Efficient Drilling of Amorphous Alloy Foils Using Low-Energy Long Pulses of a Nd:YAG Laser

Laser drilling of amorphous alloy foils was conducted using low-energy long-pulses (LP) generated using a Nd:YAG laser. Results showed that LP can drill an amorphous alloy foil more efficiently than a nanosecond pulse (NSP) can: an LP at 1 mJ can open a through-hole on an amorphous alloy foil with 25 mm thickness although single shot NSP at 20 mJ formed a crater with ca. 3 mm depth. From these findings, we infer that the markedly higher drilling efficiency of a low-energy LP than that of NSP is attributable to 1) lower plasma generation by LP than by NSP, and 2) repeated irradiation of the target material by multiple sub-pulses in an LP. Results also demonstrate that low-energy LP drilling is applicable to various metal foils and that the drilling efficiency depends on the metal species.

Femtosecond-Laser-Ablation Dynamics in Silicon Revealed by Transient Reflectivity Change

The dynamics of ablation in monocrystalline silicon, from electron-hole plasma generation to material expansion, upon irradiation by a single femtosecond laser pulse (1030 nm, 300 fs pulse duration) at a wide range of fluences is investigated using a time-resolved microscopy technique. The reflectivity evolution obtained from dynamic images in combination with a theoretical Drude model and a Two-Temperature model provides new insights on material excitation and ablation process. For all fluences, the reflectivity increased to a temporary stable state after hundreds of femtoseconds. This behavior was predicted using a temperature-dependent refractive index in the Drude model. The increase in velocity of plasma generation with increasing fluence was theoretically predicted by the Two-Temperature model. Two ablation regimes at high fluences (>0.86 J/cm2) were identified through the measured transient reflectivity and ablation crater profile. The simulation shows that the fluence triggering the second ablation regime produces a boiling temperature (silicon, 2628 K).

Spatiotemporally resolved measurements of electric field around a piezoelectric transformer using electric-field induced second harmonic (E-FISH) generation

When a piezoelectric transformer (PT) is actuated at its second harmonic frequency by a low input voltage, the generated electric field at the distal end can be sufficient to breakdown the surrounding gas, making them attractive power sources for non-equilibrium plasma generation. Understanding the potential and electric fields produced in the surrounding medium by the PT is important for effectively designing and using PT plasma devices. In this work, the spatiotemporally resolved characteristics of the electric field generated by a PT operating in open air have been investigated using the femtosecond electric field-induced second harmonic generation (E-FISH) method. Electric field components were determined by simultaneously conducting E-FISH measurements with the incident laser polarized in two orthogonal directions relative to the PT crystal. Results of this work demonstrate the spatial distribution of electric field around the PT’s output distal end and how it evolves as a function of time. Notably, the strongest electric field appears on the face of the PT’s distal surface, near the top and bottom edges and decreases by approximately 70% over 3 mm. The time delay between the PT’s input voltage and measured electric field indicates that there is an about 0.45 phase difference between the PT’s input voltage and output signal.

Numerical investigation of energy transfer efficiency from microwave radiation to plasma in a cylindrical resonant cavity

The paper presents a simplified numerical model of the hydrogen plasma generation process in a microwave resonant cavity. The model assumes electroneutrality and the prescribed electron temperature of the plasma, thus significantly reducing the computational cost. This allows for the parametric study in a wide range of operating pressures end electric field magnitudes (at a frequency of 2.45GHz). The prescribed model allows finding the effective range of operating pressures for the plasma generation. At low pressures, the collision rate is too low to effectively absorb all the emitted energy while at high pressures the electron conductivity drops which also reduces the absorption efficiency.

