A computer study of uniform-field electrodes

Effect of Electrode Profile and Polarity on Performance of Pressurized Sparkgap Switch

Sparkgap are most widely used closing switches in various high-voltage pulsed power systems and its reliable operation at desired voltage level is very essential. Conventionally by adjusting the filling gas pressure inside sparkgap switch, breakdown voltage level is altered but switching characteristics such as stability in hold-off voltage at various pressures, breakdown delay, plasma channel formation, and erosion rate are mainly dictated by adopted electrode profile and its dimensions, inter-electrode gap length and polarity. In this paper, experimental results obtained on breakdown characteristics of four different electrode geometries—Plane Parallel, Hemi-spherical, Bruce, and Rogowski and also a generalized criterion for fixing major dimensions of electrode and inter-gap length to ensure uniform electric field in the inter-electrode region are reported. All electrodes are of brass material and have common radius and thickness of 25 mm and 18 mm, respectively (surface finish <1 µm). Experiments performed on various electrode profiles in gap lengths of 2 mm to 5 mm range with pure nitrogen (N2) gas pressurization up to 50 psi reveal that among all profiles, Rogowski performs most reliably having stable hold-off voltage in wide operating range. Hold-off voltage magnitude and breakdown delay was commonly obtained higher for negative polarity in all trials. A comprehensive overview of experimental investigation reported herein compares suitability of various electrode profiles and polarity for reliable switching.

Practical approach for the design of uniform-field electrodes in transversely excited CO2 lasers

Uniform-field electrodes, which are commonly used in transversely excited ${\rm CO}_2$ lasers, are essential to produce a uniform pulsed glow discharge. In this paper, a simple and novel approach associated with practical parameters is developed for the design of Chang and Ernst profiles. This approach not only provides a maximally flat distribution of the electrode surface field but also optimizes the geometric parameter ${k_0}$. The design procedure is investigated using this method based on approximate and exact solutions; for simplicity, an iterative method will also be suggested. Furthermore, a monolithic and composite profile is presented to calculate the 3D shape of realistic electrodes that brings desired values of field uniformity and aspect ratios. The obtained distribution of the electric field is discussed to explore more detail about the proposed approach. The approximate and exact methods are in good agreement, and the boundaries of the discharge region are determined by the field distribution across the discharge midplane. The results show that a square discharge also requires optimum applied voltage.