Impurity Emission Research Articles

Colloidal 2D Layered SiC Quantum Dots from a Liquid Precursor: Surface Passivation, Bright Photoluminescence, and Planar Self-Assembly.

We report the bottom-up synthesis of colloidal two-dimensional (2D) layered silicon carbide (SiC) quantum dots with a cubic structure, lateral size of 5-10 nm, ⟨110⟩ exfoliation to few atomic layers, and surface passivation with 1-dodecene. Samples shielded from oxygen and plasma-annealed for purity exhibit narrow blue photoluminescence (PL) with quantum yields (QYs) over 60% in exceptional cases, while unshielded nanocrystals (NCs) exhibit broad blue/green/white PL with 10-15% QY. The latter scenario is attributed to excess surface carbon and oxygen accrued during synthesis and processing, with size separation through ultracentrifugation revealing size-dependent impurity emission. In contrast, the shape of the bright narrow blue PL shows little variation with NC size, while in both scenarios, the maximum QY occurs near four atomic layers. When dried under heat, the disk-like NC suspensions are observed to aggregate into microscale domains, with further self-assembly into planar superlattice domains with common crystalline orientation. The results are compared with photophysical simulations and bring clarity to the broad emission commonly reported for top-down approaches, while inspiring bottom-up schemes directed at improved material quality.

SPARC x-ray diagnostics: Technical and functional overview.

An overview is given of SPARC's three main x-ray diagnostics, with a focus on the functions they fulfill with respect to tokamak operation. The first is an in-vessel soft x-ray tomography diagnostic, aimed at providing early campaign information on plasma position, MHD activity, and impurity content. The second is an ex-vessel set of hard x-ray scintillators aimed at detecting the presence of runaway electrons, in particular during plasma startup phases. The third is a set of x-ray Bragg spectrometers, located outside of the tokamak hall, aimed at informing on the ion temperature as an indirect constraint to reduce uncertainties on the fusion power, on providing plasma rotation velocity estimates, and on observing impurity emission. Finally, more technical details are given on the beamlines at the end of which the spectrometers are located. It explains how their design allows us to ensure tritium containment and limit neutron radiation while providing a straight view into the plasma that can also be used for testing new innovative sensors.

The energy transfer of electronic excitations to impurities in dosimetric phosphors [formula omitted]-Dy

The formation of new radiative states from the combination of Dy2+-SO4- and SO43--SO4- electron trapping centers in the range of 2.95–3.1 eV has been investigated using VUV and thermal activation spectroscopy. During the excitation process, there is a charge transfer between the oxygen ion of the sulfate anion and Dy3+ leading to the formation of a combined emissive state SO43-→SO4-. These states can be formed from the electron-hole trapping centers of Dy2+-SO4- and SO43--SO4-. The combined radiative state at 2.95–3.1 eV and impurity emission at 2.16 eV and 2.56 eV are excited simultaneously by photons of 3.95 eV and 4.5 eV, respectively. During the thermal or optical excitation process, the Dy2+ and SO43- electronic centers are ionized. Electrons recombine with a hole trapped by the ground state of the impurity (SO4--Dy3+), and the released energy is transferred to the Dy3+ impurities.

Wavelength calibration and spectral analysis of vacuum ultraviolet spectroscopy in EAST

A vacuum ultraviolet (VUV) spectroscopy with a focal length of 1 m has been engineered specifically for observing edge impurity emissions in Experimental Advanced Superconducting Tokamak (EAST). In this study, wavelength calibration for the VUV spectroscopy is achieved utilizing a zinc lamp. The grating angle and charge-coupled device (CCD) position are carefully calibrated for different wavelength positions. The wavelength calibration of the VUV spectroscopy is crucial for improving the accuracy of impurity spectral data, and is required to identify more impurity spectral lines for impurity transport research. Impurity spectra of EAST plasmas have also been obtained in the wavelength range of 50–300 nm with relatively high spectral resolution. It is found that the impurity emissions in the edge region are still dominated by low-Z impurities, such as carbon, oxygen, and nitrogen, albeit with the application of full-tungsten divertors on the EAST tokamak.

Ion temperature and rotation velocity measurements of carbon and boron ions using VUV spectroscopy on EAST.

