Explicit structure-preserving geometric particle-in-cell (PIC) algorithm in curvilinear orthogonal coordinate systems is developed. The work reported represents a further development of the structure-preserving geometric PIC algorithm achieving the goal of practical applications in magnetic fusion research. The algorithm is constructed by discretizing the field theory for the system of charged particles and electromagnetic field using Whitney forms, discrete exterior calculus, and explicit non-canonical symplectic integration. In addition to the truncated infinitely dimensional symplectic structure, the algorithm preserves exactly many important physical symmetries and conservation laws, such as local energy conservation, gauge symmetry and the corresponding local charge conservation. As a result, the algorithm possesses the long-term accuracy and fidelity required for first-principles-based simulations of the multiscale tokamak physics. The algorithm has been implemented in the SymPIC code, which is designed for high-efficiency massively-parallel PIC simulations in modern clusters. The code has been applied to carry out whole-device 6D kinetic simulation studies of tokamak physics. A self-consistent kinetic steady state for fusion plasma in the tokamak geometry is numerically found with a predominately diagonal and anisotropic pressure tensor. The state also admits a steady-state sub-sonic ion flow in the range of 10 km s−1, agreeing with experimental observations and analytical calculations Kinetic ballooning instability in the self-consistent kinetic steady state is simulated. It is shown that high-n ballooning modes have larger growth rates than low-n global modes, and in the nonlinear phase the modes saturate approximately in 5 ion transit times at the 2% level by the E × B flow generated by the instability. These results are consistent with early and recent electromagnetic gyrokinetic simulations.
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Jianyuan XIAO and Hong QIN 2021 Plasma Sci. Technol. 23 055102
Weisheng CUI et al 2021 Plasma Sci. Technol. 23 075402
The dielectric barrier discharge (DBD) in air at atmospheric pressure is not suitable for industrial applications due to its randomly distributed discharge filaments. In this paper, the influence of the electric field distribution on the uniformity of DBD is theoretically analyzed and experimentally verified. It is found that a certain degree of uneven electric field distributions can control the development of electron avalanches and regulate their transition to streamers in the gap. The discharge phenomena and electrical characteristics prove that an enhanced Townsend discharge can be formed in atmospheric-pressure air with a curved-plate electrode. The spectral analysis further confirms that the gas temperature of the plasma produced by the curved-plate electrode is close to room temperature, which is beneficial for industrial applications. This paper presents the relationship between the electron avalanche transition and the formation of a uniform DBD, which can provide some references for the development and applications of the DBD in the future.
Xiang GAO et al 2021 Plasma Sci. Technol. 23 092001
High fusion triple product has been obtained in the advanced scenarios with high normalized beta (βN) on the Experimental Advanced Superconducting Tokamak (EAST). A record value of ni0Ti0τE ∼ 1.0 × 1019 m−3 keV s for EAST deuterium plasma has been achieved, which is due to the formation of strong and broad internal transport barriers (ITBs) in ne, Te and Ti profiles. Analysis shows that the strong ITB formation could be attributed to the reduction of transport from ITG modes. Based on the analysis, the physical mechanisms and methods to further improve the plasma performance are discussed.
Tetsutarou OISHI et al 2021 Plasma Sci. Technol. 23 084002
An impurity powder dropper was installed in the 21st campaign of the Large Helical Device experiment (Oct. 2019–Feb. 2020) under a collaboration between the National Institute for Fusion Science and the Princeton Plasma Physics Laboratory for the purposes of real-time wall conditioning and edge plasma control. In order to assess the effective injection of the impurity powders, spectroscopic diagnostics were applied to observe line emission from the injected impurity. Thus, extreme-ultraviolet (EUV) and vacuum-ultraviolet (VUV) emission spectra were analyzed to summarize observable impurity lines with B and BN powder injection. Emission lines released from B and N ions were identified in the EUV wavelength range of 5–300 Å measured using two grazing incidence flat-field EUV spectrometers and in the VUV wavelength range of 300–2400 Å measured using three normal incidence 20 cm VUV spectrometers. BI–BV and NIII–NVII emission lines were identified in the discharges with the B and BN powder injection, respectively. Useful B and N emission lines which have large intensities and are isolated from other lines were successfully identified as follows: BI (1825.89, 1826.40) Å (blended), BII 1362.46 Å, BIII (677.00, 677.14, 677.16) Å (blended), BIV 60.31 Å, BV 48.59 Å, NIII (989.79, 991.51, 991.58) Å (blended), NIV 765.15 Å, NV (209.27, 209.31) Å (blended), NVI 1896.80 Å, and NVII 24.78 Å. Applications of the line identifications to the advanced spectroscopic diagnostics were demonstrated, such as the vertical profile measurements for the BV and NVII lines using a space-resolved EUV spectrometer and the ion temperature measurement for the BII line using a normal incidence 3 m VUV spectrometer.
