Computational Study of Emitted Spectra from the Neon Plasma Focus

The expected emission spectra (full, Bremsstrahlung, recombination, and line) of neon focussed plasma have been studied for different conditions. Expected neon plasma spectra at certain electron temperature range have been plotted. The suitable electron temperatures ranges for neon plasma soft X-ray emission and extreme ultraviolet emission have been investigated. The X-ray ratio curves for various electron temperatures with probable electron and ion densities of the neon plasma produced have been computed with the assumption of non-local thermodynamic equilibrium model for the distribution of the ionic species. These ratio curves could be used for electron temperatures deduction of neon plasma focus.     

Characteristics of X-ray Hot Spots in a 3.5 kJ Plasma Focus Device at Different Pressures of Argon and Air

The present study examined the formation of hot spots in the plasma column of a 3.5 kJ Mather-type plasma focus device. Experiments were performed with air and argon as operating gases at 0.2–1.5 mbar of pressures. X-ray source images were obtained using a pinhole camera with dental X-ray film as X-ray detector. The objective was to investigate the effect of the operating conditions and gas type on formation and characteristics of the hot spots. Results showed that when using air in comparison to argon, the total X-ray emission is increased and therefore, the hot spots are covered by this high intensity emission and would be observed less frequently in the image. Using metal filters to attenuate the low-energy X-rays revealed that the most energetic or the most intense radiation was emitted from the hot spots region. The images of the X-ray source obtained using argon at the middle pressures (0.4–0.6 mbar) showed both the plasma column and the photons emitted from the anode surface. A pressure of 0.8–1.5 mbar using argon was most likely to observe the hot spots. For argon gas, the 0.9 mbar was the pressure in which the hot spots were more frequently observed with high reproducibility of location and number. Measurements revealed that the typical size of a hot spot was 10–300 µm and the distance from the anode surface was 0.5–20 mm.     

IONIZATION STATE DISTRIBUTION AND RADIATIVE COOLING RATE FOR ARGON IN A LOW-DENSITY PLASMA

This paper presents the coronal ionization state distribution for argon. The calculations includeab initiorate coefficients for collisional excitation followed by autoionization (EA), and rates for direct ionization and dielectronic and radiative recombination. The EA rate coefficients have been fitted to analytical expressions, and the fitting coefficients are tabulated. The paper then presents the calculated radiative cooling coefficient for argon ions in a low-density plasma as a function of temperature. The channels for power loss from argon ions include collisional-radiative (CR) line emission, dielectronic and radiative recombination, and bremsstrahlung emission. The power emitted via CR line emission for each ion is tabulated on a grid of temperatures and densities. The total power loss coefficient is fitted to an analytical expression in powers of the temperature.     

Comparative Study of Plasma Parameters in Magnetic Pole Enhanced Inductively Coupled Argon Plasmas

Langmuir probe measurements of radio frequency (RF) magnetic pole enhanced inductively coupled (MaPE-ICP) argon plasma were accomplished to obtain the electron number densities and electron temperatures. The measurements were carried out with a fixed RF frequency of 13.56 MHz in a pressure range of 7.5 mTorr to 75 mTorr at an applied RF power of 10 W and 100 W. These results are compared with a global (volume average) model. The results show good agreement between theoretical and experimental measurements. The electron number density shows an increasing trend with both RF power and pressure while the electron temperature shows decreasing trend as the pressure increases. The difference in the plasma potential and floating potential as a function of electron temperature measured from the electrical probe and that obtained theoretically shows a linear relation with a small difference in the coefficient of proportionality. The intensity of the emission line at 750.4 nm due to 2p 1 → 1s 2 (Paschen’s notation) transition closely follows the variation of n e with RF power and filling gas pressure. Measured electron energy probability function (EEPF) shows that electron occupation changes mostly in the high-energy tail, which highlights close similarity of 750.4 nm argon line to n e .     

Pulse-burst laser-based 10kHz Thomson scattering measurements

Thomson scattering(TS),as a popular and reliable diagnostic technique,has successfully measured electron temperatures and electron number densities of plasmas for many years.However,conventional TS techniques using Nd:YAG lasers operate only at tens of hertz.Here,we present the development of a high-repetition-rate TS instrument based on a high-speed,pulse-burst laser system to greatly increase the temporal resolution of measurements.Successful instrument prototype testing was carried out by collecting TS light from laboratory helium and argon plasmas at 10 kHz.Calibration of the instrument detection sensitivity using nitrogen/oxygen rotational Raman scattering signal is also presented.Quantitative electron number densities and electron temperatures of the plasma were acquired at 10 kHz,for stable plasma discharges as,respectively,～0.9 eV and ～5.37×10~(21)m~(-3) for the argon plasma,and ～1eV and ～6.5×1021 m~(-3) for the helium plasma.     

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).     

