Compton scattering with quasi-real photons in electron-positron storage rings

For electron-positron colliding-beam processes of the type e^?e⁺ → e^?e⁺, where one of the e^± particles and the photon are detected at large angle, a number of theoretical predictions are given and compared with some data of a recent experiment performed at Orsay.     

A magnetic spectrometer for electron-positron pair spectroscopy in storage rings

We report an analysis of electron-optical properties of a toroidal magnetic sector spectrometer and examine parameters for its implementation in a relativistic heavy-ion storage ring, for example the High Energy Storage ring (HESR) at the future Facility for Antiproton and Ion Research (FAIR) facility. For studies of free–free pair production in heavy-ion atom collisions, this spectrometer exhibits very high efficiencies for coincident e⁺–e⁻ pair spectroscopy over a wide range of momenta of emitted lepton pairs. The high coincidence efficiency of the spectrometer is the key for stringent tests of theoretical predictions for the phase space correlation of lepton vector momenta in free–free pair production.     

Optical beam instabilities in nonlinear nanosuspensions

We investigate the modulation instability of plane waves and the transverse instabilities of soliton stripe beams propagating in nonlinear nanosuspensions. We show that in these systems the process of modulational instability depends on the input beam conditions. On the other hand, the transverse instability of soliton stripes can exhibit new features as a result of 1D collapse caused by the exponential nonlinearity.     

Modulation instability of intense laser beam in an electron-positron plasma

Modulation instability of an intense right-hand elliptically polarized laser beam propagating through an electron-positron plasma is investigated by a new method. The nonlinear dispersion relation, in which the relativistic and ponderomotive nonlinearities are taken into account, is obtained for the laser radiation in electron-positron plasma by the Lorentz transformation. The Karpman equation is generalized to the case of three dimensions with three field components. When the nonlinear frequency shift of the electromagnetic field in plasma is involved, the nonlinear evolution equation for the slowly varying envelope of the laser field is obtained. Thus, modulation instability of the intense laser beam in electron-positron plasma is studied and the temporal growth rate of the instability is derived. The analysis shows that the growth rate of modulation instability is increased significantly near the critical surface in a laser-plasma.     

Excitation of wake-fields in an electron-positron plasma by an ultrarelativistic proton beam

The excitation of one-dimensional nonlinear relativistic wake-waves in an electron-positron plasma by an ultrarelativistic proton beam is discussed on the basis of a self-consistent analytical model. It is shown that in contrast to a common plasma with heavy ions these waves are have an oscillation character at any ratio of the beam density and that of the electron-positron plasma.     

Reduction of the beam emittance in the charged-particle storage rings with the help of periodic magnetic wigglers

Periodic magnetic structures (wigglers) have been successfully used for a long time for controlling beam parameters in charged-particle storage rings for various purposes (including the reduction of emittance). In this work, we optimize the optical functions of the storage ring gap into which a wiggler is installed for a more effective reduction of the emittance. Optimal solutions are obtained for the first time for FODOtype and theoretical minimum emittance (TME) structures. An original method is proposed for suppressing the contribution of the wiggler fields to the radiation excitation of the phase volume of the beam by modulating the field period along the wiggler axis.     

Free electron lasers in storage rings

In this paper we briefly describe the principle of the free electron laser in a storage ring and the results obtained recently at Orsay. We also discuss the expected performances of such a device in more modern storage rings.     

Low-lying quasiparticle states and hidden collective charge instabilities in parent cobaltate superconductors

We report a state-of-the-art photoemission (angle-resolved photoemission spectroscopy) study of high quality single crystals of NaxCoO2 the series focusing on the fine details of the low-energy states. The Fermi velocity is found to be small (<0.5 eV A) and only weakly anisotropic over the Fermi surface at all dopings, setting the size of the pair wave function to be on the order of 10-20 nm. In the low-doping regime, the exchange interlayer splitting vanishes and two-dimensional collective instabilities such as 120 degrees -type fluctuations become kinematically allowed. Our results suggest that the unusually small Fermi velocity and the unique symmetry of kinematic instabilities distinguish cobaltates from most other oxide superconductors.     

