Balmer Beta Research Articles

Investigating of plasma diagnostics by utilizing spectroscopic measurements of Balmer emission

Plasma technology offers revolutionary potential for particle accelerators by enabling the acceleration of electron beams to ultra-relativistic velocities in a small-scale dimension. The compact nature of plasma-based accelerators permits the creation of accelerating gradients on the GV scale. Plasma acceleration structures are created by utilizing either ultra-short laser pulses (Laser Wakefield Acceleration, LWFA) or energetic particle beams (Particle Wakefield Acceleration, PWFA), which need to be tailored to the plasma parameters. However, both methods face the challenge of limited acceleration length, which is currently only a few centimeters. To overcome this challenge, one approach is to generate plasma within a capillary tube, which can extend the acceleration length up to approximately forty centimeters or more. Consequently, it is crucial to characterize the produced plasma in terms of density and geometric structure. Optical emission spectroscopy (EOS) methods can be employed to measure and characterize the plasma electron density by analyzing the emitted plasma light. This paper presents measurements of the plasma electron density distribution for a hydrogen-filled capillary tube using both Balmer alpha (Hα) and Balmer beta (Hβ) lines. Comparing the intensities of Hα and Hβ emissions enables more precise measurements of the plasma electron density and provides additional information about other plasma properties.

On the electron density of atmospheric pressure radio frequency dielectric barrier discharge and discharge with bare electrode

Atmospheric pressure radio frequency helium plasma with two different designs: dielectric barrier discharge (DBD) and discharge with bare electrode (DBE) were investigated by means of optical emission spectroscopy. Both DBD and DBE can work at relatively low temperature and produce abundant electrons facilitating production of reactive species through electron-impact reactions. Stark broadening method of Hydrogen Balmer beta (Hβ) line was employed to analyze the electron density. When electron density is below 1020 m−3, fine-structure fitting was used to improve the accuracy of electron density estimation. At power ranged 4–20 W, DBD and DBE showed electron density 4.1–6.1 × 1019 m−3, and 3.6–8.6 × 1019 m−3, respectively. The DBD is more suitable than DBE for biomedical applications due to the wider working power range and lower gas temperature in the range of 316–344 K, depending on the power.

Forbidden component of the Be II 436.1 nm line recorded from pulsed gas discharge plasma

We report results of the experimental study of the singly charged beryllium spectral line 436.1 nm, transition , and forbidden component, transition , which is for the first time identified in this work. Beryllium lines are recorded from gas discharge, after ablation of a beryllium oxide discharge tube, running in pulsed regime with the following gases: helium with traces of hydrogen, argon with traces of hydrogen and pure krypton. The ratio of line intensities and wavelength separation of the Be II 436.1 nm line and neighbouring line located at the blue wing are followed in the electron density range (1.16–6.4) × 1022 m−3 determined from the hydrogen Balmer beta line () in the electron temperature interval between 10500 K and 15500 K. The functional dependence of the wavelength separation range and peak intensity ratio of these lines upon electron number density suggests the complex profile of the forbidden and allowed line, which can be used for diagnostics of low-temperature beryllium containing plasmas.

Novel plasma source for safe beryllium spectral line studies in the presence of beryllium dust.

Plasma source for beryllium spectral line studies in the presence of beryllium dust particles was realised. The guideline during construction was to prevent exposure to formed dust, considering the toxicity of beryllium. Plasma source characterization through determination of optimal working conditions is described. The necessary conditions for Be spectral line appearance and optimal conditions for line shape measurements are found. It is proven experimentally that under these conditions dust appears coincidently with the second current maximum. The electron density measured after discharge current maximum is determined from the peak separation of the hydrogen Balmer beta spectral line, and the electron temperature is determined from the ratios of the relative intensities of Be spectral lines emitted from successive ionized stages of atoms. Maximum values of electron density and temperature are measured to be 9.3 × 1022 m-3 and 16 800 K, respectively. Construction details and testing of the BeO discharge tube in comparison with SiO2 and Al2O3 discharge tubes are also presented in this paper.

