Cross section determination of^(27)Al(n,2n)^(26)Al reaction induced by 14-MeV neutrons uniting with D-T neutron activation and AMS techniques

Aluminum is the primary structural material in nuclear engineering,and its cross section induced by 14-MeV neutrons is of great significance.To address the issue of insufficient accuracy for the^(27)Al(n,2n)^(26)Al reaction cross section,the activation method and accelerator mass spectrometry(AMS)technique were used to determine the^(27)Al(n,2n)^(26)Al cross section,which could be used as a D-T plasma ion temperature monitor in fusion reactors.At the China Academy of Engineering Physics,neutron activation was performed using a K-400 neutron generator produced by the T(d,n)4He reaction.The^(26)Al∕^(27)Al isotope ratios were measured using the newly installed GYIG 1 MV AMS at the Institute of Geochemistry,Chinese Academy of Sciences.The neutron flux was monitored by measuring the activity of 92mNb produced by the 93Nb(n,2n)92mNb reaction.The measured results were compared with available data in the experimental nuclear reaction database,and the measured values showed a reasonable degree of consistency with partially available literature data.The newly acquired cross-sectional data at 12 neutron energy points through systematic measurements clarified the divergence,which has two different growth trends from the existing experimental values.The obtained results are also compared with the corresponding evaluated database,and the newly calculated excitation functions with TALYS−1.95 and EMPIRE−3.2 codes,the agreement with CENDL−3.2,TENDL-2021 and EMPIRE−3.2 results are generally acceptable.A substantial improvement in the knowledge of the^(27)Al(n,2n)^(26)Al reaction excitation function was obtained in the present work,which will lay the foundation for the diagnosis of the fusion ion temperature,testing of the nuclear physics model,evaluation of nuclear data,etc.

EAST 低杂波加热对同向切向中性束碰撞力矩影响的研究

为研究低杂波加热对同向切向中性束注入的束功率沉积和碰撞力矩的影响,基于低杂波加热的实验参数,使用TRANSP程序进行了模拟分析。研究结果表明,当注入功率1.3MW、能量50keV的同向切向束时,随着LHW加热束沉积功率降低,快离子电荷交换损失增加20%;离子吸收的功率占总的束沉积功率的比例由45%增加到51%。碰撞力矩与束沉积功率的比值由1.327Nm·MW^(-1)增加到1.457Nm·MW^(-1);等离子体电子温度越高,电荷交换损失和碰撞力矩与束沉积功率比值也越大,而低杂波加热期间的束碰撞力矩保持稳定。

Deep learning approaches to recover the plasma current density profile from the safety factor based on Grad–Shafranov solutions across multiple tokamaks

Many magnetohydrodynamic stability analyses require generation of a set of equilibria with a fixed safety factor q-profile while varying other plasma parameters.A neural network(NN)-based approach is investigated that facilitates such a process.Both multilayer perceptron(MLP)-based NN and convolutional neural network(CNN)models are trained to map the q-profile to the plasma current density J-profile,and vice versa,while satisfying the Grad–Shafranov radial force balance constraint.When the initial target models are trained,using a database of semianalytically constructed numerical equilibria,an initial CNN with one convolutional layer is found to perform better than an initial MLP model.In particular,a trained initial CNN model can also predict the q-or J-profile for experimental tokamak equilibria.The performance of both initial target models is further improved by fine-tuning the training database,i.e.by adding realistic experimental equilibria with Gaussian noise.The fine-tuned target models,referred to as fine-tuned MLP and fine-tuned CNN,well reproduce the target q-or J-profile across multiple tokamak devices.As an important application,these NN-based equilibrium profile convertors can be utilized to provide a good initial guess for iterative equilibrium solvers,where the desired input quantity is the safety factor instead of the plasma current density.

