Real-time control of internal transport barriers in JET
We present the results of recent experiments related to real-time control of internal transport barriers (ITBs) in JET. Using a simple criterion to characterise the ITB existence, location and strength, we have successfully controlled for the first time the radial electron temperature profile within the ITB. The dimensionless variable used in the real-time algorithm - ratio of the ion gyro-radius to the local gradient scale length of the electron temperature - is a measure of the normalised electron temperature gradient and characterises satisfactorily the main ITB features with a relatively low computational cost. We show several examples of control of this variable in various experimental conditions of toroidal field and plasma current, using different heating systems as control actuators. We also present a double-loop feedback scheme where both the global neutron rate from D-D reactions and the ITB strength are controlled simultaneously. In this case the ITB is sustained in a fully non-inductive current drive regime during several seconds. With the proposed control method, disruptions are avoided by holding the plasma performance at a prescribed target and this opens the route towards stationary operation of tokamak plasmas with ITBs. Initial results suggest that the additional control of the current profile is an important issue for achieving steady-state operation, in particular in the triggering and the sustainment of the ITB.
Bibliographic Reference: An article published in: Plasma Physics and Controlled Fusion, 44 (July 2002), pp. 1087-1104
Availability: This article can be accessed online by subscribers, and can be ordered online by non-subscribers, at: http://stacks.iop.org/0741-3335/44/1087
Record Number: 200215050 / Last updated on: 2002-07-29
Original language: en
Available languages: en