Current instabilities in dynamic random access memory storage capacitor formed with electron beam deposited Y2O3 dielectric

Metal-oxide-semiconductor (MOS) storage capacitors based on electron beam deposited Y₂O₃ extrinsic dielectric on Si show changes in capacitance density depending on the amorphous and crystalline phases. Bias stress cycle-dependent changes in capacitance density occur due to the non-equilibrium nature of defect states at the Y₂O₃/Si interface after O₂ annealing as a result of the emergence of a 4–8 nm thick SiO₂ film at the interface. Leakage currents show instability under repeated dc bias stress, the nature and extent of which depend upon the structure of the Y₂O₃ gate dielectric and the polarity of dc bias. With amorphous Y₂O₃, leakage currents drift to lower values under gate injection due to electron trapping, and to higher values under Si-injection due to the generation of holes. Though leakage current drift is minimal for crystalline Y₂O₃, its magnitude increases as the energy of injected electrons from mid-gap states is low and the local field due to asperity is high. The emergence of interfacial SiO₂ reduces the magnitude of Si-injection leakage current substantially, but causes transient changes resulting in switching to higher values at a threshold dc bias. Thermal detrapping of holes and reverse bias stress studies confirm that the instability of current is caused by an increase in the cathodic field from hole trapping at interface states. Leakage current instability limits the application of extrinsic high dielectric constant dielectrics in a high density DRAM storage capacitor, unless a new interface layer scheme other than SiO₂ and a method to form a defect-free dielectric layer can be implemented. Received: 29 October 2001 / Accepted: 22 April 2002 / Published online: 4 December 2002 RID="*" ID="*"Corresponding author. Fax: +1-413/545-4611, E-mail: rastogi@ecs.umass.edu     

Effect of fringing fields in storage rings

Electron beams in storage rings of third-generation synchrotron radiation sources feature a low emittance and extended lifetime. The provision of such characteristics requires a detailed study of higher order effects related to magnetic fields and cooperative effects associated with beam density. Fringing fields, being an unavoidable attribute of magnets of any type, may significantly affect the beam dynamics, since they appear in equations of particle motion of first and higher orders. A simple technique for evaluating the effect of fringing fields on the beam dynamics is suggested. Numerical results obtained with this technique for the quadrupoles of the CANDLE storage ring [1] are reported.     

Polarized beams at storage rings

This paper reviews modern techniques to accelerate polarized particles to high energy and to preserve their polarization in the storage rings. Possibilities of the bean polarization control are discussed for proton and electron machines.     

Plasma instabilities excited by an azimuthal electron beam

The paper describes the effect of the finite temperature T of an azimuthal electron beam on plasma stability. Only instabilities for which the longitudinal macroscopic velocity of the beam is of no importance are discussed. It is shown that at the limit of applicability the weak and strong inhomogeneity approximations give the same results.     

Resonance method of electric-dipole-moment measurements in storage rings

A "resonance method" of measuring the electric dipole moment (EDM) of nuclei in storage rings is described, based on two new ideas: (1) Oscillating particles' velocities in resonance with spin precession, and (2) alternately producing two sub-beams with different betatron tunes--one sub-beam to amplify and thus make it easier to correct ring imperfections that produce false signals imitating EDM signals, and the other to make the EDM measurement.     

Ion beam driven instabilities in unmagnetized and strongly magnetized plasmas

In this paper, the dissipative instabilities in the interaction of an ion beam with unmagnetized and strongly magnetized plasmas are investigated. In both cases, relevant dispersion equations of high-frequency and ion acoustic waves are obtained. In addition, the resonance frequencies and growth rates of the instabilities are derived. It is shown that the thermal motion of charged particles has positive effects on the resonance frequency but its influence on the growth rate of an instability depends on the plasma conditions. Although in all cases the collisions are found to have a stabilizing effect, it is shown that the dominant type of collisions (electron-neutral or ion-neutral collisions) depends on the frequency range. It is also indicated that the resonance frequency and the growth rate of an instability in the unmagnetized plasma is higher than in the strongly magnetized plasma for non-zero propagation angles.     

I. Synchrotron radiation from the large electron-positron storage ring LEP

The properties of synchrotron radiation from LEP are investigated. This radiation from LEP are investigated. This radiation is assumed to be in a parasitic mode without changing any of the operating parameters. At 86 GeV the radiation from the normal bending magnet has a critical energy of 0.4 MeV and a power of ～500 W/m, and is probably of limited interest. High photon energies (10–20 MeV) of high intensity can be obtained from normal and superconducting wiggler magnets. Undulators can give quasi-monochromatic radiation of high brightness with photon energies of up to 5 MeV. New magnet developments might increase this energy range. Quasi-monochromatic γ-rays of ～100 MeV can be created with soft Compton back scattering without disturbing the electron bean. This relies on future free electron lasers in the submillimetre range. The natural collimation, the polarization and the time structure make all these photon beams unique tools for research in nuclear physics. The synchrotron rediation can be used to produced photoneutrons with intensities of up to 10¹⁴ neutrons/s. It is foreseen that LEP will be equipped with superconducting cavities in later stage and that is energy will be increased to ～130 GeV. This will approximately double the photon energies obtained from wigglers and undulators.