A space-resolved vacuum ultraviolet spectroscopy is employed to measure impurity emission profiles (500-3200Å) on EAST. This study successfully captures C IV (1548.20 and 1550.77Å) lines emitted from carbon ions and derives ion temperatures using Doppler broadening and a collision model based on their intensity ratios. Both the emission intensity and ion temperature profiles are determined. However, the calculated results reveal a lower temperature of around 10-20eV with the collision model, suggesting a potential need for further correction in subsequent calculations. Furthermore, this study explores relative rotation velocities from the Doppler shift, indicating an increase in toroidal rotation velocity with applied neutral beam injection. The measured results exhibit concordance with the charge exchange recombination spectrometer data. Furthermore, during boron powder dropping discharges on EAST, B II (1623.60, 1623.79, 1623.95, 1624.02, 1624.17, and 1624.38Å) emission lines exhibiting a similar time behavior trend with boron powder injection are identified. Ion temperatures are measured using B II (1362.46Å) through the Doppler broadening method. These techniques hold significant promise for future impurity analysis at the edge of EAST, providing valuable insights into the behavior of carbon and boron ions.

MODELING OF GROUND WATER DYNAMICS AND ITS POLLUTION

Problem statement. Large accumulators of liquid waste (e.g., mine water ponds, tailing ponds, etc.) are long-term sources that change the hydrological regime. A negative consequence of this process is flooding of the territory. In addition, the infiltration of contaminated water from such hazardous sources changes the quality of groundwater. Therefore, it is important to analyze the impact of such anthropogenic sources on the process of flooding and deterioration of groundwater quality. To solve this problem, it is very important to use the method of mathematical modeling as an effective mean of researching problems of this class, since the use of physical modeling is practically impossible within the scope of problems of this class. The purpose of the article. Development of numerical models for predicting changes in the hydrological regime (flooding of the territory) and groundwater quality under the influence of anthropogenic pollution sources. Methodology. To assess the dynamics of changes in the hydrological regime, a two-dimensional equation of filtration of a non-pressure groundwater flow is used. A two-dimensional geomigration equation (planned model) is used to analyze changes in groundwater quality during infiltration of contaminated water from the settling pond. This equation takes into account the convective transfer of contaminants in the filtration flow, dispersion, and the intensity of contaminant infiltration into the groundwater flow. The method of total approximation is used for numerical integration of the filtration equation. For the numerical integration of the geomigration equation, an implicit splitting scheme is used. Scientific novelty. Effective numerical models for rapid assessment of changes in groundwater dynamics and quality under the influence of anthropogenic sources that change the hydrological regime are proposed. The constructed numerical models take into account a set of important physical factors that affect the process of geomigration and flooding of the territory, namely: filtration coefficient, variable depth of free-flowing groundwater, dispersion, intensity of the source of impurity emission into the groundwater flow. This makes it possible to obtain a comprehensive assessment of the process of flooding and groundwater pollution.. Practical significance. A computer code has been created that allows practical usage of the developed numerical models. This code is an effective tool for theoretical study of non-stationary processes of territory flooding and anthropogenic groundwater pollution. Conclusions. A numerical model for calculating groundwater dynamics has been developed. The model allows to predict the level of groundwater rise under the influence of a man-made source of wastewater infiltration from a settling pond. A numerical model for calculating the process of geomigration from an anthropogenic source of emissions has been developed. The model makes it possible to predict the dynamics of contamination zone formation in a non-pressure groundwater flow. The developed numerical models take into account the most important parameters that affect the formation of flooding zones and groundwater contamination.

Vacuum-Ultraviolet spectrometer system for impurity emission measurement on a Compact Torus Injection System of EAST

Recently, a compact torus injection (CTI) system was developed for central fueling on experimental advanced superconducting tokamak (EAST). As impurity generated by the interaction between CTI plasma and the electrode material can dilute the fuel particle, it is important to measure impurity content in CTI and evaluate the effect of impurity on the plasma before the application of CTI to EAST. A vacuum-ultraviolet (VUV) spectrometer that utilizes a concave holographic grating with 1200 groove mm-1 was developed and installed on EAST-CTI for impurity emission measurement and transport study. The mainly parts of the spectrometer are an entrance slit, a concave holographic grating with 1200 groove mm-1 and a charge coupled device (CCD). The spectrometer is designed to image the spectra of 50–460 nm by turning the grating. Preliminary experimental results were obtained from the recent EAST-CTI campaign. Impurity line spectra from 50 to 460 nm wavelength range were measured and identified for several impurity species, such as iron, copper, chromium, oxygen, carbon and fluorine. For example, spectra in the intervals of 150 nm to 300 nm contained strong Fe lines. Helium spectra are also measured in the form of He I and He II spectral lines as helium is the main component of the plasma. The results show that the VUV spectrometer is capable of measuring impurity radiations on EAST-CTI and will be a useful tool for impurity behavior study.

