Nature of monster sawteeth and their relationship to Alfven instabilities in tokamaks

A correlation is explored between the presence of energetic particle modes (EPM) and long-period sawtooth oscillations in tokamak plasmas heated by rf waves. The eventual crash of these sawteeth is explained in terms of the loss of the stabilizing fast particles due to the EPM. The absence of long-period sawteeth in high q(a) discharges is explained in terms of ion loss due to toroidal Alfven eigenmodes.     

Electronic and optical properties of SbSBr,SbSI and SbSeI

Band structures of SbSBr and SbSeI have been obtained by using the empirical pseudopotential method (EPM) to fit our measured optical reflectivity data and earlier gap measurements. An SbSI band structure has been determined by fitting to earlier reflectivity and Raman spectroscopic data, and the results agree better with the data than do the results of an earlier preliminary EPM calculation. Secondary conduction band minima may in part be responsible for the observed microwave oscillation (Gunn effect) in SbSI. Similar minima in SbSBr and SbSeI are reported, suggesting these crystals might also show microwave properties. The total densities of states are presented.     

Microwave preionization of the tokamak discharge at the electron cyclotron resonance

When ohmic heating power is applied during the microwave discharge at the electron cyclotron resonance, the plasma current and density build-up become fast and the loop voltage required to start the tokamak discharge decreases. The micro-wave burst observed in the initial stage is reduced and the burst of hard X-rays, occurring at the quasi-steady stage of discharge in the case of no microwave injection, disappears, suggesting that the production of run-away electrons is suppressed strongly.     

Dynamics of ionization processes during the interaction of a microwave pulse with plasma near hybrid resonance

We experimentally investigated the dynamics of ionization processes and the formation of a plasma wave channel during the interaction of intense microwave pulses with a magnetized inhomogeneous plasma in the presence of hybrid resonance. The competition between fast electron and slow ionization plasma nonlinearities was studied under conditions when the electron oscillation energy in the wave field was much higher than the atomic ionization energy of the working gas.     

Parametric channeling and collapse of beams of charged particles with internal structure in crystals: 2. Parametric processes during channeling of atomic ions, nuclei, and relativistic electrons in crystals

Features of parametric effects during channeling of atomic ions, nuclei, and relativistic electrons (positrons) in crystals were considered. It was shown that parametric coupling between ion channeling states in the field of crystal axes and planes and electronic states in the ion volume leads to the possibility of “parametric collapse” of the beam, i.e., a decrease in the oscillation amplitude of the atomic ion in the channel due to periodic transfer of the ion oscillation energy to the inner electron of the atom. The same effect can be used to cool beams due to energy transfer to intrinsic nuclear states with low energy levels. It was shown that parametric cooling of beams with a decrease in the transverse energy can also occur during axial channeling of relativistic electron beams. This process results from the parametric coupling between channeling states, which are caused by the particle charge and electron spin states in an effective magnetic field induced in the moving coordinate system.     

Dynamic of the Fluorescence of the Complex Zn++/Bis-N-Carbazolyl-Distyrylbenzene

The discrimination between similar concentrations of the different metal ions is one of the important roles of fluorescent sensors. Here we present the study of the fluorescence dynamic of the chromophore bis-N-carbazolyl-distyrylbenzene (BCDSB) in acetonitrile/water (mmol/L), doped with metal ions such as K+; Ca++; Mg++; Zn++(10 micromol/L). BCDSB has the fluorescence with lambda(max) at 448 nm by excitation at lambda(exc) = 378 nm, lifetime 1.089 ns: quantum yield of the fluorescence is 0.68. With continuation of irradiation fluorescence quenching has been registered for all investigated metal ions. However, in the presence of Zn++ oscillation of the intensity was observed. The energy activation of the oscillation as much as 15 kcal/mol was estimated. We believe, that the specificity of the complex Zn++/BCDSB, is in an asymmetrical structure, formed via binding sites of Zn++ with the electron-enriched binding sites of the BCDSB, excited in n(pi)* state. This asymmetrical complex structure can cause the photoinduced structural fluctuation in the complex coordination.     

Diffraction and attenuation of a tone burst in mono-relaxing media

The influence of intrinsic absorption in a relaxing medium and the resulting three-dimensional diffraction correction of the magnitude of the acoustic pressure averaged over the surface of a receiver is investigated for a tone burst. A rigorous formula for the damped acoustic pressure average at the receiver was obtained for arbitrary pulsed waves in a mono-relaxing medium. Depending on the pulse oscillation frequency, envelope duration, and relaxation frequency of the media, the plane wave burst envelope can be reduced, amplified, or otherwise deformed.     

