The unusually long insertion devices being prepared for Ångstrom-wavelength Free Electron Lasers (FELs) will generate spectral-angular distributions in the proposed experimental areas that are substantially different from those conventionally calculated for the far field. In this paper we provide a general overview of near-field effects and report on initial computational simulations of near vs. far field distributions for the SLAC linac Coherent Light Source (LCLS) undulator, an insertion device approximately 140 meters long. The properties of the coherent radiation as a limiting case of the near-field emission, for the special condition of a microbunched beam radiating along the undulator axis, are reviewed.
A. Agafonov, V. Androsov, J.I.M. Botman, V. Bulyak, A. Dovbnya, I. Drebot, P. Gladkikh, V. Grevtsev, Yu. Grigor'ev, A. Gvozd, V. Ivashchenko, I. Karnaukhov, N. Kovalyova, V. Kozin, V. Lapshin, A. Lebedev, V. Lyashchenko, V. Markov, N. Mocheshnikov, V. Molodkin, A. Mytsykov, I. Neklyudov, F. Peev, A. Rezaev, A. Shcherbakov, V. Skirda, V. Skomorokhov, A. Shpak, R. Tatchyn, Yu. Telegin, V. Trotsenko, A. Zelinsky, O. Zvonar'ova
Nowadays the sources of the X-rays based on a storage ring with low beam energy and Compton scattering of intense laser beam are under development in several laboratories. In the paper the state-of-art in development and construction of cooperative project of a Kharkov advanced X-ray source NESTOR based on electron storage ring with beam energy 40 - 225 MeV and Nd:YAG laser is described. The layout of the facility is presented and main results and constructing timetable are described. The designed lattice includes 4 dipole magnets with combined focusing functions, 20 quadrupole magnets and 19 sextupoles with octupole component of magnetic field. At the present time a set of quadrupole magnet is under manufacturing and bending magnet reconstruction is going on. The main parameters of developed vacuum system providing residual gas pressure in the storage ring vacuum chamber up to 10-9torr are presented along with testing measurement at NSC KIPT vacuum bench. The basic parameters of the X-rays source system such as laser system, diagnostic system, injection system are
presented. The facility is going to be in operation in the middle of 2006 and generated X-rays flux is expected to be of about 1013phot/s.
The temporal resolution of pump-flash interactions in the ultrashort (fs-as) regime is limited by the characteristic time constants of the excited states in the detector material. If the relaxation time constant is appreciably longer that the time interval between the pump and probe signals the response of the detector material to the probe represents a temporal convolution with the pump and probe responses, setting a lower limit on the resolution to which the interval between the two pulses can be measured. In most of the solid state ultrafast detection schemes that are being considered for the ultra-short pulse x-ray sources under current development at SLAC and elsewhere the characteristic time constants are related to the bound states of the atoms comprising the material or to the relaxation times of phase transitions or charge carrier populations of the lattice, setting a probable lower limit on the attainable resolution on the order of ~0.1 ps. In this paper we consider a novel detection principle predicated on the excitation of specially prepared unbound states in an ionized plasma with high pump and probe fields, and estimate its potential for extending the lower limit of resolution into the as regime.
The results of theoretical and numerical considerations of linear Compton scattering are used to evaluate characteristics of X-rays produced by collision between a low emittance electron beam and intensive laser light in an X-rays generator NESTOR of NSC KIPT. Two main generation modes have been under consideration at preliminary NESTOR design. There are the operation mode for medicine 33.4 keV X-rays production using 43 MeV electron beam and Nd:YAG laser beam and higher energy X-rays production mode providing X-rays with energy up to 900 keV with 225 MeV electron beam and Nd:YAG laser beam. It is supposed to use an optical cavity for laser beam accumulation of about 2.6 m long and an interaction angle of about 3° in both operation modes. A few more operation modes provide ossibility to expand operation range of NESTOR. Using interaction angle 10° and 150° along with optical resonator 42 or 21 cm long and the second mode of laser light it is possible to produce X-rays in energy range from a few keV till 1.5 MeV. The intensity and spectral brightness of the X-rays is expected to be ~ 1013 phot/s and ~ 1013phot/s/mm2/mrad2/0.01%BW respectively.