Triple-probe Diagnostic Measurements in Plasma of GLAST Spherical Tokamak

Triple-probe has been developed and operated successfully to characterize ECRH-assisted argon as well as hydrogen microwave plasmas in GLAST Spherical Tokamak. This technique enables to determine transient plasma parameters such as floating potential, electron temperature and electron number density in rapidly time-varying plasmas. An effective electron heating mechanism is applied to produce microwave plasma by injecting radiofrequency (RF) radiation at a frequency of 2.45 GHz in the presence of resonant toroidal magnetic field. Plasma parameters and corresponding fluctuations are measured as a function of time in different gas fill pressures for various applied magnetic fields. The results demonstrate the dependence of plasma parameters such as V _f , T _e , n _e and their fluctuations on gas fill pressure during the pre-ionization phase of the GLAST operation. Plasma behavior is observed to be closely depending on the coupling of RF power during microwave discharge. Additionally, the hydrogen plasma shows pronounced fluctuations in comparison with argon plasma with some decrease in electron temperature and densities.     

Preliminary results of optical emission spectroscopy by line ratio method in the RF negative ion source at ASIPP

Optical emission spectroscopy (OES) using the trace rare gases of Ar and Xe have been carried out in a radio frequency (RF) driven negative ion source at Institute of Plasma Physics, Chinese Academy of Science (ASIPP), in order to determine the electron temperature and density of the hydrogen plasma. The line-ratio methods based on population models are applied to describe the radiation process of the excited state particles and establish their relations with the plasma parameters. The spectral lines from the argon and xenon excited state atoms with the wavelength of 750.4 and 828.0 nm are used to calculate the electron temperature based on the corona model. The argon ions emission lines with the wavelength of 480 and 488 nm are selected to calculate the electron density based on the collisional radiative model. OES has given the preliminary results of the electron temperature and density by varying the discharge gas pressure and RF power. According to the experimental results, the typical plasma parameters is T_e ≈ 2–4 eV and n_e ≈ 1×10 ¹⁷– 8×10¹⁷ m⁻³ in front of plasma grid.     

An experimental investigation of influencing chemical factors onCs-chemisorption behavior onto stainless steel

A more accurate cesium hydroxide (CsOH)-chemisorption model is required to improve the estimation of the Cs distribution in Fukushima Daiichi Nuclear Power Station by severe-accident (SA) analysis codes. The current CsOH-chemisorption model incorporated in SA analysis codes was developed with insufficient information of chemical factors such as H₂/H₂O ratio, concentration of chemically affecting elements, heating time, and surface condition of the stainless steel (SS). Therefore, we have conducted experimental tests for CsOH-chemisorption onto SS type-304 (SS304) in order to examine the effect and dependence of such chemical factors on the CsOH-chemisorption behavior in detail. It was found that the first-order surface-reaction rate constant was influenced by not only temperature, as already known, but also H₂/H₂O ratio, CsOH concentration in the gas phase, and silicon content in SS304. Such chemical factors should be considered for the construction of the improved CsOH-chemisorption model. Another important finding is that the chemisorption behavior at lower temperatures, around 873 K, could differ from those above 1073 K. Namely, Cs–Fe–O compounds would form as the main chemisorbed Cs compounds at 873 K while Cs–Si–Fe–O compounds at more than 1073 K.     

Development of a Helicon Plasma Source for Neutral Beam Injection System of the Alborz Tokamak

Amirkabir Helicon plasma source (AHPS) has been designed and developed at the fusion laboratory of Amirkabir University of Technology for the neutral beam injection (NBI) system of the Alborz tokamak. The design parameters of the Helicon plasma source are determined to get the \( n_{e} \cong 10^{19} \,{\text{m}}^{ - 3} \) plasma density. However, the Nagoya type III antenna was used to excite the Argon plasma by the applied magneto-static field of 750 G and RF power up to 2 kW at the frequency of 13.56 MHz. Preliminary experiments are performed to confirm the Helicon mode operation of the AHPS. Mode changing from the ICP to the Helicon mode was proved by using the optical emission spectroscopy and polaroid photography technique of the plasma “blue core”. Spectroscopy measurements results show that the emission line intensity of the \( {\text{Ar}}\;{\text{II}} \) at 434.8 nm increases as the RF power increases in the range of values of 300–1000 W at the neutral background pressure of 0.7 mTorr. Also, we found that, in Helicon mode, the increase of the magneto-static field from 350 to 750 G not only increases the plasma density besides the efficiency of the RF power absorption increases.     

