The discrepancy between the experimental projections and simulation predictions stems from the fact that conditions inside ITER will be too different from those in existing tokamaks for the empirical predictions to be valid, according to Chang. Key differences include the behaviour of plasma particles within today's machines compared with the expected behaviour of particles in ITER. For example, while ions contribute significantly to the heat width in major worldwide facilities, turbulent electrons will play a greater role in ITER, rendering extrapolations unreliable.
Physicist C.S. Chang, from the Princeton Plasma Physics Laboratory.