| The nation's largest scientific project, the Spallation Neutron Source, will be built at ORNL by a partnership of six DOE national labs. The world's most powerful pulsed neutron source is expected to begin operation in June 2006. |
On top of a ridge between ORNL and
the Oak Ridge Y-12 Plant, the largest civilian construction project in the United States is under way. Trees are being cleared from the construction site on Chestnut Ridge, and a one-mile-long access road connecting the ridge with Bear Creek Road is being built for hauling building materials and equipment to the site.
 |
|
Artist’s
conception of the central laboratory and office complex of the
SNS to be built on the Chestnut Ridge site in two years.
|
By 2002 a central laboratory and office complex
will be built on the site to house some 300 design, construction, and
project management staff for the $1.4 billion Spallation Neutron Source
(SNS). The SNS is the nation's largest science project and the most
recent big-science facility project sponsored by the Department of Energy's
Office of Science. By June 2006 the SNS will be a magnet for scientists
from many nations because it will be the most advanced, powerful pulsed
neutron source in the world. Researchers will use SNS neutron beams
for neutron-scattering experiments to help them better understand the
structure and properties of physical and biological materials, ranging
from polymers to proteins.
"The SNS will be an extraordinary tool for exploring matter and for enabling world-class science," says David Moncton, executive director of
the SNS. "Information obtained from this accelerator-based facility could lead to advanced materials and products such as faster electronic devices, lubricants for more efficient cars, longer-lasting artificial joints, and more effective drugs."
The facility will include an ion source, a linear accelerator to speed up the ions, an accumulator ring to compress protons separated from the ions, a liquid mercury target for the protons, and beam lines to carry neutrons produced in the target to experimental samples that will be measured by scientific instruments. The design and construction of the SNS will be the product of a partnership among six of DOE's national laboratories with help from the principal architect-engineer and construction manager Knight Jacobs and other industry support. In addition to ORNL, the DOE teams come from Argonne (ANL), Brookhaven (BNL), Jefferson (Thomas Jefferson National Accelerator Facility), Lawrence Berkeley (LBNL), and Los Alamos (LANL) national laboratories.
Completion of the project will depend on the
continued support of the President and Congress. To get it built on
schedule, the SNS Project is counting on receiving the $281 million
proposed in the President's budget for FY 2001. DOE plans to ask for
$291.4 million for FY 2002, $224.5 million for FY 2003, $143 million
for FY 2004, $112.9 million for FY 2005, and $75 million for FY 2006
to complete the facility. Construction of the SNS will provide jobs
for up to 600 construction workers over the next six years, and when
operational, the SNS will employ 300 to 400 scientists and other personnel.
1999 Highlights
The high point for the project in 1999 was what Moncton
called the "sweet moment" for the SNS: the December 15, 1999, groundbreaking
ceremony at the SNS site. Attending and speaking at this event were
Vice President Al Gore, Secretary of Energy Bill Richardson, Governor
Don Sundquist and U.S. Senator Bill Frist of Tennessee, and members
of the Tennessee congressional delegation. Also present was Clifford
Shull, who won the Nobel Prize in physics in 1994 for his pioneering
research at ORNL in neutron scattering. Other honored guests included
Martha Krebs, retiring director of DOE's Office of Science, who provided
direction and helped muster congressional support for the project, and
Bill Appleton, then deputy director of science and technology at ORNL,
who steered the project through its first few years.
 |
|
Vice President Al Gore and outgoing Office of Science Director Martha Krebs posed after the groundbreaking with directors of five of the six national laboratories participating in the SNS partnership: From left: Charles Shank of LBNL; Krebs; John Browne of LANL; Gore; Yoon Chang, ANL’s interim director; Denis McWhan, who represented BNL’s John Marburger; and Al Trivelpiece, then ORNL director.
|
"The true beauty
of the SNS," said Gore, "is that no one can really know what this tool
will be capable of discovering. It will bring discoveries that nobody
can predict. . . We're putting America on the path of reclaiming our
leadership in the neutron scattering technology that we invented here
in the United States of America."
In the past year or so, DOE and the
SNS Project have taken many steps to move the project forward. The project's
technical, schedule, and cost baselines have been established. Cost
estimates have been scrubbed, thus making it possible to double the
budget for neutron scattering instruments.
