EFDA-JET-CP(04)03/01

Observation and Implication of MHD Modes for the Hybrid Scenario in JET

The Hybrid Scenarios (HS) of advanced tokamak operation are characterised by the presence of a wide central region with magnetic shear very close to zero and central q-values between 1 and 1.5 [1]. The main advantages of this mode of operation are improved energy confinement and improved MHD stability leading to a higher b limit. This paper deals with MHD modes observed in JET HS discharges where the target q-profile is obtained by a combination of LHCD, NBI and ICRH heating. MHD modes such as (3,2), (4,3), (5,3) NTMs, fishbone instabilities, sawtooth and ELMs were observed. In this paper the focus will be on the triggering types of the (3,2) NTM. The bN versus r* will be determined at the (3,2) NTM onset. The effect of the (3,2) NTM on the energy confinement will be examined, as well as the influence of different MHD mode types on the (3,2) NTM island width and the influence of the (3,2) NTM on the central electron and ion temperatures.
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