超晶格量子阱的沟道辐射及其谱分布

在经典物理框架内和偶极近似下, 导出了超晶格量子阱沟道辐射频率和辐射谱分布。指出了对于自发辐射谱分布, 存在一个普适的线型因子, 而粒子的最大辐射能量与相对论因子γ 有关, 且与γ3/2成正比。以正弦平方势为例进行了具体讨论。结果表明, 由于势阱深度和噪音的影响, 谐波数l只取少数几个值。超晶格量子阱沟道辐射只存在不多的几条谱线, 为进一步应用提供了可能。最后, 还给出了一种可能的实验方案, 讨论了如何利用弯晶把超晶格量子阱的沟道辐射改造为相干辐射。 In the frame of classical physics and the dipole approximation the radiation frequency and the spectral distribution are derived for the channeling radiation of a charged particle in a superlattice quantum well. It indicated that there is a line type factor f(ξ) suited to various cases in the spontaneous radiations spectrum. Results also show that the maximum radiation energy is proportional to γ3/2 , but the relativistic effects have double effects in the spontaneous radiation of a charged particle. The case for the sine squared potential is discussed specifically. The harmonic number can be defined as a few variable values by the effects of the potential well depth and noise. In general there is a few spectral lines in the channeling radiation spectrum for the superlattice quantum well, and possibilities are provided for further application. Finally, a possible experimental scheme is proposed, and it is discussed that how to transform the channeling radiation in the quantum well into the cohenent radiation by the bent crystal.     

高能电子和正电子在晶体沟道中的辐射

介绍了高能电子和正电子在晶体中的沟道辐射,对超相对论电子和正电子在周期弯曲晶体中的相干辐射进行了分析,并提出了初步的实验设想. The channeling radiation of high energy electrons and positrons in crystals was introduced. According to the new idea proposed by A.V.Korol, the coherent radiation of ultra relativistic electrons and positrons channeled in periodically bent crystals was analyzed. The characteristics of the radiation were obtained by using classic electromagnetic theory and a tentative experimental plan for testing was suggested.     

Performance of the plugged-in ^22Na based slow positron beam facility

The Beijing intense slow positron beam facility is based on the 1.3GeV linac of Beijing Electron-Positron Collider (BEPC) aiming to produce mono-energetic intense slow positron beam for material science investigation. The plugged-in ²²Na based slow positron beam section has been newly constructed to supply continuous beam time for the debugging of positron annihilation measurement stations and improve the Beijing intense slow positron beam time using efficiency. Performance testing result of the plugged-in ²²Na based slow positron beam facility are reviewed in this paper, with the measurement of the beam transport efficiency, the view of beam spot, the adjustment of beam position, the measurement of beam intensity and energy spread etc. included.     

正弦平方势与环形加速器的弯晶束流引出

在经典力学框架内和偶极近似下, 引入正弦平方势, 把粒子在弯晶中的运动方程化为具有固定力矩的摆方程。 利用Jacobian椭圆函数和椭圆积分分析了系统的相平面特征。 导出了弯晶的最大偏转能量、 退道系数和退道长度。 计算结果表明, 对于曲率半径为1 m, 能量为1.0 GeV的质子, Si(110)面沟道的引出效率为70%; 对于MeV范围的粒子, 退道长度大约是μm量级; 对于TeV范围的粒子, 退道长度可达1 m以上。 In the classical mechanics frame and the dipole approximation the particle motion equation in bent crystal is reduced to the pendulum equation with a constant momentum by using the sine squared potential.The phase planar properties are analysed by means of Jacobian elliptic function and the elliptic integral. The maximum deflected energy, the dechanneling factor and the dechanneled length are derived. The results show that the extrated efficiency is 70% for a proton beam with energy E=1.0 GeV moved in the channel on Si(110) if a radius of curvature R=1 m; and dechanneled length is of the order of μm for the particles with MeV energy; the dechanneled length is above 1 meter for the particle with TeV energy.     

Study of the e+ e－ to hadrons via ISR at BABAR

Experimental data from the PEP-II B-factory at 10.6 GeV center-of-mass （c.m.） energy, obtained via initial-state radiation （ISR） with the BABAR detector, are presented. The cross sections for many hadronic processes have been measured from the production threshold to 4-5 GeV of the e^＋e^- c.m. energy. The obtained data allow to study a number of intermediate states and determine the parameters of known resonances and their branching fractions. The exclusive cross section for some number of hadronic sub-processes are presented.     

A waveguide polarizer based on Si-coated Ti:LiNbO_3 planar structure

A novel design of a transverse magnetic (TM)-pass waveguide polarizer based on Si on an X-cut, Y-propagatiou Ti:LiNbO3 planar waveguide is presented. The eigenvalue functions of such structure have been obtained by using Wenzel-Kramers-Brillouin (WKB) method with modified Airy functions. The intervals of the silicon thickness have been found which result in transverse electric (TE) light suffering strong attenuation while TM wave propagating with fairly low loss. A planar waveguide polarizer is fabricated and its polarization-dependent measurements lead to the best polarization extinction ratio ~ 34 dB and the insertion loss < 0.4 dB.     

