Oxygen impurity radiation from Tokamak-like plasmas

We have constructed a nonhydrodynamic coronal model for calculating radiation from impurity atoms in a heated plasma. Some recent developments in the calculation of dielectronic recombination rate coefficients and collisional excitation rate coefficients are included. The model is applied to oxygen impurity radiation during the first few milliseconds of a TFR Tokomak plasma discharge, and good agreement with experimental results is obtained. Estimates of total line and continuum radiation from the oxygen impurity are given. It is shown that impurity radiation represents a considerable energy loss.     

Simultaneous effects of pressure and temperature on the binding energy and diamagnetic susceptibility of a laser dressed donor in a spherical quantum dot

Binding energies and diamagnetic susceptibility of an impurity in a spherical GaAs quantum dot under the simultaneous influence of static pressure, temperature and laser radiation are investigated. Pressure- and temperature-dependent dressed potential which is produced by the combined effects of laser radiation and impurity considerably change the energy spectrum and diamagnetic susceptibility of the system. It is shown that binding energies and diamagnetic susceptibility increase with increasing pressure. Moreover, laser radiation effects on the diamagnetic susceptibility are not significant in comparison with its effects on the binding energy.     

Magnetic properties of X<Subscript>0.5</Subscript>Mn<Subscript>0.5</Subscript>/Cu(001) overlayers,X = Fe,Mn, and Ir: ab-initio calculations

We study the effect of a magnetic impurity with spin-half on a single propagating electron in a one-dimensional model system via the tight-binding approach. Due to the spin-dependent interaction, the scattering channel for the flying qubit is split, and its transmission spectrum is obtained. It is found that, the spin orientation of the impurity plays the role as a spin state filter for a flying qubit.     

Temperature dependence of the spectrum of recombination radiation for indium phosphide n-p junctions

The spectrum of the recombination radiation from diffused indium phosphide n-p junctions was investigated at 77, 138, 210, and 298° K. The quantum energy in the maximum of the spectrum of recombination radiation differs from the corresponding energy gap values by 0.01 eV; this phenomenon is related to recombination processes at impurity levels.     

On bremsstrahlung radiation of accelerated electrons in solar flares

We have calculated the spectrum and polarization of the bremsstrahlung hard X-ray radiation produced by nonrelativistic electrons that are accelerated during a solar flare. The distribution function of accelerated electrons is taken from the self-consistent solution of the kinetic equation allowing for Coulomb collisions and an electric field of reverse current in plasma. The computed polarization of the hard X-ray polarization is shown to be appreciably lower than the value given by simplified thick-target models without considering the reverse current.     

Impurity-related optical response in a 2D and 3D quantum dot with Gaussian confinement under intense laser field

ABSTRACT

Using the two-dimensional (2D) diagonalisation method, the impurity-related electronic states and optical response in a 2D quantum dot with Gaussian confinement potential under nonresonant intense laser field are investigated. The effects of a hydrogenic impurity on the energy spectrum and binding energy of the electron and also intersubband optical absorption are calculated. The obtained numerical results show that the degeneracies of the excited electron states are broken and the absorption spectrum exhibits a redshift with the values of the laser field. The findings indicate a new degree of freedom to tune the performance of novel optoelectronic devices, based on the quantum dots and to control their specific properties by means of intense laser field and hydrogenic donor impurity. Using the same Gaussian confinement model, the electronic properties of a confined electron in the region of a spherical quantum dot are studied under the combined effects of on-centre donor impurity and a linearly polarised intense laser radiation. The three-dimensional problem is used to theoretically model, with very good agreement, some experimental findings reported in the literature related to the photoluminescence peak energy transition.     

Polarization dependence of Fano resonances in impurity photoconductivity of quantum wells doped with shallow donors

The spectrum of impurity photoabsorption of a heterostructure with quantum wells doped with shallow donors has been calculated in the energy range close to the optical phonon energy. It has been shown that the resonant feature of photoconductivity (Fano resonance) caused by the interaction of electrons with polar optical phonons depends strongly on radiation polarization when the resonance state energy is higher than the energy of the bottom of the second quantum-well subband. This dependence on polarization has been experimentally revealed in the impurity photoconductivity spectrum of the AlGaAs/GaAs heterostructure.     

