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 Stretchable biofuel cells extract energy from sweat to power wearable devices
22.08.2017 | University of California - San Diego

nachricht Laser sensor LAH-G1 - optical distance sensors with measurement value display
15.08.2017 | WayCon Positionsmesstechnik 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: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

Cholesterol-lowering drugs may fight infectious disease

22.08.2017 | Health and Medicine

Meter-sized single-crystal graphene growth becomes possible

22.08.2017 | Materials Sciences

Repairing damaged hearts with self-healing heart cells

22.08.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>