S N BATHGATE et al 2017 Plasma Sci. Technol. 19 083001
The physics of electrodeless electric thrusters that use directed plasma to propel spacecraft without employing electrodes subject to plasma erosion is reviewed. Electrodeless plasma thrusters are potentially more durable than presently deployed thrusters that use electrodes such as gridded ion, Hall thrusters, arcjets and resistojets. Like other plasma thrusters, electrodeless thrusters have the advantage of reduced fuel mass compared to chemical thrusters that produce the same thrust. The status of electrodeless plasma thrusters that could be used in communications satellites and in spacecraft for interplanetary missions is examined. Electrodeless thrusters under development or planned for deployment include devices that use a rotating magnetic field; devices that use a rotating electric field; pulsed inductive devices that exploit the Lorentz force on an induced current loop in a plasma; devices that use radiofrequency fields to heat plasmas and have magnetic nozzles to accelerate the hot plasma and other devices that exploit the Lorentz force. Using metrics of specific impulse and thrust efficiency, we find that the most promising designs are those that use Lorentz forces directly to expel plasma and those that use magnetic nozzles to accelerate plasma.
Gongshun LI et al 2024 Plasma Sci. Technol. 26 034001
In this paper we present a new experimental observation using a conventional reflectometry technique, poloidal correlation reflectometry (PCR), in the Experimental Advanced Superconducting Tokamak (EAST). The turbulence spectrum detected by the PCR system exhibits an asymmetry and induced Doppler shift during the internal kink mode (IKM) rotation phase. This Doppler shift is the target measurement of Doppler reflectometry, but captured by conventional reflectometry. Results show that the Doppler shift is modulated by the periodic changes in the effective angle between the probing wave and cutoff layer normal, but not by plasma turbulence. The fishbone mode and saturated long-lived mode are typical IKMs, and this modulation phenomenon is observed in both cases. Moreover, the value of the Doppler shift is positively correlated with the amplitude of the IKM, even when the latter is small. However, the positive and negative frequency components of the Doppler shift can be asymmetric, which is related to the plasma configuration. A simulated analysis is performed by ray tracing to verify these observations. These results establish a clear link between and IKM rotation, and are helpful for studying the characteristics of IKM and related physical phenomena.
Letian LI et al 2024 Plasma Sci. Technol. 26 034003
A gas puff imaging (GPI) diagnostic has been developed and operated on EAST since 2012, and the time-delay estimation (TDE) method is used to derive the propagation velocity of fluctuations from the two-dimensional GPI data. However, with the TDE method it is difficult to analyze the data with fast transient events, such as edge-localized mode (ELM). Consequently, a method called the spatial displacement estimation (SDE) algorithm is developed to estimate the turbulence velocity with high temporal resolution. Based on the SDE algorithm, we make some improvements, including an adaptive median filter and super-resolution technology. After the development of the algorithm, a straight-line movement and a curved-line movement are used to test the accuracy of the algorithm, and the calculated speed agrees well with preset speed. This SDE algorithm is applied to the EAST GPI data analysis, and the derived propagation velocity of turbulence is consistent with that from the TDE method, but with much higher temporal resolution.
