Diagnosing ratio of electron density to collision frequency of plasma surrounding scaled model in a shock tube using low-frequency alternating magnetic field phase shift

A non-contact low-frequency(LF)method of diagnosing the plasma surrounding a scaled model in a shock tube is proposed.This method utilizes the phase shift occurring after the transmission of an LF alternating magnetic field through the plasma to directly measure the ratio of the plasma loop average electron density to collision frequency.An equivalent circuit model is used to analyze the relationship of the phase shift of the magnetic field component of LF electromagnetic waves with the plasma electron density and collision frequency.The applicable range of the LF method on a given plasma scale is analyzed.The upper diagnostic limit for the ratio of the electron density(unit:m^(-3))to collision frequency(unit:Hz)exceeds 1×10^(11),enabling an electron density to exceed 1×10^(20)m^(-3)and a collision frequency to be less than 1 GHz.In this work,the feasibility of using the LF phase shift to implement the plasma diagnosis is also assessed.Diagnosis experiments on shock tube equipment are conducted by using both the electrostatic probe method and LF method.By comparing the diagnostic results of the two methods,the inversion results are relatively consistent with each other,thereby preliminarily verifying the feasibility of the LF method.The ratio of the electron density to the collision frequency has a relatively uniform distribution during the plasma stabilization.The LF diagnostic path is a loop around the model,which is suitable for diagnosing the plasma that surrounds the model.Finally,the causes of diagnostic discrepancy between the two methods are analyzed.The proposed method provides a new avenue for diagnosing high-density enveloping plasma.

The nature of electron density enhancement over a wide altitude range during ionosphere heating experiments at EISCAT

During the course of ionospheric heating experiments, researchers at the European Incoherent Scatter Scientific Association (EISCAT) observed an apparent electron density enhancement. The enhancement extended over a wide range of altitudes, above the reflection altitude of the high-frequency pump wave. However, whether this enhancement actually corresponds to a true enhancement in electron density remains an open question. When the dispersion relation of ion acoustic waves is followed, the frequency ratio of the enhanced ion line to the background ion line suggests that the profile of the effective ion mass may have remained unchanged. Furthermore, the solar radio flux and ion drift velocity indicate no significant changes in the ion species and their densities. In conclusion, the electron density enhancement observed at EISCAT should not, in fact, be considered a true enhancement.

Electron density measurement by the three boundary channels of HCOOH laser interferometer on the HL-3 tokamak

Far-infrared(FIR)interferometer is widely used to measure the electron density in the magnetically confined fusion plasma devices.A new FIR laser interferometer with a total of 13 channels(8 horizontal channels and 5 oblique channels)is under development on the HL-3tokamak by using the formic-acid laser(HCOOH,f=694 GHz).In order to investigate the boundary electron density activity during the divertor discharge,three horizontal interferometry channels located at Z=-97,-76,76.5 cm have been successfully developed on HL-3 in 2023,and put into operation in recent experimental campaign,with a time resolution of<1.0μs and lineintegrated electron density resolution of~7.0×10^(16) m^(-2).This paper mainly focuses on the optical design of the three-channel interferometry system,as well as optical elements and recent experimental result on HL-3.

GGA+U study of the electronic energy bands and state density of the wurtzite In_(1-x)Ga_xN

The electronic band structures, densities of states （DOSs）, and projected densities of states （PDOSs） of the wurtzite In1-xGaxN with x=0, 0.0625, 0.125 are studied using the generalized-gradient approximation （GGA） and GGA＋U in density functional theory. Our calculations suggest that in the case of wurtzite InN it is important to apply an on-site Hubbard correction to both the d states of indium and the p states of nitrogen in order to recover the correct energy level symmetry and obtain a reliable description of the InN band structure. The method is used to study the electronic properties of the wurtzite In1-xGaxN. The conduction band minimum （CBM） energy increases, while the valence band maximum （VBM） energy decreases with the increase of the gallium concentration. The effect leads to broadening the band gap （BG） and the valence band width （VBW）. Furthermore, the compressive strain in the crystal can cause the BG and the VBW to increase with the increase of gallium concentrations.

