Poloidally asymmetric distribution of impurities in Joint European Torus plasmas

Poloidally asymmetric distributions of nickel ions have been observed experimentally in Joint European Torus optimized shear tokamak plasmas following nickel laser injection experiments. Two types of asymmetries occur. In the first type of asymmetry, which has earlier been observed in high-confinement mode plasmas, nickel ions accumulate on the outboard side of the poloidal cross section. This can be explained well by fast toroidal plasma rotation driven by neutral beam injection. The second type of asymmetry was opposite in position: In a radio frequency heated optimized shear plasma, nickel ions have been seen to accumulate on the inboard side of the poloidal cross section.