Measurements Of Plasma Parameters Research Articles

In-situ observations of the three-dimensional energy cascade rate and Yaglom flux in the Earth’s magnetosheath

Abstract Measuring the energy cascade rate in space plasmas is a challenging task for several reasons. This quantity is (i) inherently three-dimensional (ii) scale-dependent, (iii) anisotropic in the interplanetary plasma, and (iv) requires measurements of plasma parameters in at least four points. Here, it is shown how three of these problems have been addressed by applying the novel lag polyhedra derivative ensemble (LPDE) technique to the magnetospheric multiscale (MMS) mission in the Earth’s magnetosheath. In particular, this technique solves the full vectorial Yaglom equation, handling problem (i), does not require the assumption of isotropy, solving problem (iii), while the application to MMS addresses constraint (iv).

On the possibility of studying the effect of magnetic reconnection in a laboratory astrophysical experiment using X-ray emission L-spectra of multiply charged ions

The paper considers the application of X-ray spectroscopy with high spatial resolution for investigation of magnetic reconnection in laboratory astrophysical experiments carried out on laser facilities of nano- and pico-second duration at moderate laser intensity on the target 1018 W/cm2. A brief overview of commonly used experimental schemes is given. We present atomic kinetic calculations for the spectra from the L-shells of Ne- and F-like iron ions (Fe, Z = 26), which demonstrate the high sensitivity of the spectra to changes in plasma parameters. An analysis of the range of applicability of various diagnostic approaches to assessing the electron temperature and laser plasma density is carried out. It is shown that transition lines in Ne-like ions are a universal tool for measuring plasma parameters, both in the region of laser interaction with the target and in the reconnection zone.

Effect of radiofrequency bias power on transmission spectrum of flat-cutoff sensor in inductively coupled plasma

Real-time monitoring of plasma parameters at the wafer plane is important because it significantly affects the processing results, yield enhancement, and device integrity of plasma processing. Various plasma diagnostic sensors, including those embedded in a chamber wall and on-wafer sensors, such as flat-cutoff sensors, have been developed for plasma measurements. However, to measure the plasma density on the wafer surface in real-time when processing plasma with bias power, such as in the semiconductor etching process, one must analyze the transmission spectrum of the flat-cutoff sensor in an environment with bias power applied. In this study, the transmission-spectrum and measured plasma-density characteristics of an electrode-embedded flat-cutoff sensor are analyzed via electromagnetic simulations and experiments under applied bias power. Our findings indicate that the flat-cutoff sensor accurately measures the plasma density, which is equivalent to the input plasma density under low bias power. Conversely, under high bias power, the plasma density measured by the sensor is lower than the input plasma density. Also, a thick-sheath layer is formed owing to the high bias power, which may complicate the measurement of plasma parameters using the flat-cutoff sensor. Plasma diagnostics using a flat-cutoff sensor in thick-sheath environments can be achieved by optimizing the flat-cutoff sensor structure. Our findings can enhance the analysis of plasma parameters on-wafer surfaces in processing environments with bias power applied.

From L-mode to the L–H transition, experiments on ASDEX upgrade and related gyrokinetic simulations

This work combines experimental observations from the ASDEX Upgrade tokamak with related gyrokinetic simulations of the turbulence moving from L-mode toward, and beyond, the L–H transition. Dedicated experiments have been performed with slow steps of increasing electron cyclotron heating power. Gyrokinetic simulations of the edge turbulence of these plasmas highlight the key roles of the non-linear electromagnetic effects and the external flow shear (E × B shear), both related to the evolution of the plasma pressure profile with increasing heating power. The increase in the plasma βe destabilizes turbulence at low toroidal mode numbers, that, in turn, is strongly suppressed by the external flow shear. This allows the plasma pressure profiles to evolve without a sharp rise in the turbulent fluxes. When all the experimentally measured plasma parameters are consistently included as inputs of the local gyrokinetic simulations, both the experimental electron and ion heat fluxes are quantitatively reproduced on the whole L-mode phase of the selected discharge. Simulations carried out with edge parameters of an ELM-free H-mode phase still show the importance of the mechanisms discussed earlier while also indicating possible limitations of the local approach.

