Overview of transport, fast particle and heating and current drive physics using tritium in JET plasmas

• Published in: Nuclear fusion Vol. 45; no. 10; pp. S181 - S194
• Main Authors: Stork, D, Baranov, Yu, Belo, P, Bertalot, L, Borba, D, Brzozowski, J.H, Challis, C.D, Ciric, D, Conroy, S, de Baar, M, de Vries, P, Dumortier, P, Garzotti, L, Hawkes, N.C, Hender, T.C, Joffrin, E, Jones, T.T.C, Kiptily, V, Lamalle, P, Mailloux, J, Mantsinen, M, McDonald, D.C, Nave, M.F.F, Neu, R, O'Mullane, M, Ongena, J, Pearce, R.J, Popovichev, S, Sharapov, S.E, Stamp, M, Stober, J, Surrey, E, Valovic, M, Voitsekhovitch, I, Weisen, H, Whiteford, A.D, Worth, L, Yavorskij, V, Zastrow, K.-D
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.10.2005
• Subjects: confinement; diii-d tokamak; iter
• ISSN: 0029-5515; 1741-4326; 1741-4326
• DOI: 10.1088/0029-5515/45/10/S15

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, nu(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 q(95) 2.8 and triangularity delta = 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, nu* and beta) and bulk energy confinement (decreases with nu* and is independent of beta). In an extended ELMy H-mode data set, with rho*, nu*, 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-phi similar to rho*(2.46) nu*(-0.23) beta(-1.01) q(2.03). In hybrid scenarios (q(min) similar to 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 nu(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 (rho(theta)* = q rho*) in a manner close to gyro-Bohm (similar to rho(sigma)*(3)), with an added inverse P 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. gamma-rays from the reactions of fusion alpha and beryllium impurities (Be-9(alpha, n gamma)C-12) characterized the fast fusion-alpha population evolution. The gamma-decay times are consistent with classical alpha plus parent fast triton slowing down times (tau(Ts) + tau(alpha s)) for high plasma currents (I-p > 2 MA) and monotonic q-profiles. In CH discharges the gamma-ray emission decay times are much lower than classical (tau(Ts) + tau(alpha s)), 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.