Dependence Of Plasma Parameters Research Articles

Langmuir Probes as a Tool to Investigate Plasma Uniformity in a Large Negative Ion Source

The Source for the Production of Ions of Deuterium Extracted from an RF plasma (SPIDER) experiment is the full-size test-bed of the negative ion sources of ITER neutral beams. It aims to extract and accelerate more than 350 A/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{2}$ </tex-math></inline-formula> of negative hydrogen ions from 1280 apertures, distributed over a surface of approximately 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{2}$ </tex-math></inline-formula> . To assess plasma uniformity, SPIDER is equipped with bi-dimensional arrays of Langmuir probes, covering the plasma grid (PG) and the bias plate (BP) plasma-facing surfaces. These sets of diagnostics are routinely used during the ion source operation and allow to investigate the plasma properties in the so-called source expansion and extraction region. The dependencies of plasma parameters on source operation parameters such as RF power, pressure, magnetic filter field, PG, and BP biases are reported and used to evaluate the uniformity of the plasma, showing the presence of plasma drifts due to the magnetic field. Finally, the correlation between plasma and beam uniformity is assessed.

Electron temperature gradient driven transport model for tokamak plasmas

A new model for electron temperature gradient (ETG) modes is developed as a component of the multi-mode anomalous transport module [Rafiq et al., Phys Plasmas 20, 032506 (2013)] to predict a time-dependent electron temperature profile in conventional and low aspect ratio tokamaks. This model is based on two-fluid equations that govern the dynamics of low-frequency short- and long-wavelength electromagnetic toroidal ETG driven drift modes. A low collisionality NSTX discharge is used to scan the plasma parameter dependence on the ETG real frequency, growth rate, and electron thermal diffusivity. Electron thermal transport is discovered in the deep core region where modes are more electromagnetic in nature. Several previously reported gyrokinetic trends are reproduced, including the dependencies of density gradients, magnetic shear, β and gradient of β (β′), collisionality, safety factor, and toroidicity, where β is the ratio of the plasma pressure to the magnetic pressure. The electron heat diffusivity associated with the ETG mode is discovered to be on a scale consistent with the experimental diffusivity determined by power balance analysis.

Packet-Pulse Dual Magnetron Sputtering

The paper presents the results of experimental study of the discharge formed by a dual (DU) magnetron sputtering system (MSS) with aluminum targets in the mode of packet-pulse magnetron sputtering of high power (called deep oscillation magnetron sputtering (DOMS) in foreign literature). A special feature of the discharge in the DOMS mode is the use of unipolar sequence of micropulses with short durations and high powers that form macropulse duration 1000–3000 μs. This mode of sputtering was previously used only in single MSS. In this paper, the DOMS mode is first investigated with a dual magnetron sputtering system. The main plasma parameters are measured using triple and single Langmuir probes. Dependences of plasma parameters on the parameters of the pulsed discharge power supply: voltage and current amplitudes, current density, and power density on the target surface are established. The results of experiments show that the use of the dual packet-pulse magnetron sputtering can significantly increase the plasma density and the ion current density on the substrate in comparison with the traditional DC and MF modes of magnetron sputtering. The ratio of the ion flux density to the flux density of neutral atoms, characterizing the degree of ion bombardment of the growing coating in the DU DOMS mode, reached a value of 28, whereas in the DC mode it was 0.8.

Investigation in the Effect of Applied Voltage and Working Pressure on Some Plasma Parameters in the Positive Column of Dc Glow Discharge

Comsol multiphysics software is established to make a simulation that is comparable with experimental device. by utilizing comsol, the positive column domain of direct-current glow discharge with argon is considered for both of different applied voltage and working gas pressure. The calculations are exhibited by using a precise collision cross sections and Townsend coefficients for the argon. The impacts of voltage and pressure on the Debye length, number of particles in Debye sphere and plasma frequency are calculated and graphically delineated. With this regard to the dependence of plasma parameters on the applied voltage and pressure, some of them are found to be compatible with the experimental results, while others are not. For example, the calculations of the COMSOL shows that the electron temperature is not always decreasing with the increase in the applied voltage, and the Debye length does not give a linearly decreasing relationship but rather an exponentially decreasing relationship. Also, the calculations do not reproduce and match the experimental results for the dependence electron density on working pressure at various potentials.

