The JET machine is equipped with 32 toroidal field coils. In order to study the effect of TF ripple on the confinement of fast particles and, more generally, on the plasma behaviour, a series of experiments was performed using only 16 TF coils. At the position of the outer limiter, this led to an increase of the ripple, delta =(Bmax-Bmin)/(Bmax+Bmin), from 1 to 12.5. The toroidal field was limited to 1.4 T, with plasma currents in the range between 2 and 3 MA. Additional heating power-levels and energy-input were kept low in order to avoid possible damage to some first wall components made out of Inconel. Experiments were carried out using 140 keV NBI injected deuterons, ICRF accelerated protons and deuterons ( approximately 0.5 to approximately 2 MeV) and 1 MeV tritons from DD reactions.
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