Zhiwei LI et al 2024 Plasma Sci. Technol. 26 045501
Streamers represent an important stage in the initiation of gap discharge. In this work, we used an eight-frame intensified charge-coupled device camera to capture the streamer development process when a lightning impulse voltage of 95%–100% U50% was applied in a 3 m rod–plate gap and the streamer velocity was analyzed. Analysis of the observations shows that streamer velocity can be defined by three stages: rapid velocity decline (stage 1), rapid velocity rise (stage 2) and slow velocity decline (stage 3). The effects of electrode shape, applied voltage and gap breakdown or withstanding on streamer velocity were analyzed. The electrode with a larger radius of curvature will result in a higher initial velocity, and a higher voltage amplitude will cause the streamer to propagate faster at stage 3. Gap withstanding or breakdown has no obvious effect on streamer velocity. In addition, the experimental results are compared with previous results and the statistical characteristics of the primary streamer discharge are discussed.
Xingkang WANG et al 2024 Plasma Sci. Technol. 26 034009
A multi-channel polarimeter–interferometer has been developed on the Keda Torus eXperiment (KTX) for the study of equilibrium dynamics and internal magnetic fluctuations. A three-wave technique based on terahertz solid-state sources (~650 GHz) is applied for simultaneous measurements of electron density and Faraday rotation angle. The output power of the microwave source is 2 mW. Faraday rotation effect using a rotating wave plate is tested with phase noise less than 0.8°, and the density phase noise is less than 0.9°. Measurement of Faraday rotation angle and density for discharges on KTX have demonstrated high sensitivity to internal MHD activities.
Weijie HUO et al 2024 Plasma Sci. Technol. 26 055501
In this study, a pulsed, high voltage driven hollow-cathode electron beam sources through an optical trigger is designed with characteristics of simple structure, low cost, and easy triggering. To validate the new design, the characteristics of hollow-cathode discharge and electron beam characterization under pulsed high voltage drive are studied experimentally and discussed by discharge characteristics and analyses of waveform details, respectively. The validation experiments indicate that the pulsed high voltage supply significantly improves the frequency and stability of the discharge, which provides a new solution for the realization of a high-frequency, high-energy electron beam source. The peak current amplitude in the high-energy electron beam increases from 6.2 A to 79.6 A, which indicates the pulsed power mode significantly improves the electron beam performance. Besides, increasing the capacitance significantly affects the high-current, lower-energy electron beam more than the high-energy electron beam.
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Weijie HUO et al 2024 Plasma Sci. Technol. 26 055501
In this study, a pulsed, high voltage driven hollow-cathode electron beam sources through an optical trigger is designed with characteristics of simple structure, low cost, and easy triggering. To validate the new design, the characteristics of hollow-cathode discharge and electron beam characterization under pulsed high voltage drive are studied experimentally and discussed by discharge characteristics and analyses of waveform details, respectively. The validation experiments indicate that the pulsed high voltage supply significantly improves the frequency and stability of the discharge, which provides a new solution for the realization of a high-frequency, high-energy electron beam source. The peak current amplitude in the high-energy electron beam increases from 6.2 A to 79.6 A, which indicates the pulsed power mode significantly improves the electron beam performance. Besides, increasing the capacitance significantly affects the high-current, lower-energy electron beam more than the high-energy electron beam.
Jinhong WEI et al 2024 Plasma Sci. Technol. 26 055502
To guide the illuminating design to improve the on-state performances of gallium arsenide (GaAs) photoconductive semiconductor switch (PCSS), the effect of spot size on the operation mode of GaAs PCSS based on a semi-insulating wafer with a thickness of 1 mm, triggered by a 1064-nm extrinsic laser beam with the rectangular spot, has been investigated experimentally. It is found that the variation of the spot size in length and width can act on the different parts of the output waveform integrating the characteristics of the linear and nonlinear modes, and then significantly boosts the PCSS toward different operation modes. On this basis, a two-channel model containing the active and passive parts is introduced to interpret the relevant influencing mechanisms. Results indicate that the increased spot length can peak the amplitude of static domains in the active part to enhance the development of the nonlinear switching, while the extended spot width can change the distribution of photogenerated carriers on both parts to facilitate the linear switching and weaken the nonlinear switching, which have been proved by comparing the domain evolutions under different spot sizes.
