Impact of Different Preheating Methods on Q-Profile Evolution in JET

Recent results on JET indicate that high performance plasmas with only a moderate heating power can be reached with a reversed q-profile whereas with a monotonic q- profile, more power is needed to trigger the ITB and reach the same performance [1]. However, it still not clear what the optimum target q-profile at the end of the preheating phase should be deeply reversed, weakly reversed or monotonic. In order to assess and optimise how much off-axis current one can or should drive, which radial location to drive it, and where to deposit the external electron heating power so that the desired target q-profile could be achieved, detailed modelling of the q-profile evolution in the preheating phase has been done. The current profile evolution during the preheating phase has been calculated with JETTO transport code [2] assuming neo-classical electrical conductivity. The following preheating methods are considered and compared: ohmic, LHCD, on-axis and off-axis minority hydrogen ICRH, on-axis and off-axis NBI as well as ECCD. The basic principle used in this study is that the power deposition and external current density profiles are calculated in a self-consistent way. Consequently, the codes to calculate the power deposition profiles are coupled to JETTO to allow a fully self-consistent simulation cycle between the transport and power deposition (plus current density) calculation with time. At present there are LHCD, NBI and ECRH/ECCD modules coupled to JETTO, but no ICRH module was found that would calculate the power deposition profiles roughly within the same time scale as the transport calculations are performed. Thus, ICRH power deposition profiles are calculated by a separate code.
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