NEW FACULTY
Joseph Bisognano
he
University of Wisconsin-Madison has a long history as a center for accelerators.
In 1952, a research group called MURA, or the Midwestern Universities
Research Association, formed to design the next large U.S. accelerator
facility. UW-Madison was key to that plan and a decade or so later the
university became home to the 240 megavolt electron storage ring Tantalus,
the first storage ring used exclusively for synchrotron radiation research.
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The Aladdin Storage
Ring at the Synchrotron Radiation Center
(54K
JPG) |
Tantalus also marked the inception
of the university’s Synchrotron
Radiation Center (SRC), located near
Stoughton. Later, a larger synchrotron radiation source called Aladdin
took its place, enabling researchers to use X-rays and ultraviolet light
to image and study everything from the biology of cells and the composition
of interstellar clouds to the superconducting properties of materials.
SRC Director Joseph
Bisognano, who joined the department
as a professor in fall 2002, studies the dynamics of the electron beam
that creates the light source to make this research possible.
His primary area of interest is collective-beam dynamics in particle
accelerators. “As you start putting more and more particles into
the accelerator, they start talking to each other, because they’ve
got charge and they push on each other,” he explains. “Coherent,
wavelike motion can result. The resulting beam motion can become unstable,
or nonlinear, and sets a limit on how much beam current an accelerator
can tolerate. Since more current means more photons, increasing the
threshold currents for this destructive behavior is critical to heightened
performance.”
Because particle beams are
high-current objects affected by long-range electromagnetic forces,
he likens his research to plasma physics and says it is a good fit for
the Department of Engineering Physics. “Accelerators embody a
broad range of technology, including electrical engineering, control
theory, cryogenics, vacuum systems, plasma physics, magnetic materials,
and so on,” he says. “So if you look at the list of disciplines
that go into accelerator science, it’s not just classical physics.
It really involves very fundamental, innovative engineering.”
Bisognano, who earned his PhD
in physics from the University of California-Berkeley in 1975, plans
to start a graduate accelerator program here and will teach his first
course in accelerators in spring 2004. He has served in both faculty
and scientific positions at such institutions as the College of William
& Mary, Lawrence Berkeley Lab, and the Thomas Jefferson National
Accelerator Facility, with its 6 GeV superconducting linear accelerator,
in Newport News, Virginia.
At Lawrence Berkeley Laboratory,
he analyzed the current limitations of its advanced light source. He
also researched the collective effects of superconducting proton colliders
and inertial-confinement fusion drivers. “All of those have high-current
particle beams, so a variety of collective effects become the limiting
phenomena,” says Bisognano, who developed the theory of how an
electronic feedback system reduces a particle beam’s temperature.
Currently he and others at
SRC are working on ways to upgrade the photon beam properties for users
by increasing the electron beam’s density. “We are now able
to offer a photon beam with a factor of two-higher flux density,”
says Bisognano. “Much other work is going on to enhance beam stability
and increase beam lifetime.”
And in his free time, Bisognano
is devoting much work to another ambitious endeavor: A house on Lake
Mendota he and his wife just bought. “It’s a real fixer-upper,”
he says, “with plenty of opportunities for upgrading performance!”
Dennis Whyte
n
a misty gray day back in November, even a casual observer could tell
that Dennis
Whyte nearly buzzed with enthusiasm.
It was the day a crane hoisted a gigantic cylindrical Pelletron ion-beam
accelerator through a third-story window and into his Engineering Research
Building laboratory.
As the accelerator soared through
the air, Whyte already talked about its collaborative research potential.
“It’s a generic tool for doing surface analysis and modification,”
explains the assistant professor, who joined the department in fall
2002.
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Installing the accelerator:
a perfect fit
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JPG) |
He hopes to use it to study,
in real time, how plasmas and surfaces affect each other, but says other
fusion research facilities on campus and around the world could use
it to study material samples. In addition, its applications include
nanofabrication and plasma-surface implantation. “It has so many
applications that it’s mindboggling, really,” says Whyte.
“Anything that works with surfaces and materials can really use
this as a tool. What’s exciting for the college is that kind of
cross-collaboration and the possibilities for that kind of work to be
going on outside of the fusion research.”
A native of Shaunavon, Saskatchewan,
Canada, Whyte received his bachelor’s degree in engineering physics
in 1986 from the University of Saskatchewan in Saskatoon. Studying at
Canada’s national fusion research facility, the Tokamak de Varennes
in Montreal, he earned a PhD in applied physics from the University
of Québec in 1992.
There he developed a system
that used high-powered lasers to create atomic beams that researchers
could inject into a tokamak plasma. The beams help them nonintrusively
track how particles (micro-sized bits of “dirt” the plasma
sloughs off the containment vessel’s inner wall) are transported
within the reactor. This dirt “poisons” the plasma and eventually
destroys potential fusion reactions.
Similarly, as a postdoctoral
fellow and later a research scientist at the University of California-San
Diego, Whyte spent the bulk of his time at the DIII-D National Fusion
Facility developing atomic-physics and measurement techniques to explain
what occurs in the plasma.
He also studied what to do
if the tokamak, or “magnetic bottle,” develops a leak. When
that occurs, the plasma escapes within a thousandth of a second and
pours massive amounts of heat and energy into what it contacts on the
way. “The idea is not to stop the disruption, but we trigger what
is essentially a safe shutdown of the plasma to minimize damage to the
components inside the reactor,” he says.
His solution was to develop
a system to inject a large gas “slug,” or jet, into the
plasma. “We try to take all the energy in the plasma and convert
it into light, and dissipate the energy by light,” he explains.
“Light is the best way because it doesn’t damage materials
as much and it more or less goes everywhere, so it kind of spreads the
pain.” The technique proved successful and Whyte recently reported
the results internationally.
In his research, both plasmas
and the materials they interact with carry equal weight. He joined the
DiMES (Diverter Material Evaluation Studies) project on the DIII-D tokamak
in 1995 and became its experimental coordinator. The project focused
mainly on testing materials for the containment vessel’s inner
wall in a realistic fusion environment. “Typically this is a very
thin layer of a few millimeters or more which basically is the contact
between the plasma and the rest of the world,” he says.
In theory, the layer should
be benign to the plasma, he says. In addition, it should extract heat
from the reactor efficiently. Given that the tokamak fuels deuterium
and tritium are forms of hydrogen, which is extremely chemically reactive,
there are few compatible materials that are mechanically feasible and
also can handle heat.
Among his group’s DiMES
discoveries were a plasma cooling method that stopped the quick erosion
of the reactor’s diverter plates, which remove power, heat and
ash from the system. In addition, the researchers conducted the first
careful physics studies of why tritium was becoming trapped in the containment
vessel’s inner wall.
It’s an ongoing question,
and one that Whyte hopes to answer at UW-Madison. In addition, he eagerly
anticipated working with students. “I’m very motivated to
attract and help train the next generation of people who will work on
this … because the problems are not going to be solved anytime
soon,” he says.
With his wife, Sandy, and daughters
Camille, 5, and Malindi, 2, he recently purchased a house here. And
after two hours daily on the road in San Diego, Whyte also is thankful
for his new “commute”: an eight-minute walk to work.
