Linac-Based Free Electron Lasers

Simple and useful approximations, valid at infrared wavelengths, to the equations for synchrotron radiation are presented and used to quantify the brightness and power advantage of current synchrotron radiation light sources over conventional infrared broadband laboratory sources. The Daresbury Synchrotron Radiation Source (SRS) and the Brookhaven National Synchrotron Light Source (vacuum ultraviolet) [NSLS(VUV)] storage rings are used as examples in the calculation of the properties of infrared synchrotron radiation. The pulsed nature of the emission is also discussed, and potential areas of application for the brightness, power, and time structure advantages are presented. The use of infrared free electron lasers and undulators on the next generation of storage ring light sources is briefly considered.

Over the last few decades, synchrotron radiation generated by storage rings has been the dominant source of high-brightness photons in a spectrum spanning from infrared to hard X-rays for a multitude of scientific applications. During those years, accelerator and source development have seen several step changes denoted by three generations of ring-based synchrotron light sources. Since the advent of third-generation sources about 20 years ago, development has continued but, until recently, had been mostly evolutionary. In the meantime, free electron lasers (FELs) have emerged as alternative sources of soft and hard X-rays, offering peak brightness many orders of magnitude higher than storage ring sources, with ultra-short photon pulses having nearly complete transverse coherence and an energy bandwidth that approaches the transform limit with seeding. Yet, in spite of these spectacular beam properties, a consensus has emerged that ring-based sources will continue to play a vital role in X-ray science into the future because they offer beam properties that are complementary to FEL sources. Storage rings provide photon beams with lower peak brightness but high average brightness and higher pulse repetition rates on a large number of parallel beamlines with excellent stability and quick tunability [1, 2]. Recent advances in accelerator physics and engineering have made it feasible to provide another step change in brightness over third-generation storage rings. The first rings applying some of those technologies are under construction now.

The Time Dependent Schrödinger Equation In A Strong Laser Field

Synchrotron radiation has been traditionally treated as an effect which only depends on the linear beam dynamics. Electrons in advanced accelerators and storage rings, however, can lose several percent of their energy in one turn, especially when the ring incorporates synchrotron radiation sources or free electron lasers. In these machines nonlinear effects can become important, not only because of the high variation of the particle's energy around the ring, but also because of the necessity to have very good beam quality in wigglers, undulators, and free electron lasers. Since these instruments can have helical structure, a general reference frame with torsion is used and the Lorenz-Dirac radiation reaction of the charged particle is taken into account. We will utilize the differential algebra technique to compute nonlinear transfer maps of general optical elements. Applications include radiation damping in multipoles, its effect on closed orbit distortion in a storage ring, and nonlinear tune shifts due to various radiating devices. The software provided will also be useful in simulating Siberian snakes.

This report is based on a BES Workshop on Compact Light Sources, held May 11-12, 2010, to evaluated the advantages and disadvantages of compact light source approaches and compared their performance to the third generation storage rings and free-electron lasers. The workshop examined the state of the technology for compact light sources and their expected progress. The workshop evaluated the cost efficiency, user access, availability, and reliability of such sources. Working groups evaluated the advantages and disadvantages of Compact Light Source (CLS) approaches, and compared their performance to the third-generation storage rings and free-electron lasers (FELs). The primary aspects of comparison were 1) cost effectiveness, 2) technical availability v. time frame, and 3) machine reliability and availability for user access. Five categories of potential sources were analyzed: 1) inverse Compton scattering (ICS) sources, 2) mini storage rings, 3) plasma sources, 4) sources using plasma-based accelerators, and 5) laser high harmonic generation (HHG) sources. Compact light sources are not a substitute for large synchrotron and FEL light sources that typically also incorporate extensive user support facilities. Rather they offer attractive, complementary capabilities at a small fraction of the cost and size of large national user facilities. In the far term they may offer the potential for a new paradigm of future national user facility. In the course of the workshop, we identified overarching R&D topics over the next five years that would enhance the performance potential of both compact and large-scale sources: Development of infrared (IR) laser systems delivering kW-class average power with femtosecond pulses at kHz repetition rates. These have application to ICS sources, plasma sources, and HHG sources. Development of laser storage cavities for storage of 10-mJ picosecond and femtosecond pulses focused to micron beam sizes. Development of high-brightness, high-repetition-rate electron sources. Development of continuous wave (cw) superconducting rf linacs operating at 4 K, while not essential, would reduce capital and operating cost.

In this paper, we study the dynamics of the electron beam in a diffraction limited storage ring with a high-gain free-electron laser. We present in detail the design, including lattice, dynamic aperture, intrabeam scattering, and coherent synchrotron radiation. The simulation of the electron storage ring combined with the free-electron laser is carried out until the electron beam reaches its equilibrium. We find that the initial exponential radiation power is reduced approximately to linear with respect to the undulator length due to the large increase of the energy spread from the free-electron laser.

The intensity of x-ray sources has increased at a rapid rate since the late 1960s by tenorders of magnitude and more through the use of synchrotron radiation produced bybending magnets, wigglers and undulators. Three generations of radiation sources havebeen identified depending on amplitude and quality of the radiation provided. While userfacilities of the third generation were being constructed, a new concept of radiationgenerating devices was being developed that offers an even larger increase in peak andaverage brightness than had been achieved till then. The new concept of the x-rayfree electron laser based on the principle of self-amplified spontaneous emissionwill be the basis of fourth generation x-ray source user facilities of this century.The paper will start with a brief history of the development of x-ray sources, it will thendiscuss some of the differences between storage ring and free electron laser basedapproaches, and will close with an update of the present development of x-ray free electronlaser user facilities.

