Power Absorption Profile Research Articles

A cost-efficient DC active load laboratory solution

The increased use of DC renewable energy resources and DC storage systems, combined with the necessary reduction of energy waste, is boosting the development of DC smart grids. In this scenario, DC load emulation is of great importance. From the hardware point of view, DC buses stability of smart grids and the different DC/DC converter topologies must be tested. From the software point of view, smart grid strategies and job schedulers must be tested with different power absorption profiles. Moreover, DC load emulation can be useful for many other purposes, such as battery characterization, power supply testing, photovoltaic I-V curve measurements, etc. In this work, a cost-efficient DC Active Load (AL) solution is proposed. The principle of the circuit topology is a buck-boost-derived converter. This solution can be designed and tested considering the required voltage, current, and maximum input power. Both simulation and experimental results are shown on a 400 W size prototype. Thermal and electrical results validate the simulation model and the AL feasibility.

Full-wave 2D modeling of helicons propagation and absorption in the spherical tokamak Globus-M2

Numerical modeling of propagation and absorption of fast waves (helicons) with frequency 200MHz in 2D inhomogeneous plasma of the spherical tokamak Globus-M2 was carried out with 2D full-wave code. Toroidal effects, poloidal magnetic field and the actual shape of the flux surfaces were taken into account. The full wave electric field and RF power absorption profiles were computed by solving plasma wave equation with electron Landau damping term. The modeling demonstrated a fairly high efficiency of helicons absorption in the bulk plasma within a wide range of experimental parameters. The waves propagate to the inner regions of the plasma column and are mainly absorbed there; less than 20% of RF energy returns back to the plasma periphery. Keywords: high temperature plasma, nuclear fusion, tokamak, high frequency plasma waves, helicons, plasma wave equation, full-wave code.

Полноволновое двумерное моделирование распространения и поглощения геликонов в плазме сферического токамака Глобус-М2

Numerical modeling of propagation and absorption of fast waves (helicons) with frequency 200 MHz in 2D inhomogeneous plasma of the spherical tokamak Globus-M2 was carried out with 2D full-wave code. Toroidal effects, poloidal magnetic field and the actual shape of the flux surfaces were taken into account. The full wave electric field and RF power absorption profiles were computed by solving plasma wave equation with electron Landau damping term. The modeling demonstrated a fairly high efficiency of helicons absorption in the bulk plasma within a wide range of experimental parameters. The waves propagate to the inner regions of the plasma column and are mainly absorbed there; less than 20% of RF energy returns back to the plasma periphery.

Full-wave 2D modeling of helicons propagation and absorption in thespherical tokamak Globus-M2

Numerical modeling of propagation and absorption of fast waves(helicons) with frequency 200 MHz in 2D inhomogeneous plasma of thespherical tokamak Globus-M2 was carried out with 2D full-wave code. Toroidal effects, poloidal magnetic field and the actual shape of the fluxsurfaces were taken into account. The full wave electric field and RF powerabsorption profiles were computed by solving plasma wave equation withelectron Landau damping term. The modeling demonstrated a fairly highefficiency of helicons absorption in the bulk plasma within a wide range ofexperimental parameters. The waves propagate to the inner regions of theplasma column and are mainly absorbed there; less than 20% of RF energyreturns back to the plasma periphery. Keywords: high temperature plasma, nuclear fusion, tokamak, high frequency plasma waves, helicons, plasma wave equation, full-wave code.\

Upgrading LHDGauss Code by Including Obliquely Propagating Wave Absorption Effect for ECH