Stark effect of Ar I lines for electric field strength diagnostics in the cathode sheath of glow discharge

We present a study of argon glow discharge which shows that measured wavenumber DC Stark shifts of two neutral argon lines, Ar I 518.75 nm and Ar I 522.127 nm, can be used for reliable determination of the electric field strength F distribution in the cathode sheath region of the discharge. In order to experimentally determine the coefficient c in quadratic correlation , manifested in a low field range (up to 15 kV/cm), the discharge is seeded with a small admixture of hydrogen, and the values of F are measured via Stark polarization spectroscopy of the hydrogen Balmer beta line. Once known, this can be used for the determination of F by a simple and inexpensive spectroscopic Stark shift measurement in discharges with other argon admixtures or pure argon. Reported shift results are in good agreement with data extrapolated from measurements performed at high electric fields (over 100 kV/cm) by Windholz (Phys. Scr., 21 (1980) 67).

Spectroscopic measurements of plasma emission light for plasma-based acceleration experiments

Advanced particle accelerators are based on the excitation of large amplitude plasma waves driven by either electron or laser beams. Future experiments scheduled at the SPARC_LAB test facility aim to demonstrate the acceleration of high brightness electron beams through the so-called resonant Plasma Wakefield Acceleration scheme in which a train of electron bunches (drivers) resonantly excites wakefields into a preformed hydrogen plasma; the last bunch (witness) injected at the proper accelerating phase gains energy from the wake. The quality of the accelerated beam depends strongly on plasma density and its distribution along the acceleration length. The measurements of plasma density of the order of 1016–1017 cm−3 can be performed with spectroscopic measurements of the plasma-emitted light. The measured density distribution for hydrogen filled capillary discharge with both Balmer alpha and Balmer beta lines and shot-to-shot variation are here reported.

Comment on “Hydrogen Balmer beta: The separation between line peaks for plasma electron density diagnostics and self-absorption test”

In this letter, we present a brief comment regarding the recently published paper by Ivković et al., J Quant Spectrosc Radiat Transf 2015;154:1–8. Reference is made to previous experimental results to indicate that self absorption must have occurred; however, when carefully considering error propagation, both widths and peak-separation predict electron densities within the error margins. Yet the diagnosis method and the presented details on the use of the hydrogen beta peak separation are viewed as a welcomed contribution in studies of laser-induced plasma.

Hydrogen Balmer beta: The separation between line peaks for plasma electron density diagnostics and self-absorption test

We propose a diagnostic technique for the measurement of plasma electron number density, Ne, based on the wavelength separation between peaks, ΔλPS, of hydrogen Balmer beta line, Hβ. In favor of the proposed diagnostic technique we demonstrate high sensitivity of ΔλPS on Ne and low sensitivity on plasma elementary processes and plasma parameters that may distort the line profile. These properties of ΔλPS enable reliable Ne plasma diagnostics in the presence of considerable self-absorption. On the basis of available theoretical data tables for the Hβ line profiles, simple Ne=f(ΔλPS) formulas are proposed. Their validity is experimentally confirmed in a low initial pressure pulsed discharge for the Ne range of (0.2–7)⁎1023m−3. The agreement of the proposed formulas with another diagnostic technique is well within 10%. In addition, the difference in Ne values obtained from peak separation and from the Hβ line width is successfully used as a self-absorption test for line profile.

