EFDA-JET-CP(04)03/41

Transport in Improved H-mode at ASDEX Upgrade and Comparison to JET

Efforts have been made to develop advanced scenarios aiming at obtaining high confinement and stability in tokamak plasmas. Internal Transport Barrier (ITB) discharges are believed to be the most promising way to attain the goal. However, the ITB discharges require supplementary elaborate control of the pressure and the current density profile and of the MHD stability in order to fulfil the demand for advances scenarios. The improved H-mode scenario, so-called ITER hybrid scenario, cut a conspicuous figure as an advanced scenario to overcome such drawback of ITB discharges. It accomplishes high confinement (H98 up to 1.4) and stability (bN up to 3) simultaneously in long pulse duration (~50 tE limited by the machine hardware). This scenario is established in many tokamak devices, such as ASDEX Upgrade, JET, DIII-D and JT-6OU, relying on low or zero magnetic shear in the centre of the plasma [1-4]. To access the improved H-mode regime in this scenario, it is a key to apply moderate heating avoiding the ITB formation in the current ramp up phase and to produce low magnetic shear in the central region of the plasma. Neutral Beam Injection (NBI) is the main heating tool for this scenario but in some discharges ICRH has been used to replace some of the NBI power. To avoid density peaking, which triggers serious NTM's and leads accumulation of impurities in the centre, ICRH or ECRH are used in addition to the NBI heating [5].
Name Size  
EFDC040341 898.70 Kb