Influence of the size of the Langmuir probe insulator on the measurements of inhomogeneous plasma parameters in a discharge with a hollow cathode

The influence of the insulator of a cylindrical Langmuir probe on the results of the plasma potential, electric field, electron energy distributions and their concentration measurements in a discharge in helium at a pressure of 3 mbar maintained by a hollow cathode was studied. The measurements were carried out using moving probes with spatial resolution along the cathode-anode axis. Two probes with the same geometry of the conductive part and different diameters of the insulators were used. It was determined that the effect of the insulator is different for different plasma parameters. An increase in its diameter leads to a decrease in the measured value of plasma potential and to an increase in the electron concentration and the average electron energy. The degree of this influence is different in various regions of inhomogeneous plasma and correlates with the local values of the average electron energy. Under experimental conditions, the differences are maximum near the cathode, weaken as the electron energy decreases with distance from it, and are negligible at average energies less than 1.5 eV.

Study of ablation phase in double-wire Z-pinch based on optical Thomson scattering

Measurement of plasma parameters during the ablation phase in the Z-pinch is crucial for investigating the dynamic behaviors. In this study, optical Thomson scattering was employed to measure the temperature and velocity of the ablation plasma in a double-wire Z-pinch. The scattering spectra profiles were fitted using a model that considered the velocity distribution. The experimental results revealed the energy evolution of ablation plasma, the establishment of the global magnetic field and the development of axial non-uniformities. The precursor plasma was found to play a key role in strengthening the global magnetic field. A resistive layer near the wire core with a size of 1.5 mm was observed in the ablation plasma after the precursor plasma column formed. The plasma underwent rapid heating in this layer, the electron temperature rises from 17 eV to 22 eV. Upon leaving this layer, electron the temperature is stable at around 22 eV. The radial distribution of the ablation rate increases and decreases, indicating the axial motion of the ablation plasma, which could be caused by the tilt motion of the stream and the secondary modulation of the natural wavelength.

Recent Upgrade of the Magnetic Diagnostic System in the Alvand-U Tokamak

The main acting parameters in tokamak plasma experiments, such as currents and electric and magnetic fields, are present inside and outside the plasma volume. To analyze the changes in the shape of tokamak plasma, it is necessary to use experimental data obtained from magnetic measurements. Until recently, a four-digit magnetic probe (MP) was used for qualitative analysis of the magnetic field, but its accuracy was low, and it could not be practically used as a diagnostic system. Following the Magnetic Confinement Group, Tokamak Laboratories’ approach to optimize and improve the measurement of plasma parameters, the use of a richer array of MPs to accurately measure changes in the magnetic field and identify plasma parameters in the Alvand tokamak was considered. In order to upgrade the magnetic diagnostic system, two MP arrays were designed and manufactured. Each array contains 12 poloidal and radial probes. The MPs of each array were attached to Mylar belts and mounted on the vacuum vessel of the tokamak. In addition, an integrator unit was designed and installed as a magnetic diagnostic subsystem. The conducted research involved the MP and calibration setup followed by preliminary tests of the array probe.

Commissioning and first results of the 174 GHz collective Thomson scattering diagnostic at Wendelstein 7-X

Collective Thomson Scattering (CTS) diagnostics measure the scattering spectrum of monochromatic incident radiation off collective fluctuations in the plasma. In this contribution, we present the first results from the upgraded CTS diagnostic at Wendelstein 7-X (W7-X) operating in the frequency range between 172 and 176 GHz. This frequency range allows for minimization of noise originating from the electron cyclotron emission in the plasma. Consequently, the good signal-to-noise ratio allows measurements of fast ions or bulk plasma parameters with higher temporal resolution compared with the previously used 140 GHz system.

A field programmable gate array based Langmuir probe system for measurement of plasma parameters at 500kHz in a high-power impulse magnetron sputtering plasma.

