Influence of Surface Radius Curvature on Laser Plasma Propulsion with Ablation Water Propellant

The surface shape of liquid water is well controlled during nanosecond pulse laser ablation plasma propulsion. In this study, we measured the effect of the shape on the coupling coefficient and the specific impulse. We found that the coupling coefficient and specific impulse could be optimized by varying the surface convexity. Based on the analysis of the surface radius curvature, we demonstrate that the convex surface changes the laser focal positions to achieve high efficiency.     

Experimental Investigation of Glass-Layer Confined Ablation in Laser Plasma Propulsion

Laser plasma propulsion in glass-layer confined ablation was experimentally investigated. The results showed that compared to that of direct ablation, the coupling coefficient was enhanced over ten times. By observing the plasma expansion and calculating the ablation pressure, it was found that a higher ablation pressure and larger glass mass resulted in a higher coupling coefficient in the confined laser ablation.     

Experimental Research on Plasma Induced by TEA CO2 Laser Propulsion

Results in the air-breathing propulsion experiments with a parabolic light craft and a self-made UV-preionized 100 J TEA CO2 laser device are presented. Air disturbance and the spectrum of the plasma after the interaction of pulsed laser radiation with the light craft were studied. It was found that the focal length of the parabolic light craft had a significant effect on the air-disturbance. Two shock waves were detected for the longer focal length, while only one shock wave detected for the short focal length. The spectrum of the laser-induced plasma, the distribution of the characteristic lines, and the temporal behaviors of the air plasma were studied in detail. The results showed that, the evolution of the laser-induced plasma lasted 20μs, and the plasma spectrum would reach the maximum intensity at 7μs.     

Experimental Investigation of the Properties of an Acoustic Wave Induced by Laser Ablation of a Solid Target in Water-Confined Plasma Propulsion

Acoustic waves generated in nanosecond pulsed-laser ablation of a solid target in both air and water-confined environments were measured experimentally. It was found that the amplitude of the acoustic wave tended to decrease with an increase in water thickness. The waves were analyzed by means of fast Fourier transform. It was shown that there are several frequency components in the acoustic waves with the dominant frequency shifting from high frequency to low frequency as the thickness of the water layer increases. Furthermore, strong acoustic pressure led to enhancement of the coupling of the laser energy to the target in laser plasma propulsion.     

Ionization Induced Scattering of Femtosecond Intense Laser Pulses in Cluster Plasmas

The 45°scattering of a femtosecond (60 fs) intense laser pulse with a 20 nm FWHM (the full width at half maximum) spectrum centered at 790 nm has been studied experimentally while focused in argon clusters at intensity - 1016 W/cm2. Scattering spectra under different backing pressures and laser-plasma interaction lengths were obtained, which showed spectral blueshifting, beam refraction and complex modulation. These ionization-induced effects reveal the modulation of laser pulses propagating in plasmas and the existing obstacle in laser cluster interaction at high laser intensity and high electron density.     

Ionization Induced Scattering of Femtosecond Intense Laser Pulses in Cluster Plasmas

The 45° scattering of a femtosecond (60 fs) intense laser pulse with a 20 nm FWHM (the full width at half maximum) spectrum centered at 790 nm has been studied experimentally while focused in argon clusters at intensity ～ 1016 W/cra2. Scattering spectra under different backing pressures and laser-plasma interaction lengths were obtained, which showed spectral blueshifting, beam refraction and complex modulation. These ionization-induced effects reveal the modulation of laser pulses propagating in plasmas and the existing obstacle in laser cluster interaction at high laser intensity and high electron density.     

The Spectral Emission Characteristics of Laser Induced Plasma on Tea Samples

Laser induced breakdown spectroscopy(LIBS) provides a useful technique for food security as well as determining nutrition contents.In this paper,optical emission studies of laser induced plasma on commercial tea samples were carried out.The spectral intensities of Mg,Mn,Ca,Al,C and CN vibration bands varying with laser energy and the detection delay time of an intensified charge coupled device were studied.In addition,the relative concentrations of six microelements,i.e.,Mg,Mn,Ca,Al,Na and K,were analyzed semi-quantitatively as well as H,for four kinds of tea samples.Moreover,the plasma parameters were explored,including electron temperature and electron number density.The electron temperature and electron number density were around 11000 K and 10~(17) cm~(-3),respectively.The results show that it is reasonable to consider the LIBS technique as a new method for analyzing the compositions of tea leaf samples.     