LHDGauss is a multi-ray tracing code to calculate microwave beam propagation and power deposition of electron cyclotron heating (ECH) using the electron density and electron temperature profiles in the Large Helical Device (LHD) plasma. LHDGauss also takes into account the injected wave polarization purity. LHDGauss uses the cold plasma dispersion to calculate ray propagation and derives the power absorption profile of ECH by using the absorption coefficient based on weakly relativistic plasmas and the wave propagating perpendicularly to the magnetic field. However, the ECH beam propagation is mainly oblique to the magnetic field in the LHD and it is necessary to take into account the angular dependence of the absorption coefficient in order to derive more accurate ECH power deposition profiles. We upgraded LHDGauss and were able to calculate the absorption coefficient using the weakly relativistic dielectric tensor which considers the influence of the angle between the magnetic field and the wave vector. We compared the power deposition profiles calculated by previous and upgraded LHDGauss with the changes of the electron temperature profile of the LHD plasma in the oblique and the perpendicular O1-mode ECH injection cases. We have obtained more reasonable power deposition profiles by using the upgraded LHDGauss in both the perpendicular and the oblique injection cases.

Electric Vehicle Ultra-Fast Battery Chargers: A Boost for Power System Stability?

As a consequence of the exponential growth of the electric vehicle (EV) market, DC fast-charging infrastructure is being rapidly deployed all around the world. Ultra-fast charging (UFC) stations are starting to pose serious challenges to the electric power system operation, mostly due to their high peak power demand and unregulated discontinuous operation. To address these issues, local energy storage can be installed, ensuring a smoother grid power absorption profile and allowing to provide grid-supporting features. In this work, a control solution for the grid-side AC/DC converter of next-generation EV UFC stations is proposed. A virtual synchronous compensator (VSC) control algorithm is implemented, in order to lessen the impact of the charging station on the utility and to provide the full spectrum of grid ancillary services (i.e., frequency regulation, reactive power compensation, harmonic reduction, short circuit current generation, etc.). The proposed control strategy is verified experimentally on a downscaled 15 kVA three-phase inverter, emulating the grid front-end of the charging station.

Light-trapping strategy for PEDOT:PSS/c-Si nanopyramid based hybrid solar cells embedded with metallic nanoparticles

In this article, we have investigated the combined role of nanopyramid (NP) array and metal nanoparticles (MNPs) in enhancing the light trapping ability and improving the photo-absorption of PEDOT:PSS/c-Si Hybrid Solar Cells (HSCs) using a 3D finite-difference time-domain (FDTD) method. A parametric optimization of the essential geometrical parameters of NPs and MNP is performed based on short circuit current density (Jsc). The optimization result reveals that maximum Jsc of 35.91 mA/cm2 is achievable with top textured NP (without MNPs) which is 24.38% higher than the planar counterpart. However, the absorption spectrum is broadened with the insertion of Al MNP at rear side of the HSC. This is also accompanied by almost two fold increase in Jsc to 41.71 mA/cm2 which is 44.47% higher the planar HSCs. The photovoltaic parameters such as Jsc, Voc, PCE and Fill Factor (FF) are calculated using the DEVICE software for NP and NP embedded with Al MNPs based c-Si Solar Cells. The physics at the interface of inorganic nanostructure and organic material layer is thoroughly described. In addition to this, we have tried to decode the underlying physics for the enhancement of photon absorption in nanopyramidal structures and MNPs structures through an extensive analysis of the photogeneration rate, electric field intensity, power absorption profiles, PCE and FF of nanopyramidal, nanopyramidal with MNP and planar HSCs.

Microwave power absorption profile of detergent surfactant agglomerates during microwave heating

ABSTRACTThe microwave energy absorption behavior of the linear alkylbenzene sulfonate (LAS) surfactant detergent agglomerates was studied while considering changes in the physical properties of the samples. Microwave heating was used to change the internal structure of the agglomerates to make a reduced density (fluffy) product. The absorption of energy within LAS samples indicated fluctuating trends as microwave heating progressed. This was associated with the dielectric properties of the material which are strongly dependent upon the nature (“free” or “bound”) and quantity of water present in them at any instant which changes during heating. Therefore, complete profiles of the energy absorbed by the samples have been recorded to determine their actual power absorption behavior/total energy consumption over time. The bulk density of the agglomerates decreased significantly when exposed to microwave fields. Hot air drying can be combined with microwave heating to reduce the total heating time. It has been observed that the pre-heating of the samples reduces the total heating time and microwave energy requirement. This is due to the temperature-dependent decomposition of hydrates releasing more “free” water.

