Numerical Simulation of Nonlinear Effects in the Weibel Instability

Radiophysics and Quantum Electronics - We analyze in detail the nonlinear effects taking place in an anisotropic plasma at different stages of the Weibel instability using a new approach to the...     

Collisional Efect on Weibel Instability with Semi-Relativistic Maxwellian Distribution Function

In this paper,the Coulomb collisional efect of electron-ion on the growth rate of Weibel instability is investigated based on the semi-relativistic Maxwellian distribution function in dense and unmagnetized plasma.An analytical expression was derived for the dispersion relation of Weibel instability for two limit cases|ξ=ω′/k|| T|||≥1 and |ξ|≤1.In limit|ξ|≥1 the dispersion relation only includes a real part and in limit|ξ|≤1 the imaginary part of the frequency of waves’instability plays a role in the dispersion relation.In limit≤|ξ|1,the two quantitiesμandη,that are due to the relativistic and collisional efects,will appear in the growth rate of Weibel instability.The growth rate of Weible istability will be increased through decreasing the Coulomb collisional frequency and also increasing the temperature anisotropic parameter in strong relativistic limit.     

Collisional Effect on Weibel Instability with Semi-Relativistic Maxwellian Distribution Function

In this paper, the Coulomb collisional effect of electron-ion on the growth rate of Weibel instability is investigated based on the semi-relativistic Maxwellian distribution function in dense and unmagnetized plasma. An analytical expression was derived for the dispersion relation of Weibel instability for two limit cases [ξ = ω＇/k‖T‖ 〉〉 1 and ｜ξ｜ 〈〈 1. In limit ｜ξ｜ 〉〉 1 the dispersion relation only includes a real part and in limit ｜ξ｜ 〈〈 1 the imaginary part of the frequency of waves＇ instability plays a role in the dispersion relation. In limit ｜ξ｜ 〈〈 1, the two quantities μ and η, that are due to the relativistic and collisional effects, will appear in the growth rate of Weibel instability. The growth rate of Weible istability will be increased through decreasing the Coulomb collisional frequency and also increasing the temperature anisotropic parameter in strong relativistic limit.     

Weibel Instability Growth Rate in Magnetized Plasmas with Quasi-Relativistic Distribution Function

The mechanism of the Weibel instability is investigated for dense magnetized plasmas. As we know, due to the electron velocity distribution, the Coulomb collision effect of electron-ion and the relativistic properties play an important role in such study. In this study an analytical expression for the growth rate and the condition of restricting the Weibel instability are derived for low-frequency limit. These calculations are done for the oscillation frequency dependence on the electron cyclotron frequency. It is shown that, the relativistic properties of the particle lead to increasing the growth rate of the instability. On the other hand the collision effects and background magnetic field try to decrease the growth rate by decreasing the temperature anisotropy and restricting the particles movement.     

Weibel Instability Growth Rate in Magnetized Plasmas with Quasi-Relativistic Distribution Function

The mechanism of the Weibel instability is investigated for dense magnetized plasmas. As we know, due to the electron velocity distribution, the Coulomb collision effect of electron-ion and the relativistic properties play an important role in such study. In this study an analytical expression for the growth rate and the condition of restricting the Weibel instability are derived for low-frequency limit. These calculations are done for the oscillation frequency dependence on the electron cyclotron frequency. It is shown that, the relativistic properties of the particle lead to increasing the growth rate of the instability. On the other hand the collision effects and background magnetic field try to decrease the growth rate by decreasing the temperature anisotropy and restricting the particles movement.     

Quasi Exact Model for the Anisotropy Driven Weibel Instability all over Fourier Space

The Weibel instability is prompted by a temperature anisotropy within a plasma. We investigate its growth rate for wave vectors making an arbitrary angle with the high temperature axis. We use a two temperatures waterbags model and derive stability conditions depending on both temperatures and wave vector orientation. It is found that the growth rate is maximum for wave vectors normal to the high temperature axis. Also, a critical angle is evidenced in the k space in which direction modes are unstable at high k although the growth rate decreases quickly in this direction. Exact results are derived in most cases. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Gyrotron Electron Beams: Velocity and Energy Spread and Beam Instabilities

The stability of the electron beams and maximum share of the electrons oscillatory energy, i.e. finally efficiency, power, and pulse duration of the gyrotron to a considerable extent depend on the velocity and the energy spread (VESP) of the HEB. The basic factors determining VESP in the helical beams are discussed. Among these factors static (initial velocities, cathode heterogeneities, space charge fields) and dynamic (negative mass and diochotron instabilities and a global instability connected with the capture of the electrons in the gyrotron adiabatic trap) factors are considered. Qualitative models of the excitation of the space charge oscillation as well the parasite electromagnetic radiation of the HEB are developed. Some experimental data of the investigation of the parasitic electromagnetic radiation spectrum in one gyrotron are discussed. The methods of the experimental investigation of the VESP are described.     