By utilizing Field Programmable Gate Arrays in a configuration similar to that of the Mirror Langmuir Probe, it is possible to bias a single probe at three precise voltages in sequence. These voltages can be dynamically adjusted in real-time based on the measured plasma electron temperature to ensure the transition region is always sampled. The first results have been obtained by employing this method and have generated real-time outputs of electron temperature, ion saturation current, and floating potential on a low temperature pulsed-DC magnetron at 500kHz. These results are in good agreement with the analysis of a conventionally swept Langmuir probe. This probe is designed with the intention of being implemented on MAST-U to aid in the study of exhaust physics and enable further investigation into filamentary behavior.

Analysis of Essential Features and Optimal Operational Parameters of an RF-ICP Torch for Waste Treatment Applications

Recently, plasma-based pyrolysis has gained increasing prominence as a technology in response to the growing challenges in waste disposal and the recognition of opportunities to generate valuable by-products. The efficiency of the pyrolysis process is intricately tied to the characteristics of the plasma involved, particularly the effective electron temperature (Teff) and plasma density (ne). This study aimed to conduct a comprehensive examination of the essential features and optimal operational parameters of a developed RF-ICP torch specifically designed for small-scale municipal solid waste (MSW) pyrolysis (mixture of paper and polypropylene) with the goal of controlling both the torch and the overall process. Using optical emission spectroscopy (OES), we measured plasma parameters, specifically (Teff) and (ne), while varying argon gas flow rates and RF powers. The (Teff) and (ne)were determined using the Boltzmann plot and Stark broadening, respectively. The RF torch was found to generate (ne) up to approximately 2.8×1020 cm−3 and (Teff) up to around 8200 K, with both parameters being controlled by the discharge power and gas flow rate. Additionally, a power-losing mechanism, namely the anomalous skin effect, was detected during the study, which is uncommon in atmospheric plasma discharge.

Feasibility study of a Heavy Ion Beam Probe for the Thailand Tokamak-1

A Heavy Ion Beam Probe (HIBP) diagnostic system can offer non-disturbing, local measurement of plasma electric potential and various plasma parameters. This paper presents results of a feasibility study for implementing a HIBP system on the Thailand Tokamak-1 (TT-1). With successful plasma discharges achieved in early 2023, TT-1, is planed for upgrades and expansion of diagnostic capabilities to conduct experiments in high confinement modes. Sector K is designated for the installation of the HIBP diagnostic system, where primary beam ions are injected through the top port and secondary beam ions emerge from the horizontal port. The HIBP system consists of two main components: (1) the primary beam injection, and (2) the detection of the secondary beam. In the injection system, the incident direction of the primary beam into the plasma is controlled by two pairs of electrostatic sweepers. For the detection of the secondary beam, the electric field produced by electrostatic sweepers, each with a length of 0.25 m and inclined at 30 degrees, ensures that the secondary beam ions enter the energy analyzer entrance at the center with normal angles. Candidate ions, such as Cs+, Rb+, and K+, with varying energies, are evaluated for their suitability based on beam attenuation and plasma density conditions. Cesium ions are suitable at lower densities (n̄e≤1×1019 m−3), while Rb+ and K+ are preferable at higher plasma densities (n̄e≥1×1019 m−3). The analysis indicates that the ratio of the attenuation current is approximately in the range of 10−3 to 10−2. This study provides valuable insights for the integration of the HIBP diagnostic system into TT-1, enabling investigations of H-mode plasma physics phenomena.

Spatio-temporal dynamics of electrons and helium metastables in uniform dielectric barrier discharges formed in He/N2

A uniform atmospheric pressure dielectric barrier discharge is operated in helium with an admixture (0.45%) of nitrogen. The discharge is ignited in the gas gap between a driven and a grounded electrode and propagates along the dielectric surface outside the gap. Plasma conditions are characterised with current and voltage measurements and by application of absolutely calibrated optical emission spectroscopy, with a focus on nitrogen molecular emission. Plasma parameters, namely electron density and reduced electric field, are determined with spatial and temporal resolution in the frame of a collisional-radiative model using a calibrated charge coupled device camera and Abel inversion of measured images. The density of an effective helium metastable state is calculated using the measured plasma parameters and compared with values of the state density measured with tunable diode laser absorption spectroscopy.