Geotechnical investigation
and qualification of the Chestnut Ridge were completed satisfactorily;
this determination was made by a team that drilled for core samples,
characterized the bedrock, assessed the site's seismic potential, and
studied the area's historical record of waste disposal and other activities.
The final environmental impact statement was approved and a Record of
Decision was issued by the Secretary of Energy, formally establishing
Oak Ridge as the SNS site.
Actions to mitigate environmental impacts
are under way, including the installation of a new air-monitoring tower
for the Oak Ridge office of the National Oceanic and Atmospheric Administration
(NOAA). The current NOAA tower in the Walker Branch Watershed, which
is close to the SNS site, monitors dry deposition of airborne pollutants.
These measurements could be affected by airborne dust stirred up by
SNS construction. During operation, the SNS facility will emit carbon
dioxide, water vapor, and heat, which NOAA likely will monitor for its
studies related to global climate change. The new tower will be located
far enough away from the SNS so that the facility's emissions will not
interfere with NOAA measurements.
 |
|
David Moncton, executive director of the SNS, calls the groundbreaking ceremony a "sweet moment" for the SNS.
|
The SNS Project successfully met several
management challenges presented by DOE and Congress. Moncton, director
of the Advanced Photon Source at ANL, was named executive director for
the SNS. In late January 2000, Tennessee Governor Sundquist signed a
bill passed unanimously by the General Assembly that exempts the SNS
Project from $28 million in state sales and use taxes, lowering the
overall cost of the project.
Improving the Neutron End
Many ORNL researchers involved with the SNS
Project are concerned with the "neutron end" of the machine.
Some of those researchers are working on the design of the mercury target
from which neutrons will be produced. Others are developing scientific
instruments that will be used to measure the energies and angles of
neutrons scattered from targets of interest.
One of the most significant
technical achievements in 1999 was the completion and operation of the
Target Test Facility (TTF) at ORNL. The TTF is a full-scale mercury
loop in ORNL's Robotics and Process Systems Division. It has been operating
with mercury since October 1999. Research at the TTF and other, smaller
mercury loops under the leadership of Tony Gabriel is aimed at answering
several questions: Which candidate materials for the target container
are the most compatible with mercury? How can the target be designed
to shield workers from the radioactivity of the proton-bombarded mercury?
Can remotely operated equipment be used to safely and reliably repair
and replace target components in hot cells? How can the output of neutrons
be maximized for research?
"Based on what we have learned from test
operations at the TTF, we are improving the design before sending it
to vendors who may want to bid on building the target," says Thom Mason,
director of the Experimental Facilities Division of the SNS. "We will
do hydraulic testing with water to simulate mercury flow. We will measure
the ability of mercury to remove heat from the stainless-steel container.
"Experiments on the effects of accelerator beams on mercury targets
are being done at Brookhaven and Los Alamos. We have studied stresses
that have developed in mercury targets bombarded by proton beams. Based
on the information we’ve obtained, we’ve concluded that mercury is the
right choice for the target."
Because of the enormous power the 1-billion-electron-volt
proton beam will deposit in the target, it was decided to use a liquid
mercury target instead of a solid material such as tantalum or tungsten.
The SNS will be the first scientific facility to use mercury as a target
for a proton beam.
"We have been improving the target design by integrating
the target group led by Tony Gabriel with the instrumentation design
group led by Kent Crawford at Argonne," Mason says. "As a result of
our R&D and preliminary design, we have made a number of improvements
in the target, which will increase the scientific performance of the
SNS for experimenters. We have adopted a more flexible shutter geometry,
allowing us to install 24 instead of only 18 instruments, an increase
of 33%."
According to Mason, fine-tuning moderator characteristics will
significantly enhance many applications because it will allow a higher-intensity
neutron beam to be produced in a temperature range of 100 K. This improvement
is achieved by changing the composition of a moderator below the target
by making it a composite of supercritical light hydrogen and light water.
The SNS will also have two cryogenic moderators above the target. Moderators
slow down the neutrons leaving the mercury target to an appropriate
energy range before they enter the beam lines that deliver neutrons
to the instruments.
"We also changed the composition of the reflector,
which bounces neutrons straying from the target back into the moderators,"
Mason says. "Instead of lead only, the reflector will be made of a composite
of lead and beryllium. As a result of this change, we will get sharper
neutron pulses, enabling higher-resolution measurements."
