X-ray free electron laser

Transmission Fresnel zone plates and x-ray waveguides are presently the best high-resolution optical elements used in x-ray microscopy and micro-probing. The spatial resolution of zone plates is defined not only by the technological limit of about 10 nm but also by the effects of volume diffraction, even for high-order zone plates. The physical nature of a waveguide limits the theoretical spatial resolution to 10 nm, corresponding to the minimum thickness of film able to fulfil the conditions necessary for optical mode formation. Here, we show that reflection zone plates and Bragg-Fresnel lenses can overcame the resolution limit of transmission zone plates and waveguides and make it possible to achieve spatial resolution into the sub-nanometer range, subject to source size limitations. Such optics can be used with existing third-generation synchrotron radiation sources, as well as with x-ray laser sources, e.g., free-electron lasers.

In order to extend the production of intense coherent radiation to angstrom wavelengths, a laser wave is employed as a laser wiggler which propagates through a magnetized plasma channel. The plasma-loaded laser wigglers increase the ability of laser guidance and electron bunching process compared to the counterpropagating laser wigglers in vacuum. The presence of the plasma medium can make it possible to propagate the laser wiggler and the electron beam parallel to each other so that the focusing of the pulse will be saved. In addition, employing an external guide magnetic field can confine both the ambient plasma and the transverse motions of the electron beam, therefore, improving the free-electron lasers' efficiency, properly. Electron trajectories have been obtained by solving the steady state equations of motion for a single particle and the fourth-order Runge-Kutta method has been used to simulate the electron orbits. To study the growth rate of a laser-pumped free-electron laser in the presence of a plasma medium, perturbation analysis has been performed to combine the momentum transfer, continuity, and wave equations, respectively. Numerical calculations indicate that by increasing the guide magnetic field frequency, the growth rate for group I orbits increases, while for group II and III orbits decreases.

In this paper, we study the nonlinear interaction of a laser beam with a periodic lattice of nanoparticles in the presence of a planar magnetostatic wiggler. The static magnetic field of the wiggler can couple with the electric field of the laser wave and change the electric field intensity of the pumped wave, leading to the formation of a nonlinear force. In consequence, the nonlinear force enhances plasmonic oscillations of the electronic cloud of each nanoparticle causing electron density modulation, which improves self-focusing property of the laser beam propagating through a periodic lattice of nanoparticles. By manipulating a classical microscopic approach into plasmonic oscillations of electronic clouds of the nanoparticles and the well-known perturbative method, a nonlinear dispersion relation describing the evolution of the laser amplitude propagating through the nanoparticle lattice has been obtained. The effect of the wiggler magnetic strength on the evolution of the laser transverse profile has been discussed. It was found that by increasing the wiggler strength, the transverse profile bandwidth shrinks and laser focusing is enhanced. In addition, further numerical results indicated that by increasing the wiggler field strength, the cutoff frequency of the body waves increases. Published by AIP Publishing.

A linearly polarized laser pulse has been employed as a wiggler in a free-electron laser (FEL) in the presence of a plasma background for generating short wavelength radiation down to the extreme ultraviolet ray and X-ray spectral regions. Introducing plasma background in the FEL interaction region would lessen the beam energy requirement and also enhance both the beam current and the electron-bunching process. This configuration affords the possibility of scaling the device to more compact FELs and would have a higher tunability by changing the plasma density and the temperature of the electron beam. Electron trajectories have been analyzed using single-particle dynamics. The effect of plasma density on electron orbits has been investigated. A polynomial dispersion relation considering longitudinal thermal motion has been derived, by employing perturbation analysis. Numerical studies indicate that by increasing plasma density, the growth rate for groups I and II decreases, while the growth rate for group III increases. In addition, the effect of beam temperature and cyclotron frequency on the growth rate has been discussed. It has been found that by increasing the thermal velocity of the electron beam, the growth rate for groups I and III trivially decreases, while it increases for group II orbits. Besides, an increase in cyclotron frequency cause growth enhancement for group I orbits, while it present a growth decrement for group II and III orbits.