An international co-operative project to develop an advanced X-ray source on the basis of Compton back-scattering is in progress. The goal is the re-configuration of the Kharkov Institute of Physics and Technology (KIPT) N-100M storage ring to support the efficient interaction of its electron beam with a high power pulsed-laser cavity. At equilibrium both the electron and X-ray beams' phase space characteristics are determined by a balance of stochastic photon cooling and emission. In this paper the operating parameters and fundamental spectral properties of the novel source are described.
Alexey Agafonov, Jan Botman, V. Bulyak, Peter Gladkikh, Alexander Kachinskiy, Ivan Karnaukhov, Andrey Lebedev, Andrey Mytsykov, Alexander Shcherbakov, Roman Tatchyn, Yuriy Telegin, Marnix van der Wiel, Andrey Zelinsky
An international co-operative project to develop an advanced X-ray source on the basis of Compton backscattering is described. The goal is the re-configuration of the Kharkov Institute of Physics and Technology (KIPT) N-100 storage ring to support the efficient interaction of its electron beam with a high power pulsed-laser cavity. At equilibrium both the electron and X-ray beams’ phase space characteristics are determined by a balance of stochastic photon cooling and emission. In this paper the operating parameters and fundamental spectral and temporal properties of the novel source are summarized and the potential for its development.into an ultra-short pulse source is discussed.
In recent months a novel femtosecond X-ray source, the Sub-Picosecond Photon Sourcxe (SPPS), has been commissioned at SLAC. The source consists of moderate-emittance electron bunches extracted from the SLAC Damping Rings, an acceleration through the SLAC 3km linac up to ~28 GeV, compression through an initial compressor chicane followed by further compression through an existing SLAC dogleg in the Final Focus Test Beam (FFTB) tunnel, and generation of X-ray pulses of about the same temporal length (~80 fs) by an APS-built 28 period transverse undulator. In this note we consider the possibility of extending the capabilities of the SPPS to produce femtosecond pulses of arbitrary polarization, which would enable the impulsive excitation and study of ultrafast magnetic phenomena, a field hitherto inaccessible to experimental science. An analysis of the expected performance of the proposed source together with requirements for linac operation are presented.
The advantages and challenges of using a powerful x-ray source for the fast ignition of compressed Inertial Confinement Fusion (ICF) targets have been considered. The requirements for such a source together with the optics to focus the x-rays onto compressed DT cores lead to a conceptual design based on Energy Recovery Linacs (ERLs) and long wigglers to produce x-ray pulses with the appropriate phase space properties. A comparative assessment of the parameters of
the igniter system indicates that the technologies for building it, although expensive, are physically achievable. Our x-ray fast ignition (XFI) scheme requires substantially smaller energy for the initiation of nuclear fusion reactions than other methods.
In this work we describe new kind of refractive lens for focusing of high flux X-ray radiation of next generation X-ray sources. It is proposed to create such lens driving relatively low electric currents inside evacuated capillary made of low-Z material. The numerical simulations show that during the 0.1 - 3 microsecond(s) , 2-6 kA current pulse, the wall sustained stable capillary discharge plasma forms a concave density profile with almost parabolic index of refraction. Compared to solid materials, the plasma is able to sustain 2-3 order of magnitude larger doze ~100 eV/atom and can operate at larger fluxes and specifically in the relatively long wavelength region 1-4 keV where solid materials have dramatically larger absorption. For radiation sources similar to LCLS, the plasma lens can be placed right at the exit of undulator and deliver 3-4 orders of magnitude larger fluxes in the focal spot.