Study of axial double layer in helicon plasma by optical emission spectroscopy and simple probe

In this work we used a passive measurement method based on a high-impedance electrostatic probe and an optical emission spectroscope (OES) to investigate the characteristics of the double layer (DL) in an argon helicon plasma.The DL can be confirmed by a rapid change in the plasma potential along the axis.The axial potential variation of the passive measurement shows that the DL forms near a region of strong magnetic field gradient when the plasma is operated in wavecoupled mode,and the DL strength increases at higher powers in this experiment.The emission intensity of the argon atom line,which is strongly dependent on the metastable atom concentration,shows a similar spatial distribution to the plasma potential along the axis.The emission intensity of the argon atom line and the argon ion line in the DL suggests the existence of an energetic electron population upstream of the DL.The electron density upstream is much higher than that downstream,which is mainly caused by these energetic electrons.     

Experimental Verification of Modified Lee’s Model Using a Newly Designed and Constructed Filippov-Type Plasma Focus Device

A new 20 kJ Filippov-type plasma focus device has been designed and constructed in Isfahan University. The paper reports on the design and construction of the Iranian Filippov-type plasma focus device (UIPFF1) using modified Lee’s model. A Rogowski coil has been used to measure the experimental discharge current. Equivalent electric circuit of the device is RLC circuit; therefore the discharge current has a sinusoidal shape which its amplitude decreases exponentially during the time. The current signal contains a set of data from physical processes in the device as well as discharge current characteristics. In a typical discharge experiment these values were obtained: the discharge current was 181 kA, period of current signal 7.9 µs, the total inductance of the device 132 nH and electrical resistance of the circuit 77 mΩ. By averaging from data obtained with a set of five experiments the calibration factor was obtained 121 kA/V. Temporal changes in plasma focus discharge current, confirmed the occurrence of pinch at a specific pressure of argon, neon and nitrogen gases. UIPFF1 has been tested between 15 and 25 kV and wide range of pressure for various gases. Experiments at various pressures and voltages have also confirmed reproducibility and stability of the plasma focus device.     

Properties of Ion Beams Generated by Nitrogen Plasma Focus

Numerical experiments have been systematically carried out using the modified Lee model code on various plasma focus devices operated with nitrogen gas. The ion beam properties (ion beam energy, ion beam flux, ion beam fluence, beam ion number, ion beam current, power flow density, and damage factor) of the plasma focus have been studied versus gas pressure for each plasma focus device. The results show that, for these studied plasma focus devices, the mean ion energies decrease with increasing gas pressure, while the beam ion number increases with higher pressure. The fluence, flux, ion current, power flow density and damage factor have maximum values at the optimum pressure. It is shown that, the maximum power flow densities range from 10¹² to 10¹⁴ W m^?2 and the damage factor values reach almost 10⁹–10¹¹ W m^?2 s^0.5. The obtained results provide much needed benchmark reference values and scaling trends for ion beams of a plasma focus operated in nitrogen gas. These results could be used as an indicator for ion properties emitted from nitrogen plasma focus for various applications including material processing.     

Diagnostics of Argon Inductively Coupled Plasma and Dielectric Barrier Discharge Plasma by Optical Emission Spectroscopy

1. IntroductionArgon plasma has been frequently used for mate-rial processing and film fabrication processes [1l [21 [31.The efficiency of these processes has very close rela-tion with plasma parameters [4][5], such as ion den-sity, electron temperature and ion energy dlstrlbu-tion. Lots of research has been done on the relation-ship between efficiency and availability of materialprocessing and plasma parameters [6][7].Both lCP dlscharge and DBD discharge are newtype plasma systems developed…     

Characteristics of Single Cathode Cascaded Bias Voltage Arc Plasma

A single cathode with a cascaded bias voltage arc plasma source has been developed with a new quartz cathode chamber,instead of the previous copper chambers,to provide better diagnostic observation and access to the plasma optical emission.The cathode chamber cooling scheme is also modified to be naturally cooled only by light emission without cooling water to improve the optical thin performance in the optical path.A single-parameter physical model has been developed to describe the power dissipated in the cascaded bias voltage arc discharge argon plasmas,which have been investigated by utilizing optical emission spectroscopy(OES) and Langmuir probe.In the experiments,discharge currents from 50 A to 100 A,argon flow rates from 800 sccm to 2000 sccm and magnetic fields of 0.1 T and 0.2 T were chosen.The results show:(a) the relationship between the averaged resistivity and the averaged current density exhibits an empirical scaling law as η∝ j~(-0.63369) and the power dissipated in the arc has a strong relation with the filling factor;(b) through the quartz,the argon ions optical emission lines have been easily observed and are dominating with wavelengths between 340 nm and 520 nm,which are the emissions of Ar~+-434.81 nm and Ar~+-442.60 nm line,and theintensities are increasing with the arc current and decreasing with the inlet argon flow rate;and(c) the electron density and temperature can reach 2.0 × 10~(19) m~(-3) and 0.48 eV,respectively,under the conditions of an arc current of 90 A and a magnetic field of 0.2 T.The half-width of the n_e radial profile is approximatively equal to a few Larmor radii of electrons and can be regarded as the diameter of the plasma jet in the experiments.     

