In the our original paper the sign of the coefficient R 56 used in numeric calculations was wrong. It has to be changed to be consistent with the sign convention assumed in the design of a bunch compressor. The sign of R 56 depicted in Fig. 1 has to be changed from negative to positive. The sign of the chirp u related to the sign of the R 56 has to be changed as well: the chirp u in the first paragraph of Sec. VI should be positive, u 39:83 m ÿ1 . These changes do not affect the formulas of the paper but slightly modify the numeric results. The results of corrected calculations are shown in Figs. 1 and 2 given below, which should replace Figs. 3 and 4 in the paper, respectively.
The coherent synchrotron radiation of a bunch in a bunch compressor may lead to the microwave instability producing longitudinal modulation of the bunch with wavelengths small compared to the bunch length. It can also be a source of an undesirable emittance growth in the compressor. We derive and analyze the equation that describes linear evolution of the microwave modulation taking into account incoherent energy spread and finite emittance of the beam. Numerical solution of this equation for the Linac Coherent Light Source bunch compressor gives the amplification factor for different wavelengths of the beam microbunching.
We report results of an on-going experiment being carried out in the X13 straight section of the NSLS X-ray Ring which explores the limits of the operation of small-gap undulators. In particular, we discuss the operation of a 16 mm period small-gap undulator. At an electron beam current of 300 mA the variable gap vacuum chamber has been closed to an inner aperture of 3.8 mm with no effect on the electron beam lifetime. Measurements of the output radiation spectrum at a magnet gap of 7.5 mm are described.
I. In f rod uc t ionThe development of high-brightness synchrotron radiation sources has been advanced by the utilization of permanent magnet insertion devices, pioneered by Klaus Halbach [l]. Such permanent magnet devices provide high field strength, excellent field quality, and impressive reliability in a very economical manner. Here, our interest is in the implementation of short-period, small-gap undulators situated in low-beta insertions of a storage ring. In particular, we report results of an on-going experiment being carried out in the X13 straight section of the NSLS X-ray Ring, which explores the limits of the operation of small-gap devices.The vertical magnetic field By in a pure-permanent-magnet undulator has an approximately sinusoidal dependence on the axial coordinate z, By=B,, sin ZazIA,, ,where A,is the undulator period length. The peak field B, depends exponentially on the full magnet gap G, B,, a (-xGlA,,).
The elliptical multipole wiggler 0 has been designed, constructed, and installed in the X13 straight section of the NSLS X-ray Ring. The EMW generates circularly polarized photons in the energy range of 0.1-10 keV with AC modulation of polarization helicity. The vertical magnetic field of 0.8 T is produced by a hybrid permanent magnet structure with a period of 16 cm. The horizontal magnetic field of 0.22 T is generated by an electromagnet, the core of which is fabricated from laminated iron to operate with a switching frequency up to 100 Hz. There are dynamic compensation t r i m magnets at the wiggler ends to control the first and second field integrals with very high accuracy throughout the AC cycle. The residual closed orbit motion due to the electromagnet AC operation is discussed.
NSLS-II is a 3 GeV ultra-high brightness storage ring planned to succeed the present NSLS rings at BNL. Ultralow emittance combined with short bunch length means that it is critical to minimize the effects of Touschek scattering and coherent instabilities. Improved lifetime and stability can be achieved by including a thirdharmonic RF cavity in the baseline design. This paper describes the required harmonic RF parameters and the expected system performance.
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