The Linac Coherent Light Source (LCLS) is a 1.5 to 15 A- wavelength free-electron laser (FEL), currently proposed for the Stanford Linear Accelerator Center (SLAC). The photon output consists of high brightness, transversely coherent pulses with duration <300 fs, together with a broad spontaneous spectrum with total power comparable to the coherent output. The output fluence, and pulse duration, pose special challenges for optical component and diagnostic designs. We discuss some of the proposed solutions, and give specific examples related to the planned initial experiments.
Free electron lasers have the promise of producing extremely high-intensity short pulses of coherent, monochromatic radiation in the 1-10 keV energy range. For example, the Linac Coherent Light Source at Stanford is being designed to produce an output intensity of 2x1014 W/cm2 in a 230 fs pulse. These sources will open the door to many novel research studies. However, the intense x-ray pulses may damage the optical components necessary for studying and controlling the output. At the full output intensity, the dose to optical components at normal incidence ranges from 1-10 eV/atom for low-Z materials (Z<14) at photon energies of 1 keV. It is important to have an understanding of the effects of such high doses in order to specify the composition, placement, and orientation of optical components, such as mirrors and monochromators. Doses of 10 eV/atom are certainly unacceptable since they will lead to ablation of the surface of the optical components. However, it is not precisely known what the damage thresholds are for the materials being considered for optical components for x-ray free electron lasers. In this paper, we present analytic estimates and computational simulations of the effects of high-intensity x-ray pulses on materials. We outline guidelines for the maximum dose to various materials and discuss implications for the design of optical components.
A unique X-ray source, of exceptional brightness and with pulse widths as low as 30 fs rms, has been proposed at the Stanford Linear Accelerator Center. Named the Sub-Picosecond Photon Source (SPPS), the facility takes 30 Gev bunches from the linac and compresses them in three stages to achieve peak currents of 30 kA in the Final Focus Test Beam (FFTB) beamline. The existing FFTB can accommodate an undulator of up to 10 m in length which will deliver ~108 1.5 A photons per pulse in a 0.1% bandwidth with a peak brightness of ~1025 photons/sec/mm2/mrad2/0.1% BW, in a pulse width of ~80 fs FWHM. The short electron bunches are also ideal for plasma and wakefield studies as well as providing abundant R&D possibilities for verifying short bunch behavior in the future Linac Coherent Light Source (LCLS).
The Linac Coherent Light Source (LCLS) is a free-electron (FEL) now in the advanced planning stage at the Stanford Linear Accelerator Center. This machine will employ the process of self-amplified spontaneous emission (SASE) to generate extremely bright pulses of hard x-ray radiation, at wavelengths d own to about 1.5A. Being the first laser to operate in this spectral region, it will produce radiation with properties that are radically different in several respects from that produced by any other x-ray source, including today's 3rd generation synchrotron sources. Using this radiation to best scientific advantage will place unprecedented demands on the x-ray optics. Most importantly, the LCLS will be a pulsed radiation source, with extremely intense, short pulses and a low duty cycle. It will be possible and desirable to collect a complete experimental data set with a single radiation pulse. This will require optics which manipulate a single pulse so as to cover the full range of parameter space to be studied. Also, because of the very high peak power, sub-picosecond pulse length, and very high coherence of the FEL pulse, optics must be robust and able to preserve the short pulse length, and able to preserve spatial coherence. Finally, since it seems likely that the LCLS FEL radiation will be right enough to promote nonlinear x-ray processes, there will be a need for optics which emphasize particular nonlinear effects.
