TUOB :: FEL Technology I: Accelerators

Date/Time: 23-Aug-05 :: 10:45—12:30
Chair: M. Cornacchia, SLAC, Menlo Park, California

Paper Title Page
TUOB001 Energy Recovery Linacs
 
  • L. Merminga
    Jefferson Lab, Newport News, Virginia
 
 

Funding: Work supported by the US DoE contract No. DE-AC05-84ER40150.

Successfully operating, pioneering Energy Recovery Linac (ERL) – based Free Electron Lasers (FELs) have paved the way towards powerful and highly efficient accelerators based on the principle of energy recovery. Pursued and envisioned ERL applications worldwide include high brilliance light sources for the production of both spontaneous and FEL radiation, high-energy electron cooling devices, and electron-ion colliders. The required electron source parameters, average beam current and beam energy of the proposed applications are a significant extrapolation from demonstrated performance. We present an overview of the accelerator physics and technology challenges encountered in the design of the various ERL projects around the world, as well as progress and development plans to achieving the required performance.

 
   
TUOB002 Accelerator Layout and Physics of X-Ray Free-Electron Lasers 243
 
  • W. Decking
    DESY, Hamburg
 
 

X-ray Free-Electron Lasers facilities are planned or already under construction around the world. This talk covers the X-Ray Free-Electron Lasers LCLS (SLAC), European XFEL (DESY) and SCSS (Spring8). All aim for self-amplified spontaneous emission (SASE) FEL radiation of approximately 0.1 nm wavelengths. The required excellent electron beam qualities pose challenges to the accelerator physicists. Space charge forces, coherent synchrotron radiation and wakefields can deteriorate the beam quality. The accelerator physics and technological challenges behind each of the projects will be reviewed, covering the critical components low-emittance electron gun, bunch-compressors, accelerating structures and undulator systems.

 
   
TUOB003 Velocity and Magnetic Compressions in FEL Drivers
 
  • L. Serafini
    INFN-Milano, Milano
 
 

We will compare merits and issues of these two techniques suitable for increasing the peak current of high brightness electron beams. The typical range of applicability is low energy for the velocity bunching and middle to high energy for magnetic compression. Velocity bunching is free from CSR effects but requires very high RF stability (time jitters), as well as a dedicated additional focusing and great cure in the beam transport: it is very well understood theoretically and numerical simulations are pretty straightforward. Several experiments of velocity bunching have been performed in the past few years: none of them, nevertheless, used a photoinjector designed and optimized for that purpose. Magnetic compression is a much more consolidated technique: CSR effects and micro-bunch instabilities are its main drawbacks. There is a large operational experience with chicanes used as magnetic compressors and their theoretical understanding is quite deep, though numerical simulations of real devices are still challenging, in particular for 3D self-consistent modeling. Most of present FEL drivers foresee in their lay-out a multiple-staged magnetic compression that brings the bunch peak current all the way from the photoinjector exit (at typically 50-100 A) up to the linac exit at a multi-kA level (total compression by a factor 30 to 60). As an alternative option, we will discuss how to integrate the two techniques into a typical FEL linac, with the aim to marry the merits of both and to mitigate the issues.

 
   
TUOB004 Bunch Compression Stability Dependence on RF Parameters 250
 
  • T. Limberg, M. Dohlus
    DESY, Hamburg
 
 

In present designs for FEL's with high electron peak currents and short bunch lengths, higher harmonic RF systems are often used to optimize the final longitudinal charge distributions. This opens degrees of freedom for the choice of RF phases and amplitudes to achieve the necessary peak current with a reasonable longitudinal bunch shape. It had been found empirically that different working points result in different tolerances for phases and amplitudes. We give an analytical expression for the sensitivity of the compression factor on phase and amplitude jitter for a bunch compression scheme involving two RF systems and two magnetic chicanes as well numerical results for the case of the European XFEL.