激光等离子体中高能电子各向异性压强的粒子模拟

直接驱动惯性约束聚变(ICF)的实现需要对靶丸进行严格的对称压缩,以达到自持热核反应(点火)所需的条件.快点火方案的应用降低了对靶丸压缩对称性以及驱动能量的要求,但压缩及核反应过程中良好的靶丸对称性无疑有助于核反应增益的提高.本文研究了快点火方案中高能电子注入高密等离子体后导致的各向异性电子的压强张量.这一现象存在于ICF快点火方案中的高能电子束"点火"及核反应阶段.鉴于高能电子加热离子过程以及靶丸核反应自持燃烧过程的时间较长,高密靶核会由于超高的各向异性压强的作用破坏高密靶丸的对称性,降低核燃料密度,进而降低了核燃料燃烧效率以及核反应增益.     

Measurements of intrinsic ion Bernstein waves in a tokamak by collective Thomson scattering

In this Letter we report measurements of collective Thomson scattering (CTS) spectra with clear signatures of ion Bernstein waves and ion cyclotron motion in tokamak plasmas. The measured spectra are in accordance with theoretical predictions and show clear sensitivity to variation in the density ratio of the main ion species in the plasma. Measurements with this novel diagnostic demonstrate that CTS can be used as a fuel ion ratio diagnostic in burning fusion plasma devices.     

Complex ray tracing study of electron cyclotron resonance heating

In the up-to-date ray tracing study of electron cyclotron resonance heating (ECRH) of fusion plasmas, energy absorption effect has never been considered into the wave trajectory computation. Thus all the work has been done in real space so far. In this paper we consider coupling of energy absorption to wave trajectory for the first time, and numerically solve the formal complex Hamilton equations in complex space, then take the real-space-projected wave trajectories and group velocities to be the corresponding concrete ones. It is shown that both ordinary wave and extraordinary wave injected from the inner side of the tokamak plasmas approach the electron cyclotron resonance surface step by step and their group velocities become exceedingly small as they move toward this surface. Those clearly show that the resonance between the electron cyclotron waves and the fusion plasmas takes place in the electron cyclotron resonance region, which is just the case the ECRH experimental results and the plasma kinetic theory of waves demonstrate.     

Fast ignition of asymmetrically compressed targets for inertial confinement fusion

It is shown that fast ignition can ensure the combustion of asymmetrically compressed targets for inertial confinement fusion with an efficiency close to the combustion of one-dimensionally compressed targets. This statement is valid not only for targets specially designed for fast ignition. Fast heating by an external energy source can ensure the ignition of a target designed for spark ignition, but where this ignition does not occur because inhomogeneities are formed in the temperature and density distributions owing to the development of hydrodynamic instabilities. The condition for ignition is the fast heating of the plasma in the combustion initiation region whose size is comparable with the sizes of compression inhomogeneities. Thus, fast ignition not only significantly reduces the ignition energy, but also is possibly a necessary stage in the inertial confinement fusion scheme when the spherically symmetric compression of a target requires very high engineering and financial expenses. The studies are based on the numerical simulation of the compression and combustion of inertial confinement fusion targets with one- and two-dimensional hydrodynamic codes.     

Impact of electron exchange-correlation on drift acoustic solitary waves

The impact of electron exchange-correlation term on the linear and nonlinear quantum ion (QIA) acoustic drift waves in a highly degenerate plasma is investigated. An analytical approach is employed to derive the differential equation which is later on turned into Sagdeev energy integral equation that can be utilized to get drift solitons under existence conditions. It is noted that phase speed/frequency of the linear drift quantum ion acoustic (QIA) waves increases with electron exchange-correlation effect, but the amplitude of the corresponding solitons decreases with inclusion of these effects. Present study is carried out with reference to highly dense plasma environments like fast ignition inertial confinement fusion and white dwarfs etc.     

