Soft X ray tomography during ELMs and impurity injection in JET

The soft X ray diagnostic at JET views the plasma from six directions with a total of 215 lines of sight. The good coverage of the plasma makes it pos sible to make detailed tomographic reconstructions of the soft X ray emissi on during various conditions. One of the tomography methods applied at JET is discussed: a grid based constrained optimization method that uses anisot ropic smoothness on flux surfaces as regularization. This method has made i t possible to study in detail the transport of heavy trace impurities injec ted into the plasma by laser blow-off. Impurity injection experiments in ho t ion H mode and optimized shear plasmas are presented and discussed. The a ddition of a number of features to the algorithm, notably a non-negativity constraint, has made it possible to reconstruct very localized soft X ray e mission from the wall during edge localized modes (ELMs). The detectors suf fer damage from the neutrons produced in deuterium-deuterium (DD) fusion re actions. This damage influences the sensitivity of the detectors, which mak es it necessary to cross-calibrate the cameras. A method based on tomograph ic reconstructions has been developed to achieve the cross-calibration.