Investigation of parameters of plasma generated by high-power impulse magnetron sputtering (HiPIMS) of graphite

High-power impulse magnetron sputtering (HiPIMS) of graphite is used for deposition of hard and wear-resistant amorphous carbon films, because tetragonal diamond-like carbon (DLC) bonds produced under subplantation mechanism at negative substrate bias voltage more intensive in the case of high-density plasma. In scientific literature one can find the fact that DLC films are more hard (37 GPa) in the case of short (7 μs) magnetron discharge pulses comparing to long (50 μs) ones (17 GPa) in HiPIMS of graphite. Likely, it is connected with denser plasma and more effective carbon subplantation in the case of short discharge pulses compared to long ones. To confirm this, it is necessary to investigate dependencies of plasma parameters (ion concentration, electron temperature, plasma and floating potentials) generated by HiPIMS of graphite on discharge pulse width. It was shown that electron temperature increased from 5.34 to 10.27 eV, and plasma density increased from 1.2⋅1010 to 2.2⋅1010 cm−3 while pulse width decreased from 100 to 15 μs. It can be explained by increase of plasma disequilibrium since pulse current and power density increased to 250 A and 39.4 W/cm2, respectively.

Angular dependence of plasma parameters and film properties during high power impulse magnetron sputtering for deposition of Ti and TiO2 layers

Angular distribution measurements have been carried out during High Power Impulse Magnetron Sputtering (HiPIMS) of a titanium target and deposition of titanium and titanium oxide films. The HiPIMS system was operated at a repetition frequency f = 100 Hz with a duty cycle of 1%. Langmuir probe diagnostics has been carried out at a distance of 7.5 cm from the target at four different angles with respect to the surface normal of the target. Film properties were investigated by means of SEM, XR, and GIXD, and a dependence of film thickness and crystalline structure on the deposition angle is observed.

Studies of plasma interactions with tungsten targets in PF-1000U facility

Abstract This paper presents results of experimental studies of tungsten samples of 99.95% purity, which were irradiated by intense plasma-ion streams. The behaviour of tungsten, and particularly its structural change induced by high plasma loads, is of great importance for fusion technology. The reported measurements were performed within a modified PF-1000U plasma-focus facility operated at the IFPiLM in Warsaw, Poland. The working gas was pure deuterium. In order to determine the main plasma parameters and to study the behaviour of impurities at different instants of the plasma discharge, the optical emission spectroscopy was used. The dependence of plasma parameters on the initial charging voltage (16, 19 and 21 kV) was studied. Detailed optical measurements were performed during interactions of a plasma stream with the tungsten samples placed at the z-axis of the facility, at a distance of 6 cm from the electrode outlets. The recorded spectra showed distinct WI and WII spectral lines. Investigation of a target surface morphology, after its irradiation by intense plasma streams, was performed by means of an optical microscope. The observations revealed that some amounts of the electrodes material (mainly copper) were deposited upon the irradiated sample surface. In all the cases, melted zones were observed upon the irradiated target surface, and in experiments performed at the highest charging voltage there were formed some cracks.

Nonstationary model of an axisymmetric mirror trap with nonequilibrium plasma

The DOL nonstationary model intended to describe plasma processes in axisymmetric magnetic mirror traps is considered. The model uses averaging over the bounce period in order to take into account the dependence of plasma parameters on the coordinate along the facility axis. Examples of calculations of trap parameters by means of the DOL code based on this model are presented. Among the features of the DOL model, one can single out two points: first, the capability of calculating the terms of the collision integral with the use of a non-Maxwellian scattering function while evaluating the distribution function of fast ions and, second, concerning the background plasma, the capability of calculating the longitudinal particle and energy fluxes in confinement modes with the particle mean free path being on the order of the trap length. The influence of the scattering function approximation used to calculate the collision integral on the solution to the kinetic equation is analyzed. The dependences of plasma parameters on the power of heating injectors and the length of the fast-ion turning zone are presented as calculation examples. The longitudinal profile of the fusion reaction rate in the case of a trap with a long fast-ion turning zone is shown to depend strongly on the input parameters of the model.