Efficiency of electron beam extraction to the atmosphere in an accelerator based on ion-electron emission

The use of a modern element base makes it possible to create power supplies with a transition from a direct mode of generation of an auxiliary discharge to a pulse-periodic mode with a pulse repetition rate at the level of several tens of kHz. This allows for a more flexible adjustment of the discharge parameters, keeping the average value of its current, but changing its amplitude with a corresponding change in the pulse duty cycle. In this work, using an electron accelerator based on ion-electron emission, generating a wide-aperture electron beam, we research the effect of auxiliary discharge generation mode (direct and pulse-periodic) on the efficiency of electron beam extraction into the ambient atmosphere. It is shown that, in a direct mode of electron beam generation at an accelerating voltage of 150 kV, the beam extraction coefficient does not exceed 0.25. The possibility of increasing the extraction coefficient to K = 0.55 at the same accelerating voltage of 150 kV was demonstrated without making changes to the design of the accelerator, but switching to a pulsed-periodic mode of emission plasma generation.

Plasma generation using dielectric barrier discharge reactor for phenol degradation in batik wastewater

Batik wastewater contains phenolic compounds. Phenolic compounds are hematotoxic, hepatotoxic, and capable of causing mutagenesis and carcinogenesis in humans and other living organisms. Therefore, phenol compounds need to be degraded. This study uses plasma electrolysis method with Dielectric Barrier Discharge (DBD) reactor to degrade phenolic compounds in Batik wastewater. The purpose of this study was to characterize the Dielectric Barrier Discharge (DBD) reactor, to determine the effect of voltage and type of catalyst on phenol concentration, and to determine the interaction between voltage and catalyst type on the response of phenol concentration through analysis of variance (ANOVA). The result obtained from the characterization of the reactor is ignition voltage at 1400 Volt. The best degradation results of phenolic compounds were obtained in the treatment of Batik wastewater with FeSO4 catalyst at 2600 Volt. The phenol reduction in the best conditions reached 88.73%. Based on analysis of variance (ANOVA), voltage and quadratic catalyst variables affect the response of phenol concentrations in batik waste.

Effect of non-ionizing reaction rate (assumed to be controllable) on the plasma generation mechanism and communication around RAMC vehicle during atmospheric reentry

Radio frequency (RF) blackout occurs during radio attenuation measurement C (RAMC) vehicle reentry due to the attenuation effect of the plasma sheath on the communication signal. In recent years, the mitigation mechanism of chemical reaction for RF blackout problem has gradually been studied numerically and experimentally. However, the effect of non-ionization reaction rate has been ignored because it does not directly involve the generation of electrons. In the present study, the influence of non-ionizing reaction rate on the plasma generation mechanism and EM wave attenuation was numerically solved by the plasma flow and multilayer transmission model. According to the simulation results, only the reaction rate of $$NO \rightleftharpoons N + O$$ N O ⇌ N + O has a significant effect on the electron number density in all non-ionizing reactions, and the degree of influence is less than the ionization reaction rate. The EM wave attenuation decreases with the decrease of the reaction rate of $$NO \rightleftharpoons N + O$$ N O ⇌ N + O . When the reaction rate is reduced by 25 times, the maximum attenuation of electromagnetic wave can be reduced by 12 dB. Finally, a potential scheme by reducing the reaction rate of $$NO \rightleftharpoons N + O$$ N O ⇌ N + O was proposed to mitigate the RF blackout problem.

Research stand for microplasma surface treatment of materials at atmospheric pressure

A research stand for microplasma treatment of object surfaces with the ability to move the discharge zone along the object using a program-controlled linear stepper motor has been developed. The design of the stand allows the use of different types of plasma generation systems, as well as processing with feeding of various gases such as air, nitrogen, oxygen, etc. into the discharge zone. The research bench is equipped with measuring equipment for monitoring the electrical and physical characteristics of the discharge (digital oscilloscopes, optical emission spectrometer, air ion meter, etc.). A microhardness tester, goniometer, interference microscope, tribometer, tensile testing machine, etc. can be used to further evaluate the quality and characteristics of the treated surfaces. Examples of the electrical characteristics of discharge devices tested as part of the research stand, optical emission spectroscopy of plasma, and results of measurements of the contact angle of treated objects surfaces are given.