Spatial and angular distribution of the heavy ion charge under channeling in crystals

A kinetic theory of passage of multiply charged heavy ions through crystals is developed that allows for diffusion in the transverse momentum space and ion-crystal charge exchange. The theory provides an adequate explanation for the observed angular distributions of heavy ions passing through oriented crystals, makes it possible to calculate the partial angular distributions of different charge states, and treats the discovered effects of “cooling” and “heating” of channeled ion beams in physical terms. The angular and spatial distribution of channeled ions with different energies is calculated. Whether a channeled beam of multiply charged heavy ions will be cooled or heated is related to the dependence of the electron capture and loss probabilities on the impact parameter when the ions interact with atomic chains. This interaction governs the run of the angular and spatial distribution of the channeled ion charge.     

Effect of shell structure on transversal heating and cooling of channeled ions

It is shown that an abrupt change in ionization potential at the transition from one shell to the next one can result in a repeated transition from the heating of channeled ion beam to the cooling and vice versa with an increase in ion velocity.     

Quantitative evaluation of space charge effects of laser-cooled three-dimensional ion system on a secular motion period scale

In this paper,we introduce a method of quantitatively evaluating and controlling the space charge effect of a lasercooled three-dimensional(3 D) ion system in a linear Paul trap.The relationship among cooling efficiency,ion quantity,and trapping strength is analyzed quantitatively,and the dynamic space distribution and temporal evolution of the 3 D ion system on a secular motion period time scale in the cooling process are obtained.The ion number influences the eigen-micromotion feature of the ion system.When trapping parameter q is ~ 0.3,relatively ideal cooling efficiency and equilibrium temperature can be obtained.The decrease of axial electrostatic potential is helpful in reducing the micromotion heating effect and the degradation in the total energy.Within a single secular motion period under different cooling conditions,ions transform from the cloud state(each ion disperses throughout the envelope of the ion system) to the liquid state(each ion is concentrated at a specific location in the ion system) and then to the crystal state(each ion is subjected to a fixed motion track).These results are conducive to long-term storage and precise control,motion effect suppression,high-efficiency cooling,and increasing the precision of spectroscopy for a 3 D ion system.     

Space charge oscillation in electron cooling devices

Electron cooling is used for improving the parameters of ion beams. The cooling efficiency depends drastically on the space charge fluctuation intensity in the beam. The fluctuations present in the cooling region cause the stochastic heating of the ions, which adversely affects the cooling efficiency and may even annihilate the ion beam. The space charge fluctuation intensity as a function of various operating parameters of a cooler is studied experimentally. A mechanism of fluctuation generation is suggested, and the effect of fluctuations on the ion beam parameters is estimated.     

掺气效应：离子冷却或湍流加热效应的减弱的讨论

The question posed in the title concerns the explanation of a well-practised technique in ECR ion sources for increasing the output of the highest charge states of the ions of interest.For a long time the most accepted model was that of ion cooling,being a‘single-particle’effect.Two recent papers,likely inspired on earlier work,are proposing a‘collective’effect due to non-linear plasma-wave interaction,giving rise to turbulent heating.The mixing gas will in that picture reduce the heating.A few experiments are suggested to help unravel the problem of stating which effect is dominating.     

Zero-degree focusing of channeled ions and crystal rainbows

We analyze here theoretically the connection between the effect of zero-degree focusing of channeled ions and the crystal rainbow effect. The calculations were performed for Ne¹⁰⁺ ions and a 〈100〉 Si thin crystal. The ion energy was 60 MeV and the crystal thickness was varied between 630 and 750 atomic layers. These conditions correspond to the neighborhood of the first maximum of the zero-degree yield of the channeled ions. The obtained results show that the effect of zero-degree focusing is influenced strongly by the crystal rainbow effect.     

Simulation of the passage of multiply charged ions through crystals

The effect of charge exchange processes on the angular distributions of quasi-isotropic beams of multiply charged ions passed through oriented crystals has been numerically simulated and the recently found effects of cooling and heating of the ion beams have been interpreted.     

Precision laser spectroscopy without optical detection

Laser spectroscopy of trapped ions is likely to be limited by the availability of suitable detection systems for fluorescence photons, especially in the infrared transition frequency domain. This restriction can be circumvented when ions are stored in a Penning trap with an additional magnetic field inhomogeneity which couples the ion oscillation frequencies to the oscillation energies in a well-defined way. In such a case, laser cooling (or heating) on the optical transition of interest can be detected electronically by a corresponding shift of the ion oscillation frequency. Thereby, the transition of interest can be determined with high accuracy using only a single stored ion and in absence of any optical detection system.     

