## Rigorous fluid model for 3D analysis of the diocotron instability

A refinement to the theory published by Finn et al. is presented here. Compression effects are taken into account by a rigorous definition of the plasma length and by modifying the expression of the velocity field. The perturbation of the plasma length is calculated exactly by a suitable Green function. Growth rates and real frequencies of the unstable m{sub {theta}} = 1 mode are compared with the experimental values, showing a good agreement when compression effects are strong (i.e., for short traps).