Assessment of Electromagnetic Absorption of Ice From Ice Core Measurements

Ice core drillings have been performed in various zones in Antarctica and Greenland to obtain climatological information, study ice properties, or analyze air and dust encapsulated in the ice during the quaternary period. During these procedures, a set of measurements to characterize the ice and to evaluate its physical and chemical properties are usually performed in situ . In particular, using known temperature and dielectric profiles (DEP measurements), it is possible to evaluate the ice electromagnetic power absorption profile, valid at the drilling site. In the last decades, bedrock characterization through radio echo sounding surveys has been improved by the analysis of the power of radar echoes. This way, analysis of the electromagnetic properties of bedrock interfaces makes it possible to assess the physical characteristics and to distinguish between wet and dry conditions. Power variation of the received echoes also depends on ice absorption and on bedrock reflectivity due to specific physical conditions of the ice. In this paper, the propagation of electromagnetic waves through the ice sheet is examined, and in particular, a new method for establishing the electromagnetic absorption profile for ice from core drilling measurements is proposed and discussed. Variation in the ice absorption is deduced, starting from the analysis of ice core data from the European Project for Ice Coring in Antarctica (EPICA) at the Concordia station (Antarctica) and from the Greenland Ice Core Project (GRIP) site (Greenland). This direct method of measurement is proposed with the aim of defining common characteristics of the ice absorption rate that are valid both in Antarctica and in Greenland.

On the interplay of gas dynamics and the electromagnetic field in an atmospheric Ar/H2 microwave plasma torch

A complementary simulation and experimental study of an atmospheric pressure microwave torch operating in pure argon or argon/hydrogen mixtures is presented. The modelling part describes a numerical model coupling the gas dynamics and mixing to the electromagnetic field simulations. Since the numerical model is not fully self-consistent and requires the electron density as an input, quite extensive spatially resolved Stark broadening measurements were performed for various gas compositions and input powers. In addition, the experimental part includes Rayleigh scattering measurements, which are used for the validation of the model. The paper comments on the changes in the gas temperature and hydrogen dissociation with the gas composition and input power, showing in particular that the dependence on the gas composition is relatively strong and non-monotonic. In addition, the work provides interesting insight into the plasma sustainment mechanism by showing that the power absorption profile in the plasma has two distinct maxima: one at the nozzle tip and one further upstream.

사각형 유도 결합 플라즈마 시스템의 수치 모델링

Low pressure inductively coupled plasma characteristics of argon and oxygen are numerically simulated for a 400 mm rectangular type system with a plasma fluid model. The results showed lower power absorption profile at the corner than a circular one in a 13.56 MHz driven 1.5 turn antenna system with a drift-diffusion and quasi-neutrality assumption. Ions controlled by electric field are more non-uniform than metastables and the power absorption profile of oxygen plasma is affected by horizontal gas flow pattern to show 25% lower power absorption at the pumping flange side. Oxygen negative ions which are generated in electron collisional dissociation of oxygen molecules was calculated as 0.1% of oxygen atoms with similar spatial profile.

Separate control between geometrical and electrical asymmetry effects in capacitively coupled plasmas

Both geometrical and electrical asymmetry effects in capacitive argon discharges are investigated using a two-dimensional particle-in-cell coupled with Monte Carlo collision model. When changing the ratio of the top and bottom electrode surface areas and the phase shift between the two applied harmonics, the induced self-bias was found to develop separately. By adjusting the ratio between the high and low harmonic amplitudes, the electrical asymmetry effect at a fixed phase shift can be substantially optimized. However, the self-bias caused by the geometrical asymmetry hardly changed. Moreover, the separate control of these two asymmetry effects can also be demonstrated from their power absorption profiles. Both the axial and radial plasma density distributions can be modulated by the electrical asymmetry effect.

