Relativistic Heavy Ion Collider (RHIC), scheduled to open at Brookhaven
National Laboratory in 1999. The quark-gluon plasma may exist in the core
of neutron stars, and it may have existed during the first millionth of
a second after the Big Bang. But on earth, it represents a new state of
matter. RHIC presents the opportunity to study matter in an unknown regime.
Creating a quark-gluon plasma in the laboratory is one of the outstanding
challenges of modern physics.
|RHIC will accelerate nuclei in two concentric beams heading in opposite
directions. The beams will collide in six chambers. Each head-on collision
will produce a small region of enormous energy density where the quark-gluon
plasma may form. These experiments will require new detectors to record
and analyze the collisions. Lawrence Berkeley Laboratory is developing
new silicon detectors based on a technology which offers lower costs and
higher yields. RHIC's detectors, like CEBAF's cavities, are examples of
new technologies developed for basic research which quickly finds industrial