Hydrogen Plasma Jet Research Articles

Investigation of the plasma jet penetration into the plasma on the Globus-M tokamak

Deep plasma fueling by the injection of high-speed high-density hydrogen plasma jet has been observed on Globus-M injection of unmagnetized hydrogen jet by a plasma gun led to a twofold increase of plasma core density. Presented here are the results of measurement of plasma jet velocities during the movement in the tokamak plasma. It is demonstrated that the deceleration times of the hydrogen and helium jets are in accordance with the predictions of the plasma jet penetration models based on consideration of the Alfvén conductivity of the plasma and inhomogeneity and curvature of the magnetic field. It is confirmed that the main mechanism governing the penetration depth of the jets in the tokamak plasma for considered conditions is the Alfvén conductivity.

Flute growth rate of plasma jet in mirror machine

The evolution of flute instability in a cold, high-density hydrogen plasma jet, injected into a mirror machine, is studied. The experiment was designed to minimize the interaction of the plasma with the walls, thus bringing it close to the ideal magnetic Rayleigh–Taylor instability conditions. The modal growth rate was measured in various settings to demonstrate the effects of the finite Larmor radius, Bohm diffusion, conductive limiter, biased limiter and neutral background gas. In this paper we will demonstrate that lowering the magnetic field increases stability, as does the insertion of a conducting ring. However, if the ring is biased, the stability is reduced due to inhomogeneous coupling between the plasma and the limiter. It was also found that heavy background gas dramatically reduces the flute instability growth rate.

Analysis of the behavior of a discharge in a coaxial plasma jet accelerator

We analyze the behavior of the discharge in a coaxial plasma jet accelerator with a pulsed supply of the working gas released by an electric discharge from titanium hydride powder. Radiation (varying with time) from the discharge in the accelerator was detected using an optical method through a narrow slit cut along the outer electrode by a Bifo Company K008 streak camera. Stable operation of the source with the highest kinetic energy of a pure hydrogen plasma jet was attained for a relatively uniform glow of the discharge along the accelerator during the entire current pulse. Conversely, local glow of the discharge at the outlet or inlet of the accelerator considerably contaminated the discharge with impurities, and the kinetic energy of the plasma jet decreased by an order of magnitude. The highest energy of the plasma jet was attained when the polarity of the electrodes was the same as at the plasma focus.

Detailed H(n = 2) density measurements in a magnetized hydrogen plasma jet

We present detailed spatial density measurements of H(n = 2), i.e. the first excited state of atomic hydrogen, in a hydrogen plasma expansion that is weakly magnetized. At a specific distance from the source of the expansion a sharp transition from a red light emitting plasma (dominated by Hα emission) to a blue light emitting plasma (dominated by Hβ and Hγ emission) occurs. Molecular processes such as dissociative recombination and processes with negative ions are suspected to be key in the understanding of the distinct emissions observed in the two different plasma regions. The relevance of the presented work is to underline these molecular processes in atomic regimes of hydrogen-containing plasmas. The first excited state density, n = 2, is determined with tunable diode laser absorption spectroscopy on the Balmer-alpha transition to investigate how important molecular processes such as dissociative recombination are in the plasma. The density of n = 2 is 1 × 1017 m−3 close to the plasma source and decreases gradually along the plasma column to 1014 m−3 at 20 cm from the plasma source exit. The presented results show that the theoretical possibility to generate a stable hydrogen laser in the visible light, i.e. population inversion of n = 3 with respect to n = 2, is not obtained due to the population of n = 2 by dissociative recombination of ions. The presence of molecular processes in the plasma is further evidenced with the use of a collisional radiative model.

Observations of magnetic flux compression in jet impact experiments

The astrophysical jet experiment at Caltech generates a T=2–5 eV, n=10^(21)–10^(22) m^(−3) plasma jet using coplanar disk electrodes linked by a poloidal magnetic field. A 100 kA current generates a toroidal magnetic field; the toroidal field pressure inflates the poloidal flux surface, magnetically driving the jet. The jet travels at up to 50 km/s for ∼20–25 cm before colliding with a cloud of initially neutral gas. We study the interaction of the jet and the cloud in analogy to an astrophysical jet impacting a molecular cloud. Diagnostics include magnetic probe arrays, a 12-channel spectroscopic system and a fast camera with optical filters. When a hydrogen plasma jet collides with an argon target cloud, magnetic measurements show the magnetic flux compressing as the plasma jet deforms. As the plasma jet front slows and the plasma piles up, the density of the frozen-in magnetic flux increases.

