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Engineering Physics

 

James Blanchard and Carl Martin

Professor James Blanchard and Carl Martin evaluated a design for an improved artificial lens. (large image)

The eyes have it:
Analysis improves artificial lens design

During cataract surgery, an ophthalmologist generally replaces a cloudy lens with an artificial one that — in theory — should help a patient see more clearly.

Made of plastic, acrylic or silicone and available in either flexible or rigid varieties, current artificial lenses aren’t designed to mimic natural lens function. Consequently, patients gain unobstructed vision but require glasses to help them focus on objects up close.

The lens design, shown in two halves

The lens design, shown in two halves. (large image)

The problem has bothered medical doctor Gerald Clarke for some time. Based in Appleton, Wisconsin, Clarke and colleagues own OptiVision Laser Centers and offer eye-care services, including LASIK vision-correction and cataract surgeries, in three Wisconsin cities.

About five years ago, Clarke developed a biomimetic artificial lens design, which takes into account the way eye muscles control lens curvature to adjust focus. He submitted a patent application for the design and asked Professor James Blanchard and Researcher Carl Martin to evaluate it before he prototypes it.

The two are conducting a finite-element analysis, but the process is anything but straightforward. Optics researchers lack a clear understanding of eye muscle forces, so Blanchard and Martin are applying assumed forces in their calculations. In addition, Clarke’s design incorporates a silicone oil “pocket” in the center of a solid lens, and few researchers have experience in finite-element models of materials that combine liquids and solids. Blanchard and Martin, however, recently applied similar techniques in a study of safe nuclear reactor design.

Although their analysis of Clarke’s lens is still under way, Blanchard’s and Martin’s initial calculations showed there’s room for improvement. “We’ve already made some design decisions based on what they’ve showed us,” says Clarke.

Nuclear research and development earns major DOE support

With more than $5 million in U.S. Department of Energy (DOE) funding, UW-Madison engineers are leading 10 cutting-edge research projects that will advance next-generation nuclear energy technologies.

Under the Nuclear Energy University Program, the DOE awarded three-year funding to 71 projects at 31 U.S. universities. In addition to their lead role on 10 projects, UW-Madison engineers are collaborating with Texas A&M University on two other projects.

According to the DOE, advanced nuclear technologies research and development is key to addressing the global climate crisis and moving the nation toward greater use of nuclear energy.

Nuclear reactors are a near-zerocarbon energy source. The advanced reactors under development will operate much more efficiently, but at the same time, must withstand higher temperatures, pressures and radiation ranges. Research in these and other areas lays the groundwork for building more efficient reactors over the next 20 years.

“The Wisconsin Institute of Nuclear Systems and the faculty and staff involved in the funded projects are uniquely positioned to provide both basic science and applied engineering research studies for generation IV nuclear reactor technologies and their associated materials and fuel cycle development,” says Wisconsin Distinguished Professor Michael Corradini .

The research projects fall primarily under two DOE thrusts: the advanced fuel-cycle initiative and next-generation nuclear plant/generation IV nuclear systems. The research includes studies of nuclear fuels and fuel coatings, nuclear waste separation technology, reactor analysis, reactor cooling technologies, advanced reactor concepts, and advanced reactor materials.

Researchers involved in the projects include Associate Professor Todd Allen, Senior Scientist Mark Anderson, Research Associate Guoping Cao, Materials Science and Engineering Professor Emeritus Y. Chang, Professor Michael Corradini, Professor Wendy Crone, Assistant Professor Dane Morgan (also <materials science and engineering), Mechanical Engineering Associate Professor Greg Nellis, Distinguished Research Professor Kumar Sridharan, Assistant Professor Izabela Szlufarska (also materials science and engineering), Adjunct Professor Tim Tautges, Associate Professor Paul Wilson and Research Associate Yong Yang.

Fusion researchers demonstrate self-organizing plasma

When Steenbock Professor Ray Fonck and his students built Pegasus, a tokamakstyle, or donut-shaped, fusion science experiment nearly 12 years ago, they hoped it would show the potential of a very low-aspect-ratio design that may allow researchers to develop smaller fusion systems in the future.

Now, they have demonstrated a technique that enables them to start Pegasus and create a stable plasma without using a solenoid. “There’s always been a need to find a way to start these tokamak plasmas without inductive current from a solenoid magnet down the center, and to hold them together without inductive current drive,” says Fonck.

The researchers published details of their advance in the June 5, 2009, issue of Physical Review Letters. They refer to their method as “lighting the match.” The method, which incorporates a plasma torch developed by UW-Madison physics researchers, addresses limits on magnetic field capacity in low-aspect-ratio tokamaks and could scale up to some of the world’s largest tokamak experiments.

For its method, Fonck’s group turns on the magnetic field that encircles Pegasus around the long, toroidal direction. Next, the researchers turn on the vertical magnetic field that holds the plasma in place — somewhat like how a tire confines an inner tube. “And so you end up with a magnetic field that spirals, because it’s got a component that goes around the torus and one that goes up,” he says. “The magnetic field lines are like a helix — they just spiral up from the bottom of the machine to the top.”

Using the plasma torches, the group injects current from below, along those helical magnetic field lines. The current spirals up and hits the top of the machine. Under appropriate conditions, it becomes unstable and naturally collapses into a lower-energy state. “The lowest-energy state under those conditions is a standard tokamak plasma,” says Fonck. “So, the plasma organizes itself into a tokamak, which is a relatively complex system.”

It stays that way until the group turns off the current, he says.

The technique has become one of the group’s main focus areas. Locally, it provides a path for the researchers to deliver current to Pegasus and someday achieve the high-pressure plasmas they’re aiming for. Globally, the technique may scale up to full-size reactors. “That’s a big deal in the international spherical tokamak community,” says Fonck.

University of Wisconsin-Madison College of Engineering University of Wisconsin-Madison