The Application of Barr Numerical Method to Realize Abel Inversion

An 8-channel HCN laser interferometer will be installed on HL-2A in near term. In order to get the spatial profile of the electron density Barr numerical method is adopted to realize the Abel inversion. In this article the result of the Abel inversion by Matlab GUI is given which can be updated to process the measured data of the 8-channel laser interferometer and provide the spatial distribution of the electron density.     

Fast Data Processing of a Polarimeter-Interferometer System on J-TEXT

A method of fast data processing has been developed to rapidly obtain evolution of the electron density profile for a multichannel polarimeter-interferometer system(POLARIS)on J-TEXT. Compared with the Abel inversion method, evolution of the density profile analyzed by this method can quickly offer important information. This method has the advantage of fast calculation speed with the order of ten milliseconds per normal shot and it is capable of processing up to 1 MHz sampled data, which is helpful for studying density sawtooth instability and the disruption between shots. In the duration of a flat-top plasma current of usual ohmic discharges on J-TEXT, shape factor u is ranged from 4 to 5. When the disruption of discharge happens, the density profile becomes peaked and the shape factor u typically decreases to 1.     

Online plasma diagnostics of a laser-produced plasma

In this study,we report a laser interferometry experiment for the online-diagnosing of a laserproduced plasma.The laser pulses generating the plasma are ultra-fast(30 femtoseconds),ultraintense(tens of Terawatt) and are focused on a helium gas jet to generate relativistic electron beams via the laser wakefield acceleration(LWFA) mechanism.A probe laser beam(λ?=?800 nm) which is split-off the main beam is used to cross the plasma at the time of arrival of the main pulse,allowing online plasma density diagnostics.The interferometer setup is based on the No Marski method in which we used a Fresnel bi-prism where the probe beam interferes with itself after crossing the plasma medium.A high-dynamic range CCD camera is used to record the interference patterns.Based upon the Abel inversion technique,we obtained a 3D density distribution of the plasma density.     

Tomography of a simply magnetized toroidal plasma

Optical emission spectroscopy is a passive diagnostic technique,which does not perturb the plasma state.In particular,in a hydrogen plasma,Balmer-alpha(Hα) emission can be easily measured in the visible range along a line of sight from outside the plasma vessel.Other emission lines in the visible spectral range from hydrogen atoms and molecules can be exploited too,in order to gather complementary pieces of information on the plasma state.Tomography allows us to capture bi-dimensional structures.We propose to adopt an emission spectroscopy tomography for studying the transverse profiles of magnetized plasmas when Abel inversion is not exploitable.An experimental campaign was carried out at the Thorello device,a simple magnetized torus.The characteristics of the profile extraction method,which we implemented for this purpose are discussed,together with a few results concerning the plasma profiles in a simply magnetized torus configuration.     

竖直圆管中泡状流含汽率径向分布的统计测量方法

为了研究竖直圆管中高含汽率泡状流的含汽率径向分布,设计了一种测量含汽率径向分布的方法.该方法通过统计投影视图中的像素信息得到泡状流的投影含汽率,根据汽泡投影重叠概率计算出截面含汽率在投影面上的边缘分布;再基于竖直圆管中含汽率分布轴对称的假设,使用改进的傅里叶级数展开方法求解Abel逆变换,计算出含汽率沿圆管径向的分布.为验证该方法的有效性,测量了较低含汽率时的泡状流径向含汽率,并与匹配方法的测量结果进行比较.实验结果表明:此方法能得到高含汽率或含汽率近壁分布等其他方法难以测量的含汽率分布.     

Investigation of Dual Polarization Reflectometry for Determination of Plasma Density and Magnetic Field in a Spherical Tokamak

The paper deals with dual polarization reflectometry as a method for determination of plasma density and poloidal magnetic field profile in low aspect ratio tokamaks. A numerical iteration algorithm is developed and solutions for integral equations for O- and X-modes are presented. The numerical calculations confirm the use of the iterative algorithm for effective reconstruction of the density and magnetic field profile.     