Taking the Users' Pulse
Mason represents the interests of the scientific community
in ensuring that the overall project meets the requirements of the academic,
industrial, and government research communities. He has organized workshops
to ensure good communication among the users and the six DOE national
laboratories participating in the design and construction of the technical
portions of the SNS facility. The SNS Project has also appointed a user
administrator, Joyce Shepherd, who will build up a group to work with
users to ensure that the SNS Project is responsive to their needs.
"Many
neutron sources were originally designed for some other purpose such
as radioisotope production, so the idea of doing neutron scattering
research at these sources was an afterthought," Mason observes. "The
SNS partnership offers the opportunity to design a neutron source specifically
optimized to meet the needs of the scientific users."
How are ORNL researchers
involved in the design of neutron science instruments to be built at
the SNS? "Some ORNL researchers are working at Argonne with Kent Crawford
to design new instruments," Mason says. "Potential users of the SNS
can influence the design of new instruments by joining instrument advisory
teams, or IATs. Research groups that can get their own funding from
sponsors to develop neutron instruments can form instrument development
teams, or IDTs. Groups at ORNL and BNL, as well as those in Denmark
and Germany, have expressed interest in forming IDTs. An IDT will get
dedicated beam time for its scientific program in return for its contribution
toward the construction and operation of the instrument."
Several groups
at ORNL have expressed interest in writing proposals to get funding
for instruments and for experiments to be performed at the new facility.
In the Physics Division, there is interest in pursuing fundamental physics
studies with cold neutrons and in making measurements of interest to
the astrophysics and nuclear structure communities. DOE's new Center
for Structural and Molecular Biology at ORNL plans to seek funding for
a neutron-scattering instrument to study the structure of biological
molecules. And a group in the Metals and Ceramics (M&C) Division is
working with the SNS Experimental Facilities Division and outside researchers
to prepare the scientific case for and define the essential characteristics
of a neutron diffractometer to study residual stress in engineering
materials.
The Ion End of the Machine
The SNS design calls for an accelerator
system consisting of an ion source being developed at LBNL, a full-power
linear accelerator being developed by LANL and the Jefferson Lab, and
a proton accumulator ring being developed at BNL that will deliver a
2-megawatt (MW) beam to the mercury target (being developed at ORNL).
The facility has been designed with the flexibility to provide additional
scientific output in the future.
A prototype negative hydrogen (H-) source
has already been tested at 45 milliamperes (mA). It will be developed
further to achieve the 70 mA needed to support 2-MW operation. The ion
beam will be delivered to a linear accelerator that will use radiofrequency
radiation and magnetic fields to accelerate, focus, and steer the ion
beam toward the accumulator ring. The decision to use superconducting
technology to power the accelerator will reduce its footprint from five
to three football fields in length. In this design, the beam is injected
into the ring through a foil that strips the two electrons off each
negatively charged hydrogen ion, making each one a proton. The protons
circulate in the ring about 1000 times before being extracted as a pulse
of less than 1 microsecond for delivery to the liquid mercury target.
Nurturing the Six-Lab Partnership
 |
|
Each
of the participating DOE national laboratories in the six-lab
SNS partnership is responsible for an important component of the
accelerator-based neutron source. Rendering by John Jordan.
|
The large-scale, six-lab partnership needed
to design and build the SNS is unique in DOE history. What must be done
to ensure that the six national lab partners work together successfully
on the design and construction of the SNS?
"The keys to making this
partnership work," says Carl Strawbridge, administrative director of
the SNS, "are the commitment of the six lab directors in the partnership;
various tools such as the interlaboratory Memorandum of Agreement; and
a strong, experienced SNS management team working with the DOE project
team."
What must be done to ensure congressional funding and support
for the SNS partnership over the next seven years? "We are fortunate
that no one in the scientific community and the political system questions
the scientific need for the SNS," Mason says. "The materials science
applications of the SNS are seen as important by everyone. We recently
enjoyed endorsements from the National Academy of Sciences' Solid State
Sciences Committee and the American Physical Society Council.
"It is
important that potential users of the SNS all over the nation speak
or write to their congressional representatives about the need for support
for the SNS. It is crucial that we get the appropriation of $281 million
for the next fiscal year so we can begin procuring accelerator components
and initiate significant construction activities onsite. We hope we
can continue to enjoy strong support for this national project."
Now
that construction of the SNS has begun on top of the ridge, SNS supporters
have even higher hopes for the project.
Beginning
of Article
