JET-R(97)16

Routes to Ignition on ITER by means of Neutral Beams

Introduction. The aim of this work is to assess the effect of Neutral Beams on the current version of ITER, principally in terms of the ability to ignite the plasma using Neutral Beam Injection (NBI). Previous work on Neutral Beams for ITER [1] modelled ITER using Rebut-Lallia-Watkins (RLW) transport [2] in L-mode. Because the RLW model is offset-linear, the confinement at high power is at least as good as for conventional H-mode scaling laws, so in effect an H-mode with excellent helium pumping properties was obtained [1]. Little attention to the LÆH mode power threshold was paid in that work, as the possibility of a high threshold had just barely started to emerge. Moreover, thanks to the offset-linear properties of the RLW model, plenty of alpha particle power is generated in L-mode, because the confinement gradually improves on L-mode scaling laws like ITER89-P with increasing input power. This enhanced L-mode confinement would make it much easier to cross the LÆH mode power threshold. The present work makes use of the JET transport model by Taroni, Cherubini, Erba, Parail and Springmann [3]. A feature of this model is that the transport in the whole of the plasma depends on the edge temperature and edge temperature gradient. The model is implemented in the JET version of the PRETOR code [1,4,5], which is the vehicle for the present simulations. To model the H-mode, an artificial barrier is introduced to the simulation code when the input power exceeds the H-mode threshold. The width of the barrier is 7.5% of the minor radius. The transport inside this barrier is chosen such, that the global confinement is L-mode or H-mode. Moreover, ELMs are explicitly modelled by switching on the L-mode for a short period of time when the ballooning limit is exceeded over the H-mode transport barrier. Using this new model, which is different to the models used before, the route to ignition on ITER by NBI is explored. Various beam energies are considered and the plasma rotation resulting from the momentum input of the beams is described.
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JETR97016 167.19 Kb