Investigation of beam– and wave–plasma interactions in spherical tokamak Globus-M

The experimental and theoretical results obtained in the last two years on the interaction of neutral particle beams and high-frequency waves with a plasma using the spherical tokamak Globus-M are discussed. The experiments on the injection of low-energy proton beam of ∼300 eV directed particle energy are performed with a plasma gun that produces a hydrogen plasma jet of density up to 3 × 1022 m−3 and a high velocity up to 250 km s−1. A moderate density rise (up to 30%) is achieved in the central plasma region without plasma disruption. Experiments on high-energy (up to 30 keV) neutral beam injection into the D-plasma are analysed. Modelling results on confinement of fast particles inside the plasma column that follows the neutral beam injection are discussed. The influence of the magnetic field on the fast particle losses is argued. A neutral beam injection regime with primary ion heating is obtained and discussed. The new regime with fast current ramp-up and early neutral beam injection shows electron temperature rise and formation of broad Te profiles until the q = 1 flux surface enters the plasma column. An energetic particle mode in the range of frequencies 5–30 kHz and toroidal Alfvén eigenmodes in the range 50–300 kHz are recorded in that regime simultaneously with the Te rise. The energetic particle mode and toroidal Alfvén eigenmodes behaviour are discussed. The toroidal Alfvén eigenmode spectrum appears in Globus-M as a narrow band corresponding to n = 1. The first experimental results on plasma start-up and noninductive current drive generation are presented. The experiments are carried out with antennae providing mostly poloidal slowing down of waves with a frequency of 920 MHz, which is higher than a lower hybrid one existing under the experimental conditions. The high current drive efficiency is shown to be high (of about 0.25 A W−1), and its mechanism is proposed. Some near future plans of the experiments are also discussed.

Oxidation–Reduction of Maleic Acid Induced by Argon–Hydrogen Plasma-Jet

Abstract Plasma-jet in aqueous solutions is known to disproportionate water to give hydrogen and hydroxyl radicals. Maleic acid, which is a carbon–carbon double bond bearing dicarboxylic acid, underwent addition of hydrogen, hydrogen plus hydroxyl, hydroxyl species under an argon–hydrogen plasma-jet. Maleic acid (10 mM) yielded 42% succinic acid (dihydrogenated product) under an argon–hydrogen (1.5 and 0.5 L min−1) plasma-jet. This demonstrates an effective reduction method for maleic acid by plasma-jet in aqueous solutions.

Hyper-Velocity Fullerene-Dusty Plasma Jets for Disruption Mitigation

High-velocity hydrogen plasma jets demonstrated deep penetration into magnetically confined tokamak plasma during fueling experiments. Disruption mitigation with plasma jets requires much larger mass (∼0.3 g for DIII-D and ∼30 g for ITER) to be delivered into the plasma core. We present a concept of using hyper-velocity C60 fullerene-dusty plasma jets for disruption mitigation of magnetically confined plasmas. The C60-fullerenes can form a compact plasma slug which can be accelerated to hyper-velocity (∼50 km/s) allowing for deep penetration into the tokamak target plasma. We evaluate the principle advantages, means to create it using a pulsed source, the atomic processes during acceleration to hyper-velocity and subsequent transport, and the interaction with the ambient target tokamak plasma during penetration.

Direct determination of gas velocity and gas temperature in an atmospheric-pressure argon–hydrogen plasma jet

Direct gas temperature and gas velocity measurements made in the exit plane of a subsonic argon–hydrogen thermal plasma jet from high-resolution lineshape analysis of laser light scattered by the plasma are reported. The lineshapes are in general a superposition of the ion feature of the Thomson-scattered light and the lineshape of Rayleigh scattered light. In the center of the jet Thomson scattering dominates while at larger radii Rayleigh scattering dominates. Because of the complexity of the lineshapes of light scattered by multicomponent plasmas, only those that are predominantly due to Thomson scattering can in practice be analyzed for gas temperature. Gas velocity can be determined from the Doppler shift of the lineshapes relative to the frequency of the incident laser if the velocity is greater than about 50 m s −1. The maximum gas temperature measured was 14,500 K±5%. The maximum gas velocity measured was 1100 m s −1±3%. Temperature values and the radial velocity profile are compared with those previously obtained from a subsonic all-argon plasma jet operated under similar conditions.

