Parallel correlation studies of fluctuations and the impact of perturbations in the magnetic configuration

The plasma turbulence in the boundary of fusion relevant experiments is kno wn to have a quasi two-dimensional nature: the scale lengths perpendicular to the magnetic field are in the order of mm to cm, but parallel to the mag netic field, the correlation lengths are in the order of several meters. Re cent parallel correlation studies with Langmuir probes at the JET tokamak o ver very long connection lengths (23 m and 66 m probe tip separation along the magnetic field) showed a correlation of less than 50 %, in contrast to the finding of 80-90 % correlation in other devices at measurements with sm aller probe tip separations. However, it was not clear if this is a genuine physical property of the electrostatic turbulence in the scrape-off layer or whether perturbations in the magnetic configuration had caused an additi onal decorrelation by a time-dependent misalignment of the two probe tips a long the connecting field line. In this contribution we analyze the effect of such perturbations in the magnetic configuration on the parallel correla tion measurements in a simple model and compare the results with those of t he measurements at JET.