ASSESSMENT OF THE ENERGY FACILITY IMPACT ON ENVIRONMENTAL POLLUTION

Problem statement. The task of assessing the influence of the boiler house on atmospheric air pollution is under consideration. Carrying out such an assessment is very important when locating boiler houses near residential areas. Since the weather conditions for each region are characterized by a change in the direction of the wind, the intensity of atmospheric diffusion, the appearance of a calm, it is important to have information about the formation of pollution zones in sedimentary zones. To solve this important problem, it is very important to use mathematical modeling, since it is currently impossible to create a sufficient number of observation posts near the objects of the fuel and energy complex. The purpose of the article. Numerical analysis of the influence of the boiler house on the intensity of atmospheric air pollution under different weather conditions. Methodology. The 3D equation of convective-diffusion transport is used to estimate the pollution zones formed in the atmospheric air when it is emitted from the boiler house pipe. The model takes into account atmospheric stratification, impurity emission intensity, wind profile, wind speed. Numerical integration of the equation of convective-diffusion transport of impurities is carried out using finite-difference schemes. The modeling equation is split into an equation for the convective transport of the pollutant and an equation for the dispersion of the pollutant due to atmospheric diffusion. The equation describing the change in the concentration of the impurity in the atmospheric air as a result of the emission of the pollutant from the pipe is solved separately. At the next stage, finite-difference schemes are built that allow solving the splitting equation. Scientific novelty. On the basis of the constructed numerical model, the zones of atmospheric air pollution during the emission of CO from the pipe of the boiler house are determined. A numerical model is proposed that allows forecasting atmospheric air pollution for different weather conditions within the framework of one program package. Practical significance. On the basis of the proposed numerical model, the forecasting of the zones of chemical pollution of the atmospheric air in the settlement zone in which the boiler house is located was carried out. The results of the computational experiment are presented.

Dynamics and impurity spectral characteristics of coaxial gun discharge plasma

<sec>The coaxial gun discharge can produce plasma jet with high velocity, high density and high energy density, and has extensive applications, such as in plasma space propulsion, simulation of the interaction between edge local mode and wall materials in ITER, fuel injection in magnetic confinement fusion devices, and laboratory astrophysics. In the pre-filled discharge mode or snowplow mode, the plasma current sheet is formed near the insulating layer surface and moves toward the end of the coaxial gun under Lorentz force. Plasma velocity, density and purity characteristics are very important research contents for the actual applications of coaxial gun. Emission spectrometry as a non-interference method can be used to diagnose a variety of plasma physical properties.</sec><sec>In this experiment, the effects of different discharge currents and gas pressures on the plasma dynamics, electron density and impurity emission spectra of coaxial gun discharge plasma are studied through the measurement of plasma photocurrent, emission spectra and the shooting of discharge images. The experimental results show that the acceleration time of the plasma in the gun decreases with current increasing in a range of 30–70 kA when the gas pressure is 10 Pa, the spectral intensity of anode and cathode impurities in plasma increase with current amplitude increasing. When the discharge current is 40 kA and the gas pressure is in a range of 10–70 Pa, the acceleration time of plasma increases with gas pressure rising, and the spectral intensity of the cathode impurity in the plasma decreases with the pressure increasing, while the spectral intensity of the anode impurity increases gradually, but its growth rate decreases continuously. The analysis indicates that the presence of metallic impurities originating from the electrode material limits the jet velocity of the plasma and is the main cause of the deviation from theoretical value. The plasma pinch effect at the nozzle of coaxial gun and the acceleration time of high-density arc in the gun are important factors affecting anode ablation. The impurity of cathode material is produced by ion bombardment sputtering, which mainly depends on the energy carried by ions. Therefore, a reasonable choice for discharge parameters is the key factor to obtain optimal plasma characteristics during the discharge of the coaxial gun.</sec>

Energy Transfer in the CaSO4−Dy Thermoluminescent Dosimeter from the Excited State of the SO42− Anionic Complex to the Impurities

