Why heavier hydrogen isotopes confine better than theory predicts
In plain words
Simple turbulence theory says heavier fuel ions should leak heat faster, yet in experiments deuterium and tritium plasmas confine heat better than hydrogen. The reason has to be known to extrapolate to deuterium-tritium reactors.
Precise statement
Local gyro-Bohm scaling predicts energy confinement time $\tau_E$ proportional to A^-0.5 ($A=\text{ion mass number}$), while experiments find tau_E increasing with A, more strongly in H-mode. Identify the mechanism (E x B shear, collisional electron dynamics, pedestal dependence, zonal flows) and predict the D-T to D confinement ratio for ITER to within 15 percent.
What would settle it
Multiscale gyrokinetic and pedestal modeling that reproduces measured H, D and D-T confinement on JET and another device.
Status in the literature
JET D-T campaigns (2021-2023) confirmed better confinement in D-T than D; no single mechanism is accepted.