Plasma screening within Rydberg atoms in circular states

A Rydberg atom embedded in a plasma can experience penetration by slowly moving electrons within its volume. The original pure Coulomb potential must now be replaced by a screened Coulomb potential which contains either a screening length R_s or a screening factor A = R_s ^-1 . For any given discrete energy level, there is a Critical Screening Factor (CSF) A_c beyond which the energy level disappears (by merging into the continuum). Analytical results are obtained for the classical dependence of the energy on the screening factor, for the CSF, and for the critical radius of the electron orbit for Circular Rydberg States (CRS) in this screened Rydberg atom. The results are derived for any general form of the screened Coulomb potential and are applied to the particular case of the Debye potential. We also show that CRS can temporarily exist above the ionization threshold and are therefore the classical counterparts of quantal discrete states embedded into continuum. The results are significant not only to Rydberg plasmas, but also to fusion plasmas, where Rydberg states of multi-charged hydrogen-like ions result from charge exchange with hydrogen or deuterium atoms, as well as to dusty/complex plasmas.     

高能离子在稠密等离子体中的传输和能量沉积

用相对论福克-普朗克方程对高能离子在稠密氘氚等离子体中的碰撞动力学进行了研究，用球谐函数来展开方程的解：格林函数，然后简明地求出了不同能量质子和α粒子在等离子体中的停止时间、减速距离、纵向弥散距离和横向偏转距离.与以前研究离子在等离子体中运动的方法相比，没有假设高能离子在等离子体中损失能量远远小于入射离子能量，求解了纵向弥散距离；并且可以求解横向偏转距离.这些计算对实验上用高能离子加热冷的稠密等离子体，然后进行科学研究具有指导作用，并且可以用来研究快点火的可能性. 关键词： 高能离子 福克-普朗克方程     

Generation of Extra-Ordinary Mode Radiation by an Electrostatic Pump in a Two-Electron-Temperature Plasma

Coherent wave-wave coupling can produce radiation with a high efficiency. Recently, there has been a great deal of interest in the study of electro-magnetic wave generation in magnetized plasmas. We have investigated theoretically the effect of finite ion temperature on the parametric instability of an electro-static upperhybrid pump into an X-mode nonthermal radiation and low frequency ion waves in a two electron temperature plasma. The latter may include the lower-hybrid, the electron-acoustic and the ion-cyclotron waves. The loss cone distribution existing permanently at low altitudes acts as a free energy source generating the upper-hybrid waves. The upper-hybrid waves can also be present because of a linear instability produced by runaway electrons. Nonlinear dispersion relation and the growth rates are derived for each case using the hydrodynamical model. We find extra numerical factor arising due to the ions of finite temperature in the growth rate expression. This study may be useful in magnetosphere, auroral ionosphere, solar wind, solar radio bursts, and laboratory plasmas where ion has finite temperature and electrons have two distinct energy distributions.     

Screening corrections in cold deuterium fusion rates

We have recalculated the fusion rates of the free deuterium molecule, ion and mesomolecule taking into account the shielding of the Coulomb barrier by the electrons and muon. Electron screening increases the rates by several orders of magnitude. The fusion of hydrogen nuclei is known to be the source of energy of stars occuring in their high-temperature, high-pressure interiors. In terrestrial conditions, one attempts currently to tap this source of nuclear fusion energy by alternative techniques, i.e. high-temperature plasmas or muon-catalyzed fusion. Very recently cold fusion in solids has achieved worldwide attention, since experimental evidence for increased hydrogenic fusion rates in palladium and titanium has been reported[1,2]. These reports have motivated us to reconsider the fusion probability of free hydrogen molecules, ions and mesomolecules, following closely the studies of Refs. [3,4,5]. Our aim however is to improve the previous estimates of the respective fusion rates by taking account of the screening effects of the electrons and muons on the nuclear Coulomb barrier which will turn out to be quite important. As in Ref. [5] we will restrict our numerical results to deuterium only.     

Modulation of ion sound excitations in electron–ion plasmas with double spectral index distribution function

Theoretical investigation of amplitude modulation of ion sound waves is presented here for an electron–ion plasma where the electrons are dictated by the double spectral index (r, q) distribution function. Using the standard reductive perturbative technique, a non-linear Schrödinger (NLS) equation is derived that describes the evolution of modulated ion sound envelope excitations. Stability analysis of the NLS equation shows that the ion sound waves remain stable for the flat-topped and kappa-like distributions, but they can become unstable for the spiky electron velocity distribution. It is shown that changing the electron population in regions of low and high phase space density regions results in remarkable features that have no equivalent in ion sound waves with Boltzmannian electrons. Different types of localized ion sound excitations are plotted for the different shapes of the distribution functions controlled by the double spectral indices, and the underlying physics is discussed in detail. The present investigation may be beneficial to understand ion sound excitations in space plasmas where the distribution functions of the shapes presented here are frequently encountered by the satellite missions.     