The creation of a combined radiative state at 2.95–3.1 eV in the phosphor CaSO4−Dy 3+ has been investigated using vacuum ultraviolet and thermoactivation spectroscopy methods. It is shown that the combined radiative electronic state is formed from the radiative electronic states of the impurity electronic trapping centers Dy 2+− SO4− and the intrinsic electronic radiative states SO43−−SO4− during the excitation of the anion complex SO42−, as a result of charge transfer from the excited anion complex O 2−−Dy 3+ to the impurities and the neighboring anion complex O2−− SO42−. In the CaSO4−Dy phosphor, the combined radiative electronic state and impurity emission of Dy 3+, 2.16 eV and 2.56 eV are excited by photons with energies of 3.95–4.0 eV and 4.5–4.6 eV. Energy transfer from the matrix to the Dy 3+ impurities is revealed upon thermal exposure as a result of the ionization of the electronic capture centers of Dy2+ and SO43−.

INVESTIGATION OF THE EFFECTIVENESS FOR PROTECTIVE SCREENS OF VARIOUS FORMS ON AIR POLLUTION REDUCTION

Problem statement. The task of evaluating the effectiveness of the use of protective screens of different geometric shapes to reduce the level of air pollution is considered. The data on the screen allow you to change the aerodynamics of the air flow and redirect the movement of polluted air away from the work areas in the other direction. The purpose of the article – study of the effectiveness of the use of protective screens of different geometric shapes to reduce the level of pollution, creation of a three-dimensional numerical model for the analysis of the effectiveness of the use of protective screens. Methodology. The method of physical experiment in laboratory conditions is used to analyze the effectiveness of screens of different geometric shapes. Three-dimensional equations of aerodynamics and mass transfer are used for mathematical modeling of impurity propagation in the presence of screens. The developed numerical model makes it possible to take into account the air flow velocity profile, atmospheric diffusion, the emission intensity of the impurity, the rate of gravitational sedimentation of the impurity in the air. For the numerical integration of the modeling equations of aerodynamics and mass transfer, finite-difference splitting schemes are used. Scientific novelty. Data on the effectiveness of the use of four protective screens, which differ in geometric shape, were obtained experimentally. Experimental data make it possible to carry out an initial assessment of the impact of various screens on reducing the level of pollution in working areas. A fast-calculating 3D numerical model was developed for solving problems of aerodynamics and mass transfer in relation to the problem of evaluating the effectiveness of the use of screens located in areas where atmospheric air pollution occurs. Practical significance. Experimental data make it possible to justify the choice of a protective screen near the highway or another area on the industrial site where the impurity emission takes place. A computer code was created on the basis of the developed mathematical model, which makes it possible to predict the intensity of air pollution in the presence of obstacles that change the aerodynamics and the direction of transport of impurities in the atmosphere. Conclusions. The results of the physical experiment allow us to imagine the regularities of the formation of areas of pollution near protective screens of different geometric shapes, the developed mathematical model allows us to estimate air pollution in areas where there are obstacles in the way of the movement of impurities. The results of physical and computational experiments are presented.

Resonance in radio frequency sheath admittance and enhanced impurity emission near the ion cyclotron frequency

Ion cyclotron resonance heating (ICRH) is of considerable interest among all auxiliary heating techniques, because it transfers power directly to ions, targets the high-density core, and involves the cheapest radio-frequency (RF) components. During ICRH operation, RF sheaths form on the ICRH antenna itself, nearby hardware, and far-field surfaces. These sheaths are associated with large hot-spot formation and impurity emissions. This work presents high-resolution numerical modelling of RF sheaths in nuclear fusion scenarios using hPIC2, a Debye-scale particle-in-cell code. The modelling reveals a new RF sheath phenomenon which occurs when the RF is resonant with a species ion cyclotron frequency or harmonic in an oblique magnetic field. This resonance of the RF sheath causes modifications of the energy-angle distributions of the ions impacting on the walls, with consequent increase in wall impurity emission. Due to the 1/R scaling of the magnetic field in a tokamak, such cases are possible on divertor or vacuum chamber surfaces, depending on the geometry of the tokamak and the RF heating scenario. A simple physics interpretation using a driven damped harmonic oscillator is proposed, where the ion sheath transit time plays the role of damping the RF sheath admittance. Critically, the resonance leads to increased ion heat flux at the wall as well as increased physical sputtering, despite a lack of increase in RF rectified sheath potential.

Comment on "Charge Transfer-Triggered Bi3+ Near-Infrared Emission in Y2Ti2O7 for Dual-Mode Temperature Sensing".