Single shot phase contrast imaging using laser-produced Betatron x-ray beams

Development of x-ray phase contrast imaging applications with a laboratory scale source have been limited by the long exposure time needed to obtain one image. We demonstrate, using the Betatron x-ray radiation produced when electrons are accelerated and wiggled in the laser-wakefield cavity, that a high-quality phase contrast image of a complex object (here, a bee), located in air, can be obtained with a single laser shot. The Betatron x-ray source used in this proof of principle experiment has a source diameter of 1.7 μm and produces a synchrotron spectrum with critical energy E(c)=12.3±2.5 keV and 10? photons per shot in the whole spectrum.     

Transfer matrix theory for the optical absorption spectrum of mixed crystals

We study the density of states and optical absorption spectrum of linear mixed crystals in the one- dimensional alloy transfer matrix approximation. Local modes, which are present in the single impurity limit, develop into collective modes by merging into a band as the impurity concentration increases. The composition dependence of local and collective like optical absorption peaks is discussed, and we show that qualitatively different behaviours are obtained for single band and split bands type density of states.     

FEB-E动态气靶偏滤器的研究

在ＦＥＢ－Ｅ设计阶段,偏波器从开放式固定板靶优化为封闭式气体靶,以改善偏滤器的杂质控制和增加离子与气体的相互作用,通过喷气和注入杂质获得的部分脱靶等离子体形成了动态气体靶,喷气能降低删削层（ＳＯＬ）处等离子体温度,沪入的杂质增加了ＳＯＬ处的辐射功率,使靶板的负载降低,用ＮＥＷＴ１Ｄ编码模拟了ＳＯＬ处等离子体和杂质（硼杂质）的输运,得到了杂质、等离本温度和等离了体密度分布。着眼于杂质的滞留物辐射,优     

Modification of Mössbauer reflection spectra of group AIIBVI single crystals with Fe<Superscript>57</Superscript> nuclei under influence of infrared radiation

Interaction of Mössbauer gamma radiation with ultrasound vibrations in group AIIBVI single crystals of CdS and CdSe with Fe⁵⁷ impurity nuclei under action of infrared radiation is investigated. It is shown that the infrared irradiation excites a phonon field in single crystals. Similar to the case of optical irradiation of single crystals the shape of their Mössbauer spectrum is modified. The effect of double modulation of resonant gamma radiation by infrared radiation has been observed.     

Linearly polarized terahertz radiation in uniaxially deformed Ge(Ga) upon the electric breakdown of an impurity

The polarization spectra of spontaneous terahertz radiation in uniaxially deformed germanium have been measured upon the electric breakdown of shallow acceptors. Lines with various degrees of polarization with respect to the compression axis have been observed in the radiation spectrum. These lines are associated with the optical transitions of holes between the excited and ground states of the acceptor, as well as with the transitions of holes from the valence band to the ground state of the impurity. At a pressure of about 3 ± 0.3 kbar in the [111] direction near the impurity breakdown, the linear polarization degree reaches ～80–90% in the main lines of terahertz radiation. As the electric field intensity increases, the depolarization of radiation is observed, which is caused by the heating of nonequilibrium holes by the electric field.     

Interplay between edge states and simple bulk defects in graphene nanoribbons

We study the interplay between the edge states and a single impurity in a zigzag graphene nanoribbon. We use tight-binding exact diagonalization techniques, as well as density functional theory calculations to obtain the eigenvalue spectrum, the eigenfunctions, as well as the dependence of the local density of states (LDOS) on energy and position. We study the strictly zero-energy eigenfunctions using symmetry considerations, as well as tight-binding techniques. Moreover, we note that roughly half of the unperturbed eigenstates in the spectrum of the finite-size ribbon hybridize with the impurity state, and the corresponding eigenvalues are shifted with respect to their unperturbed values. The maximum shift and hybridization occur for a state whose energy is inverse proportional to the impurity potential, and give rise to an impurity peak in the DOS spectrum. We find that the interference between the impurity and the edge gives rise to peculiar modifications of the LDOS of the nanoribbon, in particular to oscillations of the edge LDOS. These effects depend on the size of the system, and decay with the distance between the edge and the impurity.     