Non-stationary characteristics of instability in a single-mode Nd:YVO 4 laser with fiber feedback

Random chaotic burst generation was experimentally observed in a single-mode microchip Nd:YVO₄ laser with fiber feedback. As the feedback strength was increased, a transition from stable relaxation oscillation state to unstable random chaotic burst state appeared. Furthermore, the non-stationary characteristic of probability association was experimentally identified at the transition of the two states while similar characteristics were reported only by numerical simulations of simple dynamical systems. This implies the general feature of non-stationary property of the dynamic switching between two states at transition. The observed chaotic burst generation and non-stationary nature were reproduced numerically based on the Lang-Kobayashi model. Received 28 March 2001 and Received in final form 5 June 2001     

Generation of currents in gases by fast, highly charged ions

It is shown that an exit asymmetry of the electrons and recoil ions formed during ionization of atoms in elementary collision events with fast, highly charged ions can give rise to macroscopic electron and recoil ion currents during the bombardment of a gaseous target by a beam of fast, highly charged ions. Zh. Tekh. Fiz. 68, 20–23 (September 1998)     

Sr离子自终止和复合激光交替振荡的动力学模型

建立了一个反映高重复率脉冲放电激励的Sr离子自终止激光和复合激光交替振荡的动力学模型，得到了与实测光电脉冲波形相一致的模拟结果.给出了He-Sr放电等离子中长寿命粒子、激光上下能级粒子数密度和电子温度随时间的演化过程.分析了两种激光交替振荡的发射过程、脉冲宽度特性和粒子数反转机理，认为在放电早期和余辉期电子温度的急剧升高和降低是Sr离子自终止和复合激光实现交替振荡的关键所在. 关键词： 自终止激光 复合激光 交替振荡 动力学模型     

低能质子环束流与等离子体相互作用过程的一维混合模拟研究

运用一维混合模拟方法, 研究了垂直于等离子体磁场入射的低能质子环束流与等离子体的相互作用过程. 结果显示: 由质子环束流激发的等离子体波首先经历指数式快速增长的线性阶段, 随后出现饱和、衰减和相对稳定的非线性阶段. 在线性阶段, 质子束投掷角散射使波模共振作用迅速减弱, 波的增长很快出现饱和. 随后, 持续的投掷角散射, 使入射质子在速度空间从环状分布渐变为均匀分布, 同时初始阶段的右手共振不稳定性逐渐消失, 在最后相对稳定阶段只存在阿尔芬波. 研究发现, 背景等离子体的有效加热始于非线性阶段, 等离子体波的形成有助于将质子束动能转换为背景等离子体的热能.     

Coherent control of photofragment separation in the dissociative ionization of IBr

We have investigated coherent control of the dissociative ionization of IBr using phase-controlled two-color omega+2omega laser pulses with an intensity of 1.0 x 10(12) W/cm and a pulse duration of 130 fs. The directional asymmetries of the photofragment angular distributions showed oscillation behavior dependent on the relative phase difference between the omega and 2omega pulses. The phase dependencies of the directional asymmetries observed for iodine ions and bromine ions were out of phase with each other. This result shows that a phase-controlled omega+2omega optical field can produce molecular orientation in which the optical field discriminates between parallel and antiparallel configuration of molecules that have a permanent dipole.     

Propeller tone bursts

Intense high frequency (25–38 kHz) tone bursts have been observed in acoustic tests of a scale model of a general aviation propeller. The amplitude of the tone burst is approximately equal to the amplitude of the propeller noise signature. The conditions necessary for the production of these tone bursts are described. The experiments indicate that the origin of these bursts is a periodic flow oscillation on the suction surface of the propeller blade tips which may be due to the interaction between an oscillating shock wave and a laminar boundary layer.     

The Sawtooth Oscillation Effect on Fast-Ion Energy Spectra in ITER Plasma and Neutral Particle Analyzer Measurements

ITER plasma with parameters close to those with the inductive scenario is considered. The distribution functions of fast ions of deuterium D and tritium T are calculated while taking into account the elastic nuclear collisions with alpha particles ⁴He using the code FPP-3D. The D and T energy spectra detected by the neutral-particle analyzer (NPA) are determined. The plasma mixing effect on these spectra during sawtooth oscillations is studied. It is shown that the NPA makes it possible to detect sawtooth plasma oscillations in ITER and determine the percentage composition of the D?T mixture in it both with the presence of instabilities and without them. A conclusion is drawn on the prospects of using NPA data in automatic controllers of thermonuclear fuel isotopic composition control and plasma oscillation regulation in ITER.     