Comparing two iteration algorithms of Broyden electron density mixing through an atomic electronic structure computation

By performing the electronic structure computation of a Si atom, we compare two iteration algorithms of Broyden electron density mixing in the literature. One was proposed by Johnson and implemented in the well-known VASP code.The other was given by Eyert. We solve the Kohn-Sham equation by using a conventional outward/inward integration of the differential equation and then connect two parts of solutions at the classical turning points, which is different from the method of the matrix eigenvalue solution as used in the VASP code. Compared to Johnson＇s algorithm, the one proposed by Eyert needs fewer total iteration numbers.

Analysis of Anomalous Enhancement in TEC and Electron Density in the China Region Prior to the 17 March 2015 Geomagnetic Storm Based on Ground and Space Observations

Total Electron Content(TEC)and electron density enhancement were observed on the day before 17 March 2015 great storm in the China Region.Observations from ground-and space-based instruments are used to investigate the temporal and spatial evolution of the pre-storm enhancement.TEC enhancement was observed from 24°N to 30°N after 10:00 UT at 105°E,110°E and 115°E longitudes on March 16.The maximum magnitude of TEC enhancement was more than 10 TECU and the maximal relative TEC enhancement exceeded 30%.Compared with geomagnetic quiet days,the electron density of Equatorial Ionization Anomaly(EIA)northern peak from Swarm A/C satellites on March 16 was larger and at higher latitudes.NmF2 enhanced during 11:30—21:00 UT at Shaoyang Station and increased by 200%at~16:00 UT.However,TEC and electron density enhancement were not accompanied by a significant change of hmF2.Most research has excluded some potential mechanisms as the main driving factors for storm-time density enhancements by establishing observational constraints.In this paper,we observed pre-storm enhancement in electron density at different altitudes and Equatorial Electrojet(EEJ)strength results derived from ground magnetometers observations suggest an enhanced eastward electric field from the E region probably played a significant role in this event.

Impact of Arsenic Related Defects on Electronic Performance of ZrO2/GaAs:Density Functional Theory Calculations

Arsenic can diffuse into high-κ dielectrics during OaAs-based metal oxide semiconductor transistor process, which causes the degradation of gate dielectrics. To explore the origins of the degradation, we employ nonlocal B3LYP hybrid functional to study arsenic related defects in ZrO2. Via band alignments between the OaAs and ZrO2, we are able to determine the defect formation energy in the GaAs relative to the ZrO2 band gap and assess how they will affect the device performance. Arsenic at the interstitial site serves as a source of positive fixed charge while at the oxygen or zirconium substitutional site changes its charge state within the band gap of GaAs. Moreover, it is found that arsenic related defects produce conduction band offset reduction and gap states, which will increase the gate leakage current.

Research on the Relationship between Density of States and Conducting Properties of Single-walled Carbon Nanotubes

The analytical expression of the electronic density of states (DOS) for single-walled carbon nanotubes (SWNTs) has been derived on the basis of graphene approximation of the energy E(k) near the Fermi level EF. The distinctive properties of the DOS, the normalized differential conductivity and the current us bias for SWNTs are deduced and analyzed theoretically. The singularities in the DOS (or in the normalized differential conductivity) predict that the jump structure of current (or conductance)-bias of SWNTs exists. All conclusions from the theoretical analysis are in well agreement with the experimental results of SWNT's electronic structure and electronic transport. In other words, the simple theoretical model in this paper can be applied to understand a range of spectroscopic and other measurement data related to the DOS of SWNTs.

Real-time data processing method for CO_(2) dispersion interferometer on EAST

A real-time data processing system is designed for the carbon dioxide dispersion interferometer(CO_(2)-DI)on EAST.The system utilizes the parallel and pipelining capabilities of an fieldprogrammable gate array(FPGA)to digitize and process the intensity of signals from the detector.Finally,the real-time electron density signals are exported through a digital-to-analog converter(DAC)module in the form of analog signals.The system has been successfully applied in the CO_(2)-DI system to provide low-latency electron density input to the plasma control system on EAST.Experimental results of the latest campaign with long-pulse discharges on EAST(2022–2023)demonstrate that the system can respond effectively in the case of rapid density changes,proving its reliability and accuracy for future electron density calculation.