The X-band FEL collaboration is currently designing an X-ray free-electron laser based on X-band acceleration technology. Due to the higher accelerating gradients achievable with X-band technology, a X-band normal conducting linac can be shorter and therefore potentially cost ecient than what is achievable with lower frequency structures. This cost reduction of future FEL facilities addresses the growing demand of the user community for coherent X-rays. The X-band FEL collaboration consists of 12 institutes and universitiesthatjointlyworkonthepreparationofdesignreports for the specific FEL projects. In this paper, we report on the on-going activities, the basic parameter choice, and the integrated simulation results. We also outline the interest of the X-band FEL collaboration to use the electron linac CALIFES at CERN to test FEL concepts and technologies relevant for the X-band FEL collaboration.

Recently, the Turkic Accelerator Complex (TAC) is proposed as a regional facility for accelerator based fundamental and applied research. The complex will include linac on ring type electron-positron collider as a phi, charm and tau factory, linac based free electron laser (FEL), ring based third generation synchrotron radiation (SR) source and a few GeV proton accelerator. Preliminary estimations show that integral luminosity of hundred inverse femto-barns per year can be achieved for factory options. The FEL facility is planned to obtain laser beam between IR and soft X-ray region. In addition, SR facility will produce photon beams in UV and X-ray region. The proton accelerator will give opportunity to produce muon and neutron beams for applied research. The current status of the conceptual study of the complex is presented.

The feasibility of a CLIC-LHC based FEL-nucleus collider is investigated. It is shown that the proposed scheme satisfies all requirements of an ideal photon source for the Nuclear Resonance Fluorescence method. The tunability, monochromaticity and high polarization of the FEL beam together with high statistics and huge energy of LHC nucleus beams will give an unique opportunity to determine different characteristics of excited nuclear levels. The physics potential of the proposed collider is illustrated for a beam of Pb nuclei.

FERMI, the seeded free electron laser (FEL) in operation in Italy, is providing the User Community with unique fully coherent radiation, in the wavelength range 100–4 nm. FERMI is the first FEL fully synchronized by means of optical fibers. The optical timing system ensures an ultra-stable phase reference to its distributed clients. Several femtosecond longitudinal diagnostics verify the achieved performance; the bunch length monitor (BLM) and the bunch arrival monitor (BAM) will be presented in this paper. Feedback systems play a crucial role to guarantee the needed long-term electron beam stability. A real-time infrastructure allows shot-to-shot communication between front-end computers and the servers. Orbit feedbacks are useful in machine tuning, whereas longitudinal feedbacks control electron energy, compression and arrival time. A flexible software framework allows a rapid implementation of heterogeneous multi-input–multi-output (MIMO) longitudinal loops simply by selecting th...

This paper gives an introduction to the statistical physics of systems with long-range interaction. The main definition and direct consequences are presented, such as non-additivity and ensemble in equivalence in analyzing the mean field model. The narrative finally extends to a study of phase transitions in the N-body problem.

Analysis of current and future needs for access to optimize sources of synchrotron radiation has shown that the LSB should include undulators and multipole wigglers. The characteristics of two undulators and multipole wigglers design for optimal operation in the 0.1-1.0 keV and 1.0-20.0 keV range for undulators and multipole wigglers respectively, will be described. This includes the details of magnetic configurations (define from the Poisson/Superfish code) as well as their optical output.

The time-energy information of ultrashort X-ray free-electron laser pulses generated by the Linac Coherent Light Source is measured with attosecond resolution via angular streaking of neon 1s photoelectrons. The X-ray pulses promote electrons from the neon core level into an ionization continuum, where they are dressed with the electric field of a circularly polarized infrared laser. This induces characteristic modulations of the resulting photoelectron energy and angular distribution. From these modulations we recover the single-shot attosecond intensity structure and chirp of arbitrary X-ray pulses based on self-amplified spontaneous emission, which have eluded direct measurement so far. We characterize individual attosecond pulses, including their instantaneous frequency, and identify double pulses with well-defined delays and spectral properties, thus paving the way for X-ray pump/X-ray probe attosecond free-electron laser science.

