Six national laboratories joined hands to design and build one of the world's most complex facilities.
At 2:04 p.m. on April 28, 2006, an operator tapped a key stroke that for the first time produced neutrons at the Spallation Neutron Source. With this seemingly simple procedure, Oak Ridge began the journey to become the world's foremost center for neutron science. More important, the event reasserted American leadership in a field that for two decades had been conceded to the European scientific community. The unique partnership that led to this historic milestone is a critical chapter in the SNS story.
The Spallation Neutron Source could not have been built at Oak Ridge National Laboratory without an unprecedented level of collaboration with five Department of Energy national laboratory partners. Quite simply, no American laboratory, including ORNL, possessed the depth of expertise required to design an accelerator-based facility on the scale of the SNS. The solution lay in fashioning a partnership that in effect brought together the capabilities of the entire DOE laboratory system. What the DOE system lacked in talent and equipment would be recruited from around the world.
Six DOE laboratories—Argonne, Brookhaven, Jefferson, Lawrence Berkeley, Los Alamos, and Oak Ridge—composed the partnership to design and construct the SNS. The collaboration, one of the largest of its kind in U.S. scientific history, was an extraordinary collection of talent and experience from a variety of scientific fields. The collaboration was supplemented by additional partners from France, Germany, Great Britain, Japan, and Russia.
The breadth of the partnership was unprecedented. By their very nature, national laboratories are independent institutions that at times compete ferociously for limited research funding. Managed by various combinations of universities, corporations and not-for-profit research institutions, the laboratories represent a myriad of missions, personalities and operational cultures. As policymakers debated the viability of designing the SNS with such a diverse group, many doubted that the parties would even agree on their respective tasks. Against the backdrop of previous experience, the notion that the laboratories could deliver one of the largest and most complex science projects in history on time and on budget defied believability.
The first major challenge for the SNS was political. A commitment of $1.4 billion to the SNS meant that a number of DOE capital projects at other laboratories would need to be deferred, which in turn would lessen political enthusiasm for the SNS among the respective congressional delegations. The problem was mitigated by the decision to include five additional laboratories as a substantial part of the SNS project in Oak Ridge. Their role was not trivial in either scientific or financial terms. As a result of this strategy, the SNS gained congressional support it might not otherwise have enjoyed during the project's crucial early years.
The Sum of the Parts
Spanning the length of seven football fields, the SNS is a scientific tool of enormous size and complexity that accelerates ions and then protons to blazing speeds to produce neutrons for research. At one end is an ion source. At the other end are research instruments on neutron beam lines. In between are 100,000 interdependent control nodes designed by six laboratories that must function perfectly.
The SNS begins with the "Front End," built by Lawrence Berkeley Laboratory. Negatively charged hydrogen (H-) ions are produced in an ion source. Each ion consists of a proton orbited by two electrons. The ions are accelerated to an energy of 2.5 million electron volts (MeV) and then delivered to a linear accelerator.
Los Alamos National Laboratory designed the drift tube linac and the coupled-cavity linac, which are made of copper, operate at room temperature, and accelerate the ion beam to about 200 MeV. They were also responsible for the radiofrequency power systems that provide the accelerating energy for the whole linac.
The bulk of the ion acceleration is achieved in a super-conducting linac developed by Thomas Jefferson National Accelerator Facility. High-frequency radio waves generated by klystrons are injected into the superconducting cavities embedded in liquid helium, creating an electric field that provides the energy to propel the ions by a factor of 5 to 90% of the speed of light. This velocity corresponds to an energy of one billion electron volts (1 GeV). The SNS today has the world's highest-energy—and soon will have the most powerful—pulsed H- ion linear accelerator.
The ions are passed through thin carbon foils, which strip off each ion's two electrons, converting it to a proton. A 250 km long train of protons is collected in 1060 turns around the ring for a total of 150 trillion accelerated protons in a single, very intense bunch that is kicked out at once. In this way, an intense proton pulse less than a millionth of a second in duration (700 billionths of a second) is produced. The accumulator ring, which was designed and built by Brookhaven National Laboratory, produces, stores, and extracts short, intense proton pulses that strike the target 60 times per second.
ORNL designed and built the heavy-metal target, which consists of liquid mercury circulating in a stainless-steel container. The SNS accelerator systems deliver a proton beam with a power of 1.4 million watts to the target.
