No abstract available

[en] Short communication

[en] The development of advanced acceleration mechanisms provide new capabilities for science. At the present time, discussions are centered on particle physics where advanced accelerators are the only route to electron-positron collisions at energies significantly above that of LEP. Cost effectiveness in this application leads to requirements which can be stated roughly as: i. high acceleration gradient for a reasonable length machine, ii. small transverse emittances for a small collision spot, iii. small longitudinal emittance to minimize chromatic aberrations while working in the quantum beamstrahlung regime, iv. stable, reproducible operation. These requirements may be unique, and an acceleration technique inappropriate for this may be suitable in some other application. However, since end-use requirements have an important influence and these have been enumerated only for high energy linear colliders, this paper concentrates on advanced accelerators for particle physics. In a linear collider the beam power, center-of-mass energy, luminosity, and beamstrahlung parameter fix the longitudinal and transverse beam dimensions, the collision frequency, and number of particles. The accelerator must be designed to minimize costs while reaching the needed energy with the needed beam quality

[en] We uncovered the morphology of quantum vortex structures in positron-atom ionization collisions. By performing an exhaustive calculation of the position of vortices in the final momentum space of the problem with only one kinematic restriction, we could elucidate that quantum vortices form a closed structure, which is one of the two possible scenarios for their emergence in three dimensions. This is the first time that these structures are fully calculated for positron atom collisions. (paper)

[en] The techniques which are presently used by computer simulations of the beam-beam effect in electron-positron storage rings are presented. A summary of simulation results is also given. (author)

[en] Using the precise expression of electron, positron distribution function obtained earlier, the authors derive the rigorous analytical expression of radiator in e⁺e^- collision process. This series expression converges rapidly to the precise result required. The comparison with existing approximate expression is also given. The result benefits the precise calculation for the radiative corrections in e⁺e^- collision processes

No abstract available

[en] The singularity structure of the forward positron-atom scattering amplitude is studied within the framework of perturbation theory with the use of the Landau rules. The unphysical and anomalous regions in the positron-atom forward dispersion relations are discussed. It is shown that the unphysical region starts at E⁰ = -Vertical BarE(Ps)Vertical Bar+Vertical BarE¹Vertical Bar and the anomalous region at E_a = -(√2Vertical BarE(Ps)Vertical Bar - √Vertical BarE¹Vertical Bar )₂, where E(Ps) and E¹ are correspondingly the positronium and the atomic-electron binding energies. The anomalous region is on the physical sheet if Vertical BarE(Ps)Vertical Bar/2>Vertical BarE¹Vertical Bar

[en] Accurate results of phase shift and cross section for e⁺-H collisions at low energies were obtained with a coupled-state calculation, employing the Harris-Nesbet algebraic method. A large coupling scheme was built on the six-pseudostate [(1s, 2s-bar, 2p-bar)H-(1s, 2s-bar, 2p-bar)Ps] one with a sufficiently high number of correlation terms to take care of the various scattering effects of this system. Our results of phase shift and cross section for both e⁺-H and Ps(1s)-p scatterings agree excellently with the accurate values calculated by Mitroy in a 21-state close-coupling approximation and by Bhatia et al and Humberston et al with a variational method. We believe that the results of the present Harris-Nesbet variational calculation have reached the convergent values to within 1% or, at worst, 3%. (author)

[en] A quantum mechanical study is done of model potential theory for positron-atom systems, both bound and scattering. The difficulties of obtaining an accurate wave function to interpret the positron annihilation parameters by the variational approach, even for the simple e⁺H system, are mentioned. Existing model potentials and pseudopotentials are reviewed and none of them are found to be directly applicable to positronic systems. A simple and theoretically based model potential method is proposed which is suitable to perform the calculations to a good accuracy