Space-time Resolved Spectroscopic System Based on a Rotating Hexahedral Mirror for Measurement of Visible and Ultraviolet Spectral Line Emissions

By using a rotating hexahedral mirror placed in front of the objective lens and two sets of visible and ultraviolet monochromators coupled with a branchy quartz fiber bundle, a space-time resolved spectroscopic system has been developed on the HT-7 superconducting tokamak. A center monitoring system has been used including a Helium-Neon laser and a photodiode detector to indicate the absolute position of the measurement in order to reduce the error caused by the uncertain emissive position of the plasma. By using the asymmetric Abel inversion, the space-time resolved local emission coefficients of the spectroscopic line emissions have been obtained. Presented in this article are simultaneous measurements of two spectral line emissions such as CV-227.1 nm and OV-278.1 nm during a single plasma discharge on the HT-7. Experimental results indicate that the time resolution is better than 3 ms, the space resolution is better than 1.5cm, the ratio of signal to background is better than 10：1, and the relative error of chord-integrated emission profile is less than 10%. Compared to traditional multichannel detecting systems, this system has considerably improved measurement efficiency, reduced uncertainty, and is therefore suitable for transport studies of global particles and impurities.     

Feasibility of applying the lower cut-off frequency for the density radial coverage extension in EAST reflectometry measurement

The extraordinary mode (X-mode) lower cut-off frequency is proposed for use in the reflectometry diagnostic on ITER for the electron density profile measurement, which is a trade-off between extreme plasma parameters and the accessible probing frequency. In contemporary experiments, the lower cut-off frequency can be identified at the probing frequency below the electron cyclotron frequency (fce) under certain plasma conditions. We provide here, for the first time, the experimental validation of the use of the lower cut-off frequency for the density profiles via the reflectometry measurement on EAST. The corresponding group delay of the lower cut-off frequency evolves continuously with the upper one, revealing a reasonable radial coverage extension of reflectometry measurement toward the plasma core. It is concluded that the lower cut-off frequency can be used as a supplement to the upper one in the density profile inversion process, which is of particular interest in the high magnetic field and/or density discharge to extend the radial coverage of reflectometry measurement.     

The ITER radial neutron camera: An updated neutronic analysis

The radial neutron camera (RNC) will provide the spatial distribution and the total strength of the ITER neutron source (emissivity profile and fusion power) by means of collimated neutron measurements. Line-integrated neutron spectral measurements can also provide information on the ion temperature profile. The present design of the RNC consists of two collimating structures for a full coverage of the plasma: 36 collimated lines of sight (LOS) distributed in three different planes view the plasma core (ex-port system) and nine collimated LOS view the plasma edge (in-port system).The RNC design is based on the combined use of the MCNP Monte Carlo code and a software tool performing asymmetric Abel inversion of simulated measured neutron signals (MSST). Neutron and γ-ray transport calculations are performed with MCNP using a 3D RNC model to determine the signal/noise for each RNC channel and the spectra at the detectors. The MSST code is used to check the RNC compliance with the ITER measurement requirements for the neutron emissivity profile.In the present paper the improvement of the hard variance reduction technique applied to the MCNP neutron source (consisting in sampling neutrons only from plasma regions contributing to the detector signal) is presented and the following issues are analyzed: the possibility of reducing the length of the ex-port collimators (resulting in a significant reduction of the overall RNC dimension and weight); options for the reduction of the dose due to the neutron streaming through the RNC cut-outs in the blanket shielding module; the integration of a γ-ray detection system in the RNC by partially filling the collimators with a neutron absorbing material (LiH).     