In accelerators such as storage rings, energy recovery linacs (ERLs), and free electron lasers, bending magnets are used to alter the trajectory of a relativistic electron beam. Frequently the magnets are arranged in pairs in either a “U” or “S” configuration with an intervening straight section. In such configurations synchrotron radiation (SR) or edge radiation (ER) is produced in the bend and/or as the beam exits the field of each magnetic field region. Under certain conditions the radiation is produced in the visible region of the spectrum. The radiation from the second magnet can interfere with that of the first magnet, when a distance comparable to the coherence length of the radiation separates the two magnetic fields. For a beam with low energy spread, the visibility of the interference radiation depends on the beam divergence. To design a sensitive beam divergence diagnostic we have developed a computer code, which can calculate the far field radiation distribution produced by a relativistic electron moving along any trajectory in a magnetic field. The code model is based on the “colliding electron” approximation and reproduces all known features of SR and ER. The code can account for the spatial field distribution of the dipole magnet, the effect of beam divergence and the bandwidth of the measurement. Results of our calculations are presented for the 1.9‐GeV Cornell Electron Storage Ring and the 100‐MeV ERL at the Thomas Jefferson National Laboratory Free Electron Laser.

FLASH, the Free-electron LASer in Hamburg, is the world’s first free electron laser for extremely bright and ultra-short pulses in the extreme ultraviolet and soft X-ray range. Efficient photon beam transport and diagnostics play an essential role in exploiting the features of this new generation of light sources in a large variety of user experiments. A detailed overview of the FLASH user facility is presented.

Membrane protein structural biology using X-ray free electron lasers

The European synchrotron radiation facility: An overview

To take complete benefit of the Free Electron Laser (FEL) features, we have developed a feedback control scheme designed to suppress the dynamical instabilities affecting the FEL output intensity. The principle is to stabilize an unstable stationary state that coexists with the unwanted limit cycle. This paper gives a theoretical and experimental description of the stabilized stationary regime of a storage ring FEL in presence of the feedback control. We present a numerical model of the FEL with control, that describes the longitudinal dynamics of the laser pulse in condition of detuning between the FEL and the electron beam. These theoretical results are compared with experiments performed on the Super-ACO FEL. The established feedback control provides stable operation of the FEL.

This paper contains studies of the operation of a one-dimensional storage ring free-electron laser (FEL) using a Monte Carlo technique to generate the electron energy fluctuations produced by the FEL. The energy and phase equations of motion have been numerically integrated to calculate equilibrium values of: a) electron energy spread, b) electron phase spread (e.g. electron bunch length), and c) efficiency of conversion of electron energy into laser radiation. The operation of the storage ring free-electron laser was studied for five different FEL magnet designs. It is found that a “one-dimensional” storage ring free-electron laser can operate on a steady-state basis only with reduced overall efficiency due to the inability of the system to damp effectively the electron energy fluctuations produced by the FEL. Results of operation of a SRFEL in a pulsed mode are also presented.

Even though high-quality X- and gamma rays with photon energy below mega-electron volt (MeV) are available from large-scale X-ray free electron lasers and synchrotron radiation facilities, it remains a great challenge to generate bright gamma rays over 10 MeV. Recently, gamma rays with energies up to the MeV level were observed in Compton scattering experiments based on laser wakefield accelerators, but the yield efficiency was as low as [Formula: see text], owing to low charge of the electron beam. Here, we propose a scheme to efficiently generate gamma rays of hundreds of MeV from submicrometer wires irradiated by petawatt lasers, where electron accelerating and wiggling are achieved simultaneously. The wiggling is caused by the quasistatic electric and magnetic fields induced around the wire surface, and these are so high that even quantum electrodynamics (QED) effects become significant for gamma-ray generation, although the driving lasers are only at the petawatt level. Our full 3D simulations show that directional, ultrabright gamma rays are generated, containing [Formula: see text] photons between 5 and 500 MeV within a 10-fs duration. The brilliance, up to [Formula: see text] photons [Formula: see text] per 0.1% bandwidth at an average photon energy of 20 MeV, is second only to X-ray free electron lasers, while the photon energy is 3 orders of magnitude higher than the latter. In addition, the gamma ray yield efficiency approaches 10%-that is, 5 orders of magnitude higher than the Compton scattering based on laser wakefield accelerators. Such high-energy, ultrabright, femtosecond-duration gamma rays may find applications in nuclear photonics, radiotherapy, and laboratory astrophysics.

The “Synchrotron Radiation Workshop” (SRW) computer code is extensively used for the development of insertion devices (IDs) and X-ray beamlines at the National Synchrotron Light Source II and at other light source facilities. Among frequently used types of SRW calculations are the calculations of spontaneous emission from an ID in a storage ring, physical optics based simulations of propagation of this partially-coherent radiation through a beamline, and the simulations of propagation of 3D time-dependent radiation pulses through instruments of X-ray Free-Electron Lasers (XFELs). The two types of radiation propagation calculations are CPU-intensive, therefore for each of them parallel algorithms have been developed in SRW. For the storage ring related calculations, the parallel processing was implemented using the Message Passing Interface (MPI). For the XFEL calculations, a shared memory approach provided by the Open Multi-Processing (OpenMP) was adopted. The two parallelization methods, and their implementation in SRW, have different advantages and drawbacks: the MPI-parallelization of partially-coherent calculations for storage rings has a good scaling, but over-consumes memory, whereas the OpenMP-parallelization of time-dependent XFEL calculations is memory-efficient, but it can only scale within one multi-core server. We are reporting the results of the efficiency tests of these two types of parallel calculations, obtained for representative optical schemes. The tests were performed on an isolated server as well on a large computer cluster - the US DOE’s NERSC scientific computing facility.