Abstract: A thyratron utilizable as a circuit interrupting protective device is provided. The thyratron includes an apertured grid between anode and cathode which is divided transversely into two parts separated by an insulating layer. Both surfaces of the composite grid remote from the insulating layer carry conductive meshes which meshes cover the exits of the apertures in the composite grid. The thickness of the insulating layer and the dimensions of the meshes are such that no point within an aperture is further from a part of the grid or a mesh than the Debye distance whereby the effects of Debye shielding tend to be reduced when a negative potential is applied between two said parts of said grid to quench a discharge previously initiated by applying positive potential to both parts of the grid.

Abstract: Thyratrons have an anode and cathode with a control grid lying between them. A primary grid located between the control grid and cathode may be used to maintain a primary discharge between it and the cathode, and improve the operating characteristics of the thyratron. However, the primary discharge may penetrate into the region where the main discharge occurs and hence increase the probability of premature triggering of the thyratron.By employing the invention, the penetration of the primary discharge into the main discharge region is reduced.A primary grid comprises two elements which have apertures. The elements are arranged so that the apertures in one element do not overlap those in the other. Thus the primary discharge which penetrates through the first element is prevented from reaching the main discharge region by the second element.