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As a special phenomenon under transverse magnetic field (TMF) contacts, vacuum arc rotation deserves more attention. In this article, rotation characteristics of three typical TMF contacts, i.e., swastika-type, cup-shaped, and double-TMF contacts, are systematically studied. According to arc images, recorded by a high-speed camera, physical terms related to arc rotation such as rotation duration and rotation speed are clearly defined. The magnetic field and Lorentz force are calculated and the force balance of the moving arc is analyzed. On this basis, the effects of arc ignition mode, peak current, and contact type on arc rotation are investigated. Arc voltage noise as well as arc splashing outside caused by rotation is also discussed. The results show that the duration from ignition to rotation in two-point arc ignition (TPAI) mode is usually the shortest because of the rapidest constructed column formation. As the peak current increases, arc rotation becomes easier. Due to stronger TMF, the arc under double-TMF contacts has the longest rotation duration and the highest rotation speed. [ABSTRACT FROM AUTHOR]

In decades, the plasma ignition technology has drawn much attention due to its advantages. However, the numerical research on the plasma ignition of solid propellants is still limited. In this paper, a 1-D transient plasma ignition model of solid propellant is developed. A simplified chemical reaction mechanism of XM39 is employed in the model to explore the solid phase and gas phase chemical reactions and species transportations in the gas phase. The expansion process of the plasma jet is also investigated. The predicted surface pressure and ignition delay are compared to the experimental results. Good agreement with these data provides the necessary validation of the presented model. In the model, the calculated temperature profiles and the mass fraction distribution of the gas hexogen are used to characterize the reaction zone. In addition, the mass fraction distributions of CH2O and HCN are used to estimate the possibilities of different reaction paths. [ABSTRACT FROM AUTHOR]

Vacuum interrupter is widely used in the medium-voltage power system. Controlling the arc by the magnetic field is an effective method to improve the breaking capacity. The transverse magnetic field (TMF) forces the constricted arc to rotate to reduce local overheating. In this paper, three kinds of TMF contacts, which are Swastika-type contact, cup-shaped contact, and double-TMF contact that combines Swastika-type and cup-shaped contacts coaxially, are investigated in a demountable vacuum chamber with a high-speed camera. The arc voltage and current are also recorded. The experiments were conducted with circuit currents from 5 to 20 kA (root mean square) with a frequency of 50 Hz. There are four current levels in the experiment, which are 5, 10, 15, and 20 kA, and at least three tests are taken for each current level. The results showed that under low current (I = 10 kA), the arc of the three TMF contacts did not rotate. Under high current (I = 20 kA), it was observed that the arc of Swastika-type and double-TMF contacts rotated in the gap. The arc speed of double-TMF contacts is higher than that of Swastika-type contacts. The cup-shaped contacts have the highest arc voltage and noise among the three TMF contacts. The Swastika-type contacts were eroded most seriously. The simulation results show the force distribution of the arc on different locations. The resultant force makes the arc rotate counterclockwise. [ABSTRACT FROM AUTHOR]

In this paper, the influence of an external transverse magnetic field, in parallel with the cathode surface, on the ignition probabilities of a cathode spot (CS) in the Amperian and retrograde directions is developed assuming that the ignition probability of a new CS is proportional to the magnetic pressure around the old one. Furthermore, both stepwise and statistical models are established to simulate the random and retrograde motions of a single CS of vacuum arc, assuming that the 2-D motion of the CS in the $xy$ plane is equivalent to the synthesis of two independent 1-D movements along the $x$ - and $y$ -axis, respectively. With both models, the random and retrograde motions of a single Cu CS are simulated step by step and statistically, respectively. It was found that stepwise simulation results agree well with the statistical results, and they are also consistent with the relevant experimental results. The difference in retrograde motion velocity between the present stepwise model and that assuming that a new CS can be ignited in any direction around the old one is discussed. [ABSTRACT FROM PUBLISHER]

