Numerical Study of Radiation Emission from the Argon Plasma Focus

Ion populations and emitted spectrum of argon plasma have been calculated using the POPULATE and SPECTRA codes of the RATION suite at different conditions (electron temperatures, electron densities, ion densities, plasma size) for LTE and NLTE models. Expected argon plasma spectra at certain electron temperature range have been plotted. The suitable electron temperatures ranges for argon plasma soft X-ray (3–4 keV) emission and EUV (60–200 eV) emission have been investigated. POPULATE and SPECTRA codes have been presented as a good assisted tools for plasma focus diagnostics.     

Simulation of Nitrogen and Oxygen Spectra Emitted from High Density Hot Plasma

The expected emission spectra of nitrogen and oxygen high density plasma have been studied for different conditions. Expected nitrogen and oxygen plasma spectra at certain electron temperature range have been plotted. Suitable electron temperature ranges for nitrogen and oxygen plasma soft X-ray emission and extreme ultraviolet emission have been investigated. Numerical experiments confirm the possibility of developing nitrogen and oxygen plasma focus as a powerful X-ray radiation source for water-window X-ray microscopy, by selecting the working gas pressure, choosing corresponding design and operating parameters of the device. We have illustrated that the results obtained from XRAYFIL simulation could be used to provide spectroscopic information of the plasma focus simulated by Lee model.     

Analysis of X-ray spectra in 14.5-GHz ECR ion source for optimizing operation conditions

An electron cyclotron resonance (ECR) ion source operating at 14.5 GHz was developed for the generation of charged ions at the Korea Atomic Energy Research Institute (KAERI). Experiments were carried out to study the plasma inside the ECR ion source by analyzing the X-ray spectra generated by it. The X-ray energy distribution and electron energy inside the plasma chamber are influenced by the status of the heated plasma. That status depends on various operation parameters such as microwave power, injected gas-pressure, and solenoid and trim coil currents. X-ray spectra were recorded to find the correlation between the plasma and the X-rays for variations in the operation parameters. A standard NaI(Tl) detector was used for that purpose. The X-ray energy distribution was studied in the range of 100–500 W for radiofrequency power. The influence of the injected gas pressure and the mirror ratio in the emission of X-rays were analyzed.     

Sahand Plasma Focus Emitted More Than 35 J in Yield Neon Soft X-ray

X-ray emission from neon plasma produced in Sahand Filippov type plasma focus device is investigated. Detecting system used in our experiments is a five channel pin diode detector. Soft X-ray emissions from neon gas at different charging voltages and working gas pressures are studied and optimum condition for production of soft X-ray for Sahand plasma focus facility is obtained. Results show that for every working pressure there is a charging voltage at which the average soft X-ray yield is maximum and this optimum charging voltage increases with increasing gas pressure. For 0.25, 0.50 and 0.75 Torr neon the optimum voltages are 12, 13 and 16 kV respectively. The highest average soft X-ray yields produced at 0.50 Torr which is about 35.87 ± 1.18 J. Also soft X-ray production decreased after a certain pressure which for our experiments is 0.50 Torr. The variation of relative hard X-ray yield with charging voltage and working gas pressure is also investigated. The results show that 0.50 Torr is also the best operating gas pressure for optimum hard X-ray production in Sahand Filippov type plasma focus device.     

Soft X-ray Imaging using a Neon Filled Plasma Focus X-ray Source

A 3 kJ Mather-type UNU/ICTP plasma focus device with neon filling is used, for the first time, as a soft X-ray source for imaging of thin biological samples including insects. A charge-coupled-device (CCD) based pinhole projection system, placed in a differentially pumped chamber, is used for radiography using neon soft X-rays. The image brightness, contrast and resolution have been optimized by varying soft X-ray yield, pinhole size, camera chamber length and X-ray filters. The system can simply be modified for table-top soft X-ray microscopy of thin biological samples.     

