Plasma Temperature Te Research Articles

A model of radiofrequency and plasma coupling for compact ion sources and design

Inductive coupling of radiofrequency power to plasma is a complicate process, since it depends from the density of plasma itself, because ionization is a chain reaction process, and, at low density a capacitive coupling may mix with inductive coupling (with no Faraday screen). Plasma temperature Te , density ne and vector potential are closely coupled, giving nonlinear and singular systems of Partial Differential equations, which require slow iterative solutions, motivating the consideration of a 2D model, also as rapid design and first approximation tool. Plasma conductivity and heating depend on collision rate, which includes also the so-called stochastic collisions (mainly electron collisions with walls), proportionally more important at low gas density ng . Conductivity is also affected by static and radiofrequency magnetic fields; results for skin depth and stochastic collision estimates are reported. The transport of Te and ne inside source can be controlled by a magnetic filter B f . Considering a 5 cm radius H- ion source as example, solution of ne and Te are reported as a function of filter strength B fa, applied rf power and wall status; solver convergence methods andkey plasma observables are briefly discussed. Due to small dimension, a filter strength B fa in the order of 8 mT is needed to achieve electron temperature lower than 2 eV (for negative ion production) at extraction.

Optical emission spectroscopy of an industrial thermal atmospheric pressure plasma jet: Parametric study of electron temperature

The plasma parameters of an industrial atmospheric pressure plasma jet (APPJ) are measured as a function of the electric power of the plasma generator, the gas flow, and the distance from the jet nozzle exit. The APPJ device operates an electric discharge under Argon gas flow resulting into a continuous Argon plasma jet in the kW power range expanding into ambient air. The plasma temperature Te and electron number density Ne are determined by optical emission spectroscopy (OES) analyzing up to 17 emission lines of neutral Ar (I) and singly-ionized Ar (II) species using the Saha-Boltzmann plot (SBP) method. For the accurate determination of plasma parameters a methodology is developed to overcome fundamental limitations in OES of Argon plasma that is due to the strongly different intensities of Ar (I) and Ar (II) emission lines. The most significant step is the use of spectral bandpass filters in the optical collection system. The experimental parameters of the jet device are playing a crucial role for APPJ applications (e.g. thermal load to the workpiece, plasma chemistry interaction etc.). We measure Te and Ne in dependence of the experimental parameters and obtain consistent and accurate values of Te = 9000 ± 150 K and Ne = 5 × 1015 cm−3 (typ.). For comparison, plasma characterization using only the neutral Ar lines gives inaccurate and inconsistent Te values. This highlights the importance of using also the ionic Ar lines. The developed methodology may be diversified and applied also for OES of other rare gas plasma.

Comprehensive Analysis of Copper Plasma: A Laser-Induced Breakdown Spectroscopic Approach

The emergence of diversified applications of laser-induced breakdown spectroscopy in the biomedical field, electronics, space physics, and material processing necessitates a comprehensive understanding of plasma parameters. The present work delineates the structure and evolution of copper plasma under different ambient pressures (0.01 mbar to 100 mbar) along with other plasma parameters. The study reveals the role of ambient pressure in the increase of plasma temperature (Te), electron density (Ne), number of particles in the Debye sphere, plasma frequency, inverse bremsstrahlung absorption coefficient, electron thermal velocity, electron–ion collision frequency and in the decrease of Debye length (λD) and plasma skin depth (PSD). The experimental techniques and the theoretical explanations for the variation of plasma parameters and their applications are also detailed. As the ambient pressure increases, the motion of plasma species becomes restricted, resulting in the increase of Te, calculated using the Boltzmann plot. From the values of λD, PSD, and Ne, it is understood that the copper plasma under investigation is thermally non-relativistic and satisfies McWhirter’s criterion, thus, revealing the local thermodynamic equilibrium condition of plasma. The effects of Debye shielding and stark broadening on the spectral lines are also investigated. Thus, the study helps bring newfangled dimensions to the application of plasma by exploring the possibility of tailoring plasma parameters.