Potential energy of interaction between a fast multiply charged ion and crystal atoms with regard for the Pauli principle

Expressions for the potential energy of interaction between a fast neutral atom or a multiply charged ion and a crystal atom are obtained, both with and without regard for the Pauli principle. Results from computer simulation of the heating of silver ions with a fixed value of the charge state in passing through the (110) planar channel of a silicon crystal are presented. It is shown that the rate of dechanneling can be estimated by the form of the potential energy of interaction of an incident ion with a continuous potential of the planar crystal channel.     

Eu掺杂GaN薄膜的阴极荧光特性

通过MOCVD方法在蓝宝石衬底上生长GaN薄膜,利用离子注入方法将Eu³⁺离子注入到GaN基质中。X射线衍射结果表明：经过退火处理后,修复了部分离子注入所导致的晶格损伤。利用阴极荧光光谱可得到GaN∶Eu³⁺材料在623 nm处有很强的红光发射,该发射峰来源于Eu³⁺离子的内部4f能级跃迁。另外,Eu³⁺离子注入会在样品中引入电荷转移态,产生408 nm附近的发光。退火处理有助于获得更强的电荷转移态发光和Eu离子特征发光。GaN基质的黄光峰与Eu离子之间存在能量交换,将能量传递给Eu离子,促进Eu离子发光。     

Thermal acoustic radiation in model membranes at phase transition of lipids

The objects under investigation were model membranes, i.e., multilayer liposomes from phospholipids (dimyristoylphosphatidylcholine and dipalmitoylphosphatidylcholine). Thermal acoustic radiation was measured in the megahertz frequency range at phase transitions of lipids from a liquid crystal state to a gel (on cooling) and, vice versa, from a gel state to a liquid crystal (on heating of the liposome suspension). In this case, the intensity of thermal radiation varied, i.e., increased on cooling and decreased on heating. This effect was shown to be related to the increase in absorption in liposomes at the phase transition.     

Determination of ion quantity by using low-temperature ion density theory and molecular dynamics simulation

In this paper, we report a method by which the ion quantity is estimated rapidly with an accuracy of 4%. This finding is based on the low-temperature ion density theory and combined with the ion crystal size obtained from experiment with the precision of a micrometer. The method is objective, straightforward, and independent of the molecular dynamics(MD)simulation. The result can be used as the reference for the MD simulation, and the method can improve the reliability and precision of MD simulation. This method is very helpful for intensively studying ion crystal, such as phase transition,spatial configuration, temporal evolution, dynamic character, cooling efficiency, and the temperature limit of the ions.     

Resolution of the frozen-charge paradox in stopping of channeled heavy ions

The long-standing problem of the lacking signature of a Barkas effect in the stopping of swift heavy ions under channeling conditions has been analyzed theoretically. The stopping model provides explicit dependences on impact parameter and allows for projectile screening and higher-order Z(1) corrections. The analysis differentiates between principal target shells. A distinct Barkas correction is found in accordance with standard theory. It is less pronounced for channeled than for random stopping because of the dominance of outer target shells. Varying contributions from different target shells to the stopping force may give rise to an inversion of the commonly observed variation with ion energy and charge state of the Barkas correction.     

Poisson-Fokker-Planck model for biomolecules translocation through nanopore driven by electroosmotic flow