北京正负电子对撞机中的束流光电子不稳定性研究

高能储存环中的正电子束流辐射出光子,打在束流管道壁上产生光电子并形成电子云;多束团正电子束流与电子云相互作用,有可能发生的不稳定性,称为束流光电子不稳定性.这种不稳定性有可能在下一代高能正负电子对撞机的束流中发生,因此对这种束流不稳定性的研究,也有很重要的实际意义.文章讨论了在北京正负电子对撞机(BEPC)上开展的束流光电子不稳定性实验和模拟分析研究.     

Effects of Ions Charge-Mass Ratio on Energy and Energy Spread of Accelerated Ions in Laser Driven Plasma

Effects of ions charge-mass ratio on energy and energy spread of accelerated ions in laser driven plasma are investigated in detail by proposing a simple double-layer model for a foil target driven by an ultrastrong laser. The radiation pressure acceleration mechanism plays an important role on the studied problem. For the ions near the plasma mirror, i.e. electrons layer, the dependence of ions energy on their charge-mass ratio is derived theoretically. It is found that the larger the charge-mass ratio is, the higher the accelerated ions energy gets. For those ions far away from the layer, the dependence of energy and energy spread on ions charge-mass ratio are also obtained by numerical performance. It exhibits that, as ions charge-mass ratio increases, not only the accelerated ions energy but also the energy spread will become large.     

The impact Of impurity ion in deuterium-tritium fuel on the energy deposition pattern Of The Proton Ignitor Beam

The ignition stage of deuterium-tritium fuel in inertial confinement fusion is a challenging task affected by many undesirable processes especially material mixing processes in the hot-spot region. In this research, an alternative proposal of the enhanced energy deposition in the proton fast ignition has been suggested. It consists of two primary assumptions of the beam-plasma system. In the first place, we have adopted the proton beam generated by TNSA or RPA mechanisms, each described by a Maxwellian or Gaussian energy distributions. Next, a realistic, non-uniform fuel plasma was adopted. Then, the cumulative stopping power of a proton beam of 10 kJ energy, penetrating the low content metal-contaminated deuterium-tritium fuel has been examined. It has been shown that in the case of the very low impurity fractions, irregular spatial fluctuations in the cumulative stopping power relative to pure fuel plasma emerges. However, at the higher concentrations, a systematic pattern becomes visible such that the contribution of the deep layers in the stopping power reduces. We observe the enhanced energy deposition close to the corona/dense core interface. It has been shown that the corona/dense core energy deposition ratio differs by up to 2.5% between pure and contaminated DT plasma. In the contaminated fuel plasma, energy deposition in the TNSA regime will effectively heat the plasma corona. While in the RPA counterpart, at a similar level of contamination, most of the incident beam energy remains inside the core fuel region.     

On the Plasma Beam Instability of the Space Limited Electron Beam in a Magnetic Field

The present paper considers the plasma-beam instability of a space limited electron beam in a strong magnetic field (ω_H ? ω_o). The form of the beam was taken to be both cylindrical and plane. The threshold of the non-linear regime turned out to be weakly dependent on the beam form and independent of the magnetic field intensity. It is defined by the current and the directed velocity of the beam particles.     

激光等离子体相互作用中自生磁场及其空间演化

利用粒子模拟程序,模拟研究了超强激光与等离子体相互作用中的电子束流不稳定性的产生机制,得到了不稳定性所激发的自生磁场的线性增长率与各向异性参数之间的函数关系。观察到了激光与等离子体相互作用时产生的饱和自生磁场在表面领域上的演化过程,发现沿x方向出现的电流比较大时,饱和自生的磁场在z方向的发展比较快,临界面附近较大,但随着深度的增加,逐渐以指数形式减少。     

Energy Gain Investigation in Fast Ignition ICF with Electron Ignition Beam by Changing Fuel Characteristics

Fast ignition is a method in inertial confinement fusion （ICF） in which an ignition spark in pre-compression fuel is formed by an ultra-intense laser beam. In applying this method, a hot spot is built by relative electrons which are produced by the ultra-intense laser beam. For a better understanding, a fuel energy gain curve based on density is drawn and it can be observed that the ignition by an electron beam has the maximum energy gain. The maximum energy gain has been observed in equimolar DT fuel with a density of 500g/cma and in fuel with tritium （10%） with a density of 1000g/cm^3.     

