Plasma control in advanced steady state operation of tokamaks
This article discusses specific control issues related to the advanced tokamak scenarios in which accurate tailoring of the current density profile is a requirement in connection with MHD-stable steady state operation of tokamak in a high confinement optimised shear mode. This paper deals more specifically with the possible implementation of real time current profile control on existing devices, with the example of JET. Control experiments are suggested, which could be conducted on long pulse machines (Tore Supra) in order to provide a better basis for using the "advanced" modes of operation in future steady state tokamaks (ITER). In the aim of optimising the heating and current drive waveforms, to possibly extend the duration of the high-Q optimised shear operation in JET, various control algorithms have been studied with the help of simulations based on the analysis of real pulses from the last JET experimental campaigns. Two kinds of generic feedback schemes are discussed depending upon whether the device is operated at fixed plasma current or in a genuine continuous mode, i.e. with no primary flux consumption on the average. Operation scenarios, which could be extrapolated to the continuous regime, are discussed. It is shown that for adequate current profile control in a steady state tokamak, an accurate real-time Grad-Shafranov equilibrium and magnetic flux reconstruction is necessary, and that, for high-bootstrap current and high-Q reactor operation, a compromise must be made between the accuracy of the core safety factor control and the total duration of the current fuel density ramp-up phases.
Bibliographic Reference: Article published in: Journal of Plasma and Fusion Research Series, vol.3 (2000), pp.502-508
Record Number: 200113841 / Last updated on: 2001-10-04
Original language: en
Available languages: en