In this paper, the relationship between the external transverse magnetic field (TMF) and the ignition probability of new cathode spot in different directions is developed assuming that the ignition probability of a new cathode spot is proportional to the magnetic pressure around the old one. Furthermore, a method is established to simulate the 2-D motion of a cathode spot step-by-step. With this approach, stepwise simulations of the 2-D retrograde motion of a single Cu cathode spot are carried out in a large range of flux density of TMF ( Bem ). Simulation results indicate that, if the self-generated magnetic field Bsm exceeds the applied magnetic field Bem , i.e., B\textrm {em}\le B{sm} , there is a linear relationship between the velocity of the retrograde motion and Bem , in certain range of Bem , after which the velocity of the retrograde motion increases slowly and nonlinearly with further increase of B\textrm {em} . This phenomenon agrees well with relevant experiment results. In the linear stage, the dependence of velocity constant on the spatial step and the temporal step of the motion of cathode spot is investigated as well. Moreover, when Bem>Bsm , the velocity of cathode spot decreases with the increase of B\textrm {em} , even the macroscopic motion is still in the retrograde direction. This effect might also contribute to the reversal of cathode spot motion from the retrograde direction to the Amperian direction at strong TMF besides the predominant effect of the deflection of arc column toward the Amperian direction. [ABSTRACT FROM PUBLISHER]

Cathode spots (CSs) dynamics in the initial expansion stage of high-current triggered vacuum arc and the influence of axial magnetic field (AMF) was investigated experimentally. Experiments were conducted with butt contacts in a demountable vacuum chamber. Images of CSs were photographed with a high-speed digital camera with exposure time of 2 \(\mu \) s. The uniform and constant AMF in the intercontacts region was supplied by external magnetic field coil. In high-current triggered vacuum arc, CSs expanded across the cathode surface in basically a ring-shaped pattern. Experimental results showed that the expansion ring consisted of group CSs (GCSs) and individual CSs at the beginning of the expansion process. The GCS moved outward faster than individual CS. Research results indicated that an AMF could reduce the tendency of formation of GCS. The effect of local plasma and global plasma, which could be significantly influenced by AMF, on the motion pattern and distribution of CSs in the initial expansion stage was investigated. [ABSTRACT FROM PUBLISHER]

The expansion speed of cathode spots (CSs) in the initial expansion stage of high-current triggered vacuum arc was investigated experimentally. Experiments were conducted with butt contacts in a demountable vacuum chamber. Images of CSs were photographed with a high-speed digital camera with exposure time of 2 \mus. The uniform constant axial magnetic field (AMF) was supplied by an external magnetic field coil. The combined influence of contact gap of 2–10 mm and AMF of 0–70 mT on CSs expansion speed in the initial expansion stage was mainly investigated. Investigation results indicated that the variation of contact gap could influence the CSs expansion speed by changing the plasma density inside the cathode arc root in two ways: loss of arc plasma and constriction of arc column. AMF could weaken these two effects caused by the variation of contact gap. In addition, experimental results indicated that there existed a critical current for a given AMF. If the arc current peak was less than the critical current, the given AMF could inhibit the arc column constriction effectively both at contact gap of 8 and 10 mm, which could maintain the dependence that CSs expansion speed increased with contact gap; otherwise, the constriction of arc column played a major role in the influence on CSs expansion speed. In this case, the CSs expansion speed was lower at contact gap of 10 mm than that at 8 mm. [ABSTRACT FROM AUTHOR]

Plasma ignition mechanisms have always been the central issue in the electrothermal–chemical (ETC) launch technology. Generally, there are two types of ignition schemes, namely, the axial discharge scheme and the radial discharge scheme, and the two schemes are supposed to have different ignition characteristics. This work is devoted to study the features of different plasma ignition schemes in the ETC launch devices. A capillary discharge setup and a gap discharge setup are utilized in the experiments to represent the axial and radial discharge ignition schemes, respectively, and three types of propellants are used in the study. Using the measured data in the experiments, plasma heat fluxes are solved by a plasma–propellant interaction model. In addition, the propellant surface conditions are investigated by a scanning electron microscope after the plasma ignition experiments. The surface conditions of propellants in different ignition schemes display distinct features, which are analyzed to shed light on the characteristics of different ignition schemes and the responses of different propellants. Results are supposed to help in interpreting the plasma–propellant interaction mechanisms in different ignition schemes and provide references for the optimization design of plasma ignition installations in the ETC launch devices. [ABSTRACT FROM PUBLISHER]