First ICRF experiments on ASDEX have been performed at 67 M z , corresponding to ZECH-heating of a hydrogen plasma at Bo = ?.2T. Despite divertor operation ICRH is accompanied by a significant increase of impurity production which can drastically be reduced by means of wall carbonisation. RF power up t o 2.3 MW is routinely coupled to the plasma for pulse lengths of up to 1 sec. The rf heating is found to depend strongly on plasma preheating. In conjination with neutral beam injection the ICRF heating efficiency is even higher than the one of SI. Confinement degrades with ICRH to values in between XI-L-type and OH confinement.

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Xeutral beam (NI), ion cyclotron resonance (ICRH) and lower hybrid resonance (LIIKV) heating on ASDEX are discussed with regard to their effect on plasma confinement. Comparison of SI and ICRH shows that the L and H-regimes are universal confinenent nodes of auxiliary-heated tokamak plasmas (i.e. independent of the heating nethod), and that the edge electron temperature (or a related parameter) dictates which mode prevails. In this connection it is noted that carbonization of the vessel walls impedes transition to the H-mode in the case of SI heating. Studies of energy confinement in the intermediate regime from ohmic to SI heating reveal a gradual transition from ohnic (-se) to neutral injection L-mode (-I) scaling. At the same tine a renarkable invariance of electron tenperature profile shape with increasing heating power is observed. Changing the XI power deposition profiles fron central to off-axis leaves gross energy confinement tines unchanged while central confinement is substantially inproved. Detailed investigations of the O-linit confirn the relation &$ [ %] = 2.8 I/(a B) [HA*n-l*T-l]. They show that the &limit is independent of heating method (NI, ICRH) and confinenent regine (L or H), but strongly dependent on the current density profile. indirect evidence suggests ballooning (and possibly surface kink) nodes to be responsible for the limitation in plasma pressure. LH heating and current drive show improved energy confinement (conpared to OH) at low densities (necl -2 x 1013 ~n -~, suprathermal electrons), but a degradation in confinement at higher densities.

The H mode in ion cyclotron-resonance-heated plasmas has been investigated with and without additional neutral-beam injection. Ion cyclotron-resonance heating can cause the transition into a highconfinement regime (H mode) in combination with beam heating. The H mode, however, has also been realized -for the first time -with ion cyclotron-resonance heating alone in the hydrogen minority scheme in deuterium plasma at an absorbed rf power of 1.1 MW.PACS numbers: 52.50.Gj, 52.55.Fa, 52.55.Pi Confinement studies on many tokamak plasmas all over the world have revealed an unfavorable phenomenon, called L mode. The good confinement of resistively heated plasmas could not be maintained at high plasma temperatures.With increasing auxiliary heating power, confinement was found to deteriorate severely, obstructing the successful approach of the ignition conditions. Therefore, the discovery of a high-confinement regime, called H mode, ' which combines the virtues of good global and central confinement even with additional heating was of paramount importance for fusion research.The characteristic and directly observable signatures of the H mode are a distinct drop of the H, radiation in the divertor (which is mostly a measure of the reduced power flow across the separatrix into the divertor chamber), a rising electron density (indicating an improved particle confinement), an enhanced plasma energy content (due to the improved energy confinement), a significantly enhanced edge electron temperature, and the existence of an MHD phenomenon, called ELMs (edge localized modes). ELMs are short bursts of energy leaving the plasma, representing short transitions back to degraded confinement accompanied by enhanced power loss.Since the H mode has been observed so far only in plasmas of divertor tokamaks, heated by neutral-beam injection (NI), it is important to know whether this good-confinement regime is restricted to NI heating alone or whether it is achievable for heating in the ion cyclotron range of frequencies [ion cyclotron-resonance heating (ICRH)], too. Additionally, the realization of the H mode with different auxiliary heating methods will give some insight into the global confinement structure of tokamak plasmas. In particular, ICRH decouples heating and particle refueling, and ICRH changes the ion energy distribution of the plasma differently from NI. Thus, heating by ICRH introduces additional properties extending the range of parameters to study plasma confinement.Our investigations, where ICRH has been applied alone and together with NI, were based on an H-mode recipe which has been developed during NI experiments.Best conditions have been reported for clean deuterium plasmas (Z,tt-1 -1.5 ) in the single-null divertor configuration with the plasma shifted up by about a tenth of the minor radius, corresponding to 2 times the density and temperature falloff lengths of the scrapeoff layer. It was theoretically expected that the ion grad-8-drift direction should have a large impact on the formation of the H mode, which ...