Dynamics of double bubbles under the driving of burst ultrasound

This paper investigates the pulsations and translation of bubbles in a double-bubble system driven by burst ultrasound. Results illustrate that for two identical bubbles, decreasing the frequency of burst or increasing its amplitude can enhance the pulsations and improve the translation velocities of bubbles. In a certain scope, large bubble brings about fast translation velocity, but the velocity will fall down for too large bubble, such as the bubble with ambient radius over about its resonance radius. When the ambient radii of two bubbles are different, translation of the large bubble is smaller than that of the small bubble. In addition, the effect of initial distance between bubbles is described as well. If burst serials are used, shortening the time interval between each burst and improving the acoustic amplitude of bursts are beneficial for the translations of bubbles.     

Oscillations of Magnetized Dust Grains in Plasma Sheath with Negative Ions

The oscillations of a single magnetized dust grain in electronegative plasma sheath are investigated taking into account the existence of an external magnetic field. The influence of the content of negative ions and the magnetic field intensity on the properties of the dust vibration is analysed. The result shows that the existence of the negative ions in plasma reduces the dust oscillation frequency and drops the equilibrium position of dust, whereas the magnetic field raises the equilibrium position and also reduces the dust oscillation frequency on the condition considered.     

高产额脉冲堆爆发脉冲过程力学特性数值模拟

脉冲堆的性能主要受机械冲击引起的物理损伤的限制。高产额脉冲堆比CFBR-Ⅱ等金属铀脉冲堆追求更窄的脉冲宽度和更高的裂变产额,脉冲过程应力变化更加剧烈。为了获得高产额脉冲堆爆发脉冲过程中应力应变的分布,为新型脉冲堆设计和安全分析提供技术支持,基于圆柱型的铀钼合金快中子脉冲堆Godiva Ⅳ,以点堆方程以及MC(蒙特卡罗)方法对其中子产额以及功率分布进行了计算。并建立了快中子脉冲堆Godiva Ⅳ的三维模型,基于已知功率分布条件,利用有限元计算软件ANSYS Mechanical对其脉冲动态过程进行了瞬态的有限元计算,得到了Godiva Ⅳ圆柱型金属燃料在超临界脉冲爆发条件下的应力响应特性。     

Effects of angle of probe laser and pinhole diameter on the time-resolved optical inspection system

A real-time in-situ time-resolved optical inspection system comprising two He-Ne probe lasers, a digital oscilloscope, and three fast photodetectors is developed. The effects of angle of probe laser and pinhole diameter on the time-resolved optical inspection system are investigated during excimer laser crystallization. The longest melt duration and ablation excimer laser fluence are independent of pinhole size. The pinhole with a diameter of 0.3 mm is recommended to use in the time-resolved optical inspection system. Determination of melt duration and observation of explosive crystallization oscillation are independent of angle of probe laser, but four criteria for the relationship between probe lasers and photodetectors should be followed.     

Dense matter with eXTP

In this White Paper we present the potential of the Enhanced X-ray Timing and Polarimetry(eXTP) mission for determining the nature of dense matter; neutron star cores host an extreme density regime which cannot be replicated in a terrestrial laboratory. The tightest statistical constraints on the dense matter equation of state will come from pulse profile modelling of accretion-powered pulsars, burst oscillation sources, and rotation-powered pulsars. Additional constraints will derive from spin measurements, burst spectra, and properties of the accretion flows in the vicinity of the neutron star. Under development by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Sciences, the eXTP mission is expected to be launched in the mid 2020 s.     

Suppression of Hall-term effects by gyroviscous cancellation in steady collisionless magnetic reconnection

The formation of an ion-dissipation region, in which motions of electrons and ions decouple and fast magnetic reconnection occurs, is demonstrated during a steady state of two-dimensional collisionless driven reconnection by means of full-particle simulations. The Hall-term effect is suppressed due to the gyroviscous cancellation at scales between the ion-skin depth and ion-meandering-orbit scale, and thus ions are tied to the magnetic field. The ion frozen-in constraint is strongly broken by nongyrotropic pressure tensor effects due to ion-meandering motion, and thus the ion-dissipation region is formed at scales below the ion-meandering-orbit scale. A similar process is observed in the formation of an electron-dissipation region. These two dissipation regions are clearly observed in an out-of-plane current density profile.