A fringe jump counting method for the phase measurement in the HCN laser interferometer on EAST and its FPGA-based implementation

Electron density in fusion plasma is usually diagnosed using laser-aided interferometers. The phase difference signal obtained after phase demodulation is wrapped, which is also called a fringe jump. A method has been developed to unwrap the phase difference signal in real time using FPGA, specifically designed to handle fringe jumps in the hydrogen cyanide(HCN) laser interferometer on the EAST superconducting tokamak. This method is designed for a phase demodulator using the fast Fourier transform(FFT) method at the front end. The method is better adapted for hardware implementation compared to complex mathematical analysis algorithms, such as field programmable gate array(FPGA). It has been applied to process the phase measurement results of the HCN laser interferometer on EAST in real time. Electron density results show good confidence in the fringe jump unwrapping method. Further possible application in other laser interferometers, such as the POlarimeter-INTerferometer(POINT)system on EAST tokamak is also discussed.

First spectroscopic study of HFRC plasma

An advanced spectral diagnostic system was developed to measure the electron temperature(T_(e)),electron density(N_(e)),and ion temperature(T_(i))of the Huazhong University of Science and Technology field-reversed configuration plasma.The system consists of an optic fiber spectrometer with a wide spectral band and a 670 mm focal length high throughout Czerny-Turner monochromator equipped with both a 3600 g mm^(-1)grating and a 2400 g mm^(-1)grating to measure the line spectrum.Accompanying these components is an electronmultiplying charge-coupled device camera to capture spectral data.The relative intensity of the optical fiber spectrometer was calibrated using a standard luminance source,and the wavelength calibration of the spectrometer was accomplished using a Hg/Ar lamp.This diagnostic setup was configured to measure electron density based on the Stark effect of H_γ(n=5→n=2;434.04 nm).Doppler broadening of an OⅢ(2s^(2)2p(^(2)P^(0))3p→2s^(2)2p(^(2)P^(0))3s;375.988 nm)emission line was measured and analyzed to obtain the ion temperature,and electron temperatures were estimated from the relative strength of H_(β)(n=4→n=2;486.14 nm)(D_(β))and H_(γ)(D_(γ))spectral lines when the electron density was obtained from Stark effect measurements.The initial experimental results indicate that the highest electron temperature of the formation region was approximately 8 eV,the electron density of the colliding-and-merging region was approaching 10^(20)m^(-3),and the ion temperature reached about 40 eV.

Forward modelling of the Cotton-Mouton effect polarimetry on EAST tokamak

Measurement of plasma electron density by far-infrared laser polarimetry has become a routine and indispensable tool in magnetic confinement fusion research.This article presents the design of a Cotton-Mouton polarimeter interferometer,which provides a reliable density measurement without fringe jumps.Cotton-Mouton effect on Experimental Advanced Superconducting Tokamak(EAST)is studied by Stokes equation with three parameters(s_(1),s_(2),s_(3)).It demonstrates that under the condition of a small Cotton-Mouton effect,parameter s_(2)contains information about Cotton-Mouton effect which is proportional to the line-integrated density.For a typical EAST plasma,the magnitude of Cotton-Mouton effects is less than 2πfor laser wavelength of 432μm.Refractive effect due to density gradient is calculated to be negligible.Time modulation of Stokes parameters(s_(2),s_(3))provides heterodyne measurement.Due to the instabilities arising from laser oscillation and beam refraction in plasmas,it is necessary for the system to be insensitive to variations in the amplitude of the detection signal.Furthermore,it is shown that non-equal amplitude of X-mode and O-mode within a certain range only affects the DC offset of Stokes parameters(s_(2),s_(3))but does not greatly influence the phase measurements of Cotton-Mouton effects.

