Nuclear astrophysicists, led by principal investigator and SD Mines professor
Frank Strieder,
have successfully created the first low-energy particle accelerator
beam deep underground in the United States, bringing them one step
closer to understanding how the elements of our universe are built.
The project is called
CASPAR (Compact Accelerator System for Performing Astrophysical Research).
The team of scientists working on CASPAR will recreate the nuclear
fusion processes inside stars. The project’s principal investigator is
South Dakota School of Mines & Technology associate professor
Frank Strieder.
“CASPAR can help us answer some basic questions like: How do stars run?
How do they produce energy? How elements are made?” says Strieder.
“Where are we from? What is our cosmic heritage? I think it’s exciting
to know all of the heavier elements inside our bodies were once produced
inside stars,” he adds.
CASPAR is one of only two underground accelerators in the world.
The other is in the Laboratory for Underground Nuclear Astrophysics
(LUNA) located near Gran Sasso mountain in Italy, where Strieder worked
prior to coming to Mines.
“Installing and operating accelerators underground is a considerable challenge,” says Michael Wiescher, Freimann
Professor of Nuclear Physics at the University of Notre Dame. “CASPAR
is unique since it covers a broader energy range than the LUNA
accelerator. It allows us, for the first time, to explore reactions of
stellar helium burning, which take place in stars like Betelgeuse, at
laboratory conditions. Through these studies, we will learn about the
origin of oxygen and carbon as the most important ingredients of
biological life in the universe, and we will learn about the mechanisms
stars have developed to produce gradually heavier elements through
neutron fusion processes.”
Wiescher and research assistant professor Dan Robertson are
with the team from Notre Dame, working in collaboration with
researchers from the South Dakota School of Mines & Technology and
the Colorado School of Mines.
“The complexity of moving an accelerator facility deep underground
is greatly outweighed by the potential benefits when recreating nuclear
reactions of astrophysical interest,” says Robertson. “Currently, a
significant amount of the information we have about reactions that take
place in the exact conditions inside a star can only be extrapolated
from data in other energy ranges. This is mostly because the probability
of that reaction is so small, and without a star’s worth of material to
play with, it is difficult to measure when competing with cosmic
background. We hope to measure key reactions in elemental production
scenarios directly, providing insights into their behavior and helping
to understand how and where the material in our everyday lives was
produced.”
The 50-foot low-energy particle accelerator was assembled 4,850 feet underground in August 2015 at the Sanford Underground Research Facility (SURF)
in Lead, S.D., formerly the Homestake Gold Mine. The accelerator had to
be transported in pieces from its original home at Notre Dame to SURF
and then lowered in a cage elevator and moved via mine trolley to the
experimental space.
Taking the project underground shields it from the cosmic radiation
the Earth is exposed to on a constant basis, which can interfere with
highly sensitive physics experiments. “These kinds of studies need an
environment free of cosmic rays as only provided at places like SURF,”
says Wiescher.
The nuclear fusion that takes place inside a star is what creates
the elements that are necessary for life. Older stars, born around the
time of the Big Bang, consist of very few elements, while younger stars
include a buildup of heavier elements such as lead and gold.
Understanding that buildup of elements is just one of the many questions
researchers hope to help answer through a series of CASPAR experiments.
With operations underway, the team plans to begin data collection
in the fall. CASPAR received funding from the National Science
Foundation, the South Dakota Science and Technology Authority and the
University of Notre Dame. For more on the history of the project, visit nd.features/caspar. For a video showing SD Mines involvement in the project, click here.