Weiguo HE et al 2024 Plasma Sci. Technol. 26 055504
The Ultrasonic Electric Propulsion (UEP) system is a cutting-edge propulsion technology that is mostly used on platforms for small satellites (less than 10 kg). The characteristics of droplet partial emissions (DPEs) in the UEP system are investigated using a high-speed imaging technique (an ultra-high speed camera (NAC HX-6) and a long-distance microscope) in this work. The experiments demonstrate that there are a few partial emission modes, including left-side emission, double-side emission, and right-side emission, that are present in the droplet emission process of the UEP system. These modes are primarily caused by the partial formation of capillary standing waves (CSWs) on the emission surface of the ultrasonic nozzle. The emission rate for single- and double-sided emissions varies at different times, indicating that there are different CSWs engaged in droplet emission due to variations in the liquid film thickness and charge state of the liquid cones. Additionally, as the droplets emit continuously, a raised area on the emission surface appears, with several droplets emitting there as a result of charge accumulation. Additionally, photos of the CSWs with emitting droplets are obtained, which highlights the CSWs' distinctive wave morphology.
Jianqing CAI et al 2024 Plasma Sci. Technol. 26 055102
A neural network model with a classical annotation method has been used on the EXL-50 tokamak to predict impending disruption. However, the results revealed issues of overfitting and overconfidence in predictions caused by inaccurate labeling. To mitigate these issues, an improved training framework has been proposed. In this approach, soft labels from previous training serve as teachers to supervise the further learning process; this has lead to a significant improvement in predictive model performance. Notably, this enhancement is primarily attributed to the coupling effect of the soft labels and correction mechanism. This improved training framework introduces an instance-specific label smoothing method, which reflects a more nuanced model assessment on the likelihood of a disruption. It presents a possible solution to effectively address the challenges associated with accurate labeling across different machines.
Baoyong REN et al 2024 Plasma Sci. Technol. 26 055503
Diesel particulate matter (DPM) and hydrocarbons (HCs) emitted from diesel engines have a negative affect on air quality and human health. Catalysts for oxidative removal of DPM and HCs are currently used universally but their low removal efficiency at low temperatures is a problem. In this study, Cu-doped CeO2 loaded on Al2O3 coupled with plasma was used to enhance low-temperature oxidation of DPM and HCs. Removals of DPM and HCs at 200 °C using the catalyst were as high as 90% with plasma but below 30% without plasma. Operando plasma diffuse reflectance infrared Fourier transform spectroscopy coupled with mass spectrometry was conducted to reveal the functional mechanism of the oxygen species in the DPM oxidation process. It was found that Cu–CeO2 can promote the formation of adsorbed oxygen (–) and terminal oxygen (M=O), which can react with DPM to form carbonates that are easily converted to gaseous CO2. Our results provide a practical plasma catalysis technology to obtain simultaneous removals of DPM and HCs at low temperatures.
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Jiacheng LI et al 2023 Plasma Sci. Technol. 25 093001
Hydrogels are biomaterials with 3D networks of hydrophilic polymers. The generation of hydrogels is turning to the development of hydrogels with the help of enabling technologies. Plasma can tailor the hydrogels' properties through simultaneous physical and chemical actions, resulting in an emerging technology of plasma-activated hydrogels (PAH). PAH can be divided into functional PAH and biological tissue model PAH. This review systematically introduces the plasma sources, plasma etching polymer surface, and plasma cross-linking involved in the fabrication of PAH. The 'diffusion-drift-reaction model' is used to study the microscopic physicochemical interaction between plasma and biological tissue PAH models. Finally, the main achievements of PAH, including wound treatment, sterilization, 3D tumor model, etc, and their development trends are discussed.
Heping LI et al 2022 Plasma Sci. Technol. 24 093001
Cold atmospheric plasmas (CAPs) have shown great applicability in agriculture. Many kinds of CAP sources have been studied in agricultural applications to promote plant growth and cure plant diseases. We briefly review the state-of-the-art stimulating effects of atmospheric-pressure dielectric-barrier-discharge (AP-DBD) plasmas, after the direct or indirect treatment of plants for growth promotion and disease control. We then discuss the special demands on the characteristics of the CAP sources for their applications in plant mutation breeding. An atmospheric and room temperature plasma (ARTP) jet generator with a large plasma irradiation area, a high enough concentration of chemically reactive species and a low gas temperature is designed for direct plant mutagenesis. Experimental measurements of the electrical, thermal and optical features of the ARTP generator are conducted. Then, an ARTP-P (ARTP for plant mutagenesis) mutation breeding machine is developed, and a typical case of plant mutation breeding by the ARTP-P mutation machine is presented using Coreopsis tinctoria Nutt. seeds. Physical and agricultural experiments show that the newly-developed ARTP-P mutation breeding machine with a large irradiation area can generate uniform CAP jets with high concentrations of chemically reactive species and mild gas temperatures, and have significant mutagenesis effects on the Coreopsis tinctoria Nutt. seeds. The ARTP-P mutation breeding machine may provide a platform for systematic studies on mutation mechanisms and results for various plant seeds under different operating conditions in future research.
