Experiments in H-mode plasmas have shown that both heat and particle transport are sensitive to the ratio between electron and ion temperature (Te/Ti). While decreasing Te/Ti is beneficial for confinement, an increased electron heating in these so called hot ion plasmas deteriorates the confinement. H-mode plasmas with low Te/Ti are often accompanied by high toroidal rotation velocity (v_tor). Its gradient (grad v_tor) can destabilize the ion temperature gradient mode (ITG) through its parallel component in the parallel velocity shear, but it has also stabilizing effects since it produces an E x B shearing rate (omega_ExB). In this paper, the effects of electron heating on the ion heat transport is investigated in H-mode plasmas heated by neutral beam injection (NBI) and electron cyclotron heating (ECH). In particular, the correlation on Te/Ti and grad v_tor is studied and compared with calculations made with GLF23 and GS2. Experimentally it is shown that the normalized gradient length of the ions (R/L_Ti ) is correlated with both Te/Ti and grad(v_tor) : peaked ion temperature profiles are only obtained with low Te/Ti and high grad(v_tor) and vice-versa. When ECH is added, both ion heat and momentum transport are enhanced, leading to a drop of both the Ti and v_tor profiles. The effective growth rate gamma_eff = gamma-omega_ExB is calculated, with the mode growth rate gamma determined with GS2 and omega_ExB with GLF23. The ion transport is enhanced due to the decrease of the ITG R/L_Ti threshold with increasing Te/Ti. Comparison of the dependence of R/L_Ti on Te/Ti and grad(v_tor) between experiments and modelling indicates that the deterioration of confinement cannot be explained by the changes in only Te/Ti or grad(v_tor), but by the combined effects of both parameters. The changes in Te/Ti act directly on the ITG threshold, while the ones in grad(v_tor) modify the omega_ExB shearing rate leading to changes in the effective threshold.
Role of Te/Ti and grad(v_tor) in ion heat transport of ASDEX Upgrade H-mode plasmas
Jacchia A;
2006
Abstract
Experiments in H-mode plasmas have shown that both heat and particle transport are sensitive to the ratio between electron and ion temperature (Te/Ti). While decreasing Te/Ti is beneficial for confinement, an increased electron heating in these so called hot ion plasmas deteriorates the confinement. H-mode plasmas with low Te/Ti are often accompanied by high toroidal rotation velocity (v_tor). Its gradient (grad v_tor) can destabilize the ion temperature gradient mode (ITG) through its parallel component in the parallel velocity shear, but it has also stabilizing effects since it produces an E x B shearing rate (omega_ExB). In this paper, the effects of electron heating on the ion heat transport is investigated in H-mode plasmas heated by neutral beam injection (NBI) and electron cyclotron heating (ECH). In particular, the correlation on Te/Ti and grad v_tor is studied and compared with calculations made with GLF23 and GS2. Experimentally it is shown that the normalized gradient length of the ions (R/L_Ti ) is correlated with both Te/Ti and grad(v_tor) : peaked ion temperature profiles are only obtained with low Te/Ti and high grad(v_tor) and vice-versa. When ECH is added, both ion heat and momentum transport are enhanced, leading to a drop of both the Ti and v_tor profiles. The effective growth rate gamma_eff = gamma-omega_ExB is calculated, with the mode growth rate gamma determined with GS2 and omega_ExB with GLF23. The ion transport is enhanced due to the decrease of the ITG R/L_Ti threshold with increasing Te/Ti. Comparison of the dependence of R/L_Ti on Te/Ti and grad(v_tor) between experiments and modelling indicates that the deterioration of confinement cannot be explained by the changes in only Te/Ti or grad(v_tor), but by the combined effects of both parameters. The changes in Te/Ti act directly on the ITG threshold, while the ones in grad(v_tor) modify the omega_ExB shearing rate leading to changes in the effective threshold.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
