Overview of Transport, Fast Particle and Heating and Current Drive Physics using Tritium in JET Plasmas
Results are presented from the JET Trace Tritium Experimental (TTE) campaign using minority Tritium (T) plasmas (nT/nD<3%). Thermal tritium particle transport coefficients (DT, vT) were found to exceed neo-classical values in all regimes except in ELMy H-modes at high density , and in the region of Internal Transport Barriers (ITB) in Reversed shear plasmas. In hybrid scenarios (qmin~1, low positive shear, no sawteeth), T particle confinement was found to scale with increasing triangularity and plasma current. In ELMy H-mode dimensionless parameter scans, T particle transport scaled in a Gyro-Bohm manner in the inner plasma (r/a<0.4), whilst the outer plasma particle transport behaved more like Bohm scaling. Dimensionless parameter scans showed contrasting behaviour for particle confinement (increases with collisionality n* and b) and energy confinement (decreases with n* and independent of b). Comparing regimes (ELMy H-mode, ITB plasma, and Hybrid scenarios) outside the central plasma region (0.65<r/a<0.85), normalised tritium diffusion (DT/Bf) scaled with normalised poloidal Larmor radius (rq* = qr*) in a manner close to Gyro-Bohm (~rq*3), with an added inverse b dependence. The effects of ELMs, sawteeth and Neo-classical Tearing Modes (NTMs) on T particle transport are described. Fast-ion confinement in Current-Hole (CH) plasmas, was tested in TTE by injection of Tritium NBI into JET CH plasmas. g-rays from the reactions of fusion alphas and beryllium impurities (9Be(a, ng)12C) characterised the fast fusion-alpha population evolution. The g decay times were consistent with classical alpha plus parent fast triton slowing down times (tTs + tas) for high plasma currents (Ip >2MA) and monotonic q-profiles. In CH discharges the g-ray emission decay times were much lower than classical (tTs + tas), indicating alpha confinement degradation, due to orbit losses predicted by a 3-D Fokker Planck numerical code, and modelled by TRANSP.