Effect of gas mixing on Xe ion currents from an ECR ion source

Gas mixing technique has been used in order to increase the current of highly charged ions of Xe at the TIFR-ECRIA. The He, N₂, O₂, Ne, and Ar are used as support gases, and their effect on output currents of Xe ions is studied. The effective ion charge and the total loss rate of ions are calculated from the measured currents. It is found that molecular gases, such as N₂ and O₂, exhibit better mixing effect in the enhancement of output of highly charged Xe ions. Furthermore, we describe this 14.5-GHz ECR ion source mounted on a high voltage (400 kV) deck, with its four beamlines, as well as the control system for the remote operation.     

辐射场的起伏对囚禁离子的量子相干性的影响

研究了囚禁离子与一随机相位的驻波场相互作用时的量子动力学行为,讨论了辐射场的起伏对囚禁离子的量子崩塌-回复特性的影响.对于相位扩散模型获得了这个问题的解析解.     

The observation of field-aligned current during type-III ELM in EAST

Measurements of current-carrying filaments associated with Type-III edge localized mode (ELM) have recently been made in the Experimental Advanced Superconducting Tokamak by direct probing of the edge plasma using an advanced, fast-moving electrostatic and magnetic probe system. Contrary to expectations, no current filaments were detected near the separatrix. However, a clear signature of current filament has been observed in the far scrape-off layer (SOL) where the difference of the voltage between the divertor plates connecting a filament is sufficiently large, thus strongly suggesting that the current-carrying filaments form in the SOL, rather than being ejected from the plasma inside the separatrix. These findings provide, for the first time, information on the formation and sustainment of current filaments during type-III ELMy H-modes.     

离子辅助沉积中离子束流密度的作用

测量了End-Hall离子源在不同条件下的离子束流密度，在不同离子束流密度下进行了Ar离子辅助沉积ZrO2薄膜的实验，研究了离子束流密度对薄膜折射率、晶相的影响.根据动量传递模型分析了离子束流密度对薄膜折射率的作用;根据热尖峰理论证明了一定条件下离子束流密度不会影响薄膜晶体结构.     

Drift-wave instability excited by field-aligned ion flow velocity shear in the absence of electron current

The drift wave is observed to be destabilized by a magnetic-field-aligned ion flow velocity shear in the absence of field-aligned electron drift flow in laboratory experiments using a concentrically three-segmented plasma source. The fluctuation amplitude increases with increasing a shear strength, but the instability is found to be gradually stabilized when the shear strength exceeds a critical value. The destabilizing and stabilizing mechanisms are well explained by a plasma kinetic theory including the effect of radial density gradient.     

Effect of a combined treatment using both direct and alternating electric currents on hide bacteria in hide-soak liquor

Inactivation effect of an electric current treatment combining both 188 μA/m² DC and 251 μA/m² AC on Gram negative, Gram positive bacteria and their mixed culture, which were isolated from hides, was separately analyzed. This electric treatment, applied for 16 min was found to be fairly effective in reducing the bacterial cell count (7.10–7.48 log₁₀ colony forming units/mL) to a relatively low level (4.52–4.90 log₁₀ colony forming units/mL). At this level bacterial damage to the hides is reduced in soak liquors. Cheap and efficient electric current may be applied to rapidly reduce the destructive bacterial populations in main hide-soak liquors.     

Effect of upflowing field-aligned electron beams on the electron cyclotron waves in the auroral magnetosphere

The role of low density upflowing field-aligned electron beams (FEBs) on the growth rate of the electron cyclotron waves at the frequencies ω _r < Ω_e, propagating downward in the direction of the Earth’s magnetic field, has been analysed in the auroral region at ω _e/Ω_e < 1 where ω _e is the plasma frequency and Ω_e is the gyrofrequency. The FEBs with low to high energy (E _b) but with low temperature (T _‖b) have no effect on these waves. The FEBs with E _b < 1 keV and T _‖b (> 1.5 keV) have been found to have significant effect on the growth rate. Analysis has revealed that it is mainly the T _‖b which inhibits the growth rate (magnitude) and the range of frequency (bandwidth) of the instability mainly in the higher frequency spectrum. The inhibition in the growth rate and bandwidth increases with increase in T _‖b. The FEBs with less E _b (giving drift velocity) reduce growth rate more than the beams with larger E _b. The inhibition of growth rate increases with the increase in the ratio ω _e/Ω_e indicating that the beams are more effective at higher altitudes.      