Diagnostic Complex of the Globus-M2 Spherical Tokamak

The diagnostic complex of the Globus-M2 spherical tokamak (R = 36 cm, a = 24 cm), the onlyoperating tokamak in Russia with a divertor plasma configuration, which operates in the range of subthermonucleartemperatures (Te to 1.6 keV, Ti to 4.5 keV) and densities (ne to 2 × 1020 m–3), is described. The Globus-M2 tokamak is the unique scientific facility, which is a part of the Federal Center for Collective Use ofthe Ioffe Institute, Russian Academy of Sciences “Materials Science and Diagnostics in Advanced Technologies.”This allows third parties to perform their research using it. The work contains a list of all diagnosticscurrently available on the tokamak. The description of the diagnostics is structured in such a way that thereader gets an idea of their capabilities for measuring plasma parameters with an emphasis on the limits andaccuracy of the measured values, and also spatial and time resolution. At the same time, many technicaldetails are omitted in order to save space; references are given to papers with a more detailed description ofindividual diagnostics.

Measurement of ion temperature and toroidal flow during magnetic reconnection with a large guide field

Ion temperature and toroidal flow along the guide field direction are measured using a new ion tomographic diagnostic on the Magnetic Reconnection eXperiment (MRX) during magnetic reconnection with a guide field strength of about 1.4 and 2.1 times the strength of the reconnecting component. Strong toroidal flows, beyond what has been measured in anti-parallel and lower guide field conditions on MRX, are observed. Sustained ion heating with no discernible structure within the measurement region is also observed. Probe measurements including Langmuir and Mach probe measurements are made to support the tomographic inversion of line-integrated measurements, as well as to provide local measurements of plasma parameters. Measurements of toroidal velocity and ion temperature are supported with time series data. Energy flow into and out of the X-line region is estimated using a guiding center framework and presented in the Appendix of this manuscript, suggesting an outsized role played by parallel electric field in energizing ions. The guiding center approximation is not well satisfied in the region of interest; however, the estimates provide a springboard for future, further experimentation.

Development of a low energy ion irradiation system for erosion test of first mirror in fusion devices

A low energy ion irradiation system based on the deuterium arc ion source with a high perveance of 1 μP for a single extraction aperture has been successfully developed for the investigation of ion irradiation on plasma-facing components including the first mirror of plasma optical diagnostics system. Under the optimum operating condition for mirror testing, the ion source has a beam energy of 200 eV and a current density of 3.7 mA/cm2. The ion source comprises a magnetic cusp-type plasma source, an extraction system, a target system with a Faraday cup, and a power supply control system to ensure stable long time operation. Operation parameters of plasma source such as pressure, filament current, and arc power with D2 discharge gas were optimized for beam extraction by measuring plasma parameters with a Langmuir probe. The diode electrode extraction system was designed by IGUN simulation to optimize for 1 μP perveance. It was successfully demonstrated that the ion beam current of ∼4 mA can be extracted through the 10 mm aperture from the developed ion source. The target system with the Faraday cup is also developed to measure the beam current. With the assistance of the power control system, ion beams are extracted while maintaining a consistent arc power for more than 10 min of continuous operation.

Development of a Probe System for Measuring Plasma Parameters under Conditions of Plasma Polymerization and Synthesis of Nanostructures

Development of a Probe System for Measuring Plasma Parameters under Conditions of Plasma Polymerization and Synthesis of Nanostructures

Near substrate surface plasma characteristics of ZnO film deposition in DC reactive magnetron sputtering with water vapor

The effect of varying the water vapor content in a DC magnetron sputtering process was investigated for zinc oxide film formation. The plasma parameters near the substrate surface were measured using a single Langmuir probe, and the deposited films were characterized using X-ray diffraction, X-ray reflectivity, optical transmittance, and 4-point probe methods. In the region near the substrate surface, the addition of water changes the plasma properties, and the measured plasma parameters showed the changes corresponding to the transition in the film growth mechanism from Zn to ZnO. Depositing at 40% water content resulted to a highly transparent film with a ρ of 1.20 Ω cm. The band gap of films deposited at 40%–100% water content ranged from 3.36 to 3.34 eV, which matches the expected shallow hydrogen donor doping in ZnO.