The SLAC Linac Coherent Light Source (LCLS), an X-ray Free- Electron Laser (XRFEL) designed to operate over a fundamental energy range of 1 - 8.5 keV, is expected to produce ultra-short pulse lengths down to approximately 200 fs. Even though this represents an enormous decrease with respect to currently available high-brightness X-ray sources, it is believed that for a number of proposed LCLS applications (e.g., imaging or structural studies of molecular clusters with highly focused pulses) it will become necessary to reduce the pulse duration even further, possibly by as much as 1-2 orders of magnitude. Of the various compressive or chopping (i.e., slicing) optical techniques considered for shortening the pulse, the focus of one of our recent studies has been on a recently proposed slicing scheme based on the interaction of a longitudinally chirped LCLS pulse with a specially designed multilayer. The chopping mechanism is the selective reflection of only that sub-interval of the pulse that fulfills the multilayer Bragg condition. Of particular interest are the reflection efficiency and the distortion induced in the temporal fine structure of the reflected pulse, both of which can be critical to the efficacy of the scheme for a given application. Here we present results of selected parameter studies of different multilayer-based beam chopper systems using codes and LCLS radiation models developed at SSRL and LLNL.
In recent years, a number of studies have been conducted on the source properties of linac-driven X-Ray Free-Electron Lasers (XRFELs) operating in the Self-Amplified Spontaneous Emission (SASE) regime. In longitudinal phase space the output of such devices typically consists of a randomly-distributed train of fully-transversely-coherent micropulses of randomly varying intensity and an average length (corresponding to the coherence length) two to three orders of magnitude smaller than the transverse diameter of the beam. Total pulse lengths are typically of the same order of size as the beam diameter. Both of these properties can be shown to significantly impact the performance of otherwise conventional synchrotron radiation optics (viz., mirrors, lenses, zone plates, crystals, multilayers, etc.) designed to filter or modulate the phase space parameters of the radiation pulses. This, in turn, can influence the design and performance of beam line instrumentation (viz., monochromators, spectrometers, etc.) employed to match the phase space acceptance of an experiment to an XRFEL source. In this paper we outline a preliminary investigation of short-pulse effects on the performance and design of selected optical components and instrumentation for the proposed 1.5 Angstrom SLAC Linac Coherent Light Source (LCLS) and discuss the implication of our results for critical applications such as microfocusing and monochromatization.
High-contrast energy modulation (HCM) of high-brightness electron bunches, made possible by recent experimental or conceptual advancements in ultra-short-pulse terawatt IR/visible/UV laser and storage ring-based insertion device technologies, makes it possible to consider schemes for generating ultra-short radiation pulses based on the highly non-linear bunching induced by the modulation. In prior publications, the single-particle interaction with the laser and insertion device fields was analyzed and shown to lead to the appropriate initial conditions for bunching. In the present paper we report on continuing studies of the collective (i.e., multi-particle) dynamics of the modulated bunch region. In addition, we describe preliminary analyses that indicate that the coherent power generated by HCM sources could be made comparable to or greater than that of corresponding single-pass, gain-saturated Free Electron Lasers (FELs). Selected differences between the dynamics and performance of conventional high-harmonic FELs and Optical Klystrons (OKs) and the analyzed high-contrast modulation/bunching system are discussed. Some possible applications of HCM to the flexible tailoring of particle beam phase space parameters are mentioned.
In recent years, substantial exploratory studies have been conducted on the source properties of idealized Angstrom- wavelength Free-Electron Lasers (FELs) operating in the Self- Amplified Spontaneous Emission (SASE) regime. With the more recent advent of dedicated design studies aimed at developing SASE FEL R&D facilities, attention has focused on developing more realistic descriptions of the FEL source taking into account various anticipated departures of the electron beam from ideality. In this paper we extend prior statistical descriptions of the SASE FEL source to enable the systematic inclusion of the effects of correlated variations of the electron beam's phase-space parameters vs, e.g., longitudinal position in the bunch. Selected practical consequences of incorporating the extended source parameter space in the development or design of coherence-related methods and instruments are discussed.
