Roman Tatchyn

Bio: Roman Tatchyn is an academic researcher from Stanford University. The author has contributed to research in topics: Undulator & Particle accelerator. The author has an hindex of 18, co-authored 128 publications receiving 1161 citations. Previous affiliations of Roman Tatchyn include United States Department of Energy & University of Oregon.

Linac coherent light source (LCLS) conceptual design report

Abstract: The Stanford Linear Accelerator Center, in collaboration with Argonne National Laboratory, Brookhaven National Laboratory, Los Alamos National Laboratory, Lawrence Livermore National Laboratory, and the University of California at Los Angeles, have collaborated to create a conceptual design for a Free-Electron-Laser (FEL) R&D facility operating in the wavelength range 1.5-15 {angstrom}. This FEL, called the ''Linac Coherent Light Source'' (LCLS), utilizes the SLAC linac and produces sub-picosecond pulses of short wavelength x-rays with very high peak brightness and full transverse coherence. The first two-thirds of the SLAC linac are used for injection into the PEP-II storage rings. The last one-third will be converted to a source of electrons for the LCLS. The electrons will be transported to the SLAC Final Focus Test Beam (FFTB) Facility, which will be extended to house a 122-m undulator system. In passing through the undulators, the electrons will be bunched by the force of their own synchrotron radiation to produce an intense, spatially coherent beam of x-rays, tunable in energy from 0.8 keV to 8 keV. The LCLS will include two experiment halls as well as x-ray optics and infrastructure necessary to make use of this x-ray beam for research in a variety of disciplines suchmore » as atomic physics, materials science, plasma physics and biosciences. This Conceptual Design Report, the authors believe, confirms the feasibility of constructing an x-ray FEL based on the SLAC linac.« less

Research and development toward a 4.5−1.5 Å linac coherent light source (LCLS) at SLAC

Abstract: In recent years significant studies have been initiated on the feasibility of utilizing a portion of the 3 km S-band accelerator at SLAC to drive a short wavelength (4.5−1.5 A) Linac Coherent Light Source (LCLS), a Free-Electron Laser (FEL) operating in the Self-Amplified Spontaneous Emission (SASE) regime. Electron beam requirements for single-pass saturation in a minimal time include: 1) a peak current in the 7 kA range, 2) a relative energy spread of e = λ 4π , where λ[m] is the output wavelength. Requirements on the insertion device include field error levels of 0.02% for keeping the electron bunch centered on and in phase with the amplified photons, and a focusing beta of 8 m/rad for inhibiting the dilution of its transverse density. Although much progress has been made in developing individual components and beam-processing techniques necessary for LCLS operation down to ∼20 A, a substantial amount of research and development is still required in a number of theoretical and experimental areas leading to the construction and operation of a 4.5−1.5 A LCLS. In this paper we report on a research and development program underway and in planning at SLAC for addressing critical questions in these areas. These include the construction and operation of a linac test stand for developing laser-driven photocathode rf guns with normalized emittances approaching 1 mm-mrad; development of advanced beam compression, stability, and emittance control techniques at multi-GeV energies; the construction and operation of a FEL Amplifier Test Experiment (FATE) for theoretical and experimental studies of SASE at IR wavelengths; an undulator development program to investigate superconducting, hybrid/permanent magnet (hybrid/PM), and pulsed-Cu technologies; theoretical and computational studies of high-gain FEL physics and LCLS component designs; development of X-ray optics and instrumentation for extracting, modulating, and delivering photons to experimental users; and the study and development of scientific experiments made possible by the source properties of the LCLS.

X-ray optics design studies for the SLAC 1.5-15 Å Linac Coherent Light Source (LCLS)

Abstract: In recent years, a number of systematic studies have been carried out on the design and R&D aspects of X-ray free-electron laser (XRFEL) schemes based on driving highly compressed electron bunches from a multi-GeV linac through long (30 m – 100+ m) undulators. These sources, when operated in the self-amplified spontaneous emission (SASE) mode, feature singularly high peak output power densities and frequently unprecedented combinations of phase-space and output-parameter values. This has led to correspondingly pivotal design challenges and opportunities for the optical materials, systems, components, and experimental configurations for transporting and utilizing this radiation. In this paper we summarize the design and R&D status of the X-ray optics section of the SLAC Linac Coherent Light Source (LCLS), a 1.5 Angstrom SASE FEL driven by the last kilometer of the SLAC 3-kilometer S-band linac.