Progress of the bolometer diagnostic system on EAST

Measurements of the total radiated power and its spatial distribution are crucial for fusion research.On the experimental advanced superconducting tokamak(EAST),both the metal foil resistive bolometer and the absolute extreme ultraviolet(AXUV)photodiodes have been used to quantify the radiated power.This article introduces the latest improvement of the bolometer diagnostic system on EAST.It also details the successful design and installation of new divertor AXUV cameras,which are dedicated to the investigation of divertor physics.The shielding components of the bolometer detector have been refined,and the article provides a detailed exposition of the double shielding structures that have been verified as effective in microwave shielding.Additionally,the changes in the radiated power distribution in the divertor region during the plasma detachment process are measured using the divertor AXUV camera.Finally,the radiated power measured by the AXUV detector and metal foil resistive bolometer are compared,and different detector performances are presented.

Nonlinear dynamics of the reversed shear Alfvén eigenmode in burning plasmas

In a tokamak fusion reactor operated at steady state,the equilibrium magnetic field is likely to have reversed shear in the core region,as the noninductive bootstrap current profile generally peaks off-axis.The reversed shear Alfvén eigenmode(RSAE)as a unique branch of the shear Alfvén wave in this equilibrium,can exist with a broad spectrum in wavenumber and frequency,and be resonantly driven unstable by energetic particles(EP).After briefly discussing the RSAE linear properties in burning plasma condition,we review several key topics of the nonlinear dynamics for the RSAE through both wave-EP resonance and wave-wave coupling channels,and illustrate their potentially important role in reactor-scale fusion plasmas.By means of simplified hybrid MHD-kinetic simulations,the RSAEs are shown to have typically broad phase space resonance structure with both circulating and trapped EP,as results of weak/vanishing magnetic shear and relatively low frequency.Through the route of wave-EP nonlinearity,the dominant saturation mechanism is mainly due to the transported resonant EP radially decoupling with the localized RSAE mode structure,and the resultant EP transport generally has a convective feature.The saturated RSAEs also undergo various nonlinear couplings with other collective oscillations.Two typical routes as parametric decay and modulational instability are studied using nonlinear gyrokinetic theory,and applied to the scenario of spontaneous excitation by a finite amplitude pump RSAE.Multiple RSAEs could naturally couple and induce the spectral energy cascade into a low frequency Alfvénic mode,which may effectively transfer the EP energy to fuel ions via collisionless Landau damping.Moreover,zero frequency zonal field structure could be spontaneously excited by modulation of the pump RSAE envelope,and may also lead to saturation of the pump RSAE by both scattering into stable domain and local distortion of the continuum structure.

磁约束燃烧等离子体物理的现状与展望

本文从设计和运行托卡马克聚变堆需求的角度,简要概述了托卡马克高约束运行方案和高能量粒子约束涉及的关键物理的发展现状和挑战.过去几十年中,托卡马克高约束模式物理研究取得了重要进展,明确了聚变堆运行区的主要稳定性和约束的限制条件及其性能优化的主要调控手段,发展了感应、混合和稳态等若干可能适用于未来托卡马克聚变堆的运行方案.在反应堆阿尔法粒子加热主导的条件下,潜在主导阿尔法粒子输运损失的阿尔芬不稳定性的线性谱特征和激发机制得到了充分的理解;在阿尔芬不稳定性的非线性饱和、阿尔法粒子约束,及通过加热沉积和微观湍流对等离子体约束的影响等方面开展了大量的实验和理论探索.当前,磁约束聚变物理已进入临近点火燃烧等离子体研究的新阶段,面临着全新的挑战,如:聚变堆条件下如何实现高能量阿尔法粒子对等离子体有效自加热;在阿尔法粒子自加热为主条件下,如何通过调控等离子体关键参数分布维持等离子体稳定性和高约束性能,实现聚变堆高效安全运行;能否建立全尺度模型,实现聚变堆复杂等离子体的长时间动力学过程的准确预测等.这些关键问题的解决,可为未来聚变堆的设计和运行奠定坚实的物理基础,同时推动等离子体学科的发展.

