Distribution Of Power Deposition Research Articles

Influence Mechanism of Magnetic Field and Wave Modes on Helicon Plasma Thruster

The mechanism of energy deposition on a helicon plasma thruster under a focused magnetic field is different with a uniform magnetic field, and energy coupling efficiency has greatly improved. This paper studies the spatial distribution of power deposition under different magnetic field configurations. The results show that the magnetic field configuration can change the spatial distribution of energy deposition. A focused magnetic field configuration can couple more energy on the antenna downstream and reduce energy loss during plasma transport, which leads to improved propellant utilization efficiency and enhanced thruster performance. Then this paper studies the energy coupling efficiency and energy distribution characteristics for ionization and acceleration under different W modes, including W1 and W2. The results show that, in the W1 mode, the energy is mainly focused on ion acceleration, resulting in higher ion beam energy. In contrast, the W2 mode is focused on propellant ionization, resulting in greater efficiency of propellant utilization. The W2 mode demonstrates a higher energy coupling efficiency and has superior thruster performance compared to the W1 mode, with a thrust increase of about 1.6 times. The paper proposes several suggestions to improve the thrust-to-weight ratio and specific impulse of a helicon plasma thruster, which provides theoretical support for engineering applications.

Study on RF Heating of Implants in Different Conductivity Medium

In MRI examination, RF heating of implants will affect the safety of implant wearers. The conductivity of various tissues in the human body is significantly different, and the medium conductivity will affect the distribution of the RF electric field. Therefore, it is necessary to study the RF heating of different medium conductivity. Based on the analysis of the principle of MRI RF heating, this study build the model of the bird cage coil, ASTM standard phantom and lead, and the conductivity of several typical human tissues is selected as the conductivity in the experiment. Then calculate the power deposition of the lead at 64 MHz. The results show that the medium conductivity has no effect on the distribution of electric field and power deposition, and the hot spot distribution remains unchanged under different conductivity; The smaller the conductivity is, the larger the power deposition of the lead is, and the greater the temperature rise of the lead caused by RF heating is; The change of conductivity and power deposition is approximately linear. At the limit of 2 W/kg whole body specific absorption rate(SAR), the conductivity decreases, and the wire power deposition increases sharply.

A method for converting microdosimetric spectra in diamond to tissue in proton therapy.

Diamond has been regarded as a promising microdosimeter in radiation protection and radiotherapy due to its excellent properties. However, as the diamond is not tissue equivalent, a conversion of the measured spectra in the diamond microdosimeter to the tissue site is needed. In this work, we intend to deduce a method for converting the microdosimetric spectra from diamond to tissue in the proton therapy application based on the Chapman-Kolmogorov equation and investigate the validity of this method in spectral conversion. The comparison of stopping power and energy deposition distribution of diamond and tissue shows that the conversion of the spectra in diamond to tissue can be performed by a simple scaling factor. Therefore, the equivalence of the energy deposition spectra in the diamond microdosimeter and a tissue site of the same size in the same radiation field was studied first to obtain the scaling factor. Then, the spectra conversion method was derived from the Chapman-Kolmogorov equation and the scaling factor. The Geant4 simulation was employed to settle this study. Theoretical and Geant4 simulation results indicate that the linear stopping power ratio of diamond to tissue is adequate to convert the microdosimetric spectra in diamond to tissue of identical dimension. The conversion results indicate that the energy deposition spectra converted from diamond to bone agree well with the spectra calculated by Geant4 along the Bragg curve. As for water, a good agreement of the converted and calculated spectra was found at the plateau of the Bragg curve and the distal part of the Bragg peak. At the proximal part of the Bragg peak, the converted and calculated spectrum is poorly coincident. The method of the energy deposition spectra conversion from the diamond microdosimeter to the tissue site of equal size shows relatively good results in most situations. But the deficiency was also found. Therefore, further investigation is needed to improve the reliability of this method.