Investigation of Impurity Ion Transport with Laser Blow-off in HL-2A Tokamak

Transient perturbation methods are most appropriate to study particle transport in tokamaks. Two most commonly used techniques of impurity injection are laser blow-off and gas puffing. The laser blow-off injection technique is undoubtedly the best one to study impurity transport because the injection time and the alnount of injected material can be controlled in a certain phase of the discharge with a minimum perturbation of the plasma parameters. The information of the impurity transport is obtained from the detection of emission of injected impurity ions located in different spatial regions. The radiation includes line emission, soft X-ray emission and plasma global radiation.     

Methods for detecting acceleration radiation in a Bose-Einstein condensate

We propose and study methods for detecting Unruh-like acceleration radiation effects in a Bose-Einstein condensate in a (1+1)-dimensional setup. The Bogoliubov vacuum of a Bose-Einstein condensate is used to simulate a scalar field theory, and accelerated atom dots or optical lattices serve as detectors of phonon radiation due to acceleration effects. In particular, we study the dispersive effects of the Bogoliubov spectrum on the ideal case of exact thermalization. Our results suggest that acceleration radiation effects can be observed using currently accessible experimental methods.     

Far-infrared recombination radiation from impact-ionized donors in germanium

We studied the far-infrared emission spectrum resulting from recombination of an electron with an ionized impurity of As and Sb in germanium under impact ionization at liquid, helium temperatures. The emission peaks at the position corresponding to the transition from the 2p _± excited state to the ground state. This observation indicates that recombination occurs through the capture by the excited states of the donor impurity, which is consistent with the cascade trap model. The intensity of emission radiation is of the order of 10⁻⁷ watts for the excitation power of about one watt, which implies a dominant process of recombination to be accompanied by phonon emission.     

Impurity states of electrons in quantum dots in external magnetic fields

The influence of isolated impurity atoms on the electron energy spectrum in a parabolic quantum dot in quantizing magnetic field is studied. The impurity potential is approximated by a Gaussian separable operator which allows one to obtain the exact solution of the problem. We demonstrate that in the electron energy spectrum there is a set of local levels which are split from the Landau zone boundaries in the upward or downward direction depending on the impurity type. We have calculated the local level positions, the wave functions of electrons in bound states, and the residues of the electron scattering amplitudes by impurity atoms at the poles.     

Theory of quasimagnetic impurity in a metal: An exactly soluble model of interacting electrons

We study an impurity atom, on which two-body forces are important, dissolved in a metal, where they are negligible. With the aid of the well-known boson excitation spectrum of the electronic Fermi sea, we predict the low-energy effects of one- and two-body potentials on the impurity, in the nonmagnetic regime. We obtain for the first time exact expressions for the cutoff independent contributions to the specific heat and paramagnetic susceptibility, the spectral amplitudes or one-electron density of states on the impurity, and the scattering cross-section. The entire spectrum of manybody eigenstates is explicitly obtained. The onset of a local magnetic moment appears as a sudden breakdown of the model Hamiltonian, and occurs when the two-body potential exceeds a critical value U_c which is O(E_F) in magnitude. A study of the renormalization of the interaction parameters terminates the paper.     

Reducing the proportion of impurity emission in spectra of x-ray sources

We have studied the emission spectrum of an RT1-50 x-ray tube. Scanning the x-ray beam along the output window of the x-ray tube allowed us to establish the sources generating the impurity spectrum. We propose methods for suppressing the impurity emission.