Comparison of sample temperature effect on femtosecond and nanosecond laser-induced breakdown spectroscopy

In this paper, we investigated the emission spectra of plasmas produced from femtosecond and nanosecond laser ablations at different target temperatures in air. A brass was selected as ablated target of the experiment. The results indicated that spectral emission intensity and plasma temperature showed similar trend for femtosecond and nanosecond lasers, and the two parameters were improved by increasing the sample temperature in both cases. Moreover, the temperature of nanosecond laser-excited plasma was higher compared with that of femtosecond laser-excited plasma, and the increase of the plasma temperature in the case of nanosecond laser was more evident. In addition, there was a significant difference in electron density between femtosecond and nanosecond laser-induced plasmas. The electron density for femtosecond laser decreased with increasing the target temperature, while for nanosecond laser, the electron density was almost unchanged at different sample temperatures.     

Spatial and Excitation Variations for Different Applied Voltages in an Atmospheric Neon Plasma Jet

A neon plasma jet was generated in air,driven by a 9 kHz sinusoidal power supply.The characteristics of the plasma plume and the optical spectra with plasma propagation for different applied voltages were investigated.By increasing the applied voltage,the plasma plume first increases and then retracts to become short and bulky.The shortened effect of Ne plasma plume(about 10 mm) for the further voltage increasing is more apparent than that of He(about3 mm) and Ar(about 1 mm).Emission intensity of the N_2(337 nm) increases with the applied voltage,gradually substituting the emission intensity of Ne(702 nm and 585 nm) as the noticeable radiation.At the nozzle opening,the Ne(702 nm) emission dominates,while the Ne(585 nm)emission is most noticeable around the tip of the plasma plume.The spatial distribution of the three spectral lines indicates that Ne(702 nm) emission decreases dramatically with plasma propagation while Ne(585 nm) and N_2(337 nm) emissions reach their maxima at the middle of the plasma plume.The results indicate that the Ne(702 nm) emission is much more sensitive to the average electron temperature and the density of the high-energy electrons,so it changes greatly at the tube nozzle and little at the tip region as the voltage increases.The population of high-energy electrons,the average electron temperature,the collision with air molecules and the Penning effect between Ne metastables and air molecules may explain their different variations with plasma propagating and voltage increasing.     

Diagnosis of Electron, Vibrational and Rotational Temperatures in an Ar/N2 Shock Plasma Jet Produced by a Low Pressure DC Cascade Arc Discharge

In this paper,a low pressure Ar/N2 shock plasma jet with clearly multicycle alternating zones produced by a DC cascade arc discharge has been investigated by an emission spectral method combined with Abel inversion analysis.Plasma emission intensity,electron,vibrational and rotational temperatures of the shock plasma have been measured in the expansion and compression zones.The results indicate that the ranges of the measured electron temperature,vibrational temperature and rotational temperature are 1.1 eV to 1.6 eV,0.2 eV to 0.7 eV and 0.19 eV to 0.22 eV,respectively,and it is found for the first time that the vibrational and rotational temperatures increase while the electron temperature decreases in the compression zones.The electron temperature departs from the vibrational and the rotational temperatures due to non-equilibrium plasma efects.Electrons and heavy particles could not completely exchange energy via collisions in the shock plasma jet under the low pressure of 620 Pa or so.     

Optical Emission Spectroscopy Analysis of the Early Phase During Femtosecond Laser-Induced Air Breakdown

Single-pulse and double-pulse optical emission spectroscopy （OES） analyses were carried out in air by using ultrashort laser pulses at atmospheric pressure. The aim of this work is to use spectroscopic methods to analyze the early phase of laser-induced plasma after the femtosecond laser pulse. The temporal behavior of emission spectra of air plasma has been characterized. In comparison with the single-pulse scheme, the plasma emission obtained in the double-pulse scheme presents a more intense continuum along with several additional ionic lines. As only one line is available in the single-pulse scheme, the plasma temperature measurements were performed using only the relative line-to-continuum intensity ratio method, whereas the relative line-to-line intensity ratio method and the relative line-to-continuum intensity ratio method were used simultaneously to estimate the electron temperature in the double-pulse scheme. The results reveal that the temperature values obtained by the two methods in the double-pulse scheme agree. Moreover, this shows that the relative line-to-continuum intensity ratio method is suitable for early phase of laser-induced plasma diagnostics. The electron number density was estimated using the Stark broadening method. In the early phase of laser-induced plasma, the temporal evolution of the electron number density exhibits a power law decrease with delay time.     

