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The magnetic field enhancement caused by closely spaced, cylindrical, metallic protrusions in an rf cavity is studied theoretically and compared to field solver results for such micro-structures. It is found that the enhancement between the protrusions can be large when the magnetic field is perpendicular to the gap between them, and that the enhancement increases as this gap is reduced. This mechanism could help explain the observation of melting on normal-conducting cavity surfaces subjected to non-enhanced pulsed heating well below that required to melt the surface material. It could also help explain quenching in superconducting cavities when the nominal magnetic fields are below the critical value. [ABSTRACT FROM AUTHOR]

We propose a novel triple modulator-chicane (TMC) scheme to convert external input seed into shorter wavelengths. In this scheme, high-power seed lasers are used in the first and the third modulator, while only a very-low-power seed is used in the second modulator. By properly choosing the parameters of the lasers and chicanes, we show that ultrahigh harmonics can be generated in the TMC scheme while simultaneously keeping the energy spread growth much smaller than the beam's initial slice energy spread. As an example, we show the feasibility of generating significant bunching at 1 nm and below from a low-power (~100 kW) high harmonic generation seed at 20 nm assisted by two high-power (~100MW) UV lasers at 200 nm while keeping the energy spread growth within 40%. The supreme up-frequency conversion efficiency of the proposed TMC scheme, together with its unique advantage in maintaining beam energy spread, opens up new opportunities for generating fully coherent x-rays at sub-nanometer wavelength from external seeds. [ABSTRACT FROM AUTHOR]

Coherent synchrotron radiation (CSR) fields are generated when a bunched beam moves along a curved trajectory. A new code, named CSRZ, was developed using finite difference method to calculate the longitudinal CSR impedance for a beam moving along a curved chamber. The method adopted in the code was originated by Agoh and Yokoya [Phys. Rev. ST Accel. Beams 7 (2004) 054403]. It solves the parabolic equation in the frequency domain in a curvilinear coordinate system. The chamber considered has uniform rectangular cross-section along the beam trajectory. The code was used to investigate the properties of CSR impedance of a single or a series of bending magnets. The calculation results indicate that the shielding effect due to outer chamber wall can be well explained by a simple optical approximation model at high frequencies. The CSR fields reflected by the outer wall may interfere with each other along a series of bending magnets and lead to sharp narrow peaks in the CSR impedance. In a small storage ring, such interference effect can be significant and may cause microwave instability, according to a simple estimate of instability threshold. [ABSTRACT FROM AUTHOR]