Zhengxiong WANG et al 2022 Plasma Sci. Technol. 24 033001
This paper reviews the effects of resonant magnetic perturbation (RMP) on classical tearing modes (TMs) and neoclassical tearing modes (NTMs) from the theory, experimental discovery and numerical results with a focus on four major aspects: (i) mode mitigation, where the TM/NTM is totally suppressed or partly mitigated by the use of RMP; (ii) mode penetration, which means a linearly stable TM/NTM triggered by the externally applied RMP; (iii) mode locking, namely an existing rotating magnetic island braked and finally stopped by the RMP; (iv) mode unlocking, as the name suggests, it is the reverse of the mode locking process. The key mechanism and physical picture of above phenomena are revealed and summarized.
Zimu XU et al 2020 Plasma Sci. Technol. 22 103001
Atmospheric pressure cold plasma, with advantages such as high particle activity, no thermal damage, high efficiency and direct and friendly contact with human tissues, is considered to have great potential in biomedical applications. Therefore, 'plasma medicine' as a new interdiscipline has been developed in the past two decades. This review first briefly describes the development of typical plasma sources suitable for biomedical applications, and those with different discharge forms are simply compared, evaluated and summarized. Subsequently, measurement of the crucial gaseous reactive particles (e.g. OH and O) and their spatio-temporal distributions are introduced. Meanwhile, the generation and variation rules and the related critical macroscopic parameters of the plasma-induced aqueous reactive species are summarized. Finally, related studies in the last ten years on the mechanisms of the plasma-driven microbial inactivation and plasma-induced apoptosis of cancer cells are introduced. Moreover, some scientific problems that need to be urgently solved in the field of plasma medicine are also discussed. This review will provide useful guidance for future related research.
Min JIANG et al 2020 Plasma Sci. Technol. 22 080501
The influence of m/n = 2/1 (m and n are poloidal and toroidal mode numbers) tearing modes on plasma perpendicular flows and micro-fluctuations has been investigated in HL-2A neutral beam injection heated L-mode plasmas. It is found that the local perpendicular rotation velocity and turbulence energy are modulated by the alternation between the island X-point and O-point of the naturally rotating tearing modes. Cross-correlation analysis indicates that the modulation of density fluctuations by the tearing mode is not only limited to the island region, but also occurs in the edge region near the last closed flux surface. The turbulence exhibits distinct spectral characteristics inside and outside the island region. In addition, it is observed that the particle flux near the strike point is also significantly impacted by the tearing modes. The experimental evidence reveals that there are strong core-edge interactions between the core tearing modes and the edge transport.
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Cai et al
Seagoing vessels are responsible for more than 90% of global freight traffic, but meanwhile, emission pollutants (NOx and SOx) of seagoing vessels also cause serious air pollution. Nonthermal plasma (NTP) combined with wet scrubbing technology is considered to be a promising technology. In order to improve the oxidation efficiency and energy efficiency of the NTP reactor, the screw and rod inner electrodes of dielectric barrier discharge (DBD) reactor were investigated. To analyze the mechanism, the optical emission spectra (OES) of NTP was measured and numerical calculation was applied. The experiment results show that the NO oxidation removal efficiency of screw electrode is lower than that of rod electrode. However, the SO2 removal efficiency of screw electrode is higher. According to the OES experiment and numerical calculation, the electric field intensity of the screw electrode surface is much higher than that of the rod electrode surface, and it is easier to generate N radicals to form NO. For the same energy density condition, the OH radical generation efficiency of the screw electrode reactor is similar to that of the rod electrode, but the gas temperature in the discharge gap is higher. Therefore, the SO2 oxidation efficiency of the thread electrode is higher. This study provides guidance for the optimization of oxidation efficiency and energy consumption of DBD reactor.