Comprehensive Data Collection Device for Plasma Equipment Intelligence Studies

In this study, various diagnostic tools were constructed and plasma factors measured to evaluate the intelligence of plasma process equipment. We used an ICP (Inductively Coupled Plasma) reactor with a radio frequency (RF) power of 13.56 MHz, a power of 400 to 800 W, and a pressure of 10 to 30 mTorr. Plasma parameters such as electron density (ne), electron temperature (Te), plasma potential (Vp), and floating potential (Vf) were measured using several instruments (VI probe and mass/energy analyzer, etc.) and subsequently analyzed. Regression analysis was performed to correlate the measured data with the plasma parameters. As a result, the plasma density (ne) and temperature (Te) were observed to be in good agreement with the non-invasive measurement results. In particular, the VI probes were highly correlated with almost all the measured plasma parameters. Therefore, the results of this study provide a basis for the estimation of plasma parameters using non-invasive measurement techniques.

Observation of fully detached divertor integrated with improved core confinement for tokamak fusion plasmas

Integration of divertor detachment with a high-performance (βN ∼ 3, βp > 2, H98 ∼ 1.5) core plasma has been demonstrated in DIII-D high-βp (poloidal beta) plasmas associated with a sustained core internal transport barrier (ITB) and an H-mode edge transport barrier (ETB). Such good core-edge integration has been achieved for both neon and nitrogen seeding, for both favorable and unfavorable B-field directions, independently from the impurity puffing locations, though these variations play important roles on divertor characteristics. Compared to the standard H-mode plasmas, the high-βp plasma exhibits a much wider window of detachment compatible with high confinement core. Fully detached divertor plasmas with low plasma temperature (Te < 5 eV), low particle flux, and low heat flux across the entire divertor target plate were obtained by using nitrogen seeding. This detached high-βp plasma is compatible with a newly developed detachment control system which can help optimize the nitrogen gas flow rate. Several features, i.e., the high edge safety factor in the high-βp scenario, impurity injection, closed divertor and reduced heating power requirement due to the high confinement, facilitate the achievement of full divertor detachment at lower density. Instead of degrading global performance, the divertor detachment facilitates the access to an even stronger ITB at large radius with a relatively weak ETB through self-organized synergy between ITB and ETB, leading to sustained high confinement. The strengthening of the large-radius ITB compensates for the ETB degradation associated with divertor detachment. In addition, a weak ETB naturally has smaller edge localized modes (ELMs). In particular, with neon injection, a long-period no-ELM H-mode phase has been achieved simultaneously with high-performance core and partially detached divertor plasmas. These results demonstrate the possibility of integrating excellent core plasma performance with an effective divertor solution, an essential step toward steady-state operation of reactor-grade plasmas.

On the role of hydrogen radiation absorption in divertor plasma detachment

Transition to the detached divertor regime that allows lowering the peak power loads on the divertor targets to a tolerable level requires low plasma temperature Te ~ 1 eV and high plasma density ne ~ 1021 m−3 in front of the target. Under such conditions, radiation trapping of the Lyman lines of hydrogen isotopes becomes important. It can influence both energy balance and the ionization/recombination rates significantly. Nevertheless, opacity is typically neglected in the 2D edge transport codes used to study the divertor plasma detachment. We report on the first in-depth investigation of radiation opacity effects on transition to detachment. Simulations are performed with the SOLPS 4.3 code package using a DIII-D size tokamak as a particular example. It is found that in pure hydrogen plasma suppression of the neutral hydrogen radiation loss due to the photon absorption makes reaching the detached plasma regime more difficult. A significantly higher average separatrix plasma pressure is required to reach a similar degree of detachment. Adding plasma impurities compensates for the reduced neutral radiation and offsets the effect of opacity. In a carbon device, where the impurity source is due to erosion of the divertor components and is strongly connected to the edge plasma density, the absorbed fraction of the hydrogen radiation is easily compensated with the increasing carbon radiation loss. However, nowadays, in the more relevant case of the full-metal wall and seeded impurity with the feedback-controlled content, the increase of the edge plasma density alone is insufficient to compensate for trapping of the hydrogen radiation. In this case, achievement of the desired degree of detachment requires higher average separatrix plasma pressure or seeded impurity content than those obtained from the transparent plasma model.

