The movement of charged particles in electromagnetic and magnetostatic field gradients is examined. It is shown that when the orientation and amplitude of such gradients are suitably arranged, the mean force in relation to time acting on these particles remains constant in direction. Discussed are this mean force and, more generally, the validity of the theory of mean value in relation to time. The results are applied to the case of a low-density plasma, and a brief description is given of four possible applications of a device based upon such forces: as injector, plasma propellant, vacuum pump and direct converter of thermal energy into u.h.f. electromagnetic energy. Orders of magnitude are stated. In two annexes, the authors determine the limits of validity of the theory based on mean value, and a comparison is made with an exact theory. The curves obtained are described and classified by analogue computer.

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A theory of the physical mechanism of ion entrainment by accelerated electrons is presented. It is shown that under the influence of these fields the electrons describe helixes whose diameter and pitch vary along the axis of motion as a function of the difference between the cyclotron frequency and the frequency of the applied hf field. The space charge thus created accelerates the ions. The coupling between the equations of motion of the electron and ion fluids calls for the introduction of a tensor mass; viz., that of the relativistic mass of the electrons in the two equations in x and y describing the transverse movement of the electrons, and that of the ions in the axial motion equation in z. The physical consequences of this theoretical study are then discussed, and three typical experimental results are given that illustrate three of these consequences.

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