UW builds largest hardware in history to explore small world

A massive, exotic device, part of a larger machine called a particle detector, is about to take shape in the basement of the UW physics-astronomy building. It will be the largest single piece of apparatus assembled in the University's history.

The six-story-high device, designed by the UW's mechanical engineering and physics departments, is being built as part of an international collaboration to assemble the world's most powerful atom smasher at the European Laboratory for Particle Physics (CERN) in Switzerland. The United States has pledged $531 million in components and services for construction of the accelerator, called the Large Hadron Collider (LHC), and its two particle detectors.

The $6 billion atom smasher, due for completion in 2005, is designed to reveal the basic constituents of matter, as well as answer esoteric questions about the origin of mass.

The UW's role is a good deal more modest, costing a mere $3.5 million. But the research and assembly are every bit as complicated as the rest of the project. "The pure size of this dwarfs anything we have done before," says Henry Lubatti, UW professor of physics and the University's liaison with CERN. "In terms of physics experimental apparatus, this is one of the most challenging detectors I have been involved with."

The UW apparatus is just part of a massive, cylinder-shaped particle detector called Atlas, one of the two devices within the atom smasher whose role will be to detect the particle debris from the giant machine itself. The LHC is designed to whirl elementary particles such as protons (a group collectively known as hadrons) around a 16-mile-circumference ring. When the particles collide, the two detectors will track the results.

The UW and three other U.S. institutions will be building two cone-shaped sections of Atlas that will detect particles called muons ejected from the hadron collisions. Among these muons might be a particle whose existence is only conjectured: the Higgs boson. The discovery of the Higgs boson, says Lubatti, is the Holy Grail of modern particle physics because it is theorized to be the particle that confers mass. If its existence can be proven, he says, it will usher in a new era of physics.

The muon detector consists largely of aluminum tubes, each with a hair-thin gold-plated tungsten wire at the center. The tubes, ranging from 3 to 18 feet in length, are filled with pressurized gas. Each tube must measure the position of any muons passing through by a three-thousandths of an inch. Atlas will contain 370,000 such tubes, 120,000 of them built in the United States, including the 27,000 to be fabricated at the UW.

The UW team will glue hundreds of tubes into a trapezoidal shape (four sides, only two of them parallel) to form a chamber. In all, the team will assemble 80 such chambers, each six feet wide by 3 to 18 feet long. The challenge, says Lubatti, is not only to build something on an industrial scale, but to do so with a precision that is rarely achieved in industry.

This bravura performance in engineering is the brainchild of Colin Daly, UW professor of mechanical engineering, who first came up with the chamber design for the Superconducting Super Collider project in Texas that was canceled by the national government in 1993. Much of Daly's design was then adopted by CERN for the Atlas detector. Part of the problem, says Daly, has been to find a way of building chambers using tubes with walls only about one-hundredth of an inch thick, but which are also strong and rigid. "Physicists would prefer that these chambers have no material at all because it only scatters the particles," he says.

The UW is providing space and equipment for the project, which is being funded from an $80 million National Science Foundation grant — part of the U.S. contribution of $250 million to the two CERN detectors. A prototype of one chamber has already been built and shipped to Europe, and a dust-free clean room has been erected in the physics-astronomy department machine shop. Production tooling will be completed this year, and construction will begin in 1999.

At least 20 researchers and scores of students will be involved in the project before the completed machine is shipped to Europe in 2004. Many doctoral dissertations will emerge from this, says Lubatti.

But the big machine already has served as an interdisciplinary teaching tool. Several physics undergraduates have designed and tested parts of the assembly apparatus. And a senior design class in mechanical engineering built and tested a glue-dispensing system for the assembly of the chambers.

Images of the UW apparatus and of the Atlas detector can be found on the World WideWeb at http://www.washington.edu/newsroom/news/images/

Atlaspic.pdf shows a cross-section of the completed Atlas particle detector.

US_assy.tif and us_assy.pdf show the muon detector that the UW is helping to build. ¶

David Brand, News and Information