Enlarged spectral range in Calibration Free - Laser Induced Breakdown Spectroscopy for the qualitative and quantitative analysis of a complex bone matrix

In this work, Calibration Free - Laser Induced Breakdown Spectroscopy is applied for the qualitative and quantitative elemental analysis in the rib bone of a wild boar, which is a complex matrix. The sample was obtained from the rib bone of a wild boar. The sample contains major elements such as calcium and phosphorus and other minor and trace elements such as magnesium and strontium, among others. The LIBS application provided by NIST was used for the simulation of the plasma cooling. The intensities of emission lines were calculated at different conditions (varying plasma temperature Te and electron density ne simultaneously) depending on the plasma cooling process. The obtained results allowed the determination of the range of suitable values of ne and Te for the experimental measurements and optimization of the Saha-Boltzmann plot. The sample was measured for delay times of 100, 300, 500 and 1000 ns at a low pressure of 13 mbar in an argon atmosphere. From the measured data, suitable lines of Ca, Mg, P, Sr, O, and H were identified and chosen in Vacuum UV – NIR range for the reliable calculation of the Te of plasma for the bone sample for different delays. The Ca/P was obtained by calculating the atomic and mass percentages of the elements present in the bone sample.

Semi-analytic shape function of high-harmonic electron cyclotron emission in magnetically confined plasma

Semi-analytical expressions for the electron cyclotron emission (ECE) shape function are developed for arbitrary high harmonics. The integrand of the mth harmonic ECE shape function is fitted with the readily integrable test function parameterized by plasma temperature Te, harmonic number m, and emission angle θ. Semi-analytical formulae for high harmonic ECE emissivities are obtained by integrating the test integrand with the fitting parameters obtained from regression analysis. The semi-analytical expressions match with the numerically integrated ECE shape functions very well for a wide range of Te (100 eV–12 800 eV), m (2–10), and θ (10.0°–89.9°) values. The expressions can be applicable for rapid analysis of ECE spectra in magnetically confined fusion plasmas.

A computational tool for simulation and design of tangential multi-energy soft x-ray pin-hole cameras for tokamak plasmas.

A new tool has been developed to calculate the spectral, spatial, and temporal responses of multi-energy soft x-ray (ME-SXR) pinhole cameras for arbitrary plasma densities (n e,D), temperature (T e), and impurity densities (n Z). ME-SXR imaging provides a unique opportunity for obtaining important plasma properties (e.g., T e, n Z, and Z eff) by measuring both continuum and line emission in multiple energy ranges. This technique employs a pixelated x-ray detector in which the lower energy threshold for photon detection can be adjusted independently. Simulations assuming a tangential geometry and DIII-D-like plasmas (e.g., n e,0 ≈ 8 × 1019 m-3 and T e,0 ≈ 2.8 keV) for various impurity (e.g., C, O, Ar, Ni, and Mo) density profiles have been performed. The computed brightnesses range from few 102 counts pixel-1 ms-1 depending on the cut-off energy thresholds, while the maximum allowable count rate is 104 counts pixel-1 ms-1. The typical spatial resolution in the mid-plane is ≈0.5 cm with a photon-energy resolution of 500 eV at a 500 Hz frame rate.