We propose a systematic experimental investigation of spin-dependent fusion enhancement in deuterated metal crystals using channeled low-energy deuteron beams. Leveraging Tsyganov's crystal-channeling framework (TM-682/684), with an optional verylarge-radius pre-bender, we explore whether accelerator physics techniques can isolate spin-dependent fusion signatures in solid-state systems. The experimental design employs 70-120 keV polarized deuteron beams incident on oriented TiDx, ErDx, and PdDx crystal targets with x ≈ 0.9-1.0, using comprehensive neutron, charged particle, and photon detection. Success criteria include statistically significant spin asymmetry Aspin > 0 that reverses with magnetic field inversion and correlates with channeling alignment. This work addresses fundamental questions about the role of quantum spin states in nuclear processes within condensed matter environments.

What’s involved?
What is it about?
Nuclear Physics (Condensed Matter Fusion, Crystal Channeling). Key objects: Deuteron beam D+, Crystal targets (PdDx, TiDx, ErDx; x approx 0.9-1.0), Spin polarization P1, Channeling angle psi, Critical angle psi_c, Fusion cross-section sigma_eff, Astrophysical S-factor S(E), Gamow energy EG, Screening potential Ue, Asymmetry A_spin, Sommerfeld parameter eta, Flux concentration C(psi).
2 Formal Definitions & Theorems:
◦ Critical Channeling Angle: psi_c(E) = sqrt(2 U0 / E), for all E in [70,120] keV, U0 approx 25 eV.
◦ Enhanced Fusion Cross-Section: sigma_eff(E, Pi, Ue, psi) = S(E)/E exp(-sqrt(EG/(E+Ue))) * (1 + kappa(E) Pi) C(psi).
◦ Spin Asymmetry: A_spin = (Y(up) - Y(down))/(Y(up) + Y(down)) approx A_y(E) P1, reversible iff B vector inversion.
◦ Tsyganov Criterion (Bent Crystal Channeling): R > pv / U’_max iff stable channeling, U’_max restoring force.
◦ Sommerfeld Parameter: eta = Z1 Z2 alpha c / v iff 2 pi eta = sqrt(EG/E).
◦ Screening Strength: epsilon = Ue / E.
◦ Spin Correlation: Pi = P1 P2.
◦ Channeling Alignment: chi = psi / psi_c.
◦ Adiabaticity: Lambda = E / (h bar omega_ph).
3 Analytical Formulations:
◦ psi_c(E) approx sqrt(2 U0 / E), psi_c(100 keV) approx 22 mrad.
◦ ln Y(E) approx a - b sqrt(1/(E + Ue)).
◦ sigma_eff(E) = sigma_0(E) [1 + kappa_1(E)P1 + kappa_2(E)P1 P2].
◦ sigma(E) = sigma_0(E)[1 + A_y(E) P1].
◦ A_spin = (Y(up) - Y(down))/(Y(up) + Y(down)) approx A_y(E) P1.
◦ A_corr = (N up / L up - N down / L down)/(N up / L up + N down / L down).
◦ sigma_screened(E) approx S(E)/E exp(-sqrt(EG/(E + Ue))).
◦ C(psi) = flux into active micro-volume / flux for random incidence.
◦ sigma(E) = S(E)/E exp(-2 pi eta), 2 pi eta = sqrt(EG/E).
◦ eta = Z1 Z2 e^2 / (4 pi epsilon_0 h bar v) = Z1 Z2 alpha c / v.
◦ sigma_scr(E) approx S(E)/E exp(-sqrt(EG/(E + Ue))).
◦ V_l(r) = l(l + 1) h bar^2 / (2 mu r^2).
