Using an advanced plasma global code called XGCa, researchers at the Princeton Plasma Physics Laboratory (PPPL) have confronted the conventional view of the so-called bootstrap current with results clarifying the origin of the current at the tokamak edge.
According to their recent study, the bootstrap current is a neoclassical current that arises from collisions between magnetically trapped particles, in the so-called banana orbits, and passing particles, due to the toroidal geometry. It is directly connected with the helical shape of the magnetic field that confines the plasma in a tokamak.
In the past, physicists considered that passing electrons carried the current alone.
The discovery is of importance because the bootstrap current is a key factor in the understanding of instabilities generation at the plasma edge pedestal, i.e. the steep gradient region of the plasma edge.
“Correct modeling of the current enables accurate prediction of the instabilities” affirmed Hager, main author of the paper.
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