Low-Energy Plasma Focus as a Tailored X-Ray Source

A low-energy (2.3 kJ) plasma focus energized by a single 32-F capacitor charged at 12 kV with filling gases hydrogen, neon, and argon is investigated as an X-ray source. Experiments are conducted with a copper and an aluminum anode. Specifically, attention is given to tailoring the radiation in different windows, e.g., 1.2–1.3 keV, 1.3–1.5 keV, 2.5–5 keV, and Cu-K line radiation. The highest X-ray emission is observed with neon filling and the copper anode in the 1.2–1.3 keV window, which we speculate to be generated due to recombination of hydrogenlike neon ions with a few eV to a few 10s of eV electrons. The wall-plug efficiency of the device is found to be 4%. The other significant emission occurs with hydrogen filling, which exhibits wall-plug efficiency of 1.7% for overall X-ray emission and 0.35% for Cu-K line radiation. The emission is dominated by the interaction of electrons in the current sheath with the anode tip. The emission with the aluminum anode and hydrogen filling is up to 10 J, which corresponds to wall-plug efficiency of 0.4%. The X-ray emission with argon filling is less significant.     

Temporal and Spatial Evolution of Laser-Induced Plasma from a Slag Sample

Laser-Induced Breakdown Spectroscopy(LIBS) has been demonstrated to be an effective method for slag analysis.In order to better clarify the nature of the plasma generated from a slag sample,an Nd:YAG pulse laser at 1064 nm wavelength was used to ablate the slag sample in air.The temporal and spatial evolutions of plasma parameters,including emission intensity,electronic density and plasma temperature,have been studied.It is shown that the electron density and plasma temperature drop off rapidly with the delay time as a result of plasma expansion and cooling.It has been found that the electron density of the whole plasma is close to that of the center regions in the plasma.The results of the spatial distributions on the two-dimensional plane have shown that there is a big region with lower electron density values caused by the recombination process in the center of the plasma.The maximum of the plasma temperature takes place at the regions close to the target,and the border of the plasma front-head has higher plasma temperatures than that of the center part.     

X-ray Emission from Argon Plasma Focus Contaminated with Copper Impurities in AECS PF-2 Using Five Channel Diode Spectrometer

In this work, the X-ray ratio method using different thicknesses of Al foil absorbers was used to study the influence of copper impurities on the electron temperature determination of the focused plasma in AECS PF-2 with argon filling gas. Five channels of BPX 65 PIN diodes were employed to record the X-ray pulses generated by a low energy Mather type plasma focus device energized by a 25 μF, 15 kV (2.8 kJ) capacitor bank consisting of two capacitors each with 12.5 μF capacity connected in parallel. By comparing the ratio values experimentally obtained for a series of shots at various pressures with theoretically calculated ratios for argon plasma, the X-ray emission ratio was found to correspond to the Cu–K_α line radiation for most of the discharges and only about less than 10% of the measurements give the correct expected electron temperature of 1.5–2.5 keV for the focused argon plasma.     

Quantitative analysis of saindha salt using laser induced breakdown spectroscopy and cross-validation with ICP-MS

Saindha salt is considered to be more advantageous than the other edible salts for the patients suffering from diabetes,blood pressure and kidney diseases.To explore the constituent elements of this salt,laser induced breakdown spectroscopy(LIBS) has been exploited for its qualitative and quantitative analysis.The third harmonic(355 nm) of a Q-switched Nd:YAG laser has been used to produce the saindha salt plasma and the time integrated optical emission spectra were registered using a set of six miniature spectrometers covering the spectral range of 230-805 nm.The spectroscopic analysis of the emission spectra predominately revealed numerous neutral or singly ionized emission lines of Ca,Mg,Na,K,Fe,Sr,Si,Li and Al.The laser produced plasma was characterized by calculating the electron temperature from the Boltzmann plots and the electron number density from the Stark broadened line profile as a function of laser irradiance and distance from the target sample.The relative concentration of the constituent elements was extracted by the integrated line intensities of the strongest spectral line of each element using the self-calibration-LIBS(SC-LIBS) and one-line calibration free-LIBS(OLCF-LIBS) methods.For cross-validation,the LIBS results have been compared with that obtained from the inductively coupled plasma-mass spectroscopy(ICP-MS) showing good agreement.     