Growth of carbon allotropes and plasma characterization in linear antenna microwave plasma CVD system

Growth of diamond coatings with tunable morphology and concurrent substrate catalyst pretreatment and further growth of carbon nanotubes were studied. The dependence of plasma parameters on gas composition was studied by Langmuir probe measurement. Grown diamond coatings and carbon nanotubes were characterized by scanning electron microscopy and Raman spectroscopy and correlated with process parameters. Well-defined nanocrystalline, polycrystalline, and porous diamond films were prepared. Concurrent substrate catalyst pretreatment and further growth of carbon nanotubes were shown.

Investigation of capacitively coupled argon plasma driven at various frequencies and validation of surface waves excitation

The influence of excitation frequency (13.56–96 MHz) on the characteristics of capacitively coupled argon plasma is investigated by means of Langmuir probe and a high-voltage probe. Measurements are performed in argon pressure of 40 and 60 mTorr at a fixed discharge voltage Vpp=200 V. The measured electron energy distribution function EEPFs are a bi-Maxwellian type irrespective of the driving frequency and gas pressure. The electron density and temperatures show peak over frequency range of 54–72 MHz, beyond which it decreases. The non-monotonic dependences of plasma parameters with driving frequency were interpreted in terms of excited surface wave excited at the powered electrode.

Diagnostic of capacitively coupled radio frequency plasma by homogeneous discharge model

In this Letter, a plasma diagnostic technique is reported to evaluate the plasma parameters of capacitively coupled radio frequency argon plasma on the basis of homogeneous discharge model. The technique is implemented for wide range of operating pressure ranging from few mTorrs to atmospheric pressure. Considerable dependence of plasma parameters on the plasma series resonance effect and the drift velocity of the electron for low pressure plasma and on the ion density for atmospheric pressure plasma jet were observed.

Experimental Study of the Effect of Applied Magnetic Field on Plasma Properties of Unbalanced Magnetron Sputtering

An experimental study of the effect of applied magnetic field on the properties of the plasma and electrostatic oscillations in an unbalanced magnetron sputtering discharge was carried out. The apparatus consists of a magnetron sputtering target, using the conventional magnetic field configuration, and a coaxial coil around the target for an applied axial magnetic field. The dependencies of plasma parameters on the coil current were studied by two Langmuir probes. The resonance properties of electrostatic oscillations were observed. The results indicate that the applied magnetic field affects the plasma properties for the coil current in a range of 0 A to 8 A. The frequency bandwidth of the electrostatic oscillations in the unbalanced magnetron sputtering plasma is in a range of 0 kHz to 300 kHz. From the spectrum analysis, the eigenfrequency near the target is in a range of 20 kHz to 50 kHz under typical experimental conditions where all the magnetic field, pressure, and power etc are able to have full impact on the spectrum characteristics. The calculated value of the electron temperature as per an ion acoustic standing wave pattern inside the magnetic trap is in good agreement with the experimental result.