Focused Microwave Breast Hyperthermia Monitored by Thermoacoustic Imaging: A Computational Feasibility Study Applying Realistic Breast Phantoms

Focused microwave breast hyperthermia (FMBH) represents a newly emerging technique endowed with advantages of high accuracy and low side effect for treating breast tumors. Practical application of the FMBH approach requires monitoring of microwave power deposition in the breast. Microwave-induced thermoacoustic imaging (MITAI) is naturally feasible for such power deposition monitoring task. This work conducts a computational study to evaluate feasibility of the novel FMBH-MITAI modality using realistic breast phantoms. Basic configuration and rationale of both FMBH and MITAI are introduced. Compressive sensing (CS) technique has to be applied in MITAI for sparse acoustic measurement in the FMBH-MITAI modality. Procedure of the computational study consists of microwave simulation, thermoacoustic numerical simulation, CS imaging, and performing the iterative optimization. Simulated results show that CS based MITAI is able to serve as a reliable monitoring mechanism to efficiently guide the iterative optimization toward the best obtainable focusing condition in most of the simulated scenarios. Finally obtained thermoacoustic images agree well with simulated power deposition distribution well. This work offers valuable performance evaluation and is of significant meaning for potential clinical applications of the FMBH-MITAI modality.

Direct measurement of the transition from edge to core power coupling in a light-ion helicon source

We present time-resolved measurements of an edge-to-core power transition in a light-ion (deuterium) helicon discharge in the form of infra-red camera imaging of a thin stainless steel target plate on the Proto-Material Exposure eXperiment device. The time-resolved images measure the two-dimensional distribution of power deposition in the helicon discharge. The discharge displays a mode transition characterized by a significant increase in the on-axis electron density and core power coupling, suppression of edge power coupling, and the formation of a fast-wave radial eigenmode. Although the self-consistent mechanism that drives this transition is not yet understood, the edge-to-core power transition displays characteristics that are consistent with the discharge entering a slow-wave anti-resonant regime. RF magnetic field measurements made across the plasma column, together with the power deposition results, provide direct evidence to support the suppression of the slow-wave in favor of core plasma production by the fast-wave in a light-ion helicon source.

Thermal analysis and tests of W/Cu brazing for primary collimator scraper in CSNS/RCS

To the transverse beam collimation system in a rapid cycling synchrotron, an important component is the primary collimator, which improves emittance of the beam halo particles such that the particles outside the predefined trajectory can be absorbed by the secondary collimators. Given the material properties and power deposition distribution, the beam scraper of the primary collimator is a 0.17 mm tungsten foil on a double face-wedged copper block of 121.5 mm × 20 mm. The heat is transferred to the outside by a ϕ34 mm copper rod. In this paper, for minimizing brazing thermal stress, we report our theoretical analysis and tests on brazing the tungsten and copper materials which differ greatly in size. We show that the thermal stress effect can be controlled effectively by creating stress relief grooves on the copper block and inserting a tungsten transition layer into the copper block. This innovation contributes to the successful R&D of the primary collimator. And this study may be of help for working out a brazing plan of similar structures.

Analysis of Power Distribution on Beamline Components at Different Neutralization Efficiencies on NBI Test Stand**supported by the International Science and Technology Cooperation Program of China (No. 2014DFG61950), National Natural Science Foundation of China (No. 11405207) and the Foundation of ASIPP (No. DSJJ-15-GC03)

Neutral beam injection is recognized as one of the most effective means for plasma heating. According to the research plan of the EAST physics experiment, two sets of neutral beam injector (4–8 MW, 10–100 s) were built and operated in 2014. Neutralization efficiency is one of the important parameters for neutral beam. High neutralization efficiency can not only improve injection power at the same beam energy, but also decrease the power deposited on the heat-load components in the neutral beam injector (NBI). This research explores the power deposition distribution at different neutralization efficiencies on the beamline components of the NBI device. This work has great significance for guiding the operation of EAST-NBI, especially in long pulse and high power operation, which can reduce the risk of thermal damage of the beamline components and extend the working life of the NBI device.

Analysis of the Pipe Heat Loss of the Water Flow Calorimetry System in EAST Neutral Beam Injector**supported by the National Magnetic Confinement Fusion Science Program of China (No. 2013GB101001) and the International Science & Technology Cooperation Program of China (No. 2014DFG61950)

Neutral beam injection heating is one of the main auxiliary heating methods in controllable nuclear fusion research. In the EAST neutral beam injector, a water flow calorimetry (WFC) system is applied to measure the heat load on the electrode system of the ion source and the heat loading components of the beamline. Due to the heat loss in the return water pipe, there are some measuring errors for the current WFC system. In this paper, the errors were measured experimentally and analyzed theoretically, which lay a basis for the exact calculation of beam power deposition distribution and neutralization efficiency.