Studies on Ion Emission from the Plasma Focus Device by Using Ion Collector and Track Detector

Ion beam emission from a neon gas filled plasma focus device has been studied by using ion collector and solid state nuclear track detector. The neon ion beam emission is found to be highly pressure dependant and it is maximum at a pressure of 0.3 Torr. The maximum ion energy at 0.3 Torr is estimated to be 1 MeV. Preliminary results on solid state nuclear track detector indicate the formation of tracks in CR-39 due to exposure of neon ions. The average rim diameter of tracks is measured to be 4.35 μm and the number of track is of the order of 10¹⁰ track/m².     

Measurement of the first Townsend's ionization coefficient for atmospheric pressure neon by a dielectric barrier discharge

Fast photography and optical emission spectroscopy are implemented in a 5 mm neon gap dielectric barrier discharge (DBD) at atmospheric pressure with quartz glass used as the dielectric layer. Results show that it starts with a Townsend discharge and ends at a sub-normal glow discharge in neon DBD. Based on the Townsend discharge, the first ionization coefficient of neon is measured. The measurements are consistent with those at low pressure. Optical emission spectroscopy indicates that the spectra are mainly composed of atomic lines of neon, molecular bands and molecular ion bands originating from inevitable gas impurities (mainly nitrogen). Moreover, spectral lines emitted from atomic neon corresponding to the transitions (2p⁵ 3p → 2p⁵ 3s) are predominant. Although the second positive system of N₂(C³Π_u → B³Π_g) is observed, their intensities are too weak compared with neon's spectrum. The molecular nitrogen ion line of 391.4 nm is observed. It reveals that Penning ionization between high energy neon excited states and the inevitable gas impurities plays an important role in the value of the α coefficient.     

SUNIST球形托卡马克的研究进展

球形托卡马克为聚变能的商业应用提供了一条可能的途径。中国联合球形托卡马克SUNIST以真空室的环向和极向都有绝缘隔缝为结构特征。该装置的主要任务是研究低环径比等离子体的基本特性和等离子体的非感应加热与电流驱动。包括同轴磁螺旋性注入电流启动、电极放电辅助电子回旋波电流启动、电子伯恩斯坦波以及离子高次谐波快波加热与电流驱动。装置已经顺利组装完毕,并安装了磁测量、静电探针和软X射线等基本的诊断系统。目前正处于系统联调阶段。     

Investigation of E–H mode transition in magnetic-pole-enhanced inductively coupled neon–argon mixture plasma

In this paper, E–H mode transition in magnetic-pole-enhanced inductively coupled neon–argon mixture plasma is investigated in terms of fundamental plasma parameters as a function of argon fraction(0%–100%), operating pressure(1 Pa, 5 Pa, 10 Pa and 50 Pa), and radio frequency(RF) power(5–100 W). An RF compensated Langmuir probe and optical emission spectroscopy are used for the diagnostics of the plasma under study. Owing to the lower ionization potential and higher collision cross-section of argon, when its fraction in the discharge is increased, the mode transition occurs at lower RF power; i.e. for 0% argon and1 Pa pressure, the threshold power of the E–H mode transition is 65 W, which reduces to 20 W when the argon fraction is increased. The electron density increases with the argon fraction at afixed pressure, whereas the temperature decreases with the argon fraction. The relaxation length of the low-energy electrons increases, and decreases for high-energy electrons with argon fraction, due to the Ramseur effect. However, the relaxation length of both groups of electrons decreases with pressure due to reduction in the mean free path. The electron energy probability function(EEPF) profiles are non-Maxwellian in E-mode, attributable to the nonlocal electron kinetics in this mode; however, they evolve to Maxwellian distribution when the discharge transforms to H-mode due to lower electron temperature and higher electron density in H-mode. The tail of the measured EEPFs is found to deplete in both E-and H-modes when the argon fraction in the discharge is increased, because argon has a much lower excitation potential(11.5 eV) than neon(16.6 eV).     