First results of CO_(2) dispersion interferometer on EAST tokamak

A dispersion interferometer(DI)has been installed and operates on the Experimental Advanced Superconducting Tokamak(EAST).This DI system utilizes a continuous-wave 9.3μm CO_(2)laser source to measure line-averaged electron densities accurately.In contrast to conventional interferometers,the DI does not require substantial vibration isolations or compensating systems to reduce the impact of vibrations in the optical path.It also employs a ratio of modulation amplitudes,ensuring it remains immune to the variations in detected intensities.Without a variation compensation system,the DI system on EAST reaches a density resolution of less than1.8×10^(-2)πrad and a temporal resolution of 20μs.The measurements made by the POlarimeterINTerferometer(POINT)system and the far-infrared hydrogen cyanide(HCN)interferometer are remarkably consistent with the DI’s results.The possibility of fringe jumps and the impact of refraction in high-density discharge can be significantly decreased using a shorter wavelength laser source.A rapid density change of 3×10^(19)m^(-3)during 0.15 s has been measured accurately in shot No.114755 of EAST.Additionally,the DI system demonstrates dependability and stability under 305 s long-pulse discharges in shot No.122054.

Density-functional study of CO adsorbed on Rh_N (N=2-19) clusters

We investigate the structural, electronic and adsorption properties of one single CO molecule adsorbed on RhN （N = 2-19） clusters, using the density-functional theory in the spin-polarized generalized gradient approximation. It is found that the structural growth model of the RhN clusters transforms from double layers （N = 12-16） to three layers （N ： 17-19）. Three different adsorption types are the atop site adsorption for N = 6, 8, 9, 11, 12, the bridge site adsorption for N ： 2-5, 7, 10, 13-15, 17 and the face adsorption for N = 16, 18, 19. The adsorption abilities of RhN clusters are related to C-O bond length, vibrational frequency, adsorption energy and the charge transfer between CO and Rh clusters as well as the electronic density of state. With the increase of Rh cluster size, the adsorption energy of CO adsorbed on RhN clusters tends to be 2.2 eV-2.3 eV, which is 0.2 eV-0.3 eV larger than the theoretical value （about 2.0 eV） of CO molecule adsorption on clean Rh （111） surface.

Oxygen Vacancy-induced Electron Density Tuning of Fe_(3)O_(4) for Enhanced Oxygen Evolution Catalysis

Despite the tremendous efforts devoted to enhancing the activity of oxygen evolution reaction(OER)catalysts,there is still a huge challenge to deeply understand the electronic structure characteristics of transition metal oxide to guide the design of more active catalysts.Herein,Fe_(3)O_(4)with oxygen vacancies(Fe_(3)O_(4)-Vac)was synthesized via Ar ion irradiation method and its OER activity was greatly improved by properly modulating the electron density around Fe atoms.The electron density of Fe_(3)O_(4)-Vac around Fe atoms increased compared to that of Fe_(3)O_(4)according to the characterization of synchrotron-based X-ray absorption near-edge structure(XANES),extended X-ray absorption fine structure(EXAFS)spectra,and density functional theory(DFT)calculation.Moreover,the DFT results indicate the enhancement of the desorption of HOO^(*)groups which significantly reduced the OER reaction barrier.Fe_(3)O_(4)-Vac catalyst shows an overpotential of 353 m V,lower than that of Fe OOH(853 m V)and Fe_(3)O_(4)(415 m V)at 10 m A cm^(-2),and a low Tafel slope of 50 m V dec^(-1)in 1 M KOH,which was even better than commercial RuO_(2)at high potential.This modulation approach provides us with valuable insights for exploring efficient and robust water-splitting electrocatalysts.