Simultaneous vacuum UV and broadband UV–NIR plasma spectroscopy to improve the LIBS analysis of light elements

This work studies the ability of laser-induced breakdown spectroscopy (LIBS) to improve the detection of light elements such as silicon (Si), boron (B), carbon (C), and sulfur (S). In this study, the plasma decay over time was simulated using the LIBS application provided by NIST, obtaining spectra in the spectral range ranging from the vacuum ultraviolet (VUV) to the near infrared (NIR) region. Since the electron density (ne) and plasma temperature (Te) decrease during the decaying process, the intensities of emission lines from neutral, singly ionized, and doubly ionized species were calculated. The results allowed us to determine the range of suitable ne and Te for experimental measurements, and to construct a Saha–Boltzmann (SB) plot using neutral, singly ionized, and doubly ionized species. Samples containing Si, B, C, and S were measured at delays of 100–1000 ns after the laser shot at low pressure (13 mbar) in a helium atmosphere. From the measured data, suitable lines were chosen in the VUV range to calculate the Te of plasma for each sample at different delays. The results demonstrate that due to the inclusion of multiple species across VUV–UV–NIR, an appreciable improvement in the accuracy of Te was obtained, which is an essential factor for calibration-free LIBS (CF-LIBS).

Transition between resistive ballooning mode and toroidal drift wave mode at the edge of tokamak plasmas

The transition between the resistive ballooning mode (RBM) and toroidal drift wave (DW) mode is a possible physical mechanism triggering L-H transition in tokamaks. The two-fluid model [Rafiq et al., Phys. Plasmas 17, 082511 (2010)] developed by Rafiq et al. was improved by including ion diamagnetic effects in plasma polarization drift velocity. Based on the improved fluid model, the gyrokinetic results [Bourdelle et al., Nucl. Fusion 54, 022001 (2014)] about the transition between RBM and toroidal DW were recovered. It shows good agreement under a set of real experimental conditions. Hence the fluid theory is valid to investigate the physics of edge plasmas. A transition temperature Tmin about 80 eV, which RBM is dominant for plasma temperature Te < Tmin, but DW prevails for Te > Tmin, was found in gas puffing experiments of HL-2A tokamak. Employing the improved fluid model, we have simulated this phenomenon and the experimental result has been verified exactly.

Experimental investigation of atomic and ionic titanium lines, diatomic TiO γ transition and continuum background radiation via magnetically confined LIBS

Abstract This paper is focused on the clarification of the behaviour of various atomic, ionic, and TiOγ (A3Φ – X3Δ, Δν =0) diatomic transition lines as well as the continuum radiations in laser-induced titanium plasma plume by a pair of NdFeB. Depending on their different amount of impressionability from applied fields and electron-impact excitation rate, the responses of each component in optical emission spectrum and background continuum radiation to different applied magnetic field strengths (~ 0.42–1.12 T) are significantly different. At magnetic fields of 0.98 and 1.12 T, the amount of impressionability for Ti i: 388.2 nm is higher than others, while for TiOγ molecular transitions, the amount of impressionability factor in a 0.98 T field strength is considerable, because in the first moments after the laser pulse the continuum radiation is dominant, by applying an external magnetic field, this amount of radiation be reduced. The temporal evolution of the optical emission lines shows that choosing a suitable time delay and gate width has a considerable role in further impressionability of externally applied field in case of different elements. The electron density Ne varied from 0.99×1017 to 11.53×1017 cm−3, and the plasma temperature Te, was obtained in a range of 4835–16818 K by employing maximum applied field of 1.12 T. The supplementary investigations will be conducted towards further improvements of the purposeful analysis of each component in confined plasma by magneto-LIBS technique in order to find new approaches in the field of magnetic confinement.

Tomography of homogenized laser-induced plasma by Radon transform technique

Tomography of a laser-induced plasma in air is performed by inverse Radon transform of angle-resolved plasma images. Plasmas were induced by single laser pulses (SP), double pulses (DP) in collinear geometry, and by a combination of single laser pulses with pulsed arc discharges (SP-AD). Images of plasmas on metallurgical steel slags were taken at delay times suitable for calibration-free laser-induced breakdown spectroscopy (CF-LIBS). Delays ranged from few microseconds for SP and DP up to tens of microseconds for SP-AD excitation. The white-light and the spectrally resolved emissivity ε(x,y,z) was reconstructed for the three plasma excitation schemes. The electron number density Ne(x,y,z) and plasma temperature Te(x,y,z) were determined from Mg and Mn emission lines in reconstructed spectra employing the Saha-Boltzmann plot method. The SP plasma revealed strongly inhomogeneous emissivity and plasma temperature. Re-excitation of plasma by a second laser pulse (DP) and by an arc discharge (SP-AD) homogenized the plasma and reduced the spatial variation of ε and Te. The homogenization of a plasma is a promising approach to increase the accuracy of calibration-free LIBS analysis of complex materials.

