The chaotic, small-scale fluctuations in density, temperature, and electric fields that dominate energy and particle transport in magnetically confined plasmas — the main reason fusion confinement falls short of theoretical limits.
In a tokamak, classical collisional transport would confine plasma far better than what is actually observed. The dominant transport mechanism is turbulence-driven: micro-scale fluctuations (“drift waves”) scatter heat and particles across magnetic surfaces at rates 10–100 times the collisional prediction. Understanding and controlling turbulence is the central problem of fusion plasma physics.[1]
Several mechanisms can suppress turbulence: (1) E×B flow shear — strong sheared plasma rotation tears apart turbulent eddies, underlying the H-mode transition; (2) Zonal flows — self-generated, band-like plasma flows that regulate turbulence through a predator-prey interaction; (3) Magnetic shear — variation in field-line pitch stabilises certain modes.[2]
Gyrokinetic simulation codes (GENE, GYRO, GS2, XGC) are the primary tools for predicting turbulent transport. These codes solve the Vlasov equation on five-dimensional phase space and require some of the world’s largest supercomputers.[3]