Undoped Y2Ti2O7 exhibits impurity emission bands at low temperatures due to Mn4+ and Cr3+, as established by codoping with these ions. Contrary to a recent report by Wang et al., ACS Appl. Mater. Interfaces 2022, 14, 36834-36844, we do not observe Bi3+ emission in this codoped host, as also is the case for Fe3+. The emission reported in that paper as being due to Bi3+ in fact corresponds to Cr3+ emission. The Cr3+ and Mn4+ emissions are quenched with increasing temperature, so that Mn4+ emission is scarcely observed above 80 K. We present variable temperature optical data for Y2Ti2O7 and this host codoped with Mn, Cr, Fe, and Bi, as well as a theoretical justification of our results.

X‐Ray Luminescence and Thermally Stimulated Processes in Cesium Iodide Crystal

X‐ray luminescence spectra, thermally stimulated luminescence, and thermally stimulated conductivity of undoped cesium iodide (CsI) crystal are investigated in order to reach better understanding of the factors which govern the emission processes in this material. X‐ray luminescence spectra are recorded in the temperature range from 15 to 293 K. The low energy band at 2.2 eV emerging at heating above 120 K is assigned to the emission of residual impurities. Other two bands peaking at 3.6 and 4.3 eV at 15 K are attributed to the intrinsic emission of CsI due to the self‐trapped excitons (STEs). The parameters of the peaks observed in the thermally stimulated luminescence and conductivity of CsI crystal are calculated. Investigations of the thermally stimulated processes in CsI lead to the conclusion that the increase of luminescence of 4.3 eV observed above 70 K is due to release of trapped electrons, which subsequently interact with Vk centers and form on‐center STEs. The considerable ionic conductivity observed above 250 K can be explained by the influence of uncontrolled impurities of divalent metal atoms as well as Na+ ions.

Towards Integrated Target–SOL–Core Plasma Simulations for Fusion Devices with Liquid Metal Targets

Self-healing liquid metal divertors (LMDs) based on the Capillary Porous Structure (CPS) concept are currently being considered among the possible solutions to the power exhaust problem in future fusion reactors. Indeed, the passive replenishment of the plasma-facing surface by capillary forces and the self-shielding of the target via vapor emission can potentially improve the divertor lifetime and its resilience to transient loads. On the other hand, the LMD target erosion can be significant due to evaporation and thermal sputtering, on top of physical sputtering, possibly leading to unacceptable core plasma dilution/power losses (for a low-Z/high-Z metal such as Li and Sn, respectively). For this reason, it is necessary to assess whether an LMD is compatible with an European DEMO (EU-DEMO) plasma scenario. This requires a self-consistent model of the impurity emission from the target, the plasma in both the scrape-off layer (SOL) and the core regions and the transport of impurities therein. In this paper, an an integrated modelling approach is proposed, which is based on SOLPS-ITER and includes its coupling with a target erosion model written in FreeFem++ and a core plasma model (ASTRA/STRAHL). An application of the coupled SOL-target model to simulate experiments performed in the Magnum-PSI linear plasma device with a CPS target filled with Li is also included to provide a first demonstration of the capabilities of the approach. Results are promising, being in good agreement (within a few degrees) with the measured target temperature distribution. In perspective, the modelling framework presented here will be applied to the EU-DEMO with an Sn divertor.

Impacts of recycling impurity on the background ELM behavior during repetitive radiative divertor experiments in EAST

A significant change in the background ELM behavior prior to neon (Ne) seeding has been observed in a series of repetitive radiative divertor experiments in EAST. With similar operational parameters, the ELM behavior before Ne seeding changes from large to mixed ELMs, and finally evolves to pure small ELMs. Meanwhile, a significant increase in both Ne and high-Z impurity (W and Mo) emissions has been observed in the bulk plasma, suggesting the retention and recycling of Ne impurity from the wall surface. Experimental results show that the variation in background ELM behavior is highly correlated with the occurrence of high-Z impurity accumulation. The increased accumulation of high-Z impurities leads to a lower electron temperature both in the plasma core and edge, accompanied by a higher and more peaked electron density in the plasma core. Pedestal linear stability analysis reveals that the decreased pedestal electron temperature and thus the lower pressure gradient and lower edge current density are the primary reason for the change of background ELM behavior. The concentration of recycling Ne in the bulk plasma is estimated to be ∼1% in the discharges with pure small ELMs.

Emission and time-resolved migration rates of aromatic diamines from two flexible polyurethane foams.

