53 research outputs found

    NON-INTERCEPTING MONITOR OF BEAM CURRENT AND POSITION.

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    Impact of the Wiggler Coherent Synchrotron Radiation Impedance on the Beam Instability

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    Coherent Synchrotron Radiation (CSR) can play an important role by not only increasing the energy spread and emittance of a beam, but also leading to a potential instability. Previous studies of the CSR induced longitudinal instability were carried out for the CSR impedance due to dipole magnets. However, many storage rings include long wigglers where a large fraction of the synchrotron radiation is emitted. This includes high-luminosity factories such as DAPHNE, PEP-II, KEK-B, and CESR-C as well as the damping rings of future linear colliders. In this paper, the instability due to the CSR impedance from a wiggler is studied assuming a large wiggler parameter KK. The primary consideration is a low frequency microwave-like instability, which arises near the pipe cut-off frequency. Detailed results are presented on the growth rate and threshold for the damping rings of several linear collider designs. Finally, the optimization of the relative fraction of damping due to the wiggler systems is discussed for the damping rings.Comment: 10 pages, 7 figure

    Calculation of the Coherent Synchrotron Radiation Impedance from a Wiggler

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    Most studies of Coherent Synchrotron Radiation (CSR) have only considered the radiation from independent dipole magnets. However, in the damping rings of future linear colliders, a large fraction of the radiation power will be emitted in damping wigglers. In this paper, the longitudinal wakefield and impedance due to CSR in a wiggler are derived in the limit of a large wiggler parameter KK. After an appropriate scaling, the results can be expressed in terms of universal functions, which are independent of KK. Analytical asymptotic results are obtained for the wakefield in the limit of large and small distances, and for the impedance in the limit of small and high frequencies.Comment: 10 pages, 8 figure

    Observation of an Isotope Shift in the Superconducting Transition Temperature of La\u3csub\u3e1.85\u3c/sub\u3eSr\u3csub\u3e0.15\u3c/sub\u3eCuO\u3csub\u3e4\u3c/sub\u3e

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    An oxygen isotope shift is observed in superconducting La1.85Sr0.15CuO4 when 18O is substituted partially for 16O; the superconducting transition temperature Tc is lowered by 0.3 to 1.0 K in different samples. We examine these results using conventioanl phonon-mediated BCS theory and conclude that, for La1.85Sr0.15CuO4, phonons play an important role in the pairing mechanism

    What are the experimentally observable effects of vertex corrections in superconductors?

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    We calculate the effects of vertex corrections, of non-constant density of states and of a (self-consistently determined) phonon self-energy for the Holstein model on a 3D cubic lattice. We replace vertex corrections with a Coulomb pseudopotential, mu*, adjusted to give the same Tc, and repeat the calculations, to see which effects are a distinct feature of vertex corrections. This allows us to determine directly observable effects ofvertex corrections on a variety of thermodynamic properties of superconductors. To this end, we employ conserving approximations (in the local approximation) to calculate the superconducting critical temperatures, isotope coefficients, superconducting gaps, free-energy differences and thermodynamic critical fields for a range of parameters. We find that the dressed value of lambda is significantly larger than the bare value. While vertex corrections can cause significant changes in all the above quantities (even whenthe bare electron-phonon coupling is small), the changes can usually be well-modeled by an appropriate Coulomb pseudopotential. The isotope coefficient proves to be the quantity that most clearly shows effects of vertex corrections that can not be mimicked by a mu*.Comment: 28 pages, 12 figure
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