Line identification of extreme ultraviolet(EUV) spectra from low-Z impurity ions in EAST tokamak plasmas

Extreme ultraviolet(EUV) spectra emitted from low-Z impurity ions in the wavelength range of10–500 ? were observed in Experimental Advanced Superconducting Tokamak(EAST)discharges. Several spectral lines from K-and L-shell partially ionized ions were successfully observed with sufficient spectral intensities and resolutions for helium, lithium, boron, carbon,oxygen, neon, silicon and argon using two fast-time-response EUV spectrometers of which the spectral intensities are absolutely calibrated based on the intensity comparison method between visible and EUV bremsstrahlung continua. The wavelength is carefully calibrated using wellknown spectra. The lithium, boron and silicon are individually introduced for the wall coating of the EAST vacuum vessel to suppress mainly the hydrogen and oxygen influxes from the vacuum wall, while the carbon and oxygen intrinsically exist in the plasma. The helium is frequently used as the working gas as well as the deuterium. The neon and argon are also often used for the radiation cooling of edge plasma to reduce the heat flux onto the divertor plate. The measured spectra were analyzed mainly based on the database of National Institute of Standards and Technology. As a result, spectral lines of He Ⅱ, Li Ⅱ–Ⅲ, B Ⅳ–Ⅴ, C Ⅲ–Ⅵ, O Ⅲ–Ⅷ, Ne Ⅱ–Ⅹ,Si Ⅴ–Ⅻ, and Ar Ⅹ–XVI are identified in EAST plasmas of which the central electron temperature and chord-averaged electron density range in T_(e0)=0.6–2.8 keV and n_e=(0.5–6.0)×10~(19) m~(-3), respectively. The wavelengths and transitions of EUV lines identified here are summarized and listed in a table for each impurity species as the database for EUV spectroscopy using fusion plasmas.     

Analysis of electron temperature,impurity transport and MHD activity with multi-energy soft x-ray diagnostic in EAST tokamak

A new edge tangential multi-energy soft x-ray(ME-SXR) diagnostic with high temporal(≤ 0.1 ms) and spatial(~1 cm) resolution has been developed for a variety of physics topics studies in the EAST tokamak plasma. The fast edge electron temperature profile(approximately from r a~ 0.6 to the scrape-off layer) is investigated using ME-SXR diagnostic system. The data process was performed by the ideal ‘multi-foil' technique, with no priori assumptions of plasma profiles. Reconstructed ME-SXR emissivity profiles for a variety of EAST experimental scenarios are presented here for the first time. The applications of the ME-SXR for study of the effects of resonant magnetic perturbation on edge localized modes and the first time neon radiating divertor experiment in EAST are also presented in this work. It has been found that neon impurity can suppress the 2/1 tearing mode and trigger a 3/1 MHD mode.     

Incorporation of Nitrogen into Amorphous Carbon Films Produced by Surface-Wave Plasma Chemical Vapor Deposition

In order to study the influence of nitrogen incorporated into amorphous carbon films, nitrogenated amorphous carbon films have been deposited by using surface wave plasma chemical vapor deposition under various ratios of N2/CH4 gas flow. Optical emission spectroscopy has been used to monitor plasma features near the deposition zone. After deposition, the samples are checked by Raman spectroscopy and x-ray photo spectroscopy (XPS). Optical emission intensities of CH and N atom in the plasma are found to be enhanced with the increase in the N2/CH4 gas flow ratio, and then reach their maximums when the N2/CH4 gas flow ratio is 5%. A contrary variation is found in Raman spectra of deposited films. The intensity ratio of the D band to the G band (ID/IG) and the peak positions of the G and D bands all reach their minimums when the N2/CH4 gas flow ratio is 5%. These show that the structure of amorphous carbon films has been significantly modified by introduction of nitrogen。