The Physics and Properties of Free-Electron Lasers

We present an introduction to the operating principles of free-electron lasers, discussing the amplification process, and the requirements on the electron beam necessary to achieve desired performance

Transverse impedance of a smooth flat taper

Stupakov has used a perturbation method to estimate the transverse impedance at zero frequency of a rectangular collimator having characteristic taper length ℓ, half-width w, and average vertical half-aperture b_{0}, under the condition b_{0}≪w≪ℓ. We use the boundary perturbation method to approximate the transverse impedance of a flat, slowly tapered chamber in the complementary limit, w=∞

Analysis of the saturation of a high-gain free-electron laser

We study the saturated state of an untapered free-electron laser (FEL) in the Compton regime, arising after exponential amplification of an initially low level of radiation by an initially monoenergetic, unbunched electron beam. The saturated state of the FEL is described by oscillations about an equilibrium state. Using the two invariants of the motion and certain assumptions motivated by computer simulations we provide approximate analytic descriptions of the radiation field and electron distribution in the saturation regime. We first consider a one-dimensional approximation and later extend our approach to treat an electron beam of finite radial extent. Of note is a result on the radiated power in the case of an electron beam with a small radius

Efficient cascaded parameter scan approach for studying top-off safety in storage rings

We introduce a new algorithm, which we call the cascaded parameter scan method, to efficiently carry out the scan over magnet parameters in the safety analysis for top-off injection in synchrotron radiation storage rings. In top-off safety analysis, one must track particles populating phase space through a beam line containing magnets and apertures and clearly demonstrate that, for all possible magnet settings and errors, all particles are lost on scrapers within the properly shielded region. In the usual approach, if one considers m magnets and scans each magnet through n setpoints, then one must carry out n^{m} tracking runs. In the cascaded parameter scan method, the number of tracking runs is reduced to n×m. This reduction of exponential to linear dependence on the number of setpoints n greatly reduces the required computation time and allows one to more densely populate phase space and to increase the number n of setpoints scanned for each magnet

Multiobjective optimization of dynamic aperture

Dynamic aperture (DA) is one of the key nonlinear properties for a storage ring. Although there have been both analytical and numerical methods to find the aperture, the reverse problem of how to optimize it is still a challenging problem. A general and flexible way of optimizing the DA is highly demanded in accelerator design and operation. In this paper, we discuss the use of multiobjective optimization for DA. First we consider using objective functions based only on numerical tracking results. Data mining of these results demonstrated a correlation between DA and low-order nonlinear driving terms. Next we considered using objective functions which included both numerical tracking results and analytical estimates of low-order nonlinear driving terms. This resulted in faster convergence. The National Synchrotron Light Source II (NSLS-II) lattice was taken as an example to illustrate this method. This multiobjective approach is not limited by particular linear or nonlinear lattice settings, and can also be applied for optimizing other properties of a storage ring

Transient bunch compression using pulsed phase modulation in high-energy electron storage rings

A method for producing short electron bunches in an electron storage ring using pulsed phase modulation has been demonstrated. A simple theoretical model was validated using the particle tracking code elegant, and the bunch compression process was observed experimentally in the Advanced Photon Source storage ring using a visible light streak camera. Compression to 54% of the initial bunch length was achieved