Integrated analysis of plasma rotation effect on HL-3 hybrid scenario

The hybrid scenario,which has good confinement and moderate MHD instabilities,is a proposed operation scenario for international thermonuclear experimental reactor(ITER).In this work,the effect of plasma rotation on the HL-3 hybrid scenario is analyzed with the integrated modeling framework OMFIT.The results show that toroidal rotation has no obvious effect on confinement with a high line averaged density of n_(bar)~(7)×10^(19)m^(-3).In this case,the ion temperature only changes from 4.7 keV to 4.4 keV with the rotation decreasing from 10^(5) rad/s to 10^(3) rad/s,which means that the turbulent heat transport is not dominant.While in the scenarios characterized by lower densities,such as n_(bar)~4×10^(19)m^(-3),turbulent transport becomes dominant in determining heat transport.The ion temperature rises from 3.8 keV to 6.1 keV in the core as the rotation velocity increases from 10^(3) rad/s to 10^(5) rad/s.Despite the ion temperature rising,the rotation velocity does not obviously affect electron temperature or density.Additionally,it is noteworthy that the variation in rotation velocity does not significantly affect the global confinement of plasma in scenarios with low density or with high density.

基于Python 的等离子体平衡重建程序设计及实现

基于Python环境,设计和编写了等离子体平衡重建算法(Py-EFIT)。利用NumPy和SciPy库求解平衡重建算法中矩阵的运算问题,运用Matplotlib库实现重建算法计算结果的可视化,基于交互式可视化设计包QT Designer,使用PyQt库设计并实现该程序的用户界面。Py-EFIT的测试结果显示等离子体平衡重建过程操作更加简单、直观,为托卡马克实验数据分析提供了一种有效的工具。

Plasma current tomography for HL-2A based on Bayesian inference

An accurate plasma current profile has irreplaceable value for the steady-state operation of the plasma.In this study,plasma current tomography based on Bayesian inference is applied to an HL-2A device and used to reconstruct the plasma current profile.Two different Bayesian probability priors are tried,namely the Conditional Auto Regressive(CAR)prior and the Advanced Squared Exponential(ASE)kernel prior.Compared to the CAR prior,the ASE kernel prior adopts nonstationary hyperparameters and introduces the current profile of the reference discharge into the hyperparameters,which can make the shape of the current profile more flexible in space.The results indicate that the ASE prior couples more information,reduces the probability of unreasonable solutions,and achieves higher reconstruction accuracy.

Gyrokinetic simulations of the kinetic electron effects on the electrostatic instabilities on the ITER baseline scenario

The linear and nonlinear simulations are carried out using the gyrokinetic code NLT for the electrostatic instabilities in the core region of a deuterium plasma based on the International Thermonuclear Experimental Reactor(ITER)baseline scenario.The kinetic electron effects on the linear frequency and nonlinear transport are studied by adopting the adiabatic electron model and the fully drift-kinetic electron model in the NLT code,respectively.The linear simulations focus on the dependence of linear frequency on the plasma parameters,such as the ion and electron temperature gradientsκ_(Ti,e)≡R=L_(Ti,e),the density gradientκ_(n)≡R/L_(n)and the ion-electron temperature ratioτ=T_(e)=T_(i).Here,is the major radius,and T_(e)and T_(i)denote the electron and ion temperatures,respectively.L_(A)=-(δ_(r)lnA)^(-1)is the gradient scale length,with denoting the density,the ion and electron temperatures,respectively.In the kinetic electron model,the ion temperature gradient(ITG)instability and the trapped electron mode(TEM)dominate in the small and large k_(θ)region,respectively,wherek_(θ)is the poloidal wavenumber.The TEMdominant region becomes wider by increasing(decreasing)κ_(T_(e))(κ_(T_(i)))or by decreasingκ_(n).For the nominal parameters of the ITER baseline scenario,the maximum growth rate of dominant ITG instability in the kinetic electron model is about three times larger than that in the adiabatic electron model.The normalized linear frequency depends on the value ofτ,rather than the value of T_(e)or T_(i),in both the adiabatic and kinetic electron models.The nonlinear simulation results show that the ion heat diffusivity in the kinetic electron model is quite a lot larger than that in the adiabatic electron model,the radial structure is finer and the time oscillation is more rapid.In addition,the magnitude of the fluctuated potential at the saturated stage peaks in the ITGdominated region,and contributions from the TEM(dominating in the higher k_(θ)region)to the nonlinear transport can be neglected.In the adiabatic electron model,the zonal radial electric field is found to be mainly driven by the turbulent energy flux,and the contribution of turbulent poloidal Reynolds stress is quite small due to the toroidal shielding effect.However,in the kinetic electron model,the turbulent energy flux is not strong enough to drive the zonal radial electric field in the nonlinear saturated stage.The kinetic electron effects on the mechanism of the turbulence-driven zonal radial electric field should be further investigated.