Ion Extraction Characteristics from Photoionized Plasma by Radio-Frequency Resonance Method

In order to raise ion extraction efficiency in laser isotope separation, we have developed a radio-frequency (rf) resonance method. Then, to confirm feasibility of this method to a photoionized plasma, we experimentally studied the ion extraction characteristics.

When the rf frequency was swept under a weak magnetic field (5mT), the plasma-sheath resonance was found to occur at about 12MHz which was almost the same value as the theoretical one. Moreover, it was confirmed that the ion extraction time at the resonance frequency became the minimum.

When the magnetic field strength decreased from 5mT to zero, the ion extraction time became long. From the simulation results, this was because the plasma potential decreased with the magnetic field strength. Therefore, a magnetic field strength of more than 1mT was required to obtain a sufficient ion extraction efficiency.

To obtain the same extraction time as when applying a ?3kV dc voltage in the electrostatic method, the rf resonance method needed a voltage more than 70V_rms, in which the dc bias was ?1kV. Therefore, we confirmed that this method is feasible for the ion extraction from the photoionized plasma.     

Spectral Characterization of Laser Induced Plasma from Titanium Dioxide

Optical emission from TiO2 plasma, generated by a nanosecond laser is spectroscopically analysed. The main chemical species are identified and the spatio-temporal distribution of the plasma parameters such as electron temperature and density are characterized based on the study of spectral distribution of the line intensities and their broadening characteristics. The parameters of laser induced plasma vary quickly owing to its expansion at low background pressure and the possible deviations from local thermodynamic equilibrium conditions are tested to show its validity.     

Generation of Atmospheric Pressure Plasma by Repetitive Nanosecond Pulses in Air Using Water Electrodes

Dielectric barrier discharge （DBD） excitated by pulsed power is a promising method for producing nonthermal plasma at atmospheric pressure. Discharge characteri...     

Generation of Nonlinear Force Driven Blocks from Skin Layer Interaction of Petawatt-Picosecond Laser Pulses for ICF

The discovery of the essential difference of maximum ion energy for TW-ps laser plasma interaction compared with the 100 ns laser pulses led to the theory of a skin layer model where the control of prepulses suppressed the usual relativistic self-focusing.The subsequent generation of two nonlinear force driven blocks has been demonstrated experimentally and in extensive numerical studies where one block moves against the laser light and the other block into the irradiated target.These blocks of nearly solid state density DT plasma correspond to ion beam current densities exceeding 10^10 A/cm^2 where the ion velocity can be chosen up to highly relativistic values.Using the results of the expected ignition of DT fuel by light ion beams,a selfsustained fusion reaction front may be generated even into uncompressed solid DT fuel similar to the Nuckolls-Wood scheme where 10 kJ laser pulses produce 100 MJ fusion energy.This new and simplified scheme of laser-ICF needs and optimisation of the involved parameters.     

Spaced-Resolved Electron Density of Aluminum Plasma Produced by Frequency-Tripled Laser

1 Introduction X-ray spectra emitted from hot dense plasmas pro- vide an important diagnostic tool to infer local plasma parameters, particularly the ionization stage, density, and temperature [1]. Analysis of the emission spectra of highly stripped ions from laser-produced plasmas is potentially the most direct and reliable method for de- ducing the ultra-high-pressure plasma conditions. The development of the diagnostic methods for electron den- sity will produce important effect on the stud…     

Propagation of Intense Femtosecond Laser Pulses in Deuterated Methane and Deuterium Cluster Jets

Propagation of intense femtosecond laser pulses (60 fs, 800 nm, 120 mJ, 6×1017 W cm-2 in vacuum) in supersonic (CD4)N and (D2)N cluster jets at different background pressures was studied. Pump-probe interferometry is employed to investigate the propagation of laser beams in dense cluster jets by examining the electron density distribution of plasma channels. It was found that propagation effects, including ionization-induced defocusing and laser attenuation of incident pulses, are very different in the (CD4)N and (D2)N cluster jets. Different ionization states of CD4 and D2 molecules were observed by analyzing the transverse electron density profiles of the plasma channels and should be considered as a major reason for the differences in the propagation effects. Numerical simulations of the nonlinear propagation of femtosecond laser pulses in (CD4)N and (D2)N cluster jets were performed, and the results indicated a good reproduction of the experimental data.     

