Abstract. The plasma-wave experiment ASPI (analysis of spectra of plasma waves and instabilities) on board the INTERBALL spacecraft is a combined wave diagnostics experiment. It performs measurements of the DC and AC magnetic ®eld vector by¯ux-gate and searchcoil sensors, the DC and AC electric ®eld vector by Langmuir double probes and the plasma current by Langmuir split probe. Preliminary data analysis shows the low noise levels of the sensors and the compatibility of new data with the results of previous missions. During several months of in-orbit operation a rich collection of data was acquired, examples of which at the magnetopause and plasma sheet are presented in second part of the paper. Scienti®c objectivesThe INTERBALL project is orientated towards the investigation of the interaction between di erent parts of the magnetosphere in relation to changes in the solar wind and ionosphere. First INTERBALL-1 orbits passed through the solar wind, bow shock, magnetosheath and magnetopause regions. Several months later the orbit apogee shifted to the near-Earth magnetotail, so that INTERBALL-1 observed the tail lobes and the plasma sheet. These orbit parameters allow the neutral sheet region to be studied for several hours.Plasma waves and¯uctuations play a crucial role in the highly collisionless space plasma. Waves and¯uctu-ations are of particular importance at the plasma boundaries such as bow shock, magnetopause, neutral sheet, and plasma sheet boundary layer. Wave-particle, interactions in the plasma result in processes like: (1) anomalous transport (pitch-angle and spatial di usion, conductivity, viscosity); (2) energy redistribution and plasma heating; (3) generation of anisotropic distribution functions and their relaxation; (4) triggering of large-scale instabilities.The speci®c objectives of the ASPI wave and ®eld experiment on board INTERBALL-1 are:1. The study of the¯uctuation characteristics in di erent regions of the magnetosphere and the use of these data as high-time-resolution indicators of plasma phenomena. 2. The determination of the micro-scale plasma characteristics (e.g. di usion and anomalous transport coe cients, wave-wave and wave-particle coupling).

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