4,932 research outputs found
On the directional symmetry of the impedance
No full textThe 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
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Wake fields, potential well distortion and beam stability in the LER PEP, II
No full textLongitudinal and transverse wake fields are constructed for LER PEP-II. The effects of potential well distortion and the single bunch longitudinal stability are discussed for LER PEP-II storage ring. The coupled-bunch stability recalculated with the updated impedance
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Transverse instability driven by trapped electrons
No full textAn instability of a positron beam can be driven by electrons trapped in the combined average electric field of the beam and the magnetic field of the dipoles. An estimate of the growth rate is given. The growth rate of the instability is smaller than the growth rate of the fast ion instability by a factor 50 for the PEP-II LER parameters. Tendency to use long trains of bunches in storage rings intensified interest of stability of such trains. In the last year, two new instabilities were discovered: fast transverse instability, driven by one-turn ions for an electron storage ring, and a transverse instability driven by interaction of a positron beam with photo-electrons (Ohmi-effect). Cornell instability has been also explained as instability driven by the interaction of a beam with electrons trapped in the combined magnetic field of dipoles and the electrostatic field of distributed ion pumps (DIPs) leaking into the beam pipe. All these instabilities are caused by the effective wake fields defined by the charge density of the beam environment rather than due to geometric or resistive wall wake fields
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Study of an instability of the PEP-II positron beam: Ohmi effect and multipactoring
No full textThe 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
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Saturation of the ion induced transverse blow-up instability
No full textIn 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
Dredging Processes I: The Cutting of Sand, Clay & Rock - Theory
No full textThis book gives an overview of cutting theories. It starts with a generic model, which is valid for all types of soil (sand, clay and rock) after which the specifics of dry sand, water saturated sand, clay, rock and hyperbaric rock are covered. For each soil type small blade angles and large blade angles, resulting in a wedge in front of the blade, are discussed. The failure mechanism of sand, dry and water saturated, is the so called Shear Type. The failure mechanism of clay is the so called Flow Type, but under certain circumstances also the Curling Type and the Tear Type are possible. Rock will usually fail in a brittle way. This can be brittle tensile failure, the Tear Type, for small blade angles, but it can also be brittle shear failure, which is of the Shear Type of failure mechanism for larger blade angles. Under hyperbaric conditions rock may also fail in a more ductile way according to the Flow Type of failure mechanism. For each case considered, the equations/model for the cutting forces, power and specific energy are given. The models are verified with laboratory research, mainly at the Delft University of Technology, but also with data from literature.Marine & Transport TechnologyMechanical, Maritime and Materials Engineerin
Work among Japanese in the Salt River Valley of Arizona
No full textDocument written by S.A. Stewart Resident Missionary, East Kyushu Distict, Japan Methodist Church. Stewart discusses the events at the church and the free and restricted zones for Japanese Americans living in Glendale and Phoenix, Arizona.The Bishop James Chamberlain Baker Collection includes letters, documents, and articles about Japanese Americans during World War II. Subjects in the collection include Japanese Americans mass removal, Pearl Harbor and the aftermath, religion, and support from the non-Japanese American community. The collection was digitized and made accessible online by CSUDH Gerth Archives and Special Collections
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Investigation of the beam impedance of a slowly varying waveguide
No full textA 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
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