Effect of Radial Density Configuration on Wave Field and Energy Flow in Axially Uniform Helicon Plasma**supported by National Natural Science Foundation of China (No. 11405271)

The effect of the radial density configuration in terms of width, edge gradient and volume gradient on the wave field and energy flow in an axially uniform helicon plasma is studied in detail. A three-parameter function is employed to describe the density, covering uniform, parabolic, linear and Gaussian profiles. It finds that the fraction of power deposition near the plasma edge increases with density width and edge gradient, and decays in exponential and “bump-on-tail” profiles, respectively, away from the surface. The existence of a positive second-order derivative in the volume density configuration promotes the power deposition near the plasma core, which to our best knowledge has not been pointed out before. The transverse structures of wave field and current density remain almost the same during the variation of density width and gradient, confirming the robustness of the m=1 mode observed previously. However, the structure of the electric wave field changes significantly from a uniform density configuration, for which the coupling between the Trivelpiece-Gould (TG) mode and the helicon mode is very strong, to non-uniform ones. The energy flow in the cross section of helicon plasma is presented for the first time, and behaves sensitive to the density width and edge gradient but insensitive to the volume gradient. Interestingly, the radial distribution of power deposition resembles the radial profile of the axial component of current density, suggesting the control of the power deposition profile in the experiment by particularly designing the antenna geometry to excite a required axial current distribution.

Effect of electro-discharge circuit parameters on the destructive action of plasma channel in solid media

The results of computer blast-hole experiments with copper wire electro-explosion in the polyethylene-concrete media has been analyzed with shock and pressure wave dynamics depending on the spatiotemporal distribution of electrical power deposition in plasma channel. Pressure and stress-wave dynamics of tensely-deformed material state has been analysed by means of physical and mathematical model, which consistently describes the operation of the discharge circuit, plasma channel expansion, generation and propagation of the shock and pressure waves in the condensed media. It has been shown the significant dependence of the stress-wave profile on the pressure pulse wave shape on the borehole wall which is determined by the rate of electrical energy release in the plasma channel and is weakly depended on the time of energy release (at given rate of its release). Analysis of stress-wave dynamics have been shown that the rapid power deposition results to the higher amplitude of compressive stresses in the wave. The lower energy deposition rate in plasma channel leads to the higher amplitude of tensile stresses both in radial and tangential direction.

Erratum to: Analysis of Power Deposition on Heat Load Components for EAST Neutral Beam Injector

In the original version of this article, unfortunately the caption of Fig. 6 has been erroneously published as Fig. 6 Beam power deposition distribution on the heat load components (Orange: Theoretical results, Blue: Experiment results; Vacc = 60 kV) And the correct caption is as follows: Fig. 6 Beam power deposition distribution on the heat load components (Orange: Theoretical results, Blue: Experiment results; Vacc = 50 kV)

Radiofrequency field inhomogeneity compensation in high spatial resolution magnetic resonance spectroscopic imaging

Clinical magnetic resonance spectroscopy imaging (MRSI) is a non-invasive functional technique, whose mathematical framework falls into the category of linear inverse problems. However, its use in medical diagnostics is hampered by two main problems, both linked to the Fourier-based technique usually implemented for spectra reconstruction: poor spatial resolution and severe blurring in the spatial localization of the reconstructed spectra. Moreover, the intrinsic ill-posedness of the MRSI problem might be worsened by (i) spatially dependent distortions of the static magnetic field (B0) distribution, as well as by (ii) inhomogeneity in the power deposition distribution of the radiofrequency magnetic field (B1). Among several alternative methods, slim (Spectral Localization by IMaging) and bslim (B0 compensated slim) are reconstruction algorithms in which a priori information concerning the spectroscopic target is introduced into the reconstruction kernel. Nonetheless, the influence of the B1 field, particularly when its operating wavelength is close to the size of the human organs being studied, continues to be disregarded. starslim (STAtic and Radiofrequency-compensated slim), an evolution of the slim and bslim methods, is therefore proposed, in which the transformation kernel also includes the B1 field inhomogeneity map, thus allowing almost complete 3D modelling of the MRSI problem. Moreover, an original method for the experimental determination of the B1 field inhomogeneity map specific to the target under evaluation is also included. The compensation capabilities of the proposed method have been tested and illustrated using synthetic raw data reproducing the human brain.