Spectral response modelling of GaAs-based heterojunction phototransistors for short wavelength detection

Spectral response (SR) and optical characteristics of GaAs-based heterojunction phototransistors (HPTs) have been successfully predicted for the first time through an advanced absorption model presented in the present article. The model is based on the accurate prediction of photocarriers in the active layers of the phototransistor which, when related to the base current of transistor in forward active mode, enables the prediction of optical characteristics. The importance of collection efficiency in accurate SR modelling is highlighted and it is not considered unity like all the previous studies on HPTs. The layer dependence of the optical power absorption profile at near-bandgap wavelengths is also investigated and its generalisation as a single exponential has been refuted for GaAs-based HPTs. The measured results at 635, 780 and 850 nm show good agreement to the predicted results, validating the proposed theoretical model.

Comparisons of Electron Temperature and Density, and Ion Temperature Profiles in the TJ-II Stellarator

Charge exchange-neutral particle analyzer diagnostics are used to obtain majority ion temperature profiles for plasmas created in the TJ-II stellarator. However, because of technical limitations, measurements are limited to two radial positions per discharge. Therefore plasma reproducibility for a large number of discharges is essential for performing scans across the plasma minor radius and hence for obtaining ion temperature profiles. Such conditions have recently been achieved in the TJ-II by the implementation of a lithium wall coating which has significantly facilitated this task. In this paper, ion temperature profiles obtained under electron cyclotron resonance (ECR) and neutral beam injection (NBI) plasma heating conditions are compared with electron temperature and density profiles obtained using a Thomson Scattering diagnostic. From this, similarities in the forms of the ion temperature and electron density profiles are noted for ECR heated plasmas whilst for NBI heated plasmas similarities are observed between ion temperature and electron temperature profiles. Finally, after explaining the different behaviours of the profiles in terms of ion power absorption profile, we demonstrate the possibility of determining ion temperature profiles using two localized ion temperature measurements plus Thomson Scattering profiles.

CFD를 이용한 내장형 안테나 유도 결합 플라즈마 시스템 모델링

전산 유체 역학 코드를 사용하여 안테나 내장형 유도 결합 플라즈마 시스템의 가스 유동 특성, 전력 흡수, 전자 온도, 전자 밀도, 화학종의 분포에 대해서 살펴보았다. 복잡한 현실적 3차원 시스템에 대한 안정한 수치해의 도출을 위해서 최적화된 격자생성 전략을 구사하였으며, 이를 이용하여 플라즈마 질화 시스템을 한 예로 전력 흡수, 가스 유동, 전자 온도, 전자 밀도, 화학종의 분포를 분석하였다. 금속 노출형 안테나의 경우 전력 도입부 쪽에 전력 흡수의 불균형이 모델에서 예측되었으며 유전체피복 안테나의 한 예에서 전력 흡수 표피 깊이가 실제 보고된 값인 53 mm와 잘 일치하는 50 mm로 예측되었다. 또한 수소연료 전지 분리판을 위한 고속 질화 공정용 시스템의 모델링에서도 산업용 대량 처리 시스템에 적절한 다중 분리판의 장입 간격을 가스 유동, 활발한 질화종인 질소 원자와 질소 분자 이온의 농도를 근거로 예측하였다.