Cleaning of two mirrors in the first mirror unit using radiofrequency capacitively coupled plasma

First mirror(FM)cleaning,using radio frequency(RF)plasma,has been proposed to recover FM reflectivity in nuclear fusion reactors such as the International Thermonuclear Experimental Reactor(ITER).To investigate the influence of simultaneous cleaning of two mirrors on mirror cleaning efficiency and uniformity,experiments involving single-mirror cleaning and dual-mirror cleaning were conducted using RF capacitively coupled plasma in the laboratory.For the test and simultaneous cleaning of two mirrors,the FM and second mirror(SM),both measuring 110 mm×80 mm,were placed inside the first mirror unit(FMU).They were composed of 16 mirror samples,each with a dimension of 27.5 mm×20 mm.These mirror samples consist of a titanium-zirconium-molybdenum alloy substrate,a 500 nm Mo intermediate layer and a 30 nm Al_(2)O_(3) surface coating as a proxy for Be impurities.The cleaning of a single first mirror(SFM)and the simultaneous cleaning of the FM and SM(DFM and DSM)lasted for 9 h using Ar plasma at a pressure of 1 Pa.The total reflectivity of mirror samples on the DSM did not fully recover and varied with location,with a self-bias of−140 V.With a self-bias of−300 V,the total reflectivity of mirror samples on the SFM and DFM was fully recovered.The energy dispersive spectrometer results demonstrated that the Al_(2)O_(3) coating had been completely removed from these mirror samples.However,the mass loss of each mirror sample on the SFM and DFM before and after cleaning varied depending on its location,with higher mass loss observed for mirror samples located in the corners and lower loss for those in the center.Compared with SM cleaning,the simultaneous cleaning of two mirrors reduced the difference between the highest and lowest mass loss.Furthermore,this mass loss for the mirror samples of the DFM facing the DSM was increased.This indicated that mirror samples cleaned face to face in the FMU simultaneously could influence each other,highlighting the need for special attention in future studies.

Simulation of Rotating Asymmetric Sideways Forces during Vertical Displacement Events in CFETR

Tokamak plasmas with elongated cross sections are susceptible to vertical displacement events(VDEs),which can damage the first wall via heat flux or electromagnetic(EM)forces.We present a 3D nonlinear reduced magnetohydrodynamic(MHD)simulation of CFETR plasma during a cold VDE following the thermal quench,focusing on the relationship among the EM force,plasma displacement,and the n=1 mode.The dominant mode,identified as m/n=2/1,becomes destabilized when most of the current is contracted within the q=2 surface.The displacement of the plasma current centroid is less than that of the magnetic axis due to the presence of SOL current in the open field line region.Hence,the symmetric component of the induced vacuum vessel current is significantly mitigated.The direction of the sideways force keeps a constant phase approximately compared to the asymmetric component of the vacuum vessel current and the SOL current,which in turn keep in-phase with the dominant 2/1 mode.Their amplitudes are also closely associated with the growth of the dominant mode.These findings provide insights into potential methods for controlling the phase and amplitude of sideways forces during VDEs in the future.