Performing risk assessments (RA) on household use of flexible polyurethane (PU) foams requires access to reliable data about emission and migration of potential diamine impurities. A toluene diisocyanate (TDI) and a methylene diphenyl diisocyanate (MDI) based foam were thermally treated to enable measurements on samples with defined concentrations of the corresponding diamines, toluene diamine (TDA), and methylene dianiline (MDA). The thermally treated foams used for emission testing contained up to 15mg.kg-1 of TDA and 27mg.kg-1 of MDA. Those used for migration testing contained 5.1mg.kg-1 of TDA and 14.1mg.kg-1 of MDA. Stability of the thermally generated diamines was sufficient for testing over a 37-day period. Analytical techniques that did not decompose the polymer matrix were applied. Emission rates for TDA and MDA isomers were less than the limit of quantitation (LOQ) of 0.008-0.07μg.m-2.h-1. Migration was studied using samples of the same thermally treated foams over a 35-day period. Quantifiable migration of MDA from the MDI-based foam was only observed on Days 1 and 2. From Day 3 onward, migration rates were less than the LOQ. Quantifiable migration of TDA from the TDI-based foam rapidly decreased with time and was only observed on Days 1 thru 3. From Day 4 onward, migration rates were less than the LOQ. Theoretically, the migration rate should be inversely proportional to the square root of time (t) as t-0.5. This relationship was confirmed by the experimental data and enables extrapolating migration values to more extended time periods to conduct RAs.

Electron-hole trapping centers in Na2SO4 with a transition metal impurity Mn

The Na 2 SO 4 samples were obtained by slow evaporation method. The mechanisms of the formation of electron and hole trapping centers are investigated by spectroscopic methods. Intrinsic recombination emission of 2.9–3.1 eV and impurity emission of 1.85 eV are excited at 4.0–4.5 eV. Intrinsic SO 3− 4 −SO − 4 and impurity Mn + − SO − 4 trapping centers were revealed. The local levels corresponding between the electron and hole trapping center are 4.0–4.5 eV. The decay of intrinsic and impurity trapping centers was recorded at temperatures of 130–150 K and 280–350 K.

First-Principles and Experimental Study of Trace Impurities and Near-Infrared Emission in Alkaline Earth Hexaaluminates

First-principles calculations have been performed for bismuth and iron doped into the lattices BaAl12O19 (BAO) and CaAl12O19 (CAO). Experimental data for the optical spectra of CAO at temperatures down to 10 K are presented to support the calculation results. Even undoped samples of CAO exhibit luminescence bands due to trace impurities in the starting materials employed for synthesis. In particular, Mn4+ is ubiquitous. The near-infrared emission band at ∼810 nm in CAO is assigned to Fe3+ at the five-coordinated bipyramidal Al site. The near-ultraviolet emission of Bi-doped CAO is assigned to Bi3+ at the Ca site. The family MAO (M = Ba, Sr, and Ca) has been widely adopted for use as phosphors, when doped with transition metal or lanthanide ions, and the present study highlights the importance of reagent chemical purity in order to avoid energy losses and emission integrity via chemical impurity emissions. The emission wavelength of ∼810 nm presents interesting applications.

Hot spots induced by RF-accelerated electrons in the scrape-off layer on Experimental Advanced Superconducting Tokamak

Preventing impurity emission from hot spots on plasma-facing materials is a critical issue in the maintenance of high-performance plasma on the Experimental Advanced Superconducting Tokamak (EAST). In this study, experimental and theoretical analyses were performed to investigate the mechanism of hot spot formation. In the upper single null magnetic configuration of the EAST, two separatrices were connected to the upper (primary) and lower (secondary) X-points. Experiments on plasma configuration control indicated that the reduction in the gap between the lower (secondary) separatrix and lower hybrid antenna is effective in preventing hot spot formation on the lower divertor, which frequently emits impurities in long-duration discharges. This effectiveness was quantitatively confirmed by magnetic field lines tracking simulation and calorimetric measurement of divertors in the experiment. Two-frequency power modulation of the lower hybrid wave (LHW) was conducted to evaluate power deposition on the scrape-off layer (SOL) during propagation from the LHW antenna to the main plasma. This experiment clarified that LHW-accelerated electrons in the SOL via collision damping deliver their energies to hot spots along the magnetic field line. These findings help alleviate or even eliminate the formation of hot spots and maintain the performance of plasma.