A fast adaptive power scheme based on temperature distribution and convergence value for optimal hyperthermia treatment

Abstract To elevate tissue temperature to therapeutic level fast with optimal power deposition during hyperthermia treatment (HT) is a key treatment processing step. Traditionally we have treated the tumor volume, without considering possible existing thermally significant vessels, using a simple 1st-order temperature-based adaptive power scheme to determine optimal power deposition distributions. The objectives of this study were to reveal the difficulty of that approach when considering single large blood vessel, and proposed a novel fast scheme that could improve upon and substitute for the traditional temperature-based adaptive power scheme. In this study, we presented a novel three-coefficient-and-two-SCV 5th-order temperature-based adaptive power scheme to resolve the induced large blood vessel problem in 3-D temperature distribution and introduced the parameter, SCV (Sentinel Convergence Value), to handle interior scheme shift. Results of the novel adaptive power scheme has shown its robustness to fast approach optimal temperature distribution and power density distribution with high precision in the tumor volume when considering the existence of thermally significant blood vessel. Ultimately, we may be able to effectively calculate the absorbed power density distribution of 3-D biological tissues with a complicated vasculature [1] in the volume.

Modeling of dual frequency capacitively coupled plasma sources utilizing a full-wave Maxwell solver: I. Scaling with high frequency

Dual frequency capacitively coupled plasma (DF-CCP) tools for etching and deposition for microelectronics fabrication typically use a high frequency (HF, tens to hundreds of MHz) to sustain the plasma and a low frequency (LF, a few to 10 MHz) for ion acceleration into the wafer. With an increase in both the HF and wafer size, electromagnetic wave effects (i.e. propagation, constructive and destructive interference) can affect the spatial distribution of power deposition and reactive fluxes to the wafer. In this paper, results from a two-dimensional computational investigation of a DF-CCP reactor, incorporating a full-wave solution of Maxwell's equations, are discussed. As in single frequency CCPs, the electron density transitions from edge high to center high with increasing HF. This transition is analyzed by correlating the spatial variation of the phase, magnitude and wavelength of the HF electric field to the spatial variation of the electron energy distributions and ionization sources. This transition is sensitive to the gas mixture, particularly those containing electronegative gases due to the accompany change in conductivity. The consequences of these wave effects on the ion energy distributions incident onto the wafer are also discussed.

Adaptive Ablation Treatment Based on Impedance Imaging

The application of thermal ablation technique and, in particular, of the radiofrequency ablation (RFA), has become widely used in the treatment of solid tumors. The use of optimization methods to plan the therapy is among the emerging fields of interests. Monitoring of the ablative treatment by using electrical impedance tomography (EIT), allowing real time observations with no ionizing radiations and at low cost, is also considered a relevant goal. In this paper, a proposal for an adaptive RFA treatment based on multiple external electrodes and EIT images is presented. In particular, the distribution of Ohmic power deposition is optimized by controlling the current pattern on multiple external electrodes in such a way to achieve a suitable temperature rise in the tumour volume limiting it at the same time in healthy tissues. The optimization of the RFA heating is based on the knowledge of the electric properties of living tissues; the well known uncertain knowledge of this parameter is at least partially resolved by generating online EIT images.

Three-dimensional discharge simulation of inductively coupled plasma (ICP) etching reactor

More and more importance has been attached to inductively coupled plasma (ICP) in semiconductor manufacture. For a deep understanding of the plasma discharge process in the etching reactor, this study made a three-dimensional simulation on the Ar plasma discharge process with the commercial software CFD-ACE, which is according to the real experiment conditions and data supplied by North Microelectronic Corporation. The error of the simulation results is in the range of ±20% with credibility. The numerical results show that the three-dimentional spatial distribution of electron density is reduced from the chamber center to the wall. The distribution of electron density, electron temperature and power deposition is related to the shape and placement of the coil.