The LCLS: A fourth generation light source using the SLAC linac

Abstract: Recent technological developments make it possible to consider use of the Stanford linear accelerator to drive a linac coherent light source (LCLS)—a laser operating at hard x‐ray wavelengths. In the LCLS, stimulated emission of radiation would be achieved in a single pass of a high‐energy, extremely bright electron beam through an undulator, without the optical cavity resonator normally used in storage ring‐based free‐electron lasers. The x‐ray laser beam would be nearly diffraction limited with very high transverse coherence, and would exhibit unprecedented peak intensity and peak brightness, and sub‐picosecond pulse length. Such an x‐ray source offers unique capabilities for a large number of scientific applications.

Short wavelength FELs using the SLAC linac

Abstract: Recent technological developments have opened the possibility to construct a device which we call a linac coherent light source (LCLS) (C. Pellegrini et al., Nucl. Instr. and Meth. A 331 (1993) 223; H. Winick et al., Proc. IEEE 1993 Particle Accelerator Conf., Washington, DC, May 1993; C. Pellegrini, Nucl. Instr. and Meth. A 341 (1994) 326; J. Seeman, SPIE Meet. on Electron Beam Sources of High Brightness Radiation, San Diego, CA, July 1993 [1–4]); it would be a fourth-generation light source, with brightness, coherence, and peak power far exceeding other sources. Operating on the principle of the free electron laser (FEL), the LCLS would extend the range of FEL operation to much shorter wavelength than the 240 nm that has so far been reached. We report the results of studies of the use of the SLAC linac to drive an LCLS at wavelengths from about 3 to 100 nm initially and possibly even shorter wavelengths in the future. Lasing would be achieved in a single pass of a low emittance, high peak current, high-energy electron beam through a long undulator. Most present FELs use an optical cavity to build up the intensity of the light to achieve lasing action in a low-gain oscillator configuration. By eliminating the optical cavity, which is difficult to make at short wavelengths, laser action can be extended to shorter wavelengths by self-amplified-spontaneous-emission (SASE), or by harmonic generation from a longer wavelength seed laser. Short wavelength, single pass lasers have been extensively studied at several laboratories and at recent workshops (M. Cornacchia and H. Winick (eds.), SLAC Report 92/02; I. Ben-Zvi and H. Winick (eds.), BNL report 49651 [5,6]). The required low-emittance electron beam can be achieved with recently-developed rf photocathode electron guns (B.E. Carlsten, Nucl. Instr. and Meth. A 285 (1989) 313; J. Rosenzweig and L. Serafini, Proc. IEEE 1993 Particle Accelerator Conf., Washington, DC, 1993 [7,8]). The peak current is increased by about an order of magnitude by compressing the bunch to a lenght of about 0.2 ps (rms). Techniques for beam transport, acceleration, and compression without emittance dilution have been developed at SLAC as part of the linear-collider project (J. Seeman, Advances of Accelerator Physics and Technologies, ed. H. Schopper (World Scientific, Singapore, 1993 [9]). The undulator length required to saturate the laser varies from about 15 m for a 100 nm FEL to about 60 m at 3 nm. Initial experiments, at wavelengths down to about 50 nm are planned using the 25-m long Paladin undulator now located at LLNL. In a proposed future LCLS R&D facility the short wavelength light pulses are distributed to multiple end stations using grazing-incidence mirrors. About 10 14 photons per pulse can be produced at a 120 Hz rate, corresponding to average brightness levels of about 10 21 photons/s/mm 2 /mrad 2 within 0.1% BW and peak brightness levels of about 10 31 photons/s/mm 2 /mrad 2 within 0.1% BW. Peak power levels are several hundred megawatts to several gigawatts. Electron energies required range from about 500 MeV for the 100 nm FEL to about 7 GeV for 3 nm.