◦ sigma_pol(E) approx sum_{l,S} w_{lS}(P1, P2) sigma_{lS}(E).
◦ Y(psi) proportional to C(psi) Phi n_t L.
◦ eta = Z1 Z2 alpha c / v.
◦ epsilon = Ue / E.
◦ Pi = P1 P2.
◦ chi = psi / psi_c.
◦ Lambda = E / (h bar omega_ph).
◦ ln Y approx a - b sqrt(1/(1 + epsilon + c Pi)) + d f(chi) + ….
◦ psi_c(E) approx sqrt(2 U0 / E), U0 approx 25 eV.
◦ pv / R < U’_max iff R > R_c = pv / U’_max.
◦ psi_c(E) approx sqrt(2 U0 / E) => psi_c(90 keV, U0 = 25 eV) approx 24 mrad.
◦ psi_c(E) ~ sqrt(2 U0 / E), Delta psi_c / psi_c = -1/2 Delta E / E.
◦ Y(psi) proportional to C(psi) Phi n_t sigma_eff L.
◦ A_geom(E) approx kappa_0 psi_c(E)^2.
◦ T(psi, E, R) approx T_0(E, R) exp( - psi^2 / psi_c(E)^2 ).
◦ Y(psi, E) approx Y_0(E) T(psi, E, R) [1 + kappa_spin(E) P1].
◦ A_spin^{Config B} / A_spin^{Config A} ? >> 1.
◦ partial A_spin / partial psi approx 0, partial A_spin / partial T approx 0, partial A_spin / partial B proportional to +/- 1.
◦ partial ln Y / partial T >> partial A_spin / partial T, A_spin -> 0 when P1 -> 0.
◦ A_spin(psi >> psi_c) -> 0, A_spin(psi approx 0) >> 0, partial Y / partial psi proportional to partial A_spin / partial psi.
◦ ln Y(psi, T, x, P1) = a - b sqrt(1/(1 + epsilon(T,x) + c(T)P1 )) + d f(psi/psi_c) + cross-terms.
◦ sigma_total^2 = sigma_statistical^2 + sigma_geometry^2 + sigma_spin^2 + sigma_medium^2 + 2 sum_{i
◦ A_corr = (N up / L up - N down / L down)/(N up / L up + N down / L down), delta A approx sqrt( (1-A^2)/N_eff + sum_i delta_i^2 ).
◦ P_int approx n L sigma_d^3He(E).
◦ {x, T, psi, R, I, P1} at 1-10 Hz.
◦ A_corrected = A_raw * f_geom(psi, R) * f_temp(T) * f_loading(x).
4 Properties & Characteristics:
◦ Channeling: Geometric (C(psi)~2-5x for |psi|<=psi_c), Bounded (psi_c=20-27 mrad at 70-120 keV), Continuous trajectory oscillation.
◦ Spin Polarization: Asymmetric (A_spin 10-30%), Reversible, Correlates with partial waves.
◦ Screening: Enhanced (Ue > atomic estimates), Temperature-dependent, Exponential yield boost.
◦ Fusion: Spin-dependent (via entrance channels), Orthogonal to geometry/screening.
◦ Relations: Factorization (tunneling <=> screening, centrifugal <=> spin, flux <=> channeling); Equivalence (keV channeling approx GeV but accessible); Isomorphism (accelerator to fusion regimes).
5 Computational Methods:
◦ Ue Extraction: 1. Scan E={70,90,100,120} keV at two T, x. 2. Fit ln Y approx a - b/sqrt(E + Ue) via least-squares. 3. Cross-validate with DFT.
◦ Asymmetry Correction: 1. Collect N up/down, L up/down per spin. 2. Compute A_corr. 3. Propagate delta A with systematics.
◦ Regime Identification: 1. Vary {E,T,x,P1,psi}. 2. Fit ln Y model coefficients {b,c,d}. 3. Attribute dominance (large c => spin; b => screening; d => channeling).
◦ Dead-Time Correction: 1. Model R_obs = R_true/(1 + R_true tau). 2. Apply per spin in A_corr. 3. Verify with fake-flips, rate attenuation.