CFQS中离子温度梯度模的同位素效应研究

基于中国首台准环对称仿星器(CFQS),利用回旋动理学弗拉索夫代码GKV率先开展准环对称仿星器中离子温度梯度模(ITG)的同位素效应研究。模拟结果表明,CFQS中存在明显的ITG同位素效应,随着氢同位素质量的增加,ITG的增长率显著下降。通过扫描等离子参数,如不同氢同位素混合的比例、密度梯度以及离子与电子温度比,研究了这些等离子体参数下CFQS中同位素效应的变化。此外,在不同的环向或径向位置处研究了CFQS的三维磁场位形对ITG同位素的影响,发现ITG的同位素效应在不同的环向和径向位置均普遍存在。

美国利用人工智能技术实时预测聚变堆等离子体不稳定性

美国普林斯顿大学和普林斯顿等离子体物理实验室的研究人员研发出一个人工智能模型,能够实时预测被称为“撕裂模不稳定性”的聚变堆等离子体不稳定性。聚变能商业应用目前面临着许多重大技术和工程挑战,其中一个是等离子体可能失去稳定性,导致等离子体大规模破裂,进而导致聚变反应不能持续。研究人员使用美国DIII-D国家聚变设施的实验数据来训练这一模型。结果表明,该模型可以提前300毫秒预测撕裂模不稳定性,时间足以供人工智能控制器调整聚变堆运行参数,确保等离子体运行的稳定性。相关研究成果发表于《自然》期刊。

A numerical survey of parameters to reach ignition condition for axial compression of a large-sized field reversed configuration

Field reversed configuration(FRC)is widely considered as an ideal target plasma for magnetoinertial fusion.However,its confinement and stability,both proportional to the radius,will deteriorate inevitably during radial compression.Hence,we propose a new fusion approach based on axial compression of a large-sized FRC.The axial compression can be made by plasma jets or plasmoids converging onto the axial ends of the FRC.The parameter space that can reach the ignition condition while preserving the FRC's overall quality is studied using a numerical model based on different FRC confinement scalings.It is found that ignition is possible for a large FRC that can be achieved with the current FRC formation techniques if compression ratio is greater than 50.A more realistic compression is to combine axial with moderate radial compression,which is also presented and calculated in this work.

Experimental confirmation of the linear relation between plasma current and external vertical magnetic field in EXL-50 spherical torus energetic electron plasmas

A three-fluid equilibrium plasma with bulk plasma and energetic electrons has been observed on the Xuanlong-50(EXL-50) spherical torus, where the energetic electrons play a crucial role in sustaining the plasma current and pressure. In this study, the equilibrium of a multi-fluid plasma was investigated by analyzing the relationship between the external vertical magnetic field(B_(V)),plasma current(I_(p)), the poloidal ratio(β_(p)) and the Shafranov formula. Remarkably, our research demonstrates some validity of the Shafranov formula in the presence of multi-fluid plasma in EXL-50 spherical torus. This finding holds significant importance for future reactors as it allows for differentiation between alpha particles and background plasma. The study of multi-fluid plasma provides a significant reference value for the equilibrium reconstruction of burning plasma involving alpha particles.