First lasing and operation of an ångstrom-wavelength free-electron laser

Abstract: The Linac Coherent Light Source free-electron laser has now achieved coherent X-ray generation down to a wavelength of 1.2 A and at a brightness that is nearly ten orders of magnitude higher than conventional synchrotrons. Researchers detail the first operation and beam characteristics of the system, which give hope for imaging at atomic spatial and temporal scales.

Quantum electrodynamics

Abstract: THE subject of quantum electrodynamics is extremely difficult, even for the case of a single electron. The usual method of solving the corresponding wave equation leads to divergent integrals. To avoid these, Prof. P. A. M. Dirac* uses the method of redundant variables. This does not abolish the difficulty, but presents it in a new form, which may be dealt with in two ways. The first of these needs only comparatively simple mathematics and is directly connected with an elegant general scheme, but unfortunately its wave functions apply only to a hypothetical world and so its physical interpretation is indirect. The second way has the advantage of a direct physical interpretation, but the mathematics is so complicated that it has not yet been solved even for what appears to be the simplest possible case. Both methods seem worth further study, failing the discovery of a third which would combine the advantages of both.

Operation of a free-electron laser from the extreme ultraviolet to the water window

Abstract: We report results on the performance of a free-electron laser operating at a wavelength of 13.7 nm where unprecedented peak and average powers for a coherent extreme-ultraviolet radiation source have been measured. In the saturation regime, the peak energy approached 170 J for individual pulses, and the average energy per pulse reached 70 J. The pulse duration was in the region of 10 fs, and peak powers of 10 GW were achieved. At a pulse repetition frequency of 700 pulses per second, the average extreme-ultraviolet power reached 20 mW. The output beam also contained a significant contribution from odd harmonics of approximately 0.6% and 0.03% for the 3rd (4.6 nm) and the 5th (2.75 nm) harmonics, respectively. At 2.75 nm the 5th harmonic of the radiation reaches deep into the water window, a wavelength range that is crucially important for the investigation of biological samples.

X-Rays and Extreme Ultraviolet Radiation: Principles and Applications

Abstract: This self-contained, comprehensive book describes the fundamental properties of soft x-rays and extreme ultraviolet (EUV) radiation and discusses their applications in a wide variety of fields, including EUV lithography for semiconductor chip manufacture and soft x-ray biomicroscopy. The author begins by presenting the relevant basic principles such as radiation and scattering, wave propagation, diffraction, and coherence. He then goes on to examine a broad range of phenomena and applications. The topics covered include EUV lithography, biomicroscopy, spectromicroscopy, EUV astronomy, synchrotron radiation, and soft x-ray lasers. He also provides a great deal of useful reference material such as electron binding energies, characteristic emission lines and photo-absorption cross-sections. The book will be of great interest to graduate students and researchers in engineering, physics, chemistry, and the life sciences. It will also appeal to practicing engineers involved in semiconductor fabrication and materials science.

GENESIS 1.3: a fully 3D time-dependent FEL simulation code

Abstract: Numerical simulation codes are basic tools for designing Free Electron Lasers (FEL). They are used to study the impact of different parameters, e.g. wiggler errors and external focusing, which allow FEL users to optimize the performance. For faster execution some simulation codes assume radial symmetry or decompose the radiation field into a few azimuthal modes, although then this treatment does not include the full description of the FEL. This contribution describes the new FEL code GENESIS 1.3 which uses a fully three-dimensional representation of the FEL equations in the paraxial approximation for time-dependent and steady-state simulations of single-pass FEL. In particular this approach is suitable for cases where the radial symmetry is broken by the electron beam distribution as well as by wiggler errors, betatron motion and off axis injection of the electron beam. The results, presented here, are based on the parameters of the TESLA Test Facility FEL at DESY.