Spatial Distribution of Plasma Parameters in DC‐Energized Hollow Cathode Plasma Jet

AbstractDC energized hollow cathode plasma jet system was examined by radially movable Langmuir probe. Radial distribution of electron concentration, plasma and floating potentials and mean electron energy were obtained from measured probe characteristics at the distance 17 mm downstream of the hollow cathode – nozzle. The radial dependence of plasma parameters was measured for distances from the system axis 0–120 mm in the discharge containing Ar and O2. Two scenarios were used: addition of O2 into the nozzle and into the plasma vessel. The differences in measured floating and plasma potential, electron density and mean electron energy radial courses obtained in the two scenarios are qualitatively explained. In addition temporal dependences of main plasma parameters for discharges in clean argon and argon‐oxygen mixture were investigated that demonstrate system stability and its applicability for deposition of layers containing Ti.TiOx thin films were deposited onto glass substrates and examined by AFM and ellipsometry. It is illustrated that the differences in plasma parameters in the two scenarios of oxygen addition influence the layer properties (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A global (volume averaged) model of a Cl2/Ar discharge: II. Pulsed power modulation

A global (volume averaged) model of a time-modulated Cl2/Ar discharge is developed and applied to investigate the temporal evolution and dependence of plasma parameters on the modulation frequency, duty ratio and argon content. The model is compared with and shown to be in acceptable agreement with measurements found in the literature in pure Cl2 pulsed discharges. We demonstrated that the electronegativity and the Cl+ and Cl to positive ion flux ratios can be controlled by modulating the power to the discharge and varying the argon content. The influence of argon dilution is mostly independent of the frequency and the duty ratio, being similar to that of the continuous power Cl2/Ar discharge. The time-averaged electronegativity n−/ne versus duty ratio peaks at about 8% duty ratio and 10 kHz frequency, being 20 times larger than in the continuous power discharge. The time-averaged Cl+ to positive ion flux is even larger than in the continuous power discharge, in particular at low frequencies and low duty ratios. The time-averaged ratio of Cl to positive ion flux has a minimum versus frequency at around 50 kHz and a maximum versus duty ratio at about 10–20% duty ratio. We believe these results indicate that the improved etching characteristics of pulsed Cl2 discharges that have been reported in the literature are a result of the increased Cl to positive ion flux ratio when the power is pulsed with a 10 kHz frequency and a moderately large duty ratio.

Analysis of D/T Fuel Ratio in Power Plant Plasmas Using Integrated Equilibrium-Transport Simulation Code TOTAL

Pellet injection to D-T burning plasmas was analyzed using an integrated equilibrium-transport simulation code, TOTAL, for both tokamak and helical reactors. The condition of pellet injection required for the formation of an internal transport barrier and the dependence of plasma parameters in the steady self-burning state on the D/T ratio in the pellet were investigated. A simulation with different D/T ratios in the pellet revealed that the operational region of temperature and density varies with the D/T ratio. When a deuterium-rich pellet was employed, the amount of tritium to be used in the reactor was approximately 30%-40% less than that when the D/T ratio was 1.

Plasma power measurement and hysteresis in the E–H transition of a rf inductively coupled plasma system

An experimental investigation of the argon plasma behavior near the E–H transition in an inductively coupled Gaseous Electronics Conference reference cell is reported. Electron density and temperature, ion density, argon metastable density, and optical emission measurements have been made as function of input power and gas pressure. When plotted versus plasma power, applied power corrected for coil and hardware losses, no hysteresis is observed in the measured plasma parameter dependence at the E–H mode transition. This suggests that hysteresis in the E–H mode transition is due to ignoring inherent power loss, primarily in the matching system.

Neoclassical Transport Properties in High-Ion-Temperature Hydrogen Plasmas in the Large Helical Device (LHD)

High ion temperature (Ti) hydrogen plasmas were successfully demonstrated in the LHD in an experimental campaign (FY2006). The power increase of the perpendicular neutral beam injections (NBIs) has mainly contributed to this achievement. Ti exceeded 5 keV at the average plasma density (ne) of 1.2 × 1019 m-3 and also achieved 3 keV at ne > 3 × 1019 m-3. Neoclassical (NC) analysis was performed for such plasmas. We confirmed that even if Ti or the plasma density became higher, NC transport was remained to a certain value because of the existence of the ambipolar radial electric field (Er), which was roughly two orders of magnitude smaller for cases not involving the existence of ambipolar Er. Besides, a Ti and ne scan of discharge 75235 was also performed to consider the plasma parameter dependence of NC transport. Using these calculations, it is shown that NC ion thermal diffusivities are reduced to a small percentage of NC electron thermal diffusivites even at the fusion reactor relevant parameters such as ne ∼ 1 × 1020 m-3 and Ti ∼ Te ∼ 10 keV.

