In a fusion energy milestone, new research shows that heat from plasma fusion spreads more evenly in tokamak reactors, suggesting new ways to improve reactor efficiency and overall lifespan while reducing the potential for damage.
New findings by researchers at the US Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) in collaboration with Oak Ridge National Laboratory and ITER, currently the world’s largest fusion experiment, reveal that when commercial reactors produce large amounts of very intense heat removal during plasma fusion, may not be as potentially damaging to the interior of the reactor as previously thought.
The new research could allow new opportunities to increase the operational life of fusion reactors and challenge previous ideas about the movement of heat and particles between two critical regions at the edge of the plasma during the fusion process. The new research was led by PPPL senior research physicist Choongseok Chang.
Tokamaks are large toroidal (i.e. doughnut) devices that scientists use to produce controlled fusion reactions from hot plasma. During operation, temperatures in the tokamak can often exceed 150 million degrees Celsius to achieve fusion, mimicking the processes that occur naturally on the Sun and exceeding these solar temperatures by a factor of ten.
Tokamaks require magnetic fields to confine the plasma in the device’s core, although a few particles and excess heat escape and collide with the inner walls.
However, based on Chang and his team’s findings, these escaping particles are dispersed over a larger area than previous findings suggested, limiting the potential for serious damage.
In the past, it was assumed that the exhaust heat during fusion reactions would be focused more narrowly on what are called divertor plates. This part of the inner wall of the tokamak is essential in helping to remove waste heat and particles from the hot plasma in the tokamak. However, concentrations along the scattering plates can sometimes lead to damage, limiting the potential for commercial use.
In the new simulations by Chang and his team, which included a computer code known as the X-Point Included Gyrokinetic Code (XGC), plasma particles essentially maintain a path across the surface of the magnetic field and disrupt the boundary region separating the confined plasma inside the tokamak from the unconfined plasma that includes plasma that comes into the divertor region.
Over time, Chang’s research showed that the ions appeared to cross the boundary, concentrating the thermal load on a very concentrated area of ​​the divertor plate, and that the plasma turbulence resulted in negatively charged electrons crossing the boundary, greatly expanding the thermal zone on the divertor. plates in ITER, the multinational fusion device currently being assembled in France.
But a recent study by Chang and an international team revealed that the last confining surface, previously believed to be stable, is disrupted by plasma turbulence during fusion, leading to what the researchers describe as “homoclinic entanglements.”
Homoclinic entanglements were found to increase the width of the thermal shock zone by up to 30 percent more than past estimates based on turbulence alone. Chang and team say that the wider heat distribution they discovered in their simulations makes the divertor surface less likely to be damaged when paired with the radiative cooling that results from injecting debris into the divertor plasma.
Although the final containment surface in a tokamak cannot be completely trusted, new research nonetheless shows that this instability can actually increase fusion performance and reduce the likelihood of damage to the divertor surface in steady-state operation.
The risk of sudden release of plasma energy will also be reduced. These findings address two major performance-limiting issues that fusion energy researchers have faced regarding the future commercial use of tokamak reactors.
Micah Hanks is the editor-in-chief and co-founder of The Debrief. He can be reached by e-mail at micah@thedebrief.org. Follow his work at micahhanks.com and on X: @MicahHanks.