Yuan et al
The liquid Li divertor is one of promising alternatives for the future fusion device. In this work, a new divertor model is proposed, which is processed by 3D-printing technology to accurately control the size of the internal capillary structure. At the steady-state heat load of 10 MW/m2, the thermal stress of tungsten target is within the bearing range of tungsten by FE simulation. In order to evaluate the wicking ability of capillary structure, the wicking process at 600 °C was simulated by Fluent. Its result was identical with the corresponding experiments. Within 1 s, liquid lithium was wicked to target surface by the capillary structure of the target and quickly spread on the target surface. During the wicking process, the average wicking mass rate of lithium would reach 0.062 g/s, which could even supplement the evaporation requirement of liquid lithium under >950 °C environment. Irradiation experiments under different plasma discharge currents were carried out in linear plasma device (SCU-PSI), and the evolution process of the vapor cloud during plasma irradiation was analyzed. It was found that the target temperature tends to plateau in spite of gradually increased input current, indicating that the vapor shielding effect is gradually enhanced. The irradiation experiment also confirmed that 3D-printing tungsten structure has better heat consumption performance than that of tungsten mesh structure and multichannel structure. These results reveal the application potential and feasibility of 3D-printing porous capillary structure in plasma-facing components(PFCs) and provide a reference for further liquid-solid combined target designs.
Wang et al
In the design realm of fusion power supplies, structural component plays a pivotal role in ensuring the safety of fusion device. To verify the reliability of converter structure design in Comprehensive Research Facility for Fusion Technology (CRAFT), the meticulous analysis of the converter's dynamic impact is carefully analyzed based on the worst fault current (400 kA), firstly. Subsequently, the thermal stress analysis based on maximum allowable steady-state temperature is finished, and the equivalent thermal stress, thermal deformation, maximum shear stress of single bridge arm and whole converter are studied. Furthermore, a simple research method of current sharing characteristics of bridge arm with multi-thyristor parallel connection is proposed by combination Simplorer with Q3D in ANSYS. The results show that the current sharing characteristics is great. Finally, the structural design has been meticulously tailored to meet the established requirements.
Xiao et al
The Space Plasma Environment Research Facility (SPERF) for ground simulation of space plasma environment is a key component of Space Environment Simulation Research Infrastructure (SESRI), a major national science and technology infrastructure for fundamental researches. It is designed to investigate outstanding issues in space plasma environment, such as energetic particles acceleration, transport, and interaction with electromagnetic waves, as well as magnetic reconnection processes, in the magnetospheric plasmas, etc. Tail-Research EXperiment (TREX) is part of the SPERF for laboratory studies of space physics relevant to magnetic reconnection, dipolarization and hydromagnetic waves excitation in the magnetotail. SPERF-TREX is designed to carry out three types of experiments: the tail plasmoid for magnetic reconnection, dipolarization front formation, and magnetohydrodynamic waves excited by high speed plasma jet. In this paper, the scientific goals and three scenarios of SPERF-TREX for typical processes in space plasmas are presented, and experimental plans for SPERF-TREX are also reviewed, together with plasma sources applied to generate the plasma with desired parameters and various magnetic configurations.
Guo et al
An experiment on 100 kJ laser facility is performed to study the motive features and radiation properties of plasmas from different areas inside gas-filled cylindrical hohlraums. These hohlraums are designed to possess one open end and one laser entrance hole (LEH) with different diameters, which would or not result in the blocking of the LEH. An x-ray streak camera that is set at 16 degrees with respect to the hohlraum axis is applied to acquire the time-resolved x-ray images from the open end. Based on the images, we can study the evolutions of the wall plasma, corona bubble plasma and LEH plasma simultaneously through an equivalent view field of hohlraum interior. Multi-group flat response x-ray detectors are applied to measure the x-ray fluxes. In order to understand these characteristics, our two-dimensional radiation hydrodynamic code is used to simulate the experimental results. For the accuracy of reproduction, dielectronic recombination and two parameter corrections are applied in our code. Based on the comparison between experiments and simulations, we quantitatively understand the blocking process of LEH and the motion effects of other plasmas. The calibrated code is beneficial to design the gas-filled hohlraum in a nearby parameter space, especially the limit size of LEH.