Circumpolar ground‐based optical measurements of proton and electron shock aurora

AbstractMeridian scanning photometer (MSP) data are combined with global ultraviolet images from the Polar Ultraviolet Imager instrument to estimate the timing and propagation speed of shock auroras previously studied using solely space‐based ultraviolet auroral imagery. The multispectral nature of the MSPs, including the presence of a Balmer beta channel, enables the discrimination between proton and electron aurora. Following a near‐magnetic noon onset, the occurrence of auroral emissions created by shocked precipitating protons and electrons is observed to propagate tailward, along the auroral oval with speeds of several km/s, consistent with the shock propagation speed in the solar wind. In two cases, shock aurora propagation speeds along the auroral oval determined from satellite imagery are confirmed, to within calculated uncertainties, with ground‐based timing. The majority of instruments detect low‐energy discrete auroral arcs poleward of diffuse, higher‐energy aurora. Evidence of a previously reported two‐pulse proton aurora shock onset is detected at some, but not all, locations.

Spectroscopic application of an iterative kinetic model of the cathode-fall region in a hydrogen abnormal glow discharge

We present an iterative kinetic model of the cathode-fall (CF) region in a hydrogen abnormal glow discharge, providing efficient calculations of electric field spatial distribution and distribution functions of H atoms and H+, and ions. The model is very convenient for spectroscopic applications because the knowledge of these distributions enables calculation of virtually all spectroscopic quantities of interest, which is illustrated here by comparison of model predictions and experimental electric field distribution, and hydrogen Balmer beta line shapes recorded end-on and side-on for various positions along the CF region of the discharge.

Cathode sheath and hydrogen Balmer lines modelling in a micro-hollow gas discharge

We present a model of the cathode sheath (CS) processes responsible for the broadening of the hydrogen Balmer beta line recorded from a micro-hollow gas discharge (MHGD) and used for simultaneous diagnostics of plasma and CS parameters. The MHGD was generated in a microhole (diameter 100 μm at narrow side and 130 μm at wider side) of a gold-alumina-gold sandwich in the pressure ranges: (100–900) mbar in argon with traces of hydrogen, and (100–400) mbar in pure hydrogen. The electron number density is determined from the plasma broadened line width of the central part of Balmer beta profile, while the average value of electric field strength in the CS and the CS thickness are determined from the extended line wings induced by the dc Stark effect.

Spectroscopic diagnostics of microhollow gas discharge in hydrogen

Hydrogen Balmer beta line profile from a microhollow gas discharge (MHGD) in hydrogen is used for diagnostics of cathode sheath (CS) parameters. The profile was recorded from a MHGD microhole (diameter 100 μm at narrow and 130 μm at wider side) of a gold-alumina-gold sandwich in the pressure range (100–400) mbars. The average electric field strength in CS (25–46) kV/cm and CS thickness (60–120) μm were determined by profile fitting with the aid of model recently developed and used in argon MHGD.

Excitation and charge transfer in H-H+ collisions at 5-80 keV and application to astrophysical shocks

In astrophysical regimes where the collisional excitation of hydrogen atoms is relevant, the cross sections for the interactions of hydrogen atoms with electrons and protons are necessary for calculating line profiles and intensities. In particular, at relative velocities exceeding ~1000 km/s, collisional excitation by protons dominates over that by electrons. Surprisingly, the hydrogen-proton cross sections at these velocities do not exist for atomic levels of n >= 4, forcing researchers to utilize extrapolation via inaccurate scaling laws. In this study, we present a faster and improved algorithm for computing cross sections for the hydrogen-proton collisional system, including excitation and charge transfer to the n >= 2 levels of the hydrogen atom. We develop a code named BDSCx which directly solves the Schrodinger equation with variable (but non-adaptive) resolution and utilizes a hybrid spatial-Fourier grid. Our novel hybrid grid reduces the number of grid points needed from ~4000 n^6 (for a "brute force", Cartesian grid) to ~2000 n^4 and speeds up the computation by a factor ~50 for calculations going up to n = 4 . We present (l,m)-resolved results for charge-transfer and excitation final states for n = 2--4 and for projectile energies of 5--80 keV, as well as fitting functions for the cross sections. The ability to accurately compute proton-hydrogen cross sections to n = 4 allows us to calculate the Balmer decrement, the ratio of Balmer alpha to Balmer beta line intensities. We find that the Balmer decrement starts to increase beyond its largely constant value of 2--3 below 10 keV, reaching values of 4--5 at 5 keV, thus complicating its use as a diagnostic of dust extinction when fast (~1000$ km/s) shocks are impinging upon the ambient interstellar medium.

