THE CLUSTER MAGNETIC-FIELD INVESTIGATION

The Cluster mission provides a new opportunity to study plasma process es and structures in the near-Earth plasma environment. Four-point mea surements of the magnetic field will enable the analysis of the three dimensional structure and dynamics of a range of phenomena which shape the macroscopic properties of the magnetosphere. Difference measureme nts of the magnetic field data will be combined to derive a range of p arameters, such as the current density vector, wave vectors, and disco ntinuity normals and curvatures, using classical time series analysis techniques iteratively with physical models and simulation of the phen omena encountered along the Cluster orbit. The control and understandi ng of error sources which affect the four-point measurements are integ ral parts of the analysis techniques to be used. The flight instrument ation consists of two, tri-axial fluxgate magnetometers and an on-boar d data-processing unit on each spacecraft, built using a highly fault- tolerant architecture. High vector sample rates (up to 67 vectors s(-1 )) at high resolution (up to 8 pT) are combined with on-board event de tection software and a burst memory to capture the signature of a rang e of dynamic phenomena. Data-processing plans are designed to ensure r apid dissemination of magnetic-field data to underpin the collaborativ e analysis of magnetospheric phenomena encountered by Cluster.