Nonlinear Behavior of Electromagnetic Waves in Ultra‐Relativistic Electron‐Positron Plasmas

A set of nonlinear equations which can self‐consistently describe the behavior of high frequency Electromagnetic (EM) waves in un‐magnetized, ultra‐relativistic electron‐positron (e‐p) plasmas is obtained on the basis of Vlasov‐Maxwell equations. Nonlinear wave‐wave, wave‐particle interactions lead to the coupling of high frequency EM waves with low frequency density perturbations which result from EM waves radiation pressure. The same as that in conventional electron‐ion (e‐i) plasmas, strong EM waves in e‐p plasmas will give rise to density depletion in which itself are trapped. But on the contrary to that in e‐i plasmas, there no longer exists electrostatic acoustic–like wave in e‐p plasmas due to the absence of mass difference. For linear polarized EM waves, a stationary EM soliton with a spiky structure will be formed. The possible relation of the localized field to pulsar radio pulse is discussed (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dust ion‐acoustic solitons with trapped q‐non‐extensive electrons,dissipative processes,and streaming ions

The characteristics of dust ion‐acoustic waves (DIAWs) that are excited because of streaming ions and hot q‐non‐extensive electrons obeying a vortex‐like distribution are investigated. By exploiting a pseudo‐potential technique, we have derived an energy integral equation. The presence of non‐extensive q‐distributed hot trapped electrons and a streaming ion beam has been shown to influence soliton structure quite significantly. The evolution of the soliton‐like perturbations in complex plasmas, taking into account the dissipation processes, are also investigated, obtained by numerically solving the modified Schamel, equation whose widths are dependant on electron trapping efficiency β. Our illustrations indicate that compressive DIAWs develop in this plasma. As the plasmas in reality have a relative flow, such an analysis can be used to understand the DIA solitary structures observed in the mesospheric noctilucent clouds.     

Electron exchange-correlation effects on dispersion properties of electrostatic waves in degenerate quantum plasmas

Based on the quantum Magnetohydrodynamic (QMHD) model, the obliquely propagation of electrostatic waves in degenerate magnetized quantum plasmas with electron exchange-correlation effects are theoretically investigated. The modified linear dispersion relations of electrostatic waves are obtained and discussed in some specific cases. The analytical results clearly show that the dispersion properties of the high frequency electron waves (including the Langmuir wave and upper-hybrid wave) and the low frequency ion acoustic wave are modified by the quantum effects together with the electron exchange-correlation effects. The numerical results depict that the Langmuir wave and upper-hybrid wave can be unstable in the presence of the electron exchange-correlation effects, and it is also evidently indicated that the electron exchange-correlation effects can reduce the phase velocity of the waves, especially in the high wave number region. The corresponding results should be of relevance for identifying electrostatic fluctuations which transport in an inhomogeneous and magnetized quantum plasmas.     

Study of Coulomb collisional effects on the propagation of electromagnetic waves in a turbulent plasma

The presence of Weibel instability in laser-irradiated fuel could be detrimental to the process of ablative implosion, which is necessary for achieving thermonuclear fusion reactions. In this paper, the effect of the Coulomb collisional within the turbulent plasma on the Weibel instability growth rate has been investigated for linear and circular polarization. The results indicate that the Weibel instability growth rate at circular polarization near the ignition centre of the fuel fusion (collisional plasma) is about 10⁵ times higher than the collisional Weibel instability growth rate at linear polarization. The Weibel instability growth rate is observed near the critical density of the fuel fusion (collisionless plasma) at linear polarization and enhancement near the foot of the heat in front of the fuel fusion. By increasing the steps of the density gradient plasma in the low-density corona, electromagnetic instability occurs at a higher stress flow. Therefore, the deposition condition of electron beam energy in circular polarization of turbulent plasma can be shifted to the fuel core for suitable ignition.     

