Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Jefferson Lab technology takes center stage in the construction of SNS accelerator

28.01.2003


Jefferson Lab is once again taking center stage, as Lab scientists, engineers and technicians mobilize to provide 81 niobium cavities for 23 cryomodules for the Spallation Neutron Source under construction in Oak Ridge, Tennessee



Thermos bottles usually don’t weigh nearly five tons or measure almost 26 feet end-to-end. But these aren’t run-of-the-mill containers for soup or coffee. Rather, they’re the complex, state-of-the-art supercooled components in which particle beams are accelerated for scientific research.

The Department of Energy’s Jefferson Lab technology is once again taking center stage, as Lab scientists, engineers and technicians mobilize to provide what eventually will be 81 niobium cavities for 23 cryomodules for a new federal laboratory, the Spallation Neutron Source, or SNS, under construction in Oak Ridge, Tennessee. JLab is part of a team of federal laboratories -- including Argonne, Brookhaven, Lawrence Berkeley, Los Alamos and Oak Ridge -- assisting in the design, engineering and construction of the $1 billion-plus SNS, which will provide the most intense pulsed-neutron beams in the world for scientific research and industrial development. JLab is located in Newport News, Virginia.


"We’re definitely world leaders in this kind of technology. We’ve been trailblazers," says Isidoro Campisi, senior scientist with JLab’s Institute for Superconducting Radio Frequency Science & Technology. "We’re helping to make another generation of machines become practical."

The Lab’s engineers and technicians are creating two types of cryomodules. One is known as the "medium ? (beta)," version with three cavities per module, and is thus shorter and lighter than its four-cavity "high ?" sibling. As at JLab, superconducting radiofrequency techniques and advanced cryomodule design are being incorporated within the SNS accelerator complex to enable low-cost, high-efficiency operation.

Because the speed (represented by the ? symbol) of the SNS’s negative hydrogen-ion beam will be slightly less than the electron beam in JLab’s accelerator, the internal structure of the cavities was slightly adjusted, or "graded," to match the reduced velocities. Therefore, the shape of SNS niobium cavities are flatter ellipses, more like oversized pancakes than their fatter CEBAF predecessors. The operating frequency of RF cavities is measured in cycles per second, given the name hertz to honor the 19th century German physicist Heinrich Hertz, who carried out numerous experiments to clarify the nature of electromagnetic radiation. Most RF cavities operate at very high frequencies, where the appropriate unit is millions of hertz, or megahertz (MHz). SNS cavities operate at 805 MHz, compared to 1497 MHz for CEBAF cavities.

Electromagnetic power is fed into the superconducting cavities via RF couplers. The SNS couplers have been designed to handle a much higher power level than the original CEBAF couplers and so provide a pulsed power -- SNS operates in pulses and not in a continuous wave as CEBAF does -- with a peak value of over 100 times that of the CEBAF couplers. Campisi was responsible for development of the high-power RF coupler required for the SNS modules. "For the first time, we’re making superconducting elliptical cavities not matched to the speed of light," he points out. "Everybody is pretty excited. We’ve been working hard to get to this point. We’re the youngest of the federal labs involved in the SNS project, so we’re happy that we can deliver on what we promised."

Prototype takes "test" road trip

In October, a prototype SNS cryomodule was taken on a road trip from Newport News to Virginia’s mountains near Charlottesville. Campisi says the sojourn was essential to test the modules’ many sensitive parts -- among them the "window" that allows for the introduction of radio waves, the vacuum seals between the inner cavity and the outer cryomodule, and the welds that hold everything together -- to withstand the inevitable insults of highway travel.

"All cryomodules made here will go by truck to Oak Ridge," he explains. "So we had to evaluate all the factors in that trip. What would happen when you go over bumps in the road, or if you stopped quickly or had to accelerate suddenly? We have to make sure all parts are working correctly before we dare put power in."

In most respects, the SNS cryomodules are virtually identical to their JLab cousins. The innermost components of the cryomodules’ three-part system includes the superconducting cavities, a cooling tank to hold the liquid helium, and a Thermos-bottle-like structure known as a cryostat that provides insulation -- allowing the cavities to remain cooled to two Kelvin, or nearly absolute zero. At such a temperature the surface currents associated with the introduced radio waves lose all electrical resistance, and provide acceleration with a power dissipation of less than a millionth of that used in energizing accelerators made of normally-conducting materials, such as copper.

At the SNS, four different linear accelerators, or linacs, will accelerate a beam of hydrogen ions to 1 billion electron volts, or 1 GeV. The first three accelerators, the Radio Frequency Quadrupole (RFQ), the drift-tube linac and the coupled-cavity linac, will be made from copper, operate at room temperature and accelerate the beam to 187 million electron volts. The fourth accelerator will make use of JLab cryomodules and accelerate the hydrogen-ion beam an additional 813 MeV. Sixty times per second, the accelerator will produce a one millisecond-long burst of hydrogen ions, a pulse that would stretch for about 270 kilometers (or 168 miles) if the beam were not intercepted. Instead, the beam is wrapped around a ring of magnets, called an accumulator ring, until the whole pulse has been captured in roughly 1,000 turns, like wire on a spool. Then, the opening of an electromagnetic gate allows all the accumulated ions to be delivered to the mercury target in a single microsecond-long pulse. The resultant short, sharp bursts of neutrons are what researchers will be using for their neutron-scattering investigations.

When the SNS facility is complete, researchers will be able to obtain detailed snapshots of material structure, and stop-action images of molecules in motion. Like a strobe light providing high-speed illumination of an object, the SNS will produce pulses of neutrons every 17 milliseconds, with more than 10 times more neutrons than are produced at the most powerful pulsed-neutron sources currently available. The neutrons will scatter from materials under study in such a way as to reveal that material’s subatomic structure and properties.

JLab’s first SNS cryomodule, the medium-beta prototype, passed its travel test and has been shipped to Oak Ridge. Other production models will follow, with the first tested perhaps as early as January 2003 and shipped the following month. SNS construction is slated to be complete by 2006.

By James Schultz

Linda Ware | EurekAlert!

More articles from Power and Electrical Engineering:

nachricht New creepy, crawly search and rescue robot developed at Ben-Gurion U
19.07.2018 | American Associates, Ben-Gurion University of the Negev

nachricht The role of Sodium for the Enhancement of Solar Cells
17.07.2018 | Max-Planck-Institut für Eisenforschung GmbH

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Global study of world's beaches shows threat to protected areas

19.07.2018 | Earth Sciences

New creepy, crawly search and rescue robot developed at Ben-Gurion U

19.07.2018 | Power and Electrical Engineering

Metal too 'gummy' to cut? Draw on it with a Sharpie or glue stick, science says

19.07.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>