Physicists improve their understanding of heat and particle flow in the edge of a melter

Physicists at the Princeton Plasma Physics Laboratory (PPPL) of the Department of Energy (DOE) have uncovered valuable information on how an electrically charged gas called "plasma" flows to the periphery at the same time. interior of donut-shaped fusion devices called "tokamaks". The results are an encouraging sign for the development of fusion power generation machines that generate electricity without creating long – term hazardous waste.

The result partially corroborates previous PPPL findings that the width of heat generated by fusion reactions could be six times wider, and therefore less narrow, more concentrated and more damaging than expected. "These results are good news for ITER," said PPPL physicist C.S. Chang, lead author of a research description. Physics of plasmas, referring to the international experience of fusion under construction in France. "The results show that heat emissions in ITER will be less likely to harm the machine," Chang said.

Fusion, power that drives the sun and stars, is the fusion of light elements in the form of plasma – the state of charged and hot matter consisting of free electrons and atomic nuclei – which produces of energy. Scientists around the world are seeking to replicate the fusion on Earth to obtain a virtually inexhaustible source of energy for the production of electricity.

The superhot plasma contained in tokamaks, which can reach hundreds of millions of degrees, is confined by magnetic fields that keep the plasma out of the walls of the machines. However, particles and heat can escape from containment fields at the "magnetic separator" – the boundary between magnetically confined and unconfined plasmas. At this limit, the field lines cross at point X, the point where the heat lost and the particles escape to hit a target called "deflection plate".

The new discoveries reveal the surprising effect of the X-point on the escapement by showing that a hill-like electrical charge hump occurs at point X. This electric hill circulates the plasma around it, preventing the plasma particles to move between the upstream and downstream regions of the field lines along a straight path. Instead, like cars maneuvering around a construction site, the charged plasma particles make a detour around the hill.

The researchers produced these results with XGC, an advanced computer code developed with external collaborators at PPPL, which models the plasma as a collection of individual particles rather than a simple fluid. The model, which showed that the connection between the upstream plasma located above the X point and the downstream plasma below the X point formed in a way not provided by simpler codes, could lead to more accurate predictions on the exhaust and make future large – scale facilities less vulnerable to internal damage.

"This result shows that the previous pattern of field lines involving flux tubes is incomplete," said Mr. Chang, referring to the tubular areas surrounding magnetic flux regions, and that current understanding of the interaction between upstream and downstream plasmas is not sufficient. Our next step is to define a more precise relationship between upstream and downstream plasmas using a code like ours. This knowledge will help us develop more accurate equations and improved models, which are already underway. "