Plasma low-energy ion flux induced vertical graphene synthesis

Vertical graphene (VG) is a promising material for energy-storage, sensor, and electronic applications, owing to excellent structural, mechanical, and electrical properties. An existing method for synthesizing VG is plasma-enhanced chemical vapor deposition under high plasma ion-energy interaction on carbon surface. However, since this method can cause substrate damage, device performance degradation, and internal defects in VG, a new synthesis method using low-ion-energy is required. Accordingly, it is necessary to understand how the plasma low-ion energy contributes to the nucleation and growth of VG by interaction with the surface, but the reported studies are limited to the high-ion-energy region. Here, we report on the effects of low-energy ion flux in plasma-induced growth of vertical graphene and found the key plasma parameter for the VG growth and nucleation in a low-ion-energy environment and successfully controlled the nucleation of VG. VG deposition and plasma parameter measurements were performed in a radiofrequency inductively coupled plasma. In the low-energy region, the growth rate and nucleation of VG depended strongly on ion density, and insufficient ion flux formed highly disordered carbon. Based on these findings, VG nucleation was controlled by tailoring the ion energy and density under conditions where disordered carbon was formed.

Fusion Gain and Triple Product for the Sheared-Flow-Stabilized Z Pinch

Fusion gain Q and triple product nTτ are derived for the sheared-flow-stabilized (SFS) Z pinch by including the input power associated with driving the plasma flow and the additional advective loss of thermal energy. Plasma impurities contribute to radiative power losses and to thermal power losses by increasing the electron population. The presence of impurities increases the required plasma parameters, characterized by the triple product, to achieve fusion gain. The analysis is applied to deuterium-tritium (D-T) fusion, though the methodology can be extended to other reactions. Since D-T fusion produces an alpha particle, the possibility exists of magnetically confining the alpha with sufficiently high magnetic fields, which are self-generated by the plasma pinch current. Confined alpha particles can heat the D-T fusion fuel, reduce the needed input power, and thereby amplify the fusion gain. However, ignition (Q→∞) does not occur since the axial plasma flow must be externally driven. The impacts of alpha heating and impurity losses are considered on the fusion performance of the SFS Z pinch. Requirements, assumptions, and limitations are described that would justify a determination of “D-T equivalent Q=1 conditions” in a D-D plasma. A minimum set of experimental measurements of plasma parameters is specified that can be compared to a plasma parameter map to facilitate a “Q=1” claim, where Q is defined by instantaneous values of fusion power and input power. Corroborating measurements are also discussed that would further support extrapolation of plasma and fusion performance to D-T operation.

Splitting CO2 in Intense Pulsed Plasma Jets.

The splitting of CO2 was studied in a pulsed plasma discharge produced in a coaxial gun at voltages between ~1 and 2 kV and peak discharge currents of 7 to 14 kA. The plasma was ejected from the gun at a speed of a few km/s and had electron temperatures between 11 and 14 eV with peak electron densities ~2.4 × 1021 particles m-3. Spectroscopic measurements were carried out in the plasma plume produced at pressures between 1 and 5 Torr, and evidence of CO2 dissociation into oxygen and CO was found. An increased discharge current led to the observation of more intense spectra lines and the presence of new oxygen lines, which implies more dissociation channels. Several dissociation mechanisms are discussed, the main candidate being the splitting of the molecule by direct electron impact. Estimates of dissociation rates are made based on measured plasma parameters and interaction cross-sections available in the literature. A possible application of this technique is in future Mars missions where the coaxial plasma gun running in the atmosphere could be able to produce oxygen at a rate of the order of over 100 g per hour in a highly repetitive regime.