合肥同步辐射光源上的束腔不稳定性研究

束腔相互作用激发的束流不稳定性是目前高能电子加速器上最重要的不稳定性之一。本文从粒子纵向运动基本方程出发,详尽分析了单束团和多束团情况下束腔纵向偶极不稳定性,并给出了我国合肥同步辐射光源上的计算和实验结果。     

Measurement of the VEPP-4M Collider Energy Spread in the Entire Energy Range

Physics of Particles and Nuclei Letters - The energy spread of the VEPP-4M electron–positron collider at the Budker Institute of Nuclear Physics was measured in the 1100–4750 MeV range...     

Salient characteristics of the Ignitor experiment

Summary The Ignitor experiment was the first proposed and designed on the basis of existing technologies in order to study the conditions where the charged fusion reaction products of a deuterium-tritium, magnetically confined plasma can deposit their energy in the plasma and compensate for all its forms of thermal-energy loss. The proposal of this experiment was made possible by the discovery, through the Alcator line of experiments, of a relevant law governing the confinement of the plasma thermal energy. The Alcator experiments are characterized by high-plasma-density regimes, high magnetic fields and compact dimensions. A set of criteria to compare the potential performance of existing and future experiments is discussed. The long-range evolution of the Alcator-Ignitor line of experiments is pointed out and shown to open the possibility to verify the fusion burn condition of deuterium-deuterium or deuterium-helium 3 (the so-called clean fusion) plasma mixtures. In fact, the present design parameters of Ignitor allow for the confinement of the charged particle products of all these reactions.

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Riassunto Ignitor è il primo esperimento ad essere proposto e progettato sulla base di tecnologie esistenti per studiare le condizioni in cui, in un plasma di deuterio-trizio confinato magneticamente, le particelle cariche prodotte dalle reazioni di fusione depositano nel plasma la loro energia compensando in questo modo tutte le possibili perdite. L'ideazione di questo esperimento è stata resa possibile dalla scoperta, ottenuta con gli esperimenti Alcator, di una importante legge che è alla base delle proprietà di confinamento dell'energia termica in un plasma. Gli esperimenti Alcator sono caratterizzati da regimi di plasma di elevata densità, da forti campi magnetici e strutture e dimensioni compatte. In questo articolo si esaminano anche alcuni criteri atti a paragonare le potenzialità e le prestazioni di esperimenti presenti e futuri. Si indica inoltre come lo sviluppo a lungo termine della linea Alcator-Ignitor permetta di verificare le condizioni di accensione termonucleare di un plasma composto da deuterio-deuterio o da deuterio-elio 3 (il combustibile cioè della cosiddetta fusione pulita). In effetti i parametri di progettazione attuali di Ignitor sono piú che sufficienti per ottenere il confinamento delle particelle cariche prodotte da entrambe queste reazioni di fusione.

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Резюме Эксперимент ?Игнитор? был предложен и спланирован на основе существующей технологии, чтобы исследовать условия, при которых заряженные продукты реакции синтеза в магнитно удерживаемой длазме дейтерия и трития могут выделять свою энергию в плазме и компенсировать все формы тепловых энергетических потерь. Предложение этого эксперимента стало возможным благодаря открытию соответствующего эакона, определяющего удержание тепловой энергии в плазме, в экспериментах на Алкаторе. Эксперименты на Алкаторе характеризуются высокой плотностью плазмы, высокими магнитными полями и компактными размерами. Обсуждается система критериев для сравнения потенциального вьшолнения настоящих и будущих экспериментов. Отмечается долгосрочная эволюция экспериментов на линии ?Алкатор-Игнитор?. Показывается, что открывается возможность проверки условий синтеза в плазменных смесях дейтерия и дейтерия или дейтерия и гелия-три (так называемый чистый синтез). Действительно, предполагаемые параметры Игнитора допускают удержание заряженных частиц-продуктов всех зтих реакций.

     

同步加速器中束流能量的修正

叙述了同步加速器中束流能量测量和修正的原理,推导出关于闭合轨道畸变和校正二极子强度的束流能量的修正公式,介绍了这些公式在北京正负电子对撞机（BEPC）上的应用,并对其结果进行了讨论．     

Runaway Electron Beam Instability in Slide-Away Discharges in the HT-7 Tokamak

Slide-away discharges are achieved by decreasing the plasma density or ramping down the plasma current in runaway discharges in the HT-7 tokamak. In the case of plasma current ramp down, the ratio of the electron plasma frequency to the electron cyclotron frequency is higher than in the stationary pulses when the discharge goes into a slide-away regime. The instability regime is characterized by relaxations in the electron cyclotron emission due to relativistic anomalous Doppler effect which transfers energy from parallel to perpendicular motion. The triggering of relativistic anomalous Doppler effect at higher density by ramping down of plasma current may provide a alternative runaway energy control scenario.