Spectral Characteristics of Laser-Induced Graphite Plasma in Ambient Air

An experimental setup of laser-induced graphite plasma was built and the spectral characteristics and properties of graphite plasma were studied. From the temporal behavior of graphite plasma, the duration of CN partials(B~2∑~+→X~2∑~+) emission was two times longer than that of atomic carbon, and all intensities reached the maximum during the early stage from0.2 μs to 0.8 μs. The electron temperature decreased from 11807 K to 8755 K, the vibration temperature decreased from 8973 K to 6472 K, and the rotational temperature decreased from7288 K to 4491 K with the delay time, respectively. The effect of the laser energy was also studied, and it was found that the thresholds and spectral characteristics of CN molecular and C atomic spectroscopy presented great differences. At lower laser energies, the electron excited temperature, the electron density, the vibrational temperature and rotational temperature of CN partials increased rapidly. At higher laser energies, the increasing of electron excited temperature and electron density slow down, and the vibrational temperature and rotational temperature even trend to saturation due to plasma shielding and dissociation of CN molecules. The relationship among the three kinds of temperatures was T_(elec)T_(vib)T_(rot) at the same time. The electron density of the graphite plasma was in the order of 10~(17)cm~(-3) and 10~(18)cm~(-3).     

Plasma Confinement Characteristics in Heliotron J--Spontaneous Change of Plasma Confinement State

Spontaneous transition of the plasma confinement mode was observed in the helicalaxis heliotron device “Heliotron J“ for three different plasma heating schemes, i.e. ECHonly, NBI-only and the combination of ECH and NBI. The transition seems to occur above a certain critical density. In addition to the confinement transition, a spontaneous shift of the hitting position of the divertor plasma flux on the wall was observed. This shift could be related with the change of the edge field topology caused by non-inductive toroidal currents.     

Two-Dimensional Numerical Simulation of Ion Collection from Pulsed Laser Induced Plasma

Abstract

The process of ion collection from a plasma produced between parallel plates by pulsed lasers was simulated with a two-dimensional numerical code. The trajectories and velocities of ions in the electric field are calculated using Newton's equation of motion. Assuming the Boltzmann relation for electrons, the electric field is calculated by solving numerically the Poisson equation. The numerical results for the time development of the ion collection are shown to be in good agreement with experimental results.     

Preparation of Chitosan Coatings Containing Calcium and Phosphorus on Titanium Surface by the Cathode Liquid Phase Plasma Technology

Chitosan (CTS) coatings contained calcium (Ca) and phosphorus (P) on titanium (Ti) surface are prepared by the cathode liquid phase plasma technology (CLPT), in a certain concentration electrolyte solution with selective additions of ammonium dihydrogen phosphate and calcium nitrate. It is indicated that the parameters for a stable discharge are voltage of 400 V, frequency of 100 Hz, duty cycle of 30% based on a large amount of experiment data. The morphology, structure and composition of the coated samples are studied by SEM, FTIR, XRD, XPS. The results demonstrate that the composite coatings are uniform, and some solid particles of inorganic salt containing calcium and phosphorus dispersed on the coatings. CA[请写出全称] tests show that the samples treated by the liquid plasma became less hydrophilic. The variation of hydrophilicity on the CLPT treated titanium is attributed to the change of the function groups on the sample surface. Meanwhile, a possible formation mechanism of the composite coatings is discussed.     

Time Characterization of High Density Gas Jet from a Pulsed Supersonic Nozzle via Laser Produced Plasma

A high-density gas jet supersonic nozzle is reported in this paper. The jitter and actuation time of the nozzle is determined by the pin discharge and laser spark radiation respectively. The jitter time of the nozzle is within 10μs with the backing pressure as high as 25 bar. With a nanosecond laser pulse focused on the gas jet about 1 mm below the nozzle, the actuation time is calculated to be about 15 ms by detecting the laser produced spark radiation, which reveals the existence of the gas jet and the relative gas density evolving with time. Consequently the gas density is estimated to be well above 10^19 cm^-3, compared with theoretical simulations from the nozzle parameters.     

The Characteristics of Columniform Surface Wave Plasma Excited Around a Quartz Rod by 2.45 GHz Microwaves

A novel surface wave plasma(SWP) source excited with cylindrical Teflon waveguide has been developed in our previous work. The plasma characteristics have been simply studied.In this work, our experimental device has been significantly improved by replacing the Teflon waveguide with a quartz rod, and then better microwave coupling and higher gas purity can be obtained during plasma discharge. The plasma spatial distributions, both in radial and axial directions, have been measured and the effect of gas pressure has been investigated. Plasma density profiles indicate that this plasma source can produce uniform plasma in an axial direction at low pressure, which shows its potential in plasma processing on a curved surface such as an inner tube wall. A simplified circular waveguide model has been used to explain the principle of plasma excitation. The distinguishing features and potential application of this kind of plasma source with a hardware improvement have been shown.