HL-3先进雪花偏滤器位形的设计与敏感性分析

使用EFIT程序设计了HL-3装置雪花偏滤器位形,研究了雪花位形对HL-3装置极向场(PF)线圈电流变化的敏感性。研究发现:当PF线圈电流变化达1%时,标准雪花偏滤器转变为雪花加位形或是雪花减位形;当PF线圈电流变化超过8.8%时,雪花减位形在大偏离度下能够获得平衡位形,而雪花加位形难以获得收敛结果。

HL-3装置上离子回旋波加热对中子产额的影响

离子回旋射频(Ion Cyclotron Range of Frequencies,ICRF)波加热是托卡马克装置上至关重要的辅助加热方式之一。托卡马克装置中国环流三号(HL-3,原名HL-2M)拟安装加热功率为6 MW的ICRF加热系统。本工作利用TRANSP程序,模拟并研究了ICRF加热的频率和功率对聚变中子产额以及快离子分布的影响。研究结果表明:ICRF的频率和功率对中子产额有显著影响,固定ICRF频率时,中子产额与加热功率成正比关系,而在固定ICRF加热功率的情况下,中子产额的增加幅度显著依赖ICRF的频率,在研究参数范围内,30 MHz的ICRF对中子产额的增加具有最显著的增强作用。快离子分布的模拟结果显示,在考虑ICRF加热后,中性束和ICRF的协同加热机制能够将快离子加热至最高1 MeV,有效地提高了中子产额。此外,基于中子相机诊断的概念对中子信号进行了仿真。结果表明,中子相机能够有效地测量到由ICRF加热导致的中子产额高低和分布剖面的变化,这为将来优化中子相机诊断系统设计和测量中子空间分布提供了一定的参考。

漂移动理学效应对HL-2A托卡马克共振磁扰动等离子体响应的影响

边缘局域模(Edge Localized Modes,ELMs)的控制是国际热核聚变实验堆(International Thermonuclear Experimental Reactor,ITER)及未来磁约束聚变堆安全运行必须解决的一个关键主题。近年来,大量的理论模拟和实验研究证明,共振磁扰动(Resonant Magnetic Perturbation,RMP)是一种非常有效控制边缘局域模的技术。为了更好地理解HL-2A托卡马克中ELMs的控制,本文基于HL-2A托卡马克实验上等离子体和RMP线圈的位形,使用MARS-F/K程序,计算了高约束模式下等离子体对RMP的漂移动理学响应,并与流体模型的结果进行对比;进一步对等离子体平衡压强、环向流以及热粒子碰撞效应等关键参数进行了敏感性研究。结果表明,随着归一化比压βN的增加,流体响应模型预测的等离子体响应幅度最初相对较弱,随后在接近无壁比压极限时发生强烈变化,但这一非物理因素“跳变”在动理学响应模型中得到了修正。此外,在考虑粒子碰撞效应的动理学响应中,捕获热离子的非绝热共振贡献显著;而忽略粒子碰撞效应,捕获热电子的进动漂移共振贡献则更加显著。由此可见在高比压等离子体响应中考虑动理学效应的重要性,尤其是在考虑粒子碰撞效应时,需要考虑捕获粒子的非绝热共振贡献。

HL-2M装置内部输运垒湍流输运的GTC模拟研究

HL-2M托卡马克是我国新一代磁约束聚变等离子体装置,目前已经实现了等离子体电流1 MA的高参数运行模式。本文采用回旋动理学GTC(Gyrokinetic Toroidal Code)程序,研究了具有双输运垒结构的先进运行模式下该装置内部输运垒(Internal Transport Barrier,ITB)的湍流输运。研究结果表明:ITB湍流输运呈现两次连续饱和过程,计算获得的平均离子热扩散系数约为首次饱和水平的两倍。对湍流发展的极向谱和线性色散关系的研究表明,第一次饱和湍流输运由波长kθρi~2.15的短波模式主导,而第二次饱和以kθρi~0.49的长波模式主导;同时,体系湍流的能量由短波模式反向级联到长波模式,湍流饱和阶段径向热扩散系数在输运垒位置处呈现“M”形分布。考虑等离子体带状流结构,数值模拟结果表明:该运行模式下带状流对湍流输运饱和水平没有明显的影响。此外,输运垒等离子体温度和密度梯度最大处对应的湍流饱和期的径向离子热扩散系数最低,极大地增强了对等离子体的约束。