On the calibration of polarimetric Thomson scattering by Raman polarimetry

Polarimetric Thomson scattering (TS) is an alternative method for the analysis of Thomson scattering spectra in which the plasma temperature Te is determined from the depolarization of the TS radiation. This is a relativistic effect and therefore the technique is suitable only for very hot plasmas (Te > 10 keV) such as those of ITER. The practical implementation of polarimetric TS requires a method to calibrate the polarimetric response of the collection optics carrying the TS light to the detection system, and in particular to measure the additional depolarization of the TS radiation introduced by the plasma-exposed first mirror. Rotational Raman scattering of laser light from diatomic gases such as H2, D2, N2 and O2 can provide a radiation source of predictable intensity and polarization state from a well-defined volume inside the vacuum vessel and is therefore suitable for these calibrations. In this paper we discuss Raman polarimetry as a technique for the calibration of a hypothetical polarimetric TS system operating in the same conditions of the ITER core TS system and suggest two calibration methods for the measurement of the additional depolarization introduced by the plasma-exposed first mirror, and in general for calibrating the polarimetric response of the detection system.

Laser-induced breakdown spectroscopic study of ammonium nitrate plasma

We present the optical emission studies of the ammonium nitrate plasma produced by the fundamental (1064 nm) and second (532 nm) harmonics of a Q-switched Nd: YAG laser. The target material was placed in front of the laser beam in an open atmospheric air. The spectrum reveals numerous transitions of neutral nitrogen. We have studied the spatial behavior of the plasma temperature (Te) and electron number density (Ne) determined using the Boltzmann plot method and Stark broadened line profiles, respectively. Besides, we have studied the variation of the plasma parameters as a function of the laser irradiance.

PLASMA CHARACTERISTICS IN SQUARE PULSE ARC DISCHARGE OF PLASMA CATHODE ELECTRON SOURCE DEVICE

Plasma parameters in Plasma Cathode Electron Source Device (PCESD) are very important things because they will determine the eficiency of its electron extraction. Square pulse mode of PCESD’s arc discharge plasma current can be obtained by using Pulse Forming Network (PFN) circuits which is called Arc Discharge Power Supply (ADPS). The square pulse mode is necessity to simplify in electron irradiation dose calculation. ADPS is connected with Hollow Anode Chamber (HAC) which is placed inside of PCESD to produce arc discharge plasma. The value of arc discharge plasma current is the main key to determine plasma parameters that can be measured by using Rogowski coil. The value of the arc discharge plasma current is IADPS = 206.30 A with pulse width  = 80 μs. Whereas the plasma parameters values inside of the HAC are: the electron plasma density ne = (16.85  1019) m-3, electron plasma temperature Te = 2.609 eV, electron plasma frequency fe = 116.74 GHz, and Debye length λD = 9.958 µm respectively.

Diagnostic Study of an Fe-Ni Alloy Plasma Generated by the Fundamental (1064 nm) and Second (532 nm) Harmonics of an Nd: YAG Laser

We studied the spatial evolution of the Fe-Ni plasma generated by the fundamental (1064 nm) and second (532 nm) harmonics of a Q-switched Nd: YAG laser. The experimentally observed line profiles of the neutral iron (Fe I) have been used to extract the plasma temperature (Te) using the Boltzmann plot method, whereas the electron number density (Ne) has been determined from the Stark broadening. In addition, we studied the spatial behavior of Te and Ne with the variation of laser energy for iron plasma by placing the target material (iron-nickel alloy) in air at atmospheric pressure for both modes of the Nd: YAG laser.