Electron Density and Optical Emission Measurements of SF_6/O_2 Plasmas for Silicon Etch Processes

This work investigates internal plasma process parameters using a hairpin resonance probe and optical emission spectroscopy. The dependence of electron density and atomic fluorine on the percentage of oxygen in an SF6/O2 discharge was measured using these methods. An RIE Oxford Instruments 80 plus chamber was used for the experiments. Two different process powers （100 W and 300 W） at a constant pressure （100 mTorr） were used, and it was found that the optical emission intensity of the 703.7 nm and 685.6 nm lines of atomic fluorine increased rapidly as oxygen was added to the SF6 discharge, reached their maximum at an O2 fraction of 20% and then decreased with further addition of oxygen. The plasma electron density was also strongly influenced by the addition of O2.

Research on the Real-Time Phase Jump Process Method for Plasma Electron Density Measurement in HL-2A Tokamak

In the real-time plasma electron density measurement using far infrared （FIR） laser interferometry, the plasma electron density can be calculated by measuring the real time phase difference between the reference signal and the probe signal. A novel Real-time Phase Jump Process （RPJP） method is applied to the HL-2A tokamak. With this method, the phase difference 1 precision is up to 1/3600 fringe （1 fringe is equal to a phase shift of 2π）, and the dynamic measure- ment range is extensible 65536 fringes. The time resolution of the phase difference is 80 ns, while the feedback delay is 180 its.

Atomic Emission Spectra Diagnosis and Electron Density Measurement of Semiconductor Bridge (SCB) Plasma

Emission spectra of a semiconductor bridge （SCB） plasma in a visible range was studied in air. The electron density was measured in a conventional way from the broadening of the Al Ⅰ 394.4 nm Stark width. Based on the Saha equation, a system for recording the intensity of Si Ⅰ 390.5 nm and Si Ⅱ 413.1 nm was designed. With this technique, the SCB plasma electron density was measured well and accurately. Moreover, the electron density distribution Vs time was acquired from one SCB discharge. The individual result from the broadening of the Al Ⅰ 394.4 nm Stark width and Saha equation was all in the range of 1015 cm^-3 to 1016 cm^-3. Finally the presumption of the local thermodynamic equilibrium （LTE） condition was validated.

Laser-induced plasma electron number density:Stark broadening method versus the Saha-Boltzmann equation

We report spectroscopic studies on plasma electron number density of laser-induced plasma produced by ns-Nd：YAG laser light pulses on an aluminum sample in air at atmospheric pressure. The effect of different laser energy and the effect of different laser wavelengths were compared. The experimentally observed line profiles of neutral aluminum have been used to extract the excitation temperature using the Boltzmann plot method, whereas the electron number density has been determined from the Stark broadened as well as using the Saha-Boltzmann equation （SBE）. Each approach was also carried out by using the AI emission line and Mg emission lines. It was observed that the,SBE method generated a little higher electron number density value than the Stark broadening, method, but within the experimental uncertainty range. Comparisons of Ne determined by the two methods show the presence of a linear relation which is independent of laser energy or laser wavelength. These results show the applicability of the SBE method for Are determination, especially when the system does not have any pure emission lines whose electron impact factor is known, Also use of Mg lines gives superior results than Al lines.

Measurement of electron density and electron temperature of a cascaded arc plasma using laser Thomson scattering compared to an optical emission spectroscopic approach

As advanced linear plasma sources, cascaded arc plasma devices have been used to generate steady plasma with high electron density, high particle flux and low electron temperature. To measure electron density and electron temperature of the plasma device accurately, a laser Thomson scattering（LTS） system, which is generally recognized as the most precise plasma diagnostic method, has been established in our lab in Dalian University of Technology. The electron density has been measured successfully in the region of 4.5？×10^19m^-3 to7.1？×10^20m^-3 and electron temperature in the region of 0.18 eV to 0.58 eV. For comparison,an optical emission spectroscopy（OES） system was established as well. The results showed that the electron excitation temperature（configuration temperature） measured by OES is significantly higher than the electron temperature（kinetic electron temperature） measured by LTS by up to 40% in the given discharge conditions. The results indicate that the cascaded arc plasma is recombining plasma and it is not in local thermodynamic equilibrium（LTE）. This leads to significant error using OES when characterizing the electron temperature in a non-LTE plasma.