A remedy for the ill-posedness of the one-dimensional two-fluid model

A one-dimensional two-fluid model with explicit momentum flux parameters is proposed as a remedy for the mathematical ill-posedness of the standard one-dimensional two-fluid model. By constructing a simplified two-phase flow using existing correlations for the distribution parameter C_o and velocity profile, the momentum flux parameter is determined as a function of void fraction and density ratio for the whole range of flow regime. By performing a linear stability analysis for a two-phase flow in a channel described by the proposed model, an analytical expression for the growth factor is derived as a function of wave number, void fraction, drag coefficient, and relative velocity. From the analytical expression for the growth factor, the stability criteria are derived as a function of void faction, density ratio, and momentum flux parameters. It is shown that the two-phase flow in a channel described by the proposed model is stable in the whole range of flow regime.     

Unbiased Monte Carlo simulation of the Compton profile

Recent comparisons between analytical (deterministic) computations using the code SHAPE, and Monte Carlo (MC) simulations of Compton scattering using different codes show discrepancies in the shape of the Compton peak (the so-called Compton profile), specially for medium-low energy X-ray excitation. Considering the analytical computations as a reference model, the standard approach adopted for generating the Compton profile in different MC codes (EGSnrc, MCNP, MCSHAPE) has been studied comparatively in order to discover a reason for the difference. Apparently there is a bias in the profile generation which is common to all the codes and is related to the assumption of completely populated atomic orbitals contributing to the scattering. Such an assumption does not agree with the equivalence condition between the integrated Compton profile in the Impulse Approximation (IA) and the Waller-Hartree (WH) scattering function.In this article, we report the comparisons mentioned above for a paradigmatic case and propose an unbiased MC algorithm for the simulation of the Compton scattering.     

基于多算法的电子剂量场反演方法

为了研究精确放射治疗中多算法的电子剂量场反演方法及反演效果,建立非线性规划电子剂量场反演模型,利用体外透射剂量重建全空间电子剂量场,并通过多种算法实现。采用7个例题测试结果表明:除NMinimize算法不能实现该模型外,其他算法都能实现,其中Levenberg-Marquardt算法最精确快速。进一步测试表明,利用接近电子射程的透射剂量会带来较大的反演误差(尾差),原因可能是能谱平均带来的,因此改进方法需考虑改进对平均能量的近似。但由于反演时间较短,精度高,可实现实时剂量场反演;并且每一种算法都有特点,为实现提供多方法的选择性,满足临床上对实时剂量验证的需要。     

MHD Equilibrium with Reversed Current Density and Magnetic Islands Revisited:the Vacuum Vector Potential Calculus

The solution of Grad-Shafranov equation determines the stationary behavior of fusion plasma inside a tokamak.To solve the equation it is necessary to know the toroidal current density profile.Recent works show that it is possible to determine a magnetohydrodynamic(MHD)equilibrium with reversed current density(RCD)profiles that presents magnetic islands.In this work we show analytical MHD equilibrium with a RCD profile and analyze the structure of the vacuum vector potential associated with these equilibria using the virtual casing principle.     

Interactions of Microwave with Plasmas

When plasma size scale is comparable with the wavelength of electromagnetic waves,W.K.B.solution isn‘t applicable.In this paper a new numerical solution technique to investigate interactions of microwave with plasmas is presented by using Runge-kutta method.The results of numerical solution coincide with that of analytical solution while the model is linear electron density profile in calculated accuracy.     

Diagnosis of Electron, Vibrational and Rotational Temperatures in an Ar/N2 Shock Plasma Jet Produced by a Low Pressure DC Cascade Arc Discharge

In this paper,a low pressure Ar/N2 shock plasma jet with clearly multicycle alternating zones produced by a DC cascade arc discharge has been investigated by an emission spectral method combined with Abel inversion analysis.Plasma emission intensity,electron,vibrational and rotational temperatures of the shock plasma have been measured in the expansion and compression zones.The results indicate that the ranges of the measured electron temperature,vibrational temperature and rotational temperature are 1.1 eV to 1.6 eV,0.2 eV to 0.7 eV and 0.19 eV to 0.22 eV,respectively,and it is found for the first time that the vibrational and rotational temperatures increase while the electron temperature decreases in the compression zones.The electron temperature departs from the vibrational and the rotational temperatures due to non-equilibrium plasma efects.Electrons and heavy particles could not completely exchange energy via collisions in the shock plasma jet under the low pressure of 620 Pa or so.     