Modulation of electron energy distributions and discharge parameters in a dual frequency ICP discharge

Using a radio frequency (RF) compensated Langmuir probe, modulations in electron energy distribution (EED) and plasma potential are investigated in a discharge produced by a large-area dual frequency/dual antenna inductively coupled plasma source. The discharge is ignited using two frequencies (2 and 13.56 MHz). It is observed that the EEDs can be tailored by varying the power ratio of the two frequencies. Increasing the power level of the low frequency (P2 MHz) enhances the population density of high-energy electrons; however, increasing the high-frequency power (P13.56 MHz) increases the low-energy electron population density. At a fixed total power (P2 MHz + P13.56 MHz), the higher the low-frequency power (P2 MHz) content, the higher the population density of high-energy electrons; however, this trend reverses with high-frequency power (P13.56 MHz). The influence of power ratio on plasma density (ne), plasma temperature (Te) and plasma potential (Vp) has also been studied. It is found out that the plasma parameters have similar trends with RF power irrespective of its frequency. The value of ne increases, and Te and Vp decrease with increasing power. At a fixed P2 MHz, Vp increases with increasing P13.56 MHz. However, Vp decreases with increasing P2 MHz at a fixed value of P13.56 MHz.

Instability, collapse, and oscillation of sheaths caused by secondary electron emission

The Debye sheath is shown to be unstable under general conditions. For surface materials with sufficient secondary electron emission (SEE) yields, the surface's current-voltage characteristic has an unstable branch when the bulk plasma temperature (Te) exceeds a critical value, or when there are fast electron populations present. The plasma-surface interaction becomes dynamic where the sheath may undergo spontaneous transitions or oscillations. Using particle-in-cell simulations, we analyze sheath instabilities occurring in a high Te plasma slab bounded by walls with SEE. As the plasma evolves, whenever the sheath enters an unstable state, its amplitude rapidly collapses, allowing a large flux of previously trapped electrons to hit the wall. These hot electrons induce more than one secondary on average, causing a net loss of electrons from the wall. The sheath collapse quenches when the surface charge becomes positive because the attractive field inhibits further electrons from escaping. Sheath instabilities influence the current balance, energy loss, cross-B-field transport and even the bulk plasma properties. Implications for discharges including Hall thrusters are discussed. More generally, the results show that common theories that treat emission as a fixed (time-independent) “coefficient” do not capture the full extent of SEE effects.

Spectroscopic studies of UV lead plasmas produced by single and double-pulse laser excitation

A spectroscopic study to compare single- and double-pulse laser-induced breakdown spectroscopy (LIBS) using two Q-switched Nd:YAG lasers emitting at 532 nm is reported. The two laser beams were combined in the same direction (collinear beam geometry) to focus on the Pb targets in the open air. Various parameters, such as incident laser irradiance, placement of the laser beam focus position relative to the illuminated surface and gate delay times (delay between the incident laser pulse and the ICCD camera), were used as variables to enhance the sensitivity of LIBS signals. Several atomic and ionic emission lines of Pb were registered in the 200–290 nm UV spectral domains. In order to study the temporal evolution of plasma parameters for single- and double-pulse laser (SP and DP) configurations, the observed profiles of neutral lead lines were used to extract the plasma temperature (Te) using Boltzmann plots, whereas electron number density (ne) was determined from the profile of the Stark-broadened line. In the case of the DP configuration, the intensity of the atomic Pb I signal at 280.2 nm was enhanced eightfold. The intensity enhancement could help the analytical performance of the LIBS technique in terms of improvement of sensitivity and reduction of the self-absorption effect. This study contributes to a better understanding of the LIBS plasma dynamics by observing the temporal evolution of various emission lines of Pb. The results demonstrate a faster decay of the continuum relative to the spectral lines and a slightly longer plasma life-time for the DP configuration as compared with the SP configuration. In order to avoid inhomogeneous effects in the plasma, sufficiently high laser intensity and short delay time are required. Special attention was paid to possible self-absorption of different transitions. The micro-craters generated by SP and DP laser ablation were also compared using an optical microscope.