Electron Beam In Storage Ring Research Articles

2D Synchrotron Radiation Interferometer for Measuring the Transverse Dimensions of an Electron Beam in a Circular Accelerator

In the majority of cases, modern systems for measuring the transverse profile of the electron beam in storage rings of synchrotron type work in the x-ray range in order to overcome the resolution limit imposed by diffraction. In conjunction with devices of this type, use is frequently made of a synchrotron radiation interferometer operating in the visible wavelength range. With the help of such an interferometer, consisting of a screen with two slits (1D interferometer), it is possible to measure the transverse dimension down to a few micrometers. 1D interferometers are widely used in circular accelerators throughout the world, including a PETRA III (DESY) storage ring, where such an interferometer is used to determine the vertical dimension of the beam. It is proposed to use a 2D interferometer, consisting of a screen with four circular holes, making it possible to measure the vertical and horizontal dimensions simultaneously.

Effect of fringing fields in storage rings

Electron beams in storage rings of third-generation synchrotron radiation sources feature a low emittance and extended lifetime. The provision of such characteristics requires a detailed study of higher order effects related to magnetic fields and cooperative effects associated with beam density. Fringing fields, being an unavoidable attribute of magnets of any type, may significantly affect the beam dynamics, since they appear in equations of particle motion of first and higher orders. A simple technique for evaluating the effect of fringing fields on the beam dynamics is suggested. Numerical results obtained with this technique for the quadrupoles of the CANDLE storage ring [1] are reported.

Landau damping via the harmonic sextupole

Multibunch instabilities of a storage ring electron beam occur due to coherent particle oscillations generated through a bunch to bunch coupling via the impedances, deteriorating the beam quality. One cure for multibunch instabilities is Landau damping, i.e., introducing a spread in the oscillation frequencies among the particles of the individual bunches in order to destroy the coherence of the coupled multibunch oscillation. Measurements at ELETTRA have shown that the harmonic sextupole provides Landau damping capable of suppressing transverse multibunch instabilities. The damping is induced by the nonlinear tune spread with amplitude among the electrons within the individual bunches.

Interference diagnostics for storage ring electron beam

A beam of charged particles (e.g., electrons) in a uniform magnetic field of bending magnets emits synchrotron radiation (SR). The spectral density distribution of this radiation in the horizontal direction (i.e., in the electron orbit plane) is homogeneous. It is quite clear that the homogeneity of this distribution determines the accuracy of the measurements of the beam parameters (beam horizontal size and particle angular distribution) considerably. This work is dedicated to the possibility of a considerable increase in the accuracy of storage-ring electron beam parameter measurements using SR and some standard optical devices. For simplicity we will consider thereafter the SR in the optical spectral region. This is due to a wide range of precise optical tools and well-developed techniques at the disposal of experimenters over this spectral range.

Tracking Simulation of the Ions Trapped in the Nonlinear Field of Electron Beams in Storage Rings

Tracking simulation was performed on the ions trapped in linear and nonlinear fields of an electron beam in storage rings. The stability of the ions was investigated with regard to the homogeneous partial-fill mode and the equidistant-bunch and -burst modes of the electron beam. It was found that the oscillation amplitude of the ions trapped in the beam grows very rapidly to 100–1000 times larger than the electron beam size, even in the nonlinear field, under some ion-beam conditions. The results are expressed as a stability diagram of the ions, and the diagrams for the linear and nonlinear fields are basically similar to each other, both representing a periodic structure of the parametric resonance. The critical mass in the equidistant bunched beam is the same for the linear and nonlinear fields. The present results are consistent with the experimental results in the storage rings of European Synchrotron Radiation Facility (ESRF) and Photon Factory of National Laboratory for High Energy Physics (KEK-PF).

Phase-space measurement of stored electron beam at the Cornell Electron Storage Ring using a combination of slit array and CCD detector

A new technique for fast phase-space measurement has been developed and tested during a recent APS/CHESS undulator run. A measurement time of a few seconds was obtained by using a slit array and a high-resolution position sensitive detector system. The detector system consists of a CdWO4 scintillation crystal, an optical imaging system, and a CCD detector. The short measurement time increases the measurement accuracy by reducing the effects from the instabilities of the electron beam in storage ring. The vertical emittance at the Cornell Electron Storage Ring in single-bunch and low-current mode was measured, and reasonable agreement with the expected values for both source size and source divergence were obtained (σy=75 μm and σy′=12 μrad). The effects of the finite size of the first slit on the measurement results are discussed, and a comprehensive data analysis procedure is described.

A multiple objective magnet sorting algorithm for the Advanced Light Source insertion devices

Insertion devices for the Advanced Light Source (ALS) incorporate large numbers of permanent magnets which have a variety of magnetization orientation errors. These orientation errors can produce field errors which affect both the spectral brightness of the insertion devices and the storage ring electron beam dynamics. A perturbation study was carried out to quantify the effects of orientation errors acting in a hybrid magnetic structure. The results of this study were used to develop a multiple stage sorting algorithm which minimizes undesirable integrated field errors and essentially eliminates pole excitation errors. When applied to a measured magnet population for an existing insertion device, an order of magnitude reduction in integrated field errors was achieved while maintaining near zero pole excitation errors.

X-ray free electron laser in a crystal as distributed feedback resonator

The theory of an X-ray free electron laser inside a crystal is developed. In the Bragg diffraction geometry, a crystal provides a distributed feedback. In the low-gain regime expressions for the generation threshold are found which take absorption into account. Cold- and warm-beam regimes both for magnetic and for laser wigglers are considered. A detailed explanation of the physics of the generation condition is given. The case of an electron beam propagating in a narrow slit, without multiple scattering is considered. The advantage of a two-dimensional diffraction geometry is shown to be that it provides lower generation threshold values than those in one-dimensional geometry. The warm-beam case is found to be more preferable due to less rigid requirements for the beam quality. Realization of the given scheme requires an approximately 30-fold increase of the brightness of electron beams in storage rings.

Scattering of electrons on thermal radiation photons in electron-positron storage rings

It is shown that Compton scattering on thermal radiation photons restricts the lifetime of high energy electron beams in storage rings to a level of 30 h. At a vacuum pressure of 10 −10 Torr the probability that an electron is knocked out from the beam due to scattering on thermal photons exceeds the probability of bremsstrahlung on residual gas ( ΔE E > 1% ) by one order of magnitude, i.e. this effect can cause a considerable background in detectors.