An innovative target for the RACE HP experiment

In the RACE (reactor–accelerator coupling experiments) project, a series of ADS (accelerator driven system) experiments are envisaged for the study of the coupling of a neutron source with sub-critical reactors. In these experiments, a continuous electron beam impacts on an actively cooled solid target where it is converted through photonuclear reactions in a neutron flux, able to feed the reactor. In a RACE foreseen ‘high power’ phase, where the beam power would be enhanced from 1 to about 30 kW, the target would be submitted to very severe conditions both from the mechanical and the thermal points of view. In this paper, the development of a new concept of uranium target is described with detailed neutron production analyses, power deposition distributions, thermo-mechanical simulations and cooling schemes. Two possible solutions are envisaged in order to control the power deposition distribution.

Study of Spatial Distribution of Microwave Power Deposition for Plug ECRH in GAMMA 10

Wave propagation around the ECR layer in the GAMMA 10 plug region is analyzed by calculating the dispersion relation of an electron cyclotron wave in a hot plasma. Then, the spatial distribution of microwave power deposition and the absorption rate along each microwave ray are calculated. The absorption rate is experimentally evaluated by using an array of waveguide antennas. The calculated value well agrees with the experimental one on reasonable assumption that the extraordinary mode shares about 90% of the injected microwave power. This analysis is used to obtain an axisymmetric power deposition distribution. It is shown that the heating wave should be directed somewhat upward than the direction to the on-axis point on the resonance layer. This is because a larger power is deposited in the injection side lower side to the machine axis. For the plug in GAMMA 10, an injection beam with an elliptic cross section is suitable to obtain a circular distribution of power deposition.

Survey of intense Sun–Earth connection events (1995–2003)

We survey the interplanetary (IP) configurations associated with the largest energy and/or power inputs to the magnetosphere in 1995–2003, i.e., from the last 2 years of solar cycle 22 to the descending phase of solar cycle 23. We work in the “ ϵ” formulation of [Perreault, P., Akasofu, S.-I. A study of geomagnetic storms, Geophys. J.R. Astron. Soc., 54, 547, 1978]. Using this, we calculate the energy extracted by the magnetosphere from the solar wind, and the powering of the magnetosphere by the solar wind. We carry out a statistical survey to obtain the distribution of power deposition and energy input during this 9-year period. Large events are then defined as those whose energy exceeds 10 J m −2 and/or whose power exceeds 0.3 mW m −2. We then correlate the large events with the strength of geomagnetic disturbances they elicited, as measured by the Dst storm index. Finally, the large events are classified in terms of the IP structures involved.

Closed-form solution for the thermal dose delivered during single pulse thermal therapies

This study provides a closed form, analytical expression for the thermal dose delivered by a single heating pulse. The solution is derived using the effective cooling method and the non-linear Sapareto-Dewey equation to determine the thermal dose delivered by the time-temperature history of a treatment. The analytical solutions are used to determine the optimal treatment conditions, i.e. those that exactly deliver the desired thermal dose at a specified time. For purposes of illustration, this study focuses on a ‘conservative’ clinical approach in which the desired thermal dose is delivered at the end of the ‘cool down’ period. The analytical results show that, after a clinical strategy has been chosen (e.g. conservative, aggressive or intermediate), the user can only specify two free variables for such an optimal treatment. Results are presented which suggest that a practical approach would be to specify both (1) the desired thermal dose to be delivered to the target (the clinically relevant outcome) and (2) the peak temperature to be reached (a measurable, clinically useful, patient dependent response variable that can be employed in feedback control systems); and then determine the associated, optimal heating magnitude and duration that need to be used to reach that dose and temperature. The results also reveal that, with a given patient condition and power deposition distribution (together specifying an effective cooling time constant for the treatment) and a specified thermal dose, there is a maximum allowable peak temperature that, if exceeded, will result in ‘over-dosing’ the heated tissue. The results also show that avoiding such non-optimal ‘over-dosing’ will be difficult in most high temperature therapies since, when high temperatures are produced in tissues, the temperature decay must be very fast in order to avoid over-dosing during the cooling period. Such rapid cooling can only occur if short effective cooling time constants are present—either as a result of large tissue blood flows in the patient or due to large conduction effects induced by the use of highly localized power deposition sources.