Electric field distribution in the cathode-fall region of an abnormal glow discharge in hydrogen: experiment and theory

We present the results of an experimental and theoretical study of the electric field distribution in the cathode-fall (CF) region of an obstructed abnormal glow discharge in hydrogen. The distribution of electric field strength was measured using an improved Stark polarization spectroscopy technique of the hydrogen Balmer beta line profile. The developed technique extends field measurements to the low-field region while remaining in good agreement at larger field strengths with the well established Stark polarization peak separation electric field measurement technique. The experimental electric field distribution is modeled by a simple analytical formula, adopted after consideration of elementary processes relevant in the CF. It fits the experimental distribution within error bars and consequently enables determination of the CF parameters such as its thickness and the mean free path for electrons in the CF region.

A contribution to spectroscopic diagnostics and cathode sheath modeling of micro-hollow gas discharge in argon

In this paper, the hydrogen Balmer beta line shape from a micro-hollow gas discharge (MHGD) in argon with traces of hydrogen is used for simultaneous diagnostics of plasma and cathode sheath (CS) parameters. For this purpose, a simple model of relevant processes responsible for the line broadening is introduced and applied to the Balmer beta profile recorded from a MHGD generated in the microhole (diameter 100 μm at narrow side and 130 μm at wider side) of a gold-alumina-gold sandwich in the pressure range (100–900 mbar). The electron number density Ne in the range (0.4–4.5) × 1020 m–3 is determined from the width of the central part of the Balmer beta line profile, while, from the extended wings of the Balmer beta profile, induced by dc Stark effect, the next three parameters are determined: the average value Ea of electric field strength in the CS in the range (16–95 kV/cm), the electric field strength E0 at the cathode surface in the range (32–190 kV/cm), and the CS thickness zg in the range (18–70 μm). All four MHGD parameters, Ne, Ea, E0, and zg, compare reasonably well with results of the modeling experiment by M. J. Kushner [J. Phys. D: Appl. Phys. 38, 1633 (2005)]. The results for Ne are compared with other emission experiments.

Simultaneous plasma and electric field diagnostics of microdischarge from hydrogen Balmer line shape

Hydrogen Balmer beta line shape from a microhollow gas discharge in argon with traces of hydrogen is used for simultaneous diagnostics of plasma and cathode sheath parameters. Simple model of relevant processes responsible for line broadening is developed and results favorably compared with experiment at 500 mbar with the electron density 3.8×1020 m−3 and electric field strength of 127 kV/cm in the cathode sheath region.

Characterization of a direct dc-excited discharge in water by optical emission spectroscopy

Dc-excited discharges generated in water at the tip of a tungsten wire which is located at the orifice of a quartz capillary are investigated by time-averaged optical emission spectroscopy.Two distinctive discharge modes are observed. For small conductivities of the liquid the discharge is a streamer-like discharge in the liquid itself (liquid mode). For conductivities above typically 45 µS cm−1 a large vapour bubble is formed and a streamer discharge in this vapour bubble is observed (bubble mode).Plasma temperatures and electron densities are investigated for both modes. The gas temperature is estimated from the rotational temperature of N2(C–B) and is 1600 ± 200 K for the bubble mode and 1900 ± 200 K for the liquid mode. The rotational temperature of OH(A–X) is up to 2 times larger and cannot be used as an estimate for the gas temperature. The rotational population distribution of OH(A), ν = 0 is also non-Boltzmann with a large overpopulation of high rotational states. This discrepancy in rotational temperatures is discussed in detail.Electron densities are obtained from the Stark broadening of the hydrogen Balmer beta line. The electron densities in the liquid mode are of the order of 1021 m−3. In the bubble mode electron densities are significantly smaller: (3–4) × 1020 m−3. These values are compared with the Stark broadening of the hydrogen alpha and gamma lines and with electron densities obtained from current density measurements. The chemical reactivities of the bubble and liquid modes are compared by means of the hydrogen peroxide production rate.

