Studies of plasma behavior in tokamaks—doughnut-shaped devices designed to generate electricity through nuclear fusion—have revealed an important pattern in the distribution of particles within these systems. Inside a tokamak, superheated plasma is confined by magnetic fields, but some particles escape the central region and move toward the divertor, a system for removing excess particles and heat.

When particles reach the divertor, they collide with metal plates, cool down, and some partially return to the plasma, which helps sustain the fusion reaction. However, experiments have shown that significantly more particles settle on the inner target of the divertor than on the outer one. This uneven distribution is crucial for designing future fusion reactors, as engineers need to know precisely where particles will concentrate in order to build divertors capable of withstanding extreme temperatures and loads.

Previously, the main explanation for this asymmetry was attributed to cross-field drifts of particles along magnetic field lines. Yet, models that considered only this effect did not match experimental results, raising doubts about the reliability of the models used for reactor design.

Recent research has found that toroidal rotation of the plasma—its circular motion inside the tokamak—significantly affects the final distribution of particles in the divertor system. Using the SOLPS-ITER software suite, scientists simulated various plasma behavior scenarios, both including and excluding cross-field drifts and rotation. The results showed that only when both factors were considered together did the simulations align with experimental measurements.

To test this hypothesis, simulations were conducted on the DIII-D tokamak in California using four different scenarios. Agreement with experimental data was achieved only after adding a parameter reflecting the measured core plasma rotation speed—88.4 kilometers per second. The combined influence of cross-field drift and rotation proved to be much stronger than either factor alone.

These findings highlight the important connection between core plasma rotation and particle behavior at the system’s edge. Accurately describing this relationship is essential for predicting particle movement in future reactors. More precise forecasts will enable the creation of divertors that are more robust and better adapted to real operating conditions, ensuring efficient distribution of heat and particles.