A non-continuous electroosmotic flow model (PFP model) is built based on Poisson equation, Fokker-Planck equation and Navier-Stokse equation, and used to predict the DNA molecule translocation through nanopore. PFP model discards the continuum assumption of ion translocation and considers ions as discrete particles. In addition, this model includes the contributions of Coulomb electrostatic potential between ions, Brownian motion of ions and viscous friction to ion transportation. No ionic diffusion coefficient and other phenomenological parameters are needed in the PFP model. It is worth noting that the PFP model can describe non-equilibrium electroosmotic transportation of ions in a channel of a size comparable with the mean free path of ion. A modified clustering method is proposed for the numerical solution of PFP model, and ion current translocation through nanopore with a radius of 1 nm is simulated using the modified clustering method. The external electric field, wall charge density of nanopore, surface charge density of DNA, as well as ion average number density, influence the electroosmotic velocity profile of electrolyte solution, the velocity of DNA translocation through nanopore and ion current blockade. Results show that the ion average number density of electrolyte and surface charge density of nanopore have a significant effect on the translocation velocity of DNA and the ion current blockade. The translocation velocity of DNA is proportional to the surface charge density of nanopore, and is inversely proportional to ion average number density of electrolyte solution. Thus, the translocation velocity of DNAs can be controlled to improve the accuracy of sequencing by adjusting the external electric field, ion average number density of electrolyte and surface charge density of nanopore. Ion current decreases when the ion average number density is larger than the critical value and increases when the ion average number density is lower than the critical value. Our numerical simulation shows that the translocation velocity of DNA given by the PFP model agrees with the experimental, results better than that given by PNP model or PB model.     

Polarization-based adjustable memory behavior in relaxor ferroelectrics

The irreversible decay of the spontaneous polarization above the phase-transition temperature is a limiting factor in any application of ferroelectric crystals. Here we show that electric fields applied at high temperatures induce a preferred direction in the crystal which is stable even after repeated heating and cooling through the phase transition. This preference in direction leads to a reorientation of domains in the ferroelectric phase. We use pyroelectric measurements to show that the directional preference originates from internal charge carriers interacting with domain walls.     

Laser cooling of recombining electron-ion plasma

A method of producing and confining ultracold electron-ion plasma with a strongly nonideal ion subsystem is considered. The method is based on the laser cooling of plasma ions by the radiation resonant with the ion quantum transition. A model is developed for the laser cooling of recombining plasma. Computer simulation based on this model showed that the ion nonideality parameter can be as large as ～100. The data obtained demonstrate that the production of ultracold nonideal plasma is quite possible.     

SMIS75金属离子的多重电离

A Simple Mirror Ion Source with 75GHz pumping(SMIS 75)has been created.The confinement system is a mirror trap with magnetic field in the plug up to 5T,variable length 15—20cm and mirror ratio 3—5.The plasma of metal ions is injected into the trap by a special vacuum arc minigun.Plasma heating is performed by the microwave radiation of a gyrotron(the frequency of 75GHz,power up to 200kW,pulse duration up to 150μs).The results of the experiment have demonstrated substantial multiple ionization of metal ions.For a metal with high melting temperature(Pt),heating shifts the average ion charge from Pt~(2 ) up to Pt~(7 ).Maximum stripped observed ion is Pt~(10 ).Total current of ion beam is about 300mA.     

Resonant coherent excitation of 94 MeV/u Ar17+ ions in the $$(2\bar 20)$$ planar channel of a silicon crystal

The charge exchange and characteristic x-radiation of channeled ions under resonant coherent excitation are simultaneously described in terms of the density matrix formalism. The survival fraction of 94 MeV/u Ar¹⁷⁺ ions in the \((2\bar 20)\) planar channel of a silicon crystal is calculated, and the angular distribution of x-ray emission of these ions is analyzed.     

Dark resonances as a probe for the motional state of a single ion

Single, rf-trapped ions find various applications ranging from metrology to quantum computation. High-resolution interrogation of an extremely weak transition under best observation conditions requires an ion almost at rest. To avoid line-broadening effects such as the second-order Doppler effect or rf heating in the absence of laser cooling, excess micromotion has to be eliminated as far as possible. In this paper the motional state of a confined three-level ion is probed, taking advantage of the high sensitivity of observed dark resonances to the trapped ion’s velocity. Excess micromotion is controlled by monitoring the dark-resonance contrast with varying laser-beam geometry. The influence of different parameters such as the cooling laser intensity has been investigated experimentally and numerically.     

Structural properties of two-component coulomb crystals in linear paul traps

We report on structural properties of two-component Coulomb crystals in a linear Paul trap. The crystals consist of two laser cooled ion species, 24Mg+ and 40Ca+. The lighter 24Mg+ ions form an inner cylindrical crystal structure surprisingly similar to that of an infinitely long single component crystal, while the outermost shell of the surrounding 40Ca+ ions have a spheroidal shape, which is highly insensitive to the presence of the 24Mg+ ions. Observed changes in the radial separation of the two ion species with the radius of the inner cylindrical crystal is explained by a simple model.