Improvement of circuit oscillation generated by underwater high voltage pulse discharges based on pulse power thyristor

High voltage fracturing technology was widely used in the field of reservoir reconstruction due to its advantages of being clean, pollution-free, and high-efficiency. However, high-frequency circuit oscillation occurs during the underwater high voltage pulse discharge process, which brings security risks to the stability of the pulse fracturing system. In order to solve this problem, an underwater pulse power discharge system was established, the circuit oscillation generation conditions were analyzed and the circuit oscillation suppression method was proposed. Firstly, the system structure was introduced and the charging model of the energy storage capacitor was established by the state space average method. Next, the electrode high-voltage breakdown model was established through COMSOL software, the electrode breakdown process was analyzed according to the electron density distribution image, and the plasma channel impedance was estimated based on the conductivity simulation results. Then the underwater pulse power discharge process and the circuit oscillation generation condition were analyzed, and the circuit oscillation suppression strategy of using the thyristor to replace the gas spark switch was proposed. Finally, laboratory experiments were carried out to verify the precision of the theoretical model and the suppression effect of circuit oscillation. The experimental results show that the voltage variation of the energy storage capacitor, the impedance change of the pulse power discharge process, and the equivalent circuit in each discharge stage were consistent with the theoretical model. The proposed oscillation suppression strategy cannot only prevent the damage caused by circuit oscillation but also reduce the damping oscillation time by77.1%, which can greatly improve the stability of the system. This research has potential application value in the field of underwater pulse power discharge for reservoir reconstruction.

A study of pulsed high voltage driven hollow-cathode electron beam sources through synchronous optical trigger

In this study,a pulsed,high voltage driven hollow-cathode electron beam sources through an optical trigger is designed with characteristics of simple structure,low cost,and easy triggering.To validate the new design,the characteristics of hollow-cathode discharge and electron beam characterization under pulsed high voltage drive are studied experimentally and discussed by discharge characteristics and analyses of waveform details,respectively.The validation experiments indicate that the pulsed high voltage supply significantly improves the frequency and stability of the discharge,which provides a new solution for the realization of a high-frequency,high-energy electron beam source.The peak current amplitude in the high-energy electron beam increases from 6.2 A to 79.6 A,which indicates the pulsed power mode significantly improves the electron beam performance.Besides,increasing the capacitance significantly affects the highcurrent,lower-energy electron beam more than the high-energy electron beam.

A Control System Design to Establish Dose-Response Relationships in Wound Healing Therapy

Advanced biophysical wound healing therapies can apply mechanical, electrical, or light energy to re-stimulate healing processes in chronic wounds. Despite the growing evidence of the clinical efficacy of these therapies, the optimal treatment stimulation parameters remain unknown and there are no standard treatment protocols. We introduce a closed-loop control design as an experimental system to study the dose-response of wound healing therapy treatment within a prescribed multidimensional and multimodal stimulation parameter space. Systems engineering approaches are applied to the control problem for estimation of a transfer function and model equations derived for use in optimal model-based control. The experimental control system design consisted of simultaneous application of biophysical energies inputted into a wound system. A study design set up including the use of negative pressure wound therapy, electrical stimulation therapy, and photobiomodulation device systems was described. Treatment stimulation parameters were selected from experimental ranges used in the scientific literature. Classical control methods and model-based control were suggested for model selection and evaluation and design of the overall control system. An experimental design for multimodal biophysical wound healing therapy control system is introduced to establish the dose-response interactions for development of therapeutic applications and device design.

The Degradation of Organic Pollutants by Bubble Discharge in Water

Organic pollutants could be degraded by using bubble discharge in water with gas aeration in the discharge reactor and more plasma can be generated in the discharge process. When pulsed high voltage was applied between electrodes with gas aerated into the reactor, it showed that bubbles were broken, which meant that breakdown took place. It could also be observed that the removal rate of phenol increased with increasing discharge voltage or pulse frequency, and with reducing initial phenol concentration or solution electric conductivity. It could remove more amount of phenol by oxygen aeration. With increasing oxygen flow rate, the removal rate increased. There was little difference with air or nitrogen aeration for phenol removal. The solution temperature after discharge increased to a great extent. However, this part of energy consumption did not contribute to the reaction, which led to a reduction in the energy utilization efficiency.

Degradation of Acid Orange 7 Dye in Two Hybrid Plasma Discharge Reactors

To get an optimized pulsed electrical plasma discharge reactor and to increase the energy utilization efficiency in the removal of pollutants, two hybrid plasma discharge reactors were designed and optimized. The reactors were compared via the discharge characteristics, energy transfer efficiency, the yields of the active species and the energy utilization in dye wastewater degradation. The results showed that under the same AC input power, the characteristics of the discharge waveform of the point-to-plate reactor were better. Under the same AC input power, the two reactors both had almost the same peak voltage of 22 kV. The peak current of the point-to-plate reactor was 146 A, while that of the wire-to-cylinder reactor was only 48.8 A. The peak powers of the point-to-plate reactor and the wire-to-cylinder reactor were 1.38 MW and 1.01 MW, respectively. The energy per pulse of the point-to-plate reactor was 0.2221 J, which was about 29.4% higher than that of the wire-to-cylinder reactor （0.1716 J）. To remove 50% Acid Orange 7 （AO7）, the energy utilizations of the point-to-plate reactor and the wire- to-cylinder reactor were 1.02×10^-9 mol/L and 0.61×10^-9 mol/L, respectively. In the point-to- plate reactor, the concentration of hydrogen peroxide in pure water was 3.6 mmol/L after 40 min of discharge, which was higher than that of the wire-to-cylinder reactor （2.5 mmol/L）. The concentration of liquid phase ozone in the point-to-plate reactor （5.7×10^-2 mmol/L） was about 26.7% higher than that in the wire-to-cylinder reactor （4.5×10^-2 mmol/L）. The analysis results of the variance showed that the type of reactor and reaction time had significant impacts on the yields of the hydrogen peroxide and ozone. The main degradation intermediates of AO7 identified by gas chromatography and mass spectrometry （GCMS） were acetic acid, maleic anhydride, p- benzoquinone, phenol, benzoic acid, phthalic anhydride, coumarin and 2-naphthol. Proposed degradation pathways were elucidated in light of the analyzed degradation products.