Improved break-in-slope analysis of the plasma energy response in tokamaks

The break-in-slope method is a simple—although powerful—data analysis technique that is commonly used to determine the power absorption profiles of the plasma species during auxiliary heating experiments in tokamaks. It is based on the study of the energy response of the particles to sudden changes in the external power applied to the plasma. Even though some experimental conditions are favorable for the straightforward application of the break-in-slope analysis in its most simple form (linear fit of the experimental temperature signals), most situations require the retention of additional terms in the linearized energy conservation equation for a successful use of this technique. In this paper, important corrections necessary to extend the applicability of the traditional break-in-slope technique will be presented: (i) the numerical determination of the break-in-slope instants in the plasma energy response allowing the study of indirect (collisional) heating scenarios; (ii) the inclusion of the density variations due to the external power step based on fast density measurements; (iii) the exponential representation of the plasma energy evolution after the power break, describing the saturation of the experimental signals in slow modulation or single power step experiments; (iv) a first assessment of the influence of the change in the radiated power on the break-in-slope results. As will be shown, these corrections are particularly important in low absorption scenarios and in single power step studies, where the change in the external power cannot be considered ‘non-perturbative’ and the standard break-in-slope analysis usually leads to integrated power levels well below the actual power injected into the plasma.

Low-pressure plasma generation inside slender tubes

Low pressure ( < 50 mTorr ) argon discharges inside tubes of a few millimeters in diameter have been studied by means of one- and two-dimensional particle-in-cell Monte Carlo collision simulations. Magnetically confined DC and microwave discharges have been sustained in a coaxial configuration. For DC discharges, the magnetic field needs to be strong enough to confine secondary electrons emitted from the cathode, i.e. the amplitude of the cycloidal motion described by secondary electrons has to be smaller than the discharge gap. For microwave excited discharges, the power absorption profile depends on the magnitude of the magnetic field. Power absorption beyond the sheath boundary in the plasma bulk and better confinement for magnetic fields below the ECR condition lead to maximum densities at ω c / ω r f ∼ 0.5 .

Electron temperature measurement in SiH 4/H 2 ECR plasma produced by 915 MHz microwaves

Plasma parameters of a SiH 4/H 2 electron-cyclotron-resonance (ECR) plasma are measured in detail as a function of microwave power, where 915 MHz microwaves are used. It is observed that the electron temperature ( T e) in the magnetic field whose gradient is small varies from about 3 eV to 8 eV through the control of the external conditions. From the electromagnetic waves measurements and the simulations of the microwave power absorption, T e is found to depend on the spatial profiles of the power absorption, which suggests that T e in a SiH 4/H 2 ECR plasma can be changed by changing the power absorption profile.

Temperature gradient driven electron transport in NSTX and Tore Supra

Electron thermal fluxes are derived from the power balance for Tore Supra (TS) and NSTX discharges with centrally deposited fast wave electron heating. Measurements of the electron temperature and density profiles, combined with ray tracing computations of the power absorption profiles, allow detailed interpretation of the thermal flux versus temperature gradient. Evidence supporting the occurrence of electron temperature gradient turbulent transport in the two confinement devices is found. With control of the magnetic rotational transform profile and the heating power, internal transport barriers are created in TS and NSTX discharges. These partial transport barriers are argued to be a universal feature of transport equations in the presence of invariant tori that are intrinsic to non-monotonic rotational transforms in dynamical systems.

Ray Tracing Calculation of ECRH Power Absorption Profile in Heliotron J

Power absorption profiles of electron cyclotron resonance heating (ECRH) are calculated for a helical-axis heliotron device, Heliotron J, by a ray tracing code, TRECE. The three-dimensional structure of flux surfaces and magnetic field is considered to evaluate the power absorption profile accurately. The calculation results show that the power absorption profile can be generally controlled under the experimental conditions of the 70 GHz ECRH system by setting the appropriate launching condition. The well localized single pass power absorption can be realized when the ECRH power is launched with a tokamak-like B contour. The single pass absorption efficiency is as high as 92 % of the injected power in the case of moderate toroidally oblique launch because of the long path along the resonance region. On the other hand, the power is fully absorbed when ECRH power is perpendicularly launched at the poloidal cross section with a saddle-type B contour, although the absorption profile is wider. This is because the magnetic field gradient is gentle at the resonance region. These indicate that the control of power absorption is possible with the appropriate launching condition in the spatially winding plasmas. The calculation is compared with the experimental results on the ECRH plasma on Heliotron J.