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In boronised discharges on TEXTOR heated with tangential NBI-co alone or in combination with NBI-counter and/or ICRH, an improved confinement regime (the I-mode) has been discovered. The enhancement factor of the confinement time with respect to ITER L89P in these discharges varied between 2.2 at a central line averaged electron density of 1.8 x 1.0 E13/cm3 to 1.2 at 4.5 x 1.0 E13/cm3. The parameter domain has been extended for improved confinement to densities up to 7 x 1.0 E13/cm3, by coating the inner surface with a thin silicon layer. Under these new conditions it is possible to obtain an enhancement factor of 1.7 even at a density of 5.5 x 1.0 E13/cm3. These high densities are reached by carefully controlling the gas puffing rate during the discharge. Higher central plasma temperatures and an enhanced neutron production rate of the plasma have been observed compared to discharges obtained under boronised conditions with the same density values, in agreement with the measurements for the stored plasma energy. The fraction of the total input power which is radiated away is also localised in the outer edge of the plasma but is larger for the density range explored. No signs of impurity accumulation in the centre of the discharge have been seen. Applying balanced NBI co+NBI-counter heating resulted in supershot like peaked density profiles with central values over 1 x 1.0 E14/cm3, although the contribution of the beam fuelling to the total particle fuelling rate at these high densities is less than 10 %.

Additional information

Authors: ONGENA J ET AL., Ecole Royale Militaire, Bruxelles (BE);ESSER H G ET AL., Forschungszentrum Jülich GmbH (KFA) (DE);HILLIS D L ET AL., Oak Ridge National Laboratory (US)
Bibliographic Reference: Article: Proceedings of the 20th European Conference on Controlled Fusion and Plasma Physics, Vol. I (1993) pp. 127-130
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