Drift Orbits and Transport Consequences in Tokamaks with Broken Symmetry*
K. C. Shaing1*
1Institute for Space and Plasma Sciences, National Cheng Kung University, Tainan, Taiwan
* Presenter:K. C. Shaing
The first fusion power plant is likely to be a tokamak, in which the largest value of the fusion triple product EΤ has been achieved. Here, n is plasma density, τE is the energy confinement time, and T is plasma temperature. ITER is the largest tokamak, currently being built in southern France, with a targeted fusion energy gain factor Q = 10, were Q is the ratio of the fusion power to the external heating power. Thus, fusion power will become a reality in the near future to provide practically unlimited green energy for all. An ideal tokamak is a toroidally symmetric torus shaped like a doughnut with nested magnetic surfaces. Charged particle trajectories are tied to the magnetic surface as a result of the conservation of the toroidal canonical momentum. However, in a real tokamak such as ITER toroidal symmetry is weakly broken. Toroidal canonical momentum is no longer conserved. Charged particles readily drift off the magnetic surface to form drift orbits. The width of these drift orbits does not depend on the strength of the magnetic field. Thus, broken toroidal symmetry enhances particle, momentum, and energy losses in tokamaks. Transport fluxes can be calculated with great accuracy by solving kinetic equation using an asymptotic expansion procedure. The enhanced transport losses limit the tolerable magnitude of the symmetry breaking magnetic field in fusion reactors without degrading Q.

* This work was supported by Taiwan Ministry of Science and Technology under Grant No. 100-2112-M-006-004-MY3.


Keywords: Magnetized Plasmas, Tokamaks