Emission intensities and line ratios from a fast neutral helium beam

The emission intensities and line ratios from a fast neutral helium beam is investigated in the Madison Symmetric Torus (MST) [R. N. Dexter, D. W. Kerst, T. W. Lovell, S. C. Prager, and J. C. Sprott, Fusion Technol. 19, 131 1991]. Predicted He I line intensities and line ratios from a recently developed collisional-radiative model are compared with experiment. The intensity of singlet lines comes mostly (&amp;gt;95%) from the contribution of the ground state population and is very weakly dependent on the initial metastable fraction at the observation point in the plasma core. On the other hand, the intensity of triplet lines is strongly affected by the local metastable state (21S and 23S) populations and the initial metastable fraction plays an important role in determining line intensities. The fraction of local metastable states can only be estimated by making use of electron temperature (Te), electron density (ne), and effective ion charge (Zeff) profiles as inputs to the population balance equations. This leads triplet lines to be unusable for the investigation of their local plasma parameter dependence. The ratio of singlet lines at 667.8nm and 492.2nm (I667∕I492) as well as the ratio of 667.8nm and 501.6nm lines (I667∕I501) has been investigated for the dependence on Te and ne both theoretically and experimentally. I667∕I492 shows strong dependence on ne with weak sensitivity to Te. Measurements and predictions agree quantitatively within a factor of 2. There has been no ratio of singlet lines identified to have strong enough Te dependence yet. The ratios are expected to be reasonably insensitive to the variation of Zeff.

Dependences of Plasma Parameters on Dilution Gas Content in Inductively Coupled C2F6/Ar and C2F6/O2 Discharges

Electron energy probability functions (EEPFs) are investigated in inductive C2F6/Ar and C2F6/O2 discharges. The structure of the EEPFs changes from bi-Maxwellian to Druyvesteyn-like distributions through a Maxwellian one with increasing Ar content, whereas the EEPFs form the bi-Maxwellian structure at any oxygen content except for pure oxygen. Dependences of both the fluorine atom density measured by actinometry and the relative variation of CF2 density determined from an optical emission at 251.9 nm on the dilution gas content are also investigated. The densities of F and CF2 are independent of the Ar content, while they depend strongly on the oxygen content.

Model and probe measurements of inductively coupled CF4 discharges

A global model for electronegative plasma, in which the negative ion distribution is assumed to be a parabolic profile in the axial direction with a flat central region and a similar edge profile in the radial direction in the electronegative region, is applied to study the power and pressure dependences of plasma parameters in low-pressure CF4 discharges. The electron density increases approximately linearly with the power. The electron temperature also increases with the power due to the decrease in neutral number density with increase in power, resulting in the increase in plasma potential. The density of CF3+ is a weak function of the power, while the densities of CF2+, CF+, and F+, which are strongly correlated to the densities of the respective radicals, depend on the power. On the other hand, the decrease in electron temperature with the pressure significantly results in a decrease in the degree of dissociation. The electron density also decreases gradually with the pressure except for the case of pressure lower than 5 mTorr. The densities of CF2+, CF+, and F+ decrease gradually with the pressure at pressures higher than 5 mTorr, while the density of CF3+ increases gradually with the pressure. The electron energy probability function (EEPF) is measured with a Langmuir probe in an inductively coupled rf (13.56 MHz) CF4 discharge over a pressure range from 2 to 30 mTorr, while keeping the power injected into the plasma at about 70 W. The measured EEPFs are approximately Maxwellian at any pressure, although there is a slight deviation from a Maxwellian distribution at pressures higher than 10 mTorr. The results estimated from the measured EEPF are compared to the model and show reasonably good agreement.