NPRE Illinois Jul 03, 2018
Researchers working with the University of Illinois at Urbana-Champaign HIDRA plasma/fusion facility have had a busy and productive summer as they have prepared the facility to run experiments on techniques designed to advance fusion reactors.
Scientists at both Princeton Plasma Physics Laboratory (PPPL) and the Center for Plasma-Material Interactions (CPMI) at Illinois are examining the use of liquid lithium as the material that first comes into contact with plasma in a fusion reactor. The liquid metal is desirable because of its ability to flow and move heat away, an innovation necessary to reduce the size of fusion reactors while allowing them to produce enough energy to make them viable.
The flowing liquid lithium (FLiLi) limiter system at PPPL is based on the concept of a thin flowing film of lithium. Positioned within a fusion reactor, a limiter is a surface that helps control the size of the plasma and dictates where exhausted particles will hit a surface, so that aspects of the plasma can be limited. In FLiLi, a fusion reactor’s limiter employs a novel electro-magnetic pump designed to drive liquid lithium flow from a collector at the bottom of a limiter into a distributor at its top, thus supplying a continuously flowing liquid lithium film to the wetted plasma-facing surface.
In CPMI’s LiMIT (Lithium/Metal Infused Trenches) concept, designed by Nuclear, Plasma, and Radiological Engineering Prof. David Ruzic and his students, molten lithium self-circulates along the surface of a fusion reactor’s divertor, where excess heat and waste material are collected and removed.
CPMI researchers are preparing HIDRA to test both technologies to validate the theory and modeling behind them, said NPRE Research Assistant Prof. Daniel Andruczyk. The systems will then be tested on the Experimental Advanced Superconducting Tokamak (EAST) at the Institute of Plasma Physics in the Chinese Academy of Sciences. “Once we’re confident that they work here we will put it on the big machine and really give this thing a go,” Andruczyk said. The Chinese facility is up to 20 times larger than HIDRA.
To prepare for testing the systems, the CPMI scientists have used magnetic field line tracing to measure the shape of the plasma within HIDRA. By changing the strength of the magnetic field, the researchers can dictate where the plasma goes and, thus, control its shape. “We measured the shapes and understand what they are,” Andruczyk said. “We have chosen the particular shape that we think will work.”
Once the shape is determined, the researchers use microwave frequencies to extend the longevity of the plasma. They also use a Langmuir probe to measure the temperature and density of the plasma.
Andruczyk and his team currently are preparing to open up HIDRA for installation of LiMIT and FLiLi. This involves splitting the vacuum vessel in half to allow larger components to be installed. When installation is finished and experiments begin, both systems will be tested simultaneously. The HIDRA testing and modifications to the systems are expected to take about six months before the limiters are sent for further experiments on the Chinese EAST facility.