A compact positron annihilation lifetime spectrometer

Using LYSO scintillator coupled on HAMAMATSU R9800 (a fast photomultiplier) to form the small size γ-ray detectors, a compact lifetime spectrometer has been built for the positron annihilation experiments. The system time resolution FWHM=193 ps and the coincidence counting rate ～8 cps/μCi were achieved. A lifetime value of 219±1 ps of positron annihilation in well annealed Si was tested, which is in agreement with the typical values published in the previous lectures.     

Spatial dependent diffusion of cosmic rays and the excess of primary electrons derived from high precision measurements by AMS-02

The precise spectra of Cosmic Ray(CR) electrons and positrons have been published by the measurement of AMS-02. It is reasonable to regard the difference between the electron and positron spectra(?Φ = Φ_(e-)-Φ_(e+)) as being dominated by primary electrons. The resulting electron spectrum shows no sign of spectral softening above 20 GeV, which is in contrast with the prediction of the standard model of CR propagation. In this work, we generalize the analytic one-dimensional two-halo model of diffusion to a three-dimensional realistic calculation by implementing spatial variant diffusion coefficients in the DRAGON package. As a result, we can reproduce the spectral hardening of protons observed by several experiments, and predict an excess of high energy primary electrons which agrees with the measurement reasonably well. Unlike the break spectrum obtained for protons, the model calculation predicts a smooth electron excess and thus slightly over-predicts the flux from tens of GeV to 100 GeV. To understand this issue, further experimental and theoretical studies are necessary.     

Gain of harmonic generation in high gain free electron laser

In a planar undulator employed free electron laser (FEL), each harmonic radiation starts from linear amplification and ends with nonlinear harmonic interactions of the lower nonlinear harmonics and the fundamental radiation. In this paper, we investigate the harmonic generation based on the dispersion relation driven from the coupled Maxwell-Vlasov equations, taking into account the effects due to energy spread, emittance, betatron oscillation of electron beam as well as diffraction guiding of the radiation field. A 3D universal scaling function for gain of the linear harmonic generation and a 1D universal scaling function for gain of the nonlinear harmonic generation are presented, which promise rapid computation in FEL design and optimization. The analytical approaches have been validated by 3D simulation results in large range.     

Synergistic Effect of Triple Ion Beams on Radiation Damage in CLAM Steel

The synergistic effect of triple ion beams is investigated by simultaneous and scquential irradiations of gold, hydrogen and helium ions on the low activation martensitie steel （CLAM） developed in China. The depth profile measurements of the positron annihilation Doppler broadening S parameter are carried out as a function of slow- positron beam energy to examine the produced radiation damage. The synergistic effect of displacement damage and hydrogen and helium on the formation of radiation damage is clearly observed. In the preset case ,this effect suppresses the radiation damage in the CLAM steel due to the helium and/or hydrogen filling of vacancy clusters.     

Channeling radiation of electrons and positrons in diamond and silicon at intermediate energies: Theory and experiment

Both positron and electron channeling radiation peak energies corresponding to the planar channels in diamond and silicon are calculated and compared with experimental ones at particle energies of 28-56 MeV. The potential model used is an approximate form of the Hartree-Fock potential, proposed in our previous works. The obtained results are in good agreement with experiment.     

Electromagnetic radiation of MeV electrons in thick aligned single crystals

Abstract

Earlier published theoretical models for MeV electrons are generalized in this paper. Different theoretical predictions for planar channeling and accompanying electromagnetic radiation in thick crystals are presented. A comparative analysis of theoretical and experimental spectra of photon radiation is given. Thickness dependences of channeling quantum state populations, radiation line broadening and photon flux intensities are obtained. The existence of planar electron channeling at 54 MeV in a silicon single crystal with a thickness of several millimetres is shown.     

Radiation from 39 and 45 MeV electrons channeled in Lithium Niobate

Abstract

Channeling radiation from 39 and 45 MeV electrons channeled along the <0001> axis, the (0110) plane and the (1210) plane of a 30 μm thick LiNbO ₃ crystal has been measured. Calculations of the planar crystal potentials were performed by means of the many-beam formalism. Good agreement between theory and experiment is obtained for the planar channeling radiation. Associated with channeling additional radiation lines have been observed, which may be explained by a periodic perturbation of the continuum potential.     

New approximation for the interaction potential of light channeled particles with crystals

A new approximation for the continuous interaction potentials of atomic planes and strings with channeled electrons and positrons in crystals is proposed. A model in which atomic electron distributions within a certain atomic subshell are assumed to be exponentially decaying is used. Contrary to the Thomas-Fermi (TF) and Thomas-Fermi-Dirac (TFD) models this approach takes into account the shell structure of atoms in reasonably good agreement with the Hartree-Fock method (HF). Simple analytical expressions for the continuous plane (string) potentials are given. Calculations of several planar potentials for positrons channeled in silicon and tungsten are presented. Results are compared with widely known Lindhard and Molière approximations. Some estimates of the Kumakhov spontaneous radiation intensity under positron planar channeling conditions in the classical approximation are also given.     

