Three long-standing paradoxes in tokamak physics

The three enduring paradoxes of tokamak physics are: 1. Good neoclassical conductivity contradicts the anomalously high transport of particles. 2. Particle density has maximum at the core, while the main particle source is near the edge. 3. Improvement of confinement by plasma current ramp-down and thus weakening of the poloidal magnetic field near the edge. While resolving these paradoxes is imperative for establishing a predictive theory of tokamaks, limited discussions on these complexities exist in the literature. The authors suggest that resolution of the first paradox is a coexistence of regular and chaotic trajectories of particles; resolution of the second paradox is turbulent equipartition of particles and a decrease of the specific poloidal volume to the center; resolution of the third paradox is an increase of the specific poloidal volume near the edge, resulting in the expansion of plasma, lowered density and temperature, consequently reducing the heat flux.