Saturation of the ion induced transverse blow-up instability

In a recent paper, T. Raubenheimer and F. Zimmermann described a new, fast transverse instability caused by the interaction of a train of bunches with the residual gas. Ions produced by transversely offset bunches in the head of a train induce oscillations of the tail of the train. The ions may be cleared out by a gap after one revolution, but the memory remains in the train. Amplitude of oscillations keeps growing exponentially as exp s{top}s{sub c}, until the amplitude of a bunch centroid is on the order of the transverse rms {sigma} of a bunch. The rise time s{sub c}, of the oscillations of a bunch centroid for the PEP-II HER was found to be a fraction of a millisecond, even taking into account the spread of ion frequencies.Computer simulations confirm the exponential growth. However, the results of the simulations show that the exponential regime holds only for a short period of time and then changes to a much slower growth. Initial growth is rapid; it would be difficult to observe it directly in experiments. From a practical point of view, the important questions are, what is the amplitude at which a transition to slow growth takes place and, secondly, what is the growth rate after that transition compared to the rate, which could be handled with a reasonable feedback system. The exponential regime is limited by nonlinearity of the beam-ion interaction. As a result, exponential growth at large amplitudes is replaced by a linear dependence of the amplitude on time. The transition from exponential growth to a linear regime depends on the initial conditions: exponential growth is noticeable only for very small initial amplitudes. An estimate of the growth rate at large amplitude is obtained and compared with computer simulations

Study of an instability of the PEP-II positron beam (Ohmi effect and multipactoring)

The paper is organized in the following way. First, Ohmi effect induced by direct flow of primary photoelectrons is studied for the PEP-II parameters. The production rate and kinematics take into account the antechamber of the LER. We discuss the effect of the secondary emission of electrons in the AL chamber, where the yield is larger than one. Resonance multipactoring is considered, and then the average density of the secondary electrons is estimated taking into account the space-charge effect and the interaction with the beam. We show that in the extreme case there is a self-consistent regime similar to the regime of the space-charge dominated cathode. Finally, the rate of ion production by accumulated electrons and the possibility of the ion induced pressure instability is discussed

On the directional symmetry of the impedance

The independence of the impedance on the beam direction is an important feature of an accelerator structure, in particular, for the electron-positron storage rings where bunches of opposite charges travel through the same vacuum chamber in opposite directions. Recently Gluckstern and Zotter considered a cylindrically symmetric but longitudinally asymmetric cavity with side pipes of equal radii. They were able to prove that for a relativistic particle the longitudinal impedance of the cavity with an arbitrary shape is independent of the direction in which the beam travels through it. Their result corroborates numerical observations of the independence of the wakefield obtained with the code TBCI. Bisognano gave an elegant proof of the same statement. His approach is based on a reciprocity relation applied to the tensor Green's function. I follow here his idea in a somewhat simpler way to obtain more general and physically transparent proof of this property for both longitudinal and transverse impedances. The result is valid for a cavity with no azimuthal symmetry and for arbitrary particle velocity, as soon as it may be considered constant. At the same time the limits of its validity are shown

Investigation of the beam impedance of a slowly varying waveguide

A perturbation method is used to obtain analytic expressions for the multipole longitudinal and universe beam impedance for an arbitrary waveguide whose radius is slowly varying and for the specific case of a symmetric small-angle taper. This method is also applicable for a particle in a wiggler undergoing periodic motion

Bunch heating by coherent synchrotron radiation

The authors discuss here effects which define the steady-state rms energy spread of a microbunch in a storage ring. It is implied that the longitudinal microwave instability is controlled by low {alpha} lattice. In this case the coherent synchrotron radiation, if exists, may be the main factor defining the bunch temperature. Another effect comes from the fact that a nonlinear momentum compaction of such lattices makes Haissinskii equation not applicable, and the coherent synchrotron radiation may effect not only bunch lengthening but the energy spread as well

First-principles study of bulk and surface oxygen vacancies in SrTiO 3 crystal

61.72.jd Vacancies, 71.15.Ap Basis sets and related methodology, 61.72.jn Color centers,

SuperB: A High-Luminosity Asymmetric e+e- Super Flavour Factory. Conceptual Design Report.

May 18, 2007. 480pp., Available on the World Wide Web, with figures in full color, at http://www.pi.infn.it/SuperB/?q=CDRThe physics objectives of SuperB, an asymmetric electron-positron collider with a luminosity above 10^36/cm^2/s are described, together with the conceptual design of a novel low emittance design that achieves this performance with wallplug power comparable to that of the current B Factories, and an upgraded detector capable of doing the physics in the SuperB environment