In recent years, comprehensive design studies have been initiated on angstrom-wavelength free-electron laser (FEL) schemes based on driving highly compressed electron bunches from a multi-GeV linac through long undulators. The output parameters of these sources, when operated in the so-called self-amplified spontaneous emission mode, include lasing powers in the 10-100 GW range, full transverse and low-to- moderate longitudinal coherence, pulse durations in the 50- 500 fs range, broad spontaneous spectra with total power comparable to the coherent output, and flexible polarization parameters. In this paper we summarize the status of design studies of the x-ray optics system and components to be utilized in the SLAC linac coherent light source, a 1.5-15 angstrom FEL driven by the last kilometer of the SLAC three kilometer S-band linac. Various aspects of the overall optical system, selected instrumentation and individual components, radiation modeling, and issues related to the interaction of intense sub-picosecond x-ray pulses with matter, are discussed.
The nonlinear simulation of x ray free-electron lasers is dealt with using the non-wiggler-averaged MEDUSA simulation code and realistic wiggler model built up from the contributions of permanent magnets in a Halbach configuration in conjunction with a model for a FODO lattice for enhanced focusing. The specific parameters of interest are relevant to the linac coherent light source design at SLAC and deals with a 15 GeV/5 kA electron beam, and a wiggler with a 3.0 cm period and an on-axis amplitude of approximately 12.7 kG which results in x ray emission at wavelengths in the vicinity of 1.3 angstrom.
In recent years, substantial design studies have been initiated on angstrom-wavelength free-electron laser (FEL) schemes based on driving highly compressed electron bunches from a multi-GeV linac through long (30 m - 100 m) undulators. Within the context of the technologies considered, the attainment of such parameters involves the development of large, complex, and highly costly technical systems, and the preliminary or concomitant execution of complex demonstration experiments to study self-amplified spontaneous emission (SASE), or other gain mechanisms, on lower-energy linacs at longer wavelengths. In all phases of the FEL gain processes undertaken by such studies, the strength of the FEL radiation field in the electron bunch rest frame is typically no more than a fraction of a percent of the transformed undulator field. In contrast, recently developed terawatt lasers in the IR/visible/UV regimes could be made to match or exceed a transformed undulator's field strength in an electron bunch of suitable energy, enabling high-level control of the FEL gain process, and thereby of the spectral and temporal parameters of the FEL output. Due to the highly non-linear nature of the radiation/electron bunch interaction, control and generation of high-power FEL radiation with such lasers could, in principle, be extended well into the soft x-ray regime. In this presentation we discuss selected schemes for attaining high-power x ray FEL output in radiation pulses of conventional or ultra-short duration, and examine ways in which lower-cost, equivalent studies of SASE gain at lower energies could be achieved. Selected applications to particle beam diagnostics are also examined.
John Seeman, Karl Bane, R. Boyce, G. Loew, P. Morton, Heinz-Dieter Nuhn, J. Paterson, Piero Pianetta, T. Raubenheimer, Roman Tatchyn, V. Vylet, Herman Winick, Claudio Pellegrini, James Rosenzweig, Gil Travish, Donald Prosnitz, Ernst Scharlemann, Klaus Halbach, Kwang Kim, Ming Xie
We describe the possible use of the SLAC linac to drive a unique, powerful, short wavelength Linac Coherent Light Source. Using the FEL principle, lasing is achieved in a single pass of a high peak current electron beam through a long undulator by self-amplified-spontaneous- emission (SASE). The main components are a high-brightness electron RF gun with a photocathode, two electron bunch length compressors, the existing SLAC linac, beam diagnostics, and a long undulator combined with a FODO quadrupole focusing system. The RF gun, to be installed about 1 km from the end of the SLAC linac, would produce a single bunch of 6 X 109 electrons with an invariant emittance of about 3 mm-mrad and a bunch length of about 500 micrometers . That bunch is then accelerated to 100 MeV and compressed to a length of about 200 micrometers . The main SLAC linac accelerates the bunch to 2 GeV where a second bunch compressor reduces the length to 30 - 40 micrometers and produces a peak current of 2 - 3 kA. The bunch is then accelerated to 7 - 8 GeV and transported to a 50 - 70 m long undulator. Using electrons below 8 GeV, the undulator could operate at wavelengths down to 2 nm, producing about 10 GW peak power in sub-ps light pulses.
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