CONFINEMENT IN ASDEX WITH NEUTRAL BEAM AND RF HEATING
Neutral beam (NI), ion cyclotron resonance (ICRH) and lower hybrid resonance (LHRH) heating on ASDEX are discussed with regard to their effect on plasma confinement. Comparison of NI and ICRH shows that the L and H- regimes are universal confinement modes of auxiliary heated tokamak plasmas (i.e. independent of the heating method), 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 NI heating. Studies of energy confinement in the intermediate regime from ohmic to NI heating reveal a gradual transition from ohmic (about e-) to neutral injection L mode (about I) scaling. At the same time a remarkable invariance of electron temperature profile shape with increasing heating power is observed. Changing the NI power deposition profiles from central to off-axis leaves gross energy confinement times unchanged while central confinement is substantially improved. Detailed investigations of the beta limit confirm the relation beta**dia-max (%) =2.8 I/(a B) (MA x m**-1 x T**- 1-). They show that the beta limit is independent of heating method (NI, ICRH) and confinement regime (l or H), but strongly dependent on the current density profile. Indirect evidence suggests ballooning (and possibly surface kink) modes to be responsible for the limitation in plasma pressure. LH heating and current drive show improved energy confinement (compared to OH) at low densities (-e-< 1 - 2 x 10**13 cm**-3, suprathermal electrons), but a degradation in confinement at higher densities.
Bibliographic Reference: 12TH EUROPEAN CONFERENCE ON CONTROLLED FUSION AND PLASMA PHYSICS, BUDAPEST (HUNGARY), SEPT. 2-6, 1985 WRITE TO MAX-PLANCK-INSTITUT FUER PLASMAPHYSIK, 8046 GARCHING BEI MUENCHEN (GERMANY), MENTIONING REPORT IPP III/107, 1985, PP. 3-15.
Record Number: 1989124086500 / Last updated on: 1987-01-01
Available languages: en