This is Cold Fusion. More precisely Lattice Confinement Fusion.

We propose a systematic experimental investigation of spin-dependent fusion enhancement in deuterated metal crystals using channeled low-energy deuteron beams. Leveraging Tsyganov's crystal-channeling framework (TM-682/684), with an optional verylarge-radius pre-bender, we explore whether accelerator physics techniques can isolate spin-dependent fusion signatures in solid-state systems. The experimental design employs 70-120 keV polarized deuteron beams incident on oriented TiDx, ErDx, and PdDx crystal targets with x ≈ 0.9-1.0, using comprehensive neutron, charged particle, and photon detection. Success criteria include statistically significant spin asymmetry Aspin > 0 that reverses with magnetic field inversion and correlates with channeling alignment. This work addresses fundamental questions about the role of quantum spin states in nuclear processes within condensed matter environments.

Feasibility studies on planar millimeter-wave cavity structures have been made. The structures could be used for linear accelerators, free-electron lasers, mm-wave amplifiers, or mm-wave undulators. The cavity structures are intended to be manufactured by using DXL (deep x-ray lithography) microfabrication technology. The frequency of operation can be about 30 GHz to 300 GHz. For most applications, a complete structure consists of two identical planar half structures put together face-to-face. Construction and properties of the constant gradient structures that have been investigated so far will be discussed. These cavity structures have been designed for 120 GHz 2π/3-mode operation.

bv 8 contractor of the U. S. Gwernment under contract No. W-31-lqOENG-38. Accordingly. the U. S Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do 90. for

PAL-XFEL, the new XFEL project of Pohang Acceler- ator Laboratory, aim to emit hard X-ray of 1 − 1.5 ˚ A, al- though its beam energy is only 3.7 GeV. To achieve the goal, coherent third harmonic radiation will be utilized. This paper discusses schemes of hard X-ray generation with 3.7 GeV electron beam and concludes that use of the third harmonic is the only possible way.

X-ray free-electron lasers based on self-amplified spontaneous emission promise users unprecedented X-radiation that is extremely bright, extremely short and transversely coherent. However, hard X-ray free-electron laser facilities under construction are all huge and expensive, consisting of high-energy linear accelerators and long undulators. The benefit of hard X-ray free-electron lasers may be limited to only a few regions in the world, unless it is possible to reduce the size. This paper discusses how small a hard X-ray free-electron laser facility can be. It is shown that a 1.5 A ˚X-ray free-electron laser is achievable using electron energy down to 4.5 GeV or lower if we use the third-harmonic radiation, but at the expense of the transverse coherence.

This document is presented by over 200 members of the UK Scientific Community and contains the scientific case for the establishment of the 4 th Generation Light Source (4GLS) at CLRC Daresbury Laboratory. It forms a part of the proposal to establish a National Centre for Accelerator Science Imaging and Medicine (CASIM) at the laboratory which was first submitted to the North West Science Review Committee in 2000. The proposal for 4GLS will be assessed through the 'Gateway Process', with peer review organised by EPSRC on behalf of OST. The mechanism of this process is described in Appendix I. In line with the stages of this process, the purpose of this document is to present the outline science case only for peer review. The full business case with a complete analysis of costs and risks will be presented at the appropriate stage of the process, following a design study. The UK has had an established and documented need for a low energy SR source for at least 15 years and the initial drive to establish such a source was borne out of the need to provide scientists both in the UK and internationally 1 with access to a world class source of high quality UV -XUV radiation. However, developments in accelerator technology during this period have now allowed us to propose a facility that will realise long-awaited scientific goals in the field of dynamics and nanoscience that far surpass our original expectations. This in turn brings together two previously rather independent communities, the 'low energy SR' community and the 'laser' community, and allows the synergies between SR and laser sources to be exploited to the full, for the first time, in cutting-edge experiments. This document is a proposal to establish the world's leading low energy source. 4GLS is a suite of accelerator-based light sources designed to complement the ESRF and diamond by providing state-of-the-art radiation in the low energy photon regime -from the far-infrared (IR) to the extreme ultraviolet (XUV). At its heart is a low energy ring based on a superconducting energy recovery linac (ERL) which will provide optimised synchrotron radiation from a variety of free electron lasers (IR to XUV), undulators and bending magnets. Contents THE 4GLS VISION .

lJesign requirements for a visible wavelength free-electron laser being developed at the Accelerator Test Facility at Brookhaven National Laboratory are presented along with predictions of laser performance from 3-D numerical simulations. The design and construction of the optical resonator, its alignment and control systems are also described. L [*] Work supported, in part, by a contract 0406594 from Broold-aven National Laboratory. , Also, under DOE contract no. DE-ACO2-76CH00016.