Density limits and control in the Globus-M spherical tokamak

The results of the experimental campaign on Globus-M (R = 0.36 m, a = 24 m) devoted to investigating density limits and density control are reported. The experiments were performed at Btor = 0.4 T, Ip = 0.18–0.25 MA, q95 = 3.5–5 and plasma vertical elongation, κ ∼ 1.5–1.7. The density limits achieved with the gas puffing method of density control in the previous periods in ohmic heating (OH) regime are discussed. The progress made in OH scenario optimization helped the density to approach the Greenwald limit. Co-current neutral beam of deuterium with the power in the range of 0.45–0.6 MW at the beam energy of 28–29 keV was injected into deuterium target plasma at the early stage of the discharge, which allowed the density to overcome the Greenwald limit. Line averaged densities in excess of 1.5 × 1020 m−3 were achieved, during the external gas puff. An ion temperature increase, measured by NPA was accompanied by a definite increase in the electron energy content, registered by Thomson scattering. Injection of a pure, highly ionized hydrogen plasma jet with a density up to 1022 m−3, total number of accelerated particles (1–5) × 1019 and a flow velocity of ∼110 km s−1 was used as another instrument for density control. It increased plasma particle inventory in the Globus-M by ∼50% (from 0.65 × 1019 to 1 × 1019) in a single shot without target OH plasma parameter degradation. The injection resulted in a fast density increase with the time much shorter than with gas puff fuelling, which was confirmed by Thomson scattering measurements.

High kinetic energy plasma jet generation and its injection into the Globus-M spherical tokamak

Progress in the theoretical and experimental development of the plasma jet source and injection of hydrogen plasma and neutral gas jets into the Globus-M spherical tokamak is discussed. An experimental test bed is described for investigation of intense plasma jets that are generated by a double-stage plasma gun consisting of an intense source for neutral gas production and a conventional pulsed coaxial accelerator. A procedure for optimizing the accelerator parameters so as to achieve the maximum possible flow velocity with a limited discharge current and a reasonable length of the coaxial electrodes is presented. The calculations are compared with experiment. Plasma jet parameters, among them pressure distribution across the jet, flow velocity, plasma density, etc, were measured. Plasma jets with densities of up to 1022 m−3, total numbers of accelerated particles (1–5) × 1019, and flow velocities of 50–100 km s−1 were successfully injected into the plasma column of the Globus-M tokamak. Interferometric and Thomson scattering measurements confirmed deep jet penetration and a fast density rise (<0.5 ms) at all spatial points up to a radius r≈ 0.3a. The plasma particle inventory increase by ∼50% (from 0.65 × 1019 to 1 × 1019) did not result in plasma degradation.

Behavior of the H atom velocity distribution function within the shock wave of a hydrogen plasma jet.

The evolution of the ground-state hydrogen atom velocity distribution function throughout the stationary shock wave of a supersonic hydrogen plasma jet (3<Mach number<4) is studied using laser-induced fluorescence spectroscopy. The H atom velocity distribution function may be decomposed into two Maxwellian distributions. The fast component of the distribution corresponds to the unhampered supersonic conditions. The slow component corresponds to the conditions in the shock region, i.e., within the shock front, the mean velocity and the temperature of this atom group vary. Across the shock wave, the H atom population is gradually transferred from the fast to the slow component by means of collisions. The development of the mean axial velocity is modeled using the Mott-Smith approach. Departure from the theoretical shock profile is interpreted in terms of the nonconservation of both the H atom forward flux and momentum across the shock wave.

