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 (n_T/n_D < 3%). Thermal tritium particle transport coefficients (D_T, v _T) are found to exceed neo-classical values in all regimes, except in ELMy H-modes at high densities and in the region of internal transport barriers (ITBs) in reversed shear plasmas. In ELMy H-mode dimensionless parameter scans, at q₉₅ ∼ 2.8 and triangularity δ ≤ 0.2, the T particle transport scales in a gyro-Bohm manner in the inner plasma (r/a < 0.4), whilst the outer plasma particle transport scaling is more Bohm-like. Dimensionless parameter scans show contrasting behaviour for the trace particle confinement (increases with collisionality, ν^* and β) and bulk energy confinement (decreases with ν^* and is independent of β). In an extended ELMy H-mode data set, with ρ^*, ν^*, β and q varied but with neo-classical tearing modes (NTMs) either absent or limited to weak, benign core modes (4/3 or above), the multiparameter fit to the normalized diffusion coefficient in the outer plasma (0.65 < r/a < 0.8) gives D _T/B_φ ∼ ρ ^*2.46ν^*-0.23β^-1.01q ^2.03. In hybrid scenarios (q_min ∼ 1, low positive shear, no sawteeth), the T particle confinement is found to scale with increasing triangularity and plasma current. Comparing regimes (ELMy H-mode, ITB plasma and hybrid scenarios) in the outer plasma region, a correlation of high values of D_T with high values of v_T is seen. The normalized diffusion coefficients for the hybrid and ITB scenarios do not fit the scaling derived for ELMy H-modes. The normalized tritium diffusion scales with normalized poloidal Larmor radius in a manner close to gyro-Bohm , with an added inverse β dependence. The effects of ELMs, sawteeth and NTMs on the T particle transport are described. Fast-ion confinement in current-hole (CH) plasmas was tested in TTE by tritium neutral beam injection into JET CH plasmas. γ-rays from the reactions of fusion alpha and beryllium impurities ( ⁹Be(α, nγ)¹²C) characterized the fast fusion-alpha population evolution. The γ-decay times are consistent with classical alpha plus parent fast triton slowing down times (τ_Ts + τ_αs) for high plasma currents (I_p > 2 MA) and monotonic q-profiles. In CH discharges the γ-ray emission decay times are much lower than classical (τ_Ts+τ_αs), indicating alpha confinement degradation, due to the orbit losses and particle orbit drift predicted by a 3-D Fokker-Planck numerical code and modelled using TRANSP.