Influence of quantum fluctuations on the stochastic dynamics of the channeling effect of relativistic electrons and positrons

A system of equations describing multiple scattering by crystal nuclei and electrons, and also quantum fluctuations of the coordinate and momentum operators of fast charged particles has been obtained. Quantum corrections to the classical equations of motion have been determined in quasiclassical approximations. A computer simulation of 855-MeV electron and positron motion in the (110) planar channel of a Si crystal has been carried out. The inclusion of quantum fluctuations in the equation of motion affects the dynamics of the electron channeling effect in planar crystal channels considerably; in particular, intense dechanneling (heating) occurs. Intense rechanneling (cooling) occurs in the case of positrons.     

正弦平方势与小振幅近似下的弯晶沟道辐射

在理想情况下和经典力学框架内,引入正弦平方势,把粒子在弯晶中的运动方程化为具有外力矩的摆方程。并对系统的相平面特征进行了数值分析。在小振幅近似下,把粒子运动方程化为具有硬特性的弹簧-振子系统,用Jacobian椭圆函数和椭圆积分解析地给出系统的解和粒子运动周期。讨论了弯晶沟道辐射频率、无量纲偏转角和辐射谱的一般特征。指出利用沟道辐射作为激光的可能性。以正电子在碳单晶中沟道辐射为例进行了具体计算,得到了与其他工作基本一致的结果。     

Measurement of spin rotation in particle channeling as a means for experimentally testing the correctness of the method for deriving the equation of motion for a spin

Two alternative approaches to deriving the equation of motion for a spin are compared. It is shown that the conventional approach leads to the conclusion that the spin of a positron is rotated through a large angle as the result of planar positron channeling in a straight crystal. The quantum-mechanical approach based on the Foldy-Wouthuysen transformation predicts no spin rotation in this case. Experimental measurements can reliably discriminate between the two methods for deriving the equation of motion for a spin.     

Channeling radiation: Theory,semi-classical simulations

Abstract

An introduction to channeling and channeling (Kumakhov) radiation is given. Relativistic and quantum-mechanical effects are discussed in function of the electron or positron energy. Phenomena of Quantum Electrodynamics in strong macroscopic field, which can be tested in channeling conditions, are described. Recipees for semi-classical Monte-Carlo simulations are presented and one of them compared with experiments at 10 and 150 GeV.     

正电子面沟道辐射的非线性特征

经典物理学指出,在电磁场中作加速运动的带电粒子将不断向外辐射能量.在晶体沟道中运动的带电粒子也不例外,晶格场可以使带电粒子的辐射能量达到很高.对于10MeV的正电子,辐射能量可达keV量级.粒子在沟道中的运动行为决定于粒子晶体的相互作用势,常用的相互作用势有Lindhard势、Moliere势和正弦平方势.由于粒子在沟道中的运动行为十分类似于震荡器中运动的自由电子,可望把沟道辐射改造为Χ射线激光或γ射线激光.从Lindhard势出发,将其展开到四次项,在经典力学框架内,粒子的运动方程可以化为含立方项的二阶非线性微分方程,并利用Jacobian椭圆函数和第一类全椭圆积分解析地表示了系统的解和粒子运动周期,导出了正电子面沟道辐射的瞬时辐射强度、平均辐射强度和最大辐射频率,指出了利用沟道辐射作为γ激光的可能性.     

Channeling radiation: Past achievements and future prospects

Abstract

When a relativistic charged particle passes through a single crystal very nearly along a major crystalline plane or axis so that it is channeled in that direction, it undergoes periodic motion in the plane transverse to this direction and hence it can radiate. Quantum mechanically, this channeling radiation corresponds to a radiative transition between two eigenstates of the transverse crystalline potential; when the transition occurs between two bound states, a sharp spectral line is emitted. When there are only two bound states (for incident electrons), or when the interplaner potential is nearly harmonic (as for incident positrons), the emitted radiation is nearly monochromatic. Since the discovery of channeling radiation at the LLNL Electron-Positron Linear Accelerator, many of its properties have been delineated, both there and elsewhere. For example, channeling radiation is very intense, forward-directed, easily tunable, and for the planar case, linearly polarized. Channeling radiation has been used as a probe both of the interplanar potentials and other properties of perfect crystals and of the effects of impurities and defects in imperfect crystals. Finally, channeling radiation has great potential use as a photon source for numerous other applications in several fields of science and technology.

This paper is intended to keynote the first International Conference on Coherent Radiation Processes in Strong Fields by recalling some history of the discovery and exploitation to date of channeling radiation. Studies of channeling radiation, in addition to elucidating the physics of the process itself, its application to the determination of properties of perfect and imperfect crystals, and its potential application to a large variety of fields by its use as an intense, monochromatic, forward-directed, tunable, and polarized photon source, have spawned an entire industry of studies of other coherent radiation processes, all consisting of photon production from beams of relativistic charged particles traversing periodic structures, which constitute the principal subject matter of this Conference. This paper will be limited to the discussion of channeling radiation and some of its applications. It will be in the nature of an illustrative exposition, showing many of the features of channeling radiation and its applications in a qualitative way. Several detailed studies of channeling radiation will be presented later in the Conference.