Properties of microwave plasma torch operating at a low pressure

A microwave plasma torch system is attached to a low-pressure chamber in this study. The electric field induced in a quartz discharge tube by microwave radiation breaks down the gas at a sufficiently low pressure, igniting the plasma, which is continuously sustained by the microwave radiation. The plasma profile at a very low pressure is shown to be asymmetric with higher density on the incoming side of the microwaves. The gas temperature at the bright spot of the torch plasma measured via the optical emission from hydroxide radicals is shown to increase drastically upon high-pressure operation as the microwave power increases. The electron density at the torch flame is measured by recording the Stark broadening of the hydrogen Balmer beta line. The plasma density increases as the microwave power increases. The typical argon plasma density of a plasma torch powered at 500W under a pressure of 150Torr is on the order of 1014∕cm3. The electron temperature in the argon torch plasma was estimated to be 1.5 eV, thereby effectively exciting the molecules in the torch gas. Disintegration of nitrogen fluoride (NF3) indicates that a microwave plasma torch operating at a low pressure can efficiently generate an abundant amount of chemical radicals.

Light emission from ion-bombarded Ge(1 0 0) surfaces under continuous germane and silane exposures

The intensities of the optical spectral lines emitted from a Ge(1 0 0) surface under Ar + ion bombardment are studied as a function of the ion kinetic energy (1–5 keV) and the partial pressure (5 × 10 −6–5 × 10 −4 Torr) of either germane or silane. For germane exposures, the Ge (GeI, 265 nm and 304 nm), H Balmer beta (486 nm) and H Balmer gamma (434 nm) optical lines are observed. For silane, additional peaks due to excited neutral Si (SiI, 288 nm) and molecular SiH (A 2Δ–X 2Π, 414 nm) are visible. The ion kinetic energy dependence of the GeI photon yields (265 nm and 304 nm) is analyzed in terms of the electron exchange mechanism. The similarity between the measured de-excitation parameters for germane and silane pressure between 5 × 10 −6 and 5 × 10 −4 Torr implies that the de-excitation mechanism does not change significantly. For both germane and silane exposures, the intensities of excited neutral Ge, H beta and H gamma optical lines increase with either larger partial pressures or ion kinetic energy. A similar trend is found for neutral SiI and molecular SiH emission during silane exposures. In contrast, the intensity of the H Balmer alpha transition (656 nm) decreases with increasing incident ion kinetic energy at all measured partial pressures. Both trends are similar to that observed for either silane or germane exposed Si(1 0 0) surfaces under ion bombardment.

Ultrahigh-speed etching of organic films using microwave-excited nonequilibrium atmospheric-pressure plasma

An ultrahigh etch rate (24μm∕min at 155°C and 0.3mm∕min at 325°C) of an organic film was successfully achieved using a microwave-excited nonequilibrium atmospheric-pressure plasma source employing He and O2 gases. This has the potential to be applied to various kinds of fabrication of structures for microelectromechanical systems and bionanotechnology. A stable glow discharge was realized between the narrow gap (200μm) electrodes covered with a dielectric film in atmospheric pressure. The etching characteristics were investigated by changing the O2 flow rate and the distance of the substrate from the electrode. In order to clarify the ultrahigh etching mechanism, in situ diagnostic methods, including two-dimensional imaging of optical emissions in the plasma with an intensified charge-coupled device camera, electron-density evaluation using the Stark-broadened profile of the hydrogen Balmer beta line in optical emission spectroscopy, and two dimensional spatial distribution of ozone density measured with ultraviolet absorption spectroscopy, have been performed. It was found that O atoms were the dominant etching species for ultrahigh-speed etching of the organic film, and the effect of ozone on the etching process was negligible.