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For many years, scientists around the world have sought an ultra-low-emittance ring-based light source that offers greater performance than existing third-generation light sources. Pioneering work on the seven-bend lattice for MAX IV [1] initiated these efforts. Another significant development was the scheme for nonlinearity control based on “phase-matched” sextupole pairs. This configuration, first introduced in a light source design by the ESRF design group [2], efficiently suppresses strong nonlinear resonances induced by sextupoles for chromaticity correction. Since a small dynamic aperture due to the strong nonlinearities mentioned earlier presents a great obstacle when we attempt to lower the beam emittance of a high-energy light source using individual bending magnets with small deflection angles, the ESRF scheme contributes significantly to the emittance reduction that can be practically achieved. [ABSTRACT FROM PUBLISHER]

A circular waveguide polarizer for 2.45 GHz microwaves has been designed and produced for electron Bernstein (EB) wave heating and current drive experiments on the low aspect ratio Torus experiment (LATE) device. In the experiments the microwaves are injected obliquely to the toroidal field to drive current carrying fast electrons. In the LATE case of the oblique injection of long free space wavelength waves onto a small plasma the coupling to the EB waves from the injected electromagnetic waves is improved when the injected waves have appropriate elliptical polarizations depending on the injection angle and the density gradient at the upper hybrid resonance layer (Igami et al 2006 Plasma Phys. Control. Fusion48 573). Any elliptically polarized mode can be generated from a circular TE11 mode by the combination of a half wave section and a quarter wave section of circular waveguide. The transformation of polarization arises from the difference in axial wave numbers between an orthogonal pair of modified circular TE11 modes, which is realized by the insertion of a Teflon plate in a circular waveguide made of aluminum. Such a polarized wave is launched from the open end of a circular waveguide toward the plasma. An elliptically polarized mode adjusted to a steep density gradient and injected obliquely to the toroidal field has been found to be effective to sustain a highly over-dense plasma. [ABSTRACT FROM AUTHOR]

Abstract: We propose a scheme to suppress leakage of an injection bump orbit caused by sextupole magnets within the bump orbit. Since the bump leakage excites a stored beam oscillation synchronized with beam injection, its suppression is one of the most crucial issues for achieving top-up operation at third generation synchrotron radiation (SR) sources. In the common case where sextupole magnets are located within the bump orbit, the condition for closing the bump depends on the amplitude of the bump orbit due to the nonlinear kicks by the sextupole magnets. Accordingly the bump orbit never closes for all amplitudes even under ideal condition. To solve this problem, we use a minimal condition for emittance increase due to the bump leakage caused by sextupole magnets in the lowest order of the nonlinear perturbation. The condition is obtained by optimizing linear optics and satisfying specific relation among integrated strengths of the sextupole magnets within the bump orbit. Furthermore, the condition does not depend on the bump amplitude. Calculations using the perfectly similar field patterns reveal that the proposed scheme can reduce the rms of the stored beam oscillation down to a few tens of microns for all bump amplitudes. The residual oscillation is negligibly small compared to the horizontal beam sizes presently achieved in the SR sources. The suppression effect of the scheme was also confirmed experimentally by the results obtained at the SPring-8 storage ring. [Copyright &y& Elsevier]