Influence of surface chemistry on the transport of H atoms in a supersonic hydrogen plasma jet

The transport of ground-state hydrogen atoms in the expansion of a thermal hydrogen plasma created by a cascaded arc is studied by means of two-photon absorption laser induced fluorescence. The low-dissociation degree measured at the source exit implies that H atoms flow in a H2 environment. It is shown that the H atom expansion pattern is in disagreement with the neutral gas supersonic expansion theory. Indeed the transport of H atoms in the plasma jet is strongly influenced by surface-recombination processes. Because of the large density gradients between the core of the jet and its surroundings induced by the recombination of H atoms at the reactor walls, hydrogen atoms diffuse out of the plasma jet in the course of the expansion. When the surface loss probability is high, i.e., the combination of a large wall-recombination probability with a long residence time, the losses of radicals by diffusion cannot be avoided even when the mass of the carrier gas is close to the mass of the radical.

Determination of the gas kinetic temperature of a supersonic hydrogenplasma jet by using a monochromator with built-in planar Fabry-Pérotinterferometer

An investigation of gas kinetic temperatures in a supersonichydrogen plasma jet has been performed. Under the conditions used thebroadening of the Balmer alpha line is predominantly caused by Dopplerbroadening due to thermal motion. The spectral resolution needed was achievedby the insertion of a planar Fabry-Pérot interferometer into the paralleloptical path of a conventional scanning 1 m focal-length Czerny-Turnermonochromator. Considering the fine structure of the lines as well as theinstrument function of the interferometer, gas kinetic temperatures weredetermined from the measured line shapes. Gas kinetic temperatures of thesupersonic hydrogen plasma jet ranging from 1200 to 2300 K with anexperimental error of ±10% were obtained. Temperatures obtained wereweighted averages along the line of sight with a lateral resolution of about8 mm.

Reduction of Chemical Reactions in Nitrogen and Nitrogen-Hydrogen Plasma Jets Flowing into Atmospheric Air

The large number of possible chemical reactions represents a severe burdenfor modeling of even relatively simple plasma systems. Reduced sets ofchemical reactions have been obtained for numerical simulations of nitrogenand nitrogen-hydrogen plasma jets flowing into an atmospheric airenvironment. The important or active reactions are determined based on asimplified reduction method. A reaction is considered active if it leadsto higher sensitivities than a specified cutoff sensitivity of 1%. Theactive reactions exert a significant influence on main plasma parameters,such as velocity, temperature, and species concentrations. The sensitivityanalysis for the specified systems shows that two NO reactions, known asZel'dovich reactions (N2+O⇌NO+N andNO+O⇌O2+N),(1) are both active in a nitrogenplasma jet. On the other hand, the latter is not active and may be omittedin a nitrogen–hydrogen plasma jet. A nitrogen–hydrogen plasmajet requires contribution of two active charge exchange reactions:N2+N+⇌N+ 2+N andN+H+⇌N+ +H, while only the former is needed in a nitrogen plasmajet. The dissociation reactions are all active in both plasma jets, exceptthe dissociation of OH.

Reduction and separation of silica-alumina mixture with argon–hydrogen thermal plasmas

Thermal plasma reduction of a SiO 2–Al 2O 3 mixture for metal production was investigated. The understanding of the reaction mechanism would be applied to metal recovery from coal ash. Thermal equilibrium and free energy of formation of the reaction systems were estimated to predict the evaporated species and to evaluate the predominant reactions. Atomic hydrogen plays an important role in the reduction of the SiO 2–Al 2O 3 mixture. Argon and argon–hydrogen plasma jets were used for the treatment of the SiO 2–Al 2O 3 mixture with various compositions. The argon plasma produces gaseous silicon and SiO from the SiO 2–Al 2O 3 mixture, though the recovered amount was very little, while Al 2O 3 has not been reduced. The argon–hydrogen plasma produces mainly gaseous silicon with some additions of gaseous SiO and aluminum. Both of the argon and the argon–hydrogen plasmas produce the silicon component collected as the fumes having the purity of 98–99% from the SiO 2–Al 2O 3 mixture.