Spatial Evolution Study of EEDFs and Plasma Parameters in RF Stochastic Regime by Langmuir Probe

An RF compensated cylindrical Langmuir probe system has been developed and used to characterize an RF capacitive two temperature plasma discharge in a stochastic mode. The novelty of the work presented here is the use of the driven electrode （cathode） without ground shield. Measurements of the electron energy distribution function （EEDF） and plasma parameters were achieved under the following conditions： 50 W of RF power and 5× 10-2 mbar of argon pressure. The probe measurements are performed at 3 cm above the electrode and the probe was shifted radially （r direction） from the center （r = 0 cm） of the inter-electrodes region towards the chamber wall （R = 10.75 cm）. The results show that the EEDF is bi-Maxwellian and its shape remains the same through the scanned region. The farther the probe from the central region, the lower the EEDF maximum. The plasma density is observed to decrease according to a Gaussian profile along the radial direction and falls to 50% of its maximum when close to the cathode edge （r = 5.5 cm）. At the same time the effective electron temperature remains constant for r〈4 cm and increases for r≥4 cm. The high-temperature and low-temperature electrons＇ densities and temperatures are also discussed in the article.     

Modeling of Heat Fluxes in Edge Plasma of Small Size Divertor Tokamak

The heat flows out from the tokamak core region are collected on the divertor plates and external wall. Control of heat flux exhaust in the SOL and divertor plates regions is one of the important issues in tokamak physics. There are important phenomena affecting heat flows were simulated. The simulation is based on the B2SOLPS5.0 2D multifluid code. It is demonstrated that, the following results: (1) The simulation shows that, the operation of small size divertor tokamak, the divertor plate with/without impurities influence on profiles of electron, ion temperatures, and heat loads significantly. (2) Under normal direction of parallel (toroidal) magnetic field and different values of edge plasma density, strong “SOL” heat flow exists directed towards the LFS (outer) plate. (3) The simulation results show that, the increasing of the plasma density strong influence on the ion and electron poloidal heat fluxes profile significantly. The ion and electron polodial heat flux increase by factor “~8” and “2.4” times. (4) The simulation results show that the in–out asymmetry of heat fluxes was reversed when switching on/off E × B drifts in the edge plasma of this tokamak. (5) The simulation results show correlation between the in–out asymmetry divertor heat fluxes and E × B drift velocity. (6) The observed heat loads asymmetry between HFS and LFS plates can be explained with the radial electric field in SOL. (7) Also the simulation results performed result in, the in–out asymmetry strong influence on the characteristic length of ion poloidal heat flux.     

Comparison of heating mechanisms of argon helicon plasma in different wave modes with and without blue core

In this work,we investigated the discharge characteristics and heating mechanisms of argon helicon plasma in different wave coupled modes with and without blue core.Spatially resolved spectroscopy and emission intensity of argon atom and ion lines were measured via local optical emission spectroscopy,and electron density was measured experimentally by an RFcompensated Langmuir probe.The relation between the emission intensity and the electron density was obtained and the wavenumbers of helicon a...     

Initial Plasma Formation in the GLAST-II Spherical Tokamak

This paper reports the initial plasma formation in glass spherical tokamak (GLAST-II) with electron cyclotron resonance pre-ionization assisted startup. Initially, a plasma current of 3 kA has been produced for duration of about 0.5 ms after establishing optimum conditions for microwave absorption at 2.45 GHz. Plasma current is then enhanced up to 5 kA by applying a small vertical magnetic field that provides additional plasma heating and shaping. Applied vertical field is optimized experimentally and optimal value is found to be 40 Gauss for this experiment. Plasma current and loop voltage are monitored by using Rogowski coil and toroidal loop of wire. A fast framing camera (5000 fps) is used for temporal investigation of plasma during the discharge scenario. A fast photodiode (BPX-65) and USB4000 spectrometer are used to record the signature of plasma current and the impurity content (O₂, H etc.). Cross-sectional average electron temperature is also estimated from plasma resistivity and found to be 6.1 eV for maximum plasma current of 5 kA.     

Angular Distribution of Argon Ions and X-Ray Emissions in the Apf Plasma Focus Device

Angular distribution of ion beam emission from an argon gas-filled plasma focus devices has been investigated using an array of five Faraday cups. The argon ion beam emission is found to be highly pressure-dependent and reaches its maximum at the pressure of 1 torr. The ions flux decreased as the working pressure increased; the maximum ion density at 1 torr was estimated to be around 9.24 × 10²⁴ ions/steradian. Also, the study on the angular distribution of X-rays has been carried out using TLD-100 dosimeters. The intensity of ions reduced significantly at angles higher than ±11° but the X-ray distribution was bimodal, peaked approximately at ±15°.