The Accelerator Test Facility (ATF) at Brookhaven National Laboratory (BNL) is an accelerator and beam physics user facility capable of producing a highbrightness, 70-MeV electron beam. Currently, a highgain harmonic generation (HGHG) free-electron laser (FEL) experiment is underway at the ATF. This is a collaborative effort between BNL and the Advanced Photon Source (APS). The experiment consists of two phases: 1) self-amplified spontaneous emission (SASE) and 2) HGHG. Here, a brief introduction to the HGHG theory, measurements in the SASE phase, the recent modifications in preparation for the HGHG phase, and future plans will be discussed.

The proposed UV-FEL user's facility at Brookhaven National Laboratory will require a photocathode gun capable of producing short (< 6 psec) bunches of electrons at high repetition rates (5 kHz), low energy spread (< 1.5 %), a peak current of 300 A (after compression) and a total bunch charge of up to 2 nC. At the highest charge the normalized transverse emittance should be less than 7 n: mm-mrad. We are presently' designing a gun that is expected to exceed these requirements. This gun will consist of 31/2 cells, constructed of GlidCop-t5, an aluminum oxide dispersion strengthened copper alloy. The gun will be capable of operating at duty factors in excess of 1%. Extensive beam dynamics studies of the gun were used to determine the effect of , varying the length of the f'trst cell, shaping the apertures between cells, and increasing the number of cells. In addition, a detailed thermal and mechanical study of the gun was performed to ensure , that the thermal stresses were well within the allowable limits and that copper erosion of the water channels would not occur.

For photoinjector, non-uniform laser beams generate non- uniform electron bunch charge density that experiences emittance growth on a time scale of the plasmas period. Experiments were performed at the Brookhaven Accelerator Test Facility (ATF) to investigate the emittance growth due to the non-uniform laser beams in the transverse dimension. Several laser masks were made to generate various laser distributions. Significant

The Brookhaven Accelerator Test Facility (ATF) uses a photocathode ff gun to provide a high-brightness electron beam intended for FEL and laser-acceleration exper-1 cells driven at 2856 MHz in _r-mode with a maximum iments. The ff gun consists of 1 cathode field of 100 MV/m. To achieve long lifetimes, the photocathode development concentrates on robust metals such as copper, yttrium and samarium. We illuminate these cathodes with a 10-ps, frequency-quadrupled Nd:YAG laser. We describe the initial ope,,'ation of the gun, including measurements of tr_,nsverse and ,ongitudinal emittance, quantum efficiencies, and peak current. These results are compared to models. * Work supported by DOE Contract No. DE-ACO2-76-CH00016.

The 500 nm Free-Electron Laser(FEL) at the Accelerator Test Facility (ATF) of the BrookhavenNational Laboratory isreviewed. We present an overview ofthe ATF, a highbrightness, 50-MEV, electron accelerator and laser complex which is a users' facility for accelerator and beam physics. A number of laser acceleration and FEL experiments are under construction at the ATF. The visible FEL experiment is based on a novel superferric 8.8 mm period undulator. The electron beam parameters, the undulator, the optical resonator, optical and electron beam diagnostics are discussed. The operational status of the experiment is presented. This report was prepared as an account of work sponsored by an agency of the United Stat¢s Government. Neither the United State, s Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer-cnc¢ heroin to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise dots not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

We report results from characterization of the output of a high-gain harmonic-generation (HGHG) free-electron laser (FEL). A CO 2 seed laser at a wavelength of 10.6 µm is amplified and frequencydoubled in the FEL to produce 5.3-µm output. The wavelength spectrum, pulse duration, and correlation length of the output verify that the light is longitudinally coherent. Comparisons of the measured electron energy distribution and the nonlinear harmonics of the 5.3-µm radiation with values obtained from numerical models are consistent with saturated HGHG FEL operation. In addition, a brief discussion of the extension of this technique to ever-shorter wavelengths as well as wavelength tailoring for specific experiments will be discussed.

The NSLS at Brookhaven National Laboratory is proposing the construction of a UV-FEL operating in 'the wavelength range from visible to 1000_. Nano-Coulomb electron pulses will be generated at a laser photo-cathode RF gun at a repetition "r_te of 10 'KHz, The 6 ps "" pulses will be accelerated to 250 MeV in a superconducting linac. The FEL consists of an exponential growth section followed by a tapered section. The amplifier input is a harmonic of a tunable visