Igor V. Lisitsyn

Thermal processes in a streamer discharge in water

The propagation features of a streamer discharge in water have been investigated. Based on the experimental data obtained in the study of water discharges in a nonuniform electric field, due propagation of streamers is explained as the evaporation of water at the tip of the streamer and around it. The energy balance in the process of the streamer propagation is calculated for a sub-microsecond discharge in distilled water. It is shown that the energy released in the pre-breakdown process is sufficient to evaporate the liquid in the streamer channels. Similar velocity of the streamer propagation in both tap and distilled water substantiates negligible effect of ionic current density onto the streamer propagation process. These estimations, based on experiment, have relevance to the discussion of the nature of the dielectric breakdown of water.

Drilling of hard rocks by pulsed power

The drilling and demolition by low-duration, high-voltage electric pulses is based on the fact that, for very short times, the breakdown inside the solid dielectric occurs faster than the surface flashover benveen the electrodes. It was shown that most solid dielectrics could be broken down in insulating liquids, such as transformer oil, diesel fuel, and even in water. This study includes experimental and theoretical results on the drilling of rocks in insulating liquids, including transformer oil and diesel fuel.

Streamer discharge reactor for water treatment by pulsed power

The streamer discharges are effectively used for biological and chemical cleaning of air and water. Uniform streamer discharges were obtained in water at pulsed electric loading. The volume of these discharges exceeds 400 cm3 and the energy delivered to the discharge reached 40–400 J depending on the applied voltage. The reliable and durable reactor for water treatment by pulsed streamer discharges is designed and tested. High voltage pulse amplitude applied to the reactor requires improved electric insulation to prevent flashover along the reactor surface both in water and air. High mechanical stress due to high discharge current adds the requirements to the mechanical durability of the system. A small-size reactor with the volume of approximately 1 l withstands successfully both high electrical and mechanical stresses. The reactor is designed for research purposes, however it can be upgraded to use in a high repetition-rate regime necessary for industrial applications.

BREAKDOWN AND DESTRUCTION OF HETEROGENEOUS SOLID DIELECTRICS BY HIGH VOLTAGE PULSES

A mechanism explaining the breakdown of dielectrics with high intrinsic inhomogeneity like natural rocks and concrete is proposed and proved experimentally. This work has a very promising industrial application in the drilling and demolition of natural and artificial solid materials by electric pulses. The mechanism includes the breakdown of gas cavities inside the dielectric and on its surface. At a very high applied voltage, the high electric field causes the breakdown in the cavities. The displacement and conduction currents flowing through a number of such cavities result in the heating of the plasma and high pressure pulse generation. The pulsed pressure results in crack formation and finally, in the destruction of a solid material.

Pulsed Electric Breakdown and Destruction of Granite

There are various methods of rock drilling and demolition. Recently, a method utilizing pulsed power technology has appeared. This method is based on the difference of the dynamic breakdown field strength of liquid and solid dielectrics. The applicability of this method was examined using a very hard rock–granite. The features of the rock destruction have been studied. The X-ray computer tomography was used to confirm the penetration of the electrical discharge into the rock. Well-resolved marks of the electric discharge channel could be observed using this technique. Destruction effectiveness was examined for various experimental conditions. The volume of the rock destroyed in a shot and the energy consumption in the destruction process are dependent on the generator voltage. The distance between electrodes has the optimum value for a given voltage.

Drilling and demolition of rocks by pulsed power

There are various methods of rock drilling and demolition. Recently, a method utilizing pulsed power technology has appeared. This method is based on the difference of the dynamic breakdown field strength of liquid and solid dielectrics. The applicability of this method was examined. The features of the rock destruction have been studied. The mechanism explaining the breakdown of the dielectrics with high intrinsic inhomogeneity like natural rocks and concrete is proposed and proved experimentally. An inductive energy storage-opening switch system for the destruction of solid materials is designed allowing higher destruction efficiency. The experimental results using advanced diagnostics such as an image converter camera and X-ray computer tomography of samples are presented. High pulse energy experiments (up to 60 kT in pulse) have been conducted.

Role of electron clusters-Ectons-in the breakdown of solid dielectrics

A new approach is proposed for the description of early breakdown phenomena in solid dielectrics based on the appearance and action of the ectons—electron clusters in the contact point metal–solid dielectric–insulating liquid. An ecton is a result of the electric microexplosion of the electrode inhomogeneity at the triple point by the prebreakdown current described as the displacement current in a dynamic plasma-to-ground capacitor. Ecton appearance becomes possible due to the existence of partial flashover with plasma formation in these points. An ecton is a high-power source of charged particles and pulsed pressure. Injection of the charged particles into a solid dielectric and its local mechanical destruction by the pressure pulses result finally in the breakdown of the solid dielectric.

Cable guns as a plasma source in a plasma opening switch

The characteristics of a plasma generated by cable plasma guns have been studied by a laser interferometer. Cable plasma guns are frequently used as a plasma source in plasma opening switches. In our experiments, the plasma source consists of eight coaxial cable guns mounted on the outer electrode of concentric coaxial electrodes. The reproducibility of the gun in subsequent shots is found to be better than 10%, and the gun-to-gun difference is less than 15%. Assuming a symmetry of eight guns, the contour maps of the electron plasma density are plotted as functions of time. The plasma density becomes maximum near the gun nozzle and near the inner coaxial electrode. The plasma density is low in the area between the coaxial electrodes during the early time of the discharge. At a later time, the plasma fills the space between the two guns more uniformly. Still photographs of the plasma luminosity show a good correspondence with the plasma density plots which were taken 10 /spl mu/s after the discharge initiation. The plasma gun system is designed for use in a 400-kA inductive voltage adder with the inductive energy storage system.

Features of shock wave formation in a wire induced surface flashover

Explosive wire induced surface flashover has been studied as a promising method for destruction of solid materials. This method exhibits very high efficiency of electric energy transformation into the discharge and effective shock wave generation. The framing photography method is applied in order to clarify the discharge dynamics and the mechanism of the shock wave formation and propagation. The experiments performed allow to suggest the model of the pressure wave generation in the wire explosion process.

All-solid-state triggerless repetitive pulsed power generator utilizing a semiconductor opening switch

The repetitive pulsed power generator was constructed with the semiconductor opening switch (SOS) realizing the pulse compression by inductive energy storage scheme. For the preliminary pulse compression, the magnetic pulse compression system was employed. The saturable inductors and transformers transferred the stored electrical energy from the primary storage capacitor to the SOS compressing the pulse. For the final stage of the generator, the SOS was used. At the time when the SOS interrupts the current, the inductive energy stored in the circuit inductance is quickly released and transferred to the load. By tuning the current fed to the SOS, the amplitude and pulse width of the generated voltage at the 300-/spl Omega/ resistive load were 150 kV and 60 ns, respectively. The SOS allows the decrease in size, hence cost of the generator, and improves the reproducibility and reliability under the repetitive operation. Moreover, the system does not require gas discharge-based spark-gap switches or semiconductor closing switches accompanying an external trigger source, and can operate at 60 pps. Such all solid configuration and exclusion of possibility of miss-firing provide easy-to-use generator system and long lifetime.