Reactions of hydrocarbons in a supersonic vacuum plasma jet

The plasma plume of a hydrogen plasma jet used for diamond synthesis is analyzed by a Pitot tube and by mass spectrometry. In the investigated pressure range of 2–10 mbar, supersonic gas velocities with Mach numbers of up to 2 were observed, which decreased with increasing pressure and increasing distance from the nozzle. The injection of the carbon-containing species either at the exit of the jet nozzle or simply into the background gas of the reaction chamber confirmed the importance of recirculation of background gas into the plasma plume. In the case of background injection the rise of the total carbon content in the plume with increasing distance from the nozzle is much slower than in the case of nozzle injection. The results of a numerical model of the hydrocarbon gas-phase reactions in the jet are presented. The model considers the entrainment of background gas into the plasma plume. Two domains along the jet axis can be distinguished. The first one in the vicinity of the nozzle is dominated by methyl radicals, the second one by atomic carbon. Increase of the hydrogen dissociation level results in the broadening of the atomic carbon domain and the rise of C2 far from the nozzle. Background injection of CH4 leads to lower total carbon content in the plume but has little effect on the species distribution along the jet axis.

Diamond growth in a direct-current low-pressure supersonic plasmajet

Abstract A direct-current, water-cooled hydrogen plasmajet was designed and built. The arc burning between a thoriated tungsten cathode and a Laval nozzle acting as anode was operated at a power level of 4 kW. The plasmajet expands supersonically into a vacuum vessel in which a pressure of a few millibars is sustained. Methane as carbon-containing species is mixed into the decaying plasma close to the exit of the Laval nozzle. Molybdenum plates were used as substrates for diamond deposition. The substrates were placed on a water-cooled movable substrate holder, which allowed depositions at distances ranging from 2 to 30 cm. The bulk temperature of the substrate was monitored by a thermocouple. The deposited coatings were analysed by Raman spectroscopy for diamond phase purity and by scanning electron microscopy for morphology. The film thickness was determined by a Talley Surf profilometer and by optical thickness analysis. At the conditions investigated, a maximum growth rate of about 6 μm h−1 was observed. The growth rate showed a maximum at a distance of 6–10 cm from the nozzle. With increasing distance from the nozzle the growth rate as well as the crystallite size decreases and the diamond phase purity as reflected in the Raman spectra deteriorates. An alteration of arcjet power had only little effect on growth rate and no effect on film quality.

Diagnostics of the magnetized low-pressure hydrogen plasma jet: Molecular regime

Optical emission and absorption spectroscopy and double Langmuir probe diagnostics have been applied to measure the plasma parameters of an expanding magnetized hydrogen plasma jet. The rotational temperature of the excited state H2(d2Πu) has been determined by analyzing the intensity distribution of the spectral lines of the Fulcher-α system of H2. The gas temperature in the plasma, which is twice the value of the rotational temperature is equal to ≂ 520 K. Several clear indications of presence of the ‘‘hot’’ electrons have been observed in the plasma: (1) Langmuir probe measurements (Te≂1.4 eV), (2) appearance of the Fulcher-α system of H2 (excitation potential ΔE=13.87 eV), (3) low rotational temperature (T*rot≂260 K) of the excited H2(d3Πu) molecules, (4) local excitation in the plasma of Ar I(ΔE=15.45 eV), and Ar II(ΔE=19.68 eV) spectral lines, (5) local excitation in the plasma of He I(ΔE=23.07 eV and ΔE=24.04 eV) spectral lines. Optical actinometry has been applied to measure the absolute density of hydrogen atoms and hydrogen dissociation degree in the plasma. The measured absolute density of hydrogen atoms are in the (1–1.4)×1020 m−3 range, and the corresponding dissociation degree of the hydrogen plasma is in the range of 8%–13%.

Modeling of nonequilibrium effects in a high-velocity nitrogen-hydrogen plasma jet

A numerical simulation has been performed of a high-velocity nitrogen hydrogen plasma jet in air at atmospheric pressure including finite-rate chemical kinetics. Ions, electrons, and neutral atoms and molecules are treated as separate species in the plasma mixture. The chemical reactions considered are dissociation of molecular species, ionization of atomic species, charge exchange and dissociatioe recombination of nitrogen, and hydrogen-oxygen reactions. The calculational results show that strong departures from ionization and dissociation equilibrium develop in the downstream region as the chemical reactions freeze out at lower temperatures, in spite of the assumed chemical equilibrium at the nozzle exit. The calculations also show that ionized species are over-populated throughout the flow, while dissociated species in the core of the jet are underpopulated near the nozzle exit and become over-populated farther downstream. This initial underpopulation is due to diffusive depletion of dissociated species and enrichment of molecular species in the core of the jet.