Effect of electric fields on the ion current signals in a constant volume combustion chamber

Ion current sensing has the potential to become a promising combustion diagnostic technique for mass productive engines. In this paper, the effect of electric fields on ion current signals measured from a series of methane/air flames in a constant volume combustion chamber (CVCC) is investigated both experimentally and numerically. Based on simultaneous flame Schlieren imaging and ion current measurement, the relation between the flame/electrodes contact area and the ion current signal waveform is explored under different electric field configurations. A CFD model, which incorporates flame plasma hydrodynamics, neutral/charged species reaction kinetics and ion-electric field interactions, is constructed. The effect of the electric field on the ion distribution and the charged species flux are analyzed, and the signal amplitude and timing are well predicted under the equivalence ratio range of Ф?=?0.7–1.1. Besides, the behavior of electrons, which is normally neglected in previous studies, is also analyzed in this work. The results show that it will affect the signal as well. The electron produced in the flame front zone can hardly diffuse into the pre-flame zone (<?350?K) even its mobility is 3-4 order higher than those of the positive ions. Therefore, the anode of the ion probe, which placed in the pre-flame zone, cannot detect the ion current signal until it contacts the flame front.     

不同体系下氢键对聚丙烯酰胺光谱的影响

采用红外,紫外光谱分析不同体系下氢键对部分水解高分子聚丙烯酰胺光谱的影响。研究表明,高分子聚丙烯酰胺中的酰胺基与部分水解的羧酸基能形成分子内氢键导致酰胺基中游离-NH₂特征吸收峰向低频方向移动;聚丙烯酰胺在水溶液中随浓度的增大主要形成分子内氢键使最大吸收波长发生红移;在含中等浓度钠离子和钙离子的水溶液体系下,分子内氢键和分子间氢键同时存在,在含高浓度钠离子和钙离子体系下,则主要形成分子间氢键。不同体系下,氢键对聚丙烯酰胺光谱的影响不同：在水溶液体系下,其最大吸收波长红移8 nm,在钠离子单独存在的体系下,最大吸收波长红移4 nm,在钙离子和钠离子同时存在的体系下,最大吸收波长红移2 nm。     

二维介观环中持续电流的梯度无序效应

基于紧束缚模型,考虑无序的梯度衰减,研究了无序-有序二维介观环体系中无序梯度及结构尺寸等因素对持续电流的影响.在表面无序区无梯度衰减时,持续电流随无序度的变化先减小后增大,观察到类弹道和局域性的转变.当存在梯度衰减时,无序区部分区域无序度相应减小,对有序区产生较强散射,典型电流比没有无序衰减时偏小.有趣的是,当无序度指数衰减时,上述类弹道和局域性的转变却消失了,揭示了介观实验中能否观察到该转变与无序的梯度分布密切相关.此外,计算表明表面无序渗透的深度和环的宽度对持续电流也有重要影响,呈现奇异的量子尺寸效应.这不同于以前的理论预言. 关键词： 介观环 梯度无序 持续电流     

Linear ion trap imperfection and the compensation of excess micromotion

Quantum computing requires ultracold ions in a ground vibrational state,which is achieved by sideband cooling.We report our recent efforts towards the Lamb-Dicke regime which is a prerequisite of sideband cooling.We first analyse the possible imperfection in our linear ion trap setup and then demonstrate how to suppress the imperfection by compensating the excess micromotion of the ions.The ions,after the micromotion compensation,are estimated to be very close to the Doppler-cooling limit.     

进气量对强流正离子源反向电子流的影响研究

分析了EAST-NBI离子源束引出过程中反向电子的产生及物理特性,对典型情况下的进气量对离子源的影响进行了计算和实验研究.实验结果发现,质子比受进气量影响较小,进气量与反向电子流呈明显正相关.     

Curvature and Zeeman effects on persistent currents in a multi-walledcarbon nanotorus

Taking into account both the intrinsic curvature and Zeeman effects, persistent currents in a multi-walled carbon nanotorus are explored by using a supercell method, within the tight-binding formalism. It is shown that in the absence of the Zeeman effect, the intrinsic curvature induces some dramatic changes in energy spectra and thus changes in the shape of the flux-dependent current. A paramagnetism--diamagnetism transition is observed. With consideration of the Zeeman splitting energy, the period of persistent current is destroyed, and a diamagnetism--paramagnetism transition is obtained at high magnetic field. In addition, we further explore the effect of external electric field energy (E_ef) on persistent current, indicating that it changes unmonotonously with E_ef.     