离子-电子非平衡机制降低中心热斑点火条件

提出通过离子-电子非平衡物理模型来降低惯性约束聚变中心热斑点火的聚变点火条件。在该物理模型中,强调离子比电子具备更高的温度,从而使得热斑的热核聚变反应增强,轫致辐射和电子热传导造成的能量漏失相对降低。通过对中心热斑的自加热分析和热斑燃烧动力学分析,发现相对于平衡聚变点火模型,非平衡模型可以显著扩大聚变点火区在热斑面密度和热斑温度空间的范围。同时采用LARED-S程序的数值模拟,研究了通过尖峰脉冲波形、二次冲击物理机制强化中心热斑聚变点火的非平衡性。     

Collisionless Drift Waves Ranging from Current‐Driven,Shear‐Modified,and Electron‐Temperature‐Gradient Modes

The specific history of collisionless drift waves is marked by focusing upon current‐driven, shear‐modified, and electron‐temperature‐gradient modes. Studies of current‐driven collisionless drift waves started in 1977 using the Innsbruck Q machine and was continued over 30 years until 2009 with topics such as plasma heating by drift waves in fusion‐oriented confinement and space/astrophysical plasmas. Superposition of perpendicular flow velocity shear on parallel shear intensively modifies the drift wave characteristics through the variation of its azimuthal structure, where the parallel‐shear driven instability is suppressed for strong perpendicular shears, while hybrid‐ion velocity shear cause unexpected stabilization of the parallel‐shear‐modified drift wave. An electron temperature gradient can be formed easily by control of thermionic electron superimposed on ECR plasma, and is found to excite low‐frequency fluctuation in the range of drift waves (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

基于现役装置的冲击点火可行性概念研究

以冲击点火物理特性的研究为基础, 分析冲击点火对高功率激光驱动器的物理需求, 然后从总体层面概括给出基于现役装置(神光III等间接驱动中心点火高功率激光装置) 研究冲击点火面临的关键技术问题. 研究表明, 基于现役装置的冲击点火主要面临两个层面的问题, 首先是非均匀光路排布下实现均匀辐照的工程层面问题, 其次是在现役装置上高效实现冲击点火激光脉冲的激光技术层面问题. 通过研究 分别对两个层面的问题提出相应的解决思路, 为后续研究奠定基础.     

离子-电子非平衡机制降低中心热斑点火条件

提出通过离子-电子非平衡物理模型来降低惯性约束聚变中心热斑点火的聚变点火条件。在该物理模型中,强调离子比电子具备更高的温度,从而使得热斑的热核聚变反应增强,轫致辐射和电子热传导造成的能量漏失相对降低。通过对中心热斑的自加热分析和热斑燃烧动力学分析,发现相对于平衡聚变点火模型,非平衡模型可以显著扩大聚变点火区在热斑面密度和热斑温度空间的范围。同时采用LARED-S程序的数值模拟,研究了通过尖峰脉冲波形、二次冲击物理机制强化中心热斑聚变点火的非平衡性。     

HT-7 Tokamak离子回旋波和低杂波等离子体逃逸电子行为研究

HT-7 Tokamak拥有离子回旋波(ICRF)和低杂波(LHW)两套加热系统.ICRF主要对加热离子有比较好的加热效果,LHW则主要是通过电子Landau阻尼加热电子.除此之外,在ICRF和LHW协同加热的条件下,可以对等离子体产生更有效的加热效果,增加等离子体的聚变反应截面,增加聚变中子产额.本文报道了LHW对改善ICRF和等离子体耦合的重要作用,ICRF和LHW加热等离子体中电子温度随时间的演化过程,计算了放电过程中电子逃逸的阈值能量,分析了逃逸电子的产生过程,以及放电过程中的中子产额.研究结果发     

Ion acoustic solitary waves with adiabatic ions in magnetized electron-positron-ion plasmas

Linear and nonlinear ion acoustic waves in the presence of adiabatically heated ions in magnetized electron-positron-ion plasmas are studied. The Sagdeev potential approach is employed to obtain the energy integral equation in such a mulitcomponent plasma using fluid theory. It is found that electron density humps are formed in the subsonic region in magnetized electron-positron-ion plasmas. The amplitude of electron density hump is decreased with the increase of hot ion temperature in electron-positron-ion plasmas. However, the increase in positron concentration and obliqueness of the wave increases the amplitude of nonlinear structure. The increase in positron concentration also reduces the width of the nonlinear structure in a magnetized multicomponent plasma. The numerical solutions in the form of solitary pulses are also presented for different plasma cases. The results may be applicable to astrophysical plasma situations, where magnetized electron-positron-ion plasma with hot ions can exist.