Bootstrap current fraction scaling for a tokamak reactor design study

We have derived new bootstrap current fraction scalings for systems codes by solving the Hirshman–Sigmar model, which is valid for arbitrary aspect ratios and collision conditions. The bootstrap current density calculation module in the ACCOME code was used with the matrix inversion method without the large aspect ratio assumption. Nine self-consistent MHD equilibria, which cover conventional, advanced and spherical tokamaks with normal or reversed shear, were constructed using numerical calculations in order to compare the bootstrap current fraction values with those of the new model and all six existing models. The Wilson formula successfully predicted the bootstrap current fraction, but it requires current density profile index for the calculation. The new scaling formulas and IPDG accurately estimated the bootstrap current fraction for the normal and weakly reversed shear tokamaks, regardless of the aspect ratio. However, none of the existing models except the Wilson formula can accurately estimate the bootstrap current fraction for the reversed shear tokamaks, which is promising for the advanced tokamak operation mode.     

Implementation and preliminary investigation of analytical methodsfor correction of distance-dependent resolution variation and uniformattenuation in 3D brain SPECT

Spatial resolution variation as a function of distance from collimator surface in single photon emission computed tomography (SPECT) is a major obstacle for quantitative imaging. This work investigated two analytical inversion methods for correcting the distance-dependent resolution variation, as well as uniform attenuation in brain SPECT studies. The first one utilizes an accurately measured resolution variation kernel, but derives an approximated inversion formula. The second one derives an accurate inversion formula, but approximates the resolution variation kernel. Reconstructed images using the first method showed a better resolution recovery at the periphery of field-of-view (FOV), consistent with the theory that the inversion formula is approximated for far-field regions. The second method restored resolution better at the central area of FOV, consistent with the approach that the resolution kernel is approximated for near-field regions. The second method is more sensitive to the approximation. The first one is more robust to the approximation and, therefore, can be a better choice for quantitative SPECT imaging     

Development of the W-band density profile and fluctuation reflectometer on EAST

A X-mode polarized W-band reflectometer for plasma density profile and fluctuation measurement is designed and installed on EAST. In measuring the density profile, a voltage controlled oscillator (VCO) is used as the source, allowing a high temporal resolution measurement. The density profile in a plasma with high magnetic field (3.0 T) has been measured by combination of V- and W-band reflectometers. For fluctuation measurements, a frequency synthesizer is used instead of the VCO as a microwave source. The core density fluctuations during sawtooth activity are measured and analyzed.     

回溯算法在燃耗计算中的应用

采用解析解的线性核素链方法在进行燃耗计算时首先根据分治和递归的策略将燃耗矩阵进行解耦,形成具有马尔科夫特性的线性核素链。然后通过对每一条链的解析计算得到所有相关核素的核密度、活度、衰变热等数据。然而在核素链的构建过程中需对每一个可能的核反应路径进行计算。欲保证计算的精度和效率,需寻求一种既能覆盖所有反应路径、又能根据问题描述和约束条件进行自动搜索的算法。本文通过对各种搜索算法的分析和比较并根据燃耗链构建过程的特点,最终采用回溯算法进行深度优先搜索,在搜索过程中完成燃耗链的构建和计算,从而形成问题相关的、具有高精度的自适应燃耗算法。同时结合燃耗过程和回溯算法的特点进行了解空间和时间复杂性的分析。将所开发的多群点燃耗计算程序与蒙特卡罗输运计算程序MCMG-Ⅱ进行耦合,通过对中国实验快堆首炉堆芯燃耗的计算和分析完成程序的初步验证。