Measurement of the secular motion frequency and the space charge density in the linear ion trap

This paper reports that a cloud of laser-cooled 40 Ca + is successfully trapped and manipulated in the home-built linear ion trap constructed for quantum information processing (QIP).The frequency of the secular motion and the space charge density of the ion cloud are measured,which help knowing the characteristic of the trapping potential and are the prerequisite of QIP with the trapped ions.     

Generation of adjustable pure spin currents in negative-U systems

Single-particle sequential tunneling is studied through a negative-U center hybridized with a superconducting, a ferromagnetic, and a normal metal electrodes. In stark contrast to the case of positive U, the single-particle tunneling in attractive charging energy is usually prohibited by ground states with electrons in pairs. We find a microscopic mechanism to induce single-particle sates from pair states. As a consequence, in the nonpolarized metal terminal a remarkable pure spin current with no charge currents survives over a wide range of gate- and bias- voltages, which is rather crucial for experimental observation and design of spintronic devices. In addition, a significant spin-filter effect is presented in certain bias regime.     

磁场对介观耦合金属环中持续电流的影响

在考虑电荷是量子化的基础上，研究了外加磁场对介观耦合金属环中持续电流的影响.结果表明：由于存在耦合，介观金属环中总是存在附加的持续电流，附加的持续电流与电路参数及耦合系数有关.当外加磁通量按正弦规律变化时，介观耦合金属环中出现倍频与分频效应. 关键词： 介观耦合金属环 持续电流 磁场     

Spatial-temporal ion structures in the earth’s magnetotail: Beamlets as a result of nonadiabatic impulse acceleration of the plasma

The properties of high-energy ion beams (beamlets) observed in the boundary layer of the plasma sheet of the Earth’s magnetotail during short time intervals (1–2 min) have been considered. Beamlets are induced by nonlinear impulse accelerating processes occurring in the current sheet of the far regions of the geomagnetic tail. Then, moving toward the Earth along the magnetic field lines, they are detected in the magnetotail (in the plasma sheet boundary layer) and in the high-latitude part of the auroral zone in the form of short bursts of high-energy ions (with energies of several tens of keVs). The size of the localization region of the beamlets in the magnetotail and auroral zone has been determined by the epoch-superposition method, and it has been shown that beamlets are concentrated in a narrow region near the plasma sheet boundary, whose latitude size is no more than 0.8δ. This conclusion corroborates the theoretical prediction that the nonadiabatic resonant acceleration of ions occurs in a spatially localized region near the separatrix separating the open magnetic field lines and closed field lines, which contain the hot and isotropic plasmas of the plasma sheet. Based on the CLUSTER multisatellite measurements, the spatial structure of beamlets is analyzed and it has been found that the Alfvén wave arises due to the excitation of fire-hose instability at the instant of the exit of the ion beam from the current sheet to the high-latitude region of the far tail of the Earth’s magnetosphere. The longitudinal (along the magnetic field) and transverse sizes of a beamlet are estimated. It has been found that the beamlet is a dynamic plasma structure whose longitudinal size is several hundred times larger than its transverse size.     

囚禁离子在大失谐双色驻波场中的崩塌-回复特性

讨论了囚禁离子与两驻波场相互作用时的量子相干性.在大失谐的条件下,离子的振动能量呈现崩塌-回复的相干性特征,表明离子的振动态具有压缩效应.无量纲压缩参数G3愈大,囚禁离子的振动态压缩效应愈显著.进一步增大参数G3,所能得到的最大压缩反而减小.     

Influence of oxygen on the track etch rate along light ion trajectories in CR-39

The role of oxygen for stabilising radicals to form permanent damages in irradiated samples which are basically important for the etching process of track detectors has been studied. Samples of CR-39 were irradiated with 4 MeV -particles with a fluence of 30 000 particles per cm². The irradiations were performed in three different regimes:

• variation of out-gassing time in vacuum before irradiation;

• no out-gassing time but varied post-irradiation storage times in vacuum;

• variation of both storage times in vacuum before and after irradiation.

Generally, the absence of dissolved oxygen in the irradiated sample results in a decreased detection sensitivity in comparison with the detection properties and track parameters of samples irradiated in air. To determine the sensitivity the depth dependence of the track etch rate v_T(x) along the particle trajectory has been measured. From the observation of the dependence of the decreasing sensitivity on the post-irradiation storage time in vacuum, a lifetime of free radicals of 30 min could be derived. The amount of permanent damages responsible for the etching mechanism is related to the concentration profile of back-diffused oxygen and the REL-dependent radical concentration. This confirms previous results that the detection sensitivity is not a simple function of REL but depends on both REL and x the stronger the deeper within the irradiated sample.