When a high-energy proton bombards a heavy atomic nucleus, such as mercury, some neutrons are "spalled," or knocked out, in a nuclear reaction called spallation. Other neutrons are "boiled off" as the bombarded nucleus heats up. The process is similar to a pitching machine that repeatedly throws a baseball at a bucket of baseballs, resulting in a few being immediately ejected and many more bouncing around and falling out. For every proton striking the nucleus, 20 to 30 neutrons are expelled.
Corresponding pulses of neutrons freed by the spallation process are slowed down in one of four ORNL-built moderators filled with water or liquid hydrogen. The neutrons are then guided through beam lines to research areas containing special instruments. Once there, neutrons of different energies can be used in a wide variety of experiments. Argonne National Laboratory and ORNL had joint responsibility for developing the beam lines and instruments.
Resembling a flashing strobe light providing high-speed illumination of an object, the SNS will produce pulses of neutrons every 17 milliseconds, with at least 10 times more neutrons than are produced at the most powerful pulsed neutron sources currently available. Much like water spraying from a rock being washed by an intense stream from a garden hose, neutrons from a beam will "scatter" from a target material in a way that reveals its structure and microscopic origins of physical, electrical, magnetic, chemical, and biological properties. Some 2000 scientists each year will come to Oak Ridge to perform experiments with these powerful neutron pulses.
A Successful Collaboration
"The value of the multilab partnership is most apparent in the accelerator division," says Norbert Holtkamp, an accelerator physicist who previously worked at DOE's Fermi National Accelerator Laboratory and DESY laboratory in Hamburg, Germany. Holtkamp came to ORNL because of the "technical challenges of SNS and the multilab partnership." He points out that four national labs were involved in designing and building the accelerator. "The multilab partnership approach is the right way to build large, complex science facilities, and, surprising to some, it is a better, more efficient way of managing resources. My role in managing the multilab partnership ranged from developing and maintaining expertise to bringing in and phasing out manpower. The facts speak for themselves. The collaboration was a success."
Holtkamp had primary responsibility for the design and construction of the ion source, linear accelerator, and accumulator ring. At the peak of construction of these SNS subsystems, the Accelerator Systems Division had 550 employees. By January 2006, all of these subsystems had been commissioned and were ready for operation. Meanwhile division payroll had ramped down to 180 people.
"But we didn't have to fire 370 people," Holtkamp stresses. "They worked for SNS as employees from six different national labs. When their work for SNS was completed, they returned to their jobs at their home labs. For a large and complex project, the multilab partnership is a much better way to maintain the expertise needed to design and build a facility than the conventional approach of hiring and then laying off large numbers of people."
An SNS colleague used to joke that a properly managed multilaboratory partnership would result in "equal distribution of pain," a phrase that Holtkamp likes.
"Equal distribution of pain also means that everybody has to come out of this project as a winner," Holtkamp asserts. "We felt it important to manage the project so people are recognized for their scientific credentials and feel they are appreciated for the subsystems they built here. They should share the success."
The project's scientific quality was apparent even before the SNS was completed. Staff members of the Accelerator Systems Division published hundreds of papers in conference proceedings and scientific journals. The project has also generated patents.
"The SNS from the beginning was designed to be upgraded to double the available beam power and, therefore, the number of neutrons," he says. "That DOE authorized the power upgrade before construction of SNS was complete is a tribute to the success of the project."
Ready to Lead the World
A little more than six years after the frigid December morning when Vice President Al Gore turned the first shovel of dirt in the middle of the woods on Chestnut Ridge, the SNS is a reality. Built on time, on budget and on scope under the supervision of UT-Battelle and the Department of Energy, the SNS is a vindication of the belief that the U.S. government is still capable of delivering the kind of large scale projects that have marked the nation's history.
The SNS was perhaps the most international project ever undertaken. Engineers and scientists joined the SNS Oak Ridge team from 23 states and 15 countries. More than 680 managers, scientific and technical, administrative, and engineering staff worked on the SNS at six locations. An estimated 500 engineers representing all disciplines – chemical, civil, computer, construction, electrical, mechanical, and nuclear—designed, installed, and tested the SNS systems and components. The work force peaked at about 1,300 in November 2002, and included more than 3,800 employees over the seven-year span of the project.
To some of Oak Ridge's oldest residents, the SNS reminded them of the excitement and energy of the Manhattan Project 60 years earlier. During that marvelous period, hundreds of scientists from America and abroad were thrown together to build something many thought impossible. They succeeded, and in so doing established America's scientific leadership for the remainder of the 20th century. Their story has been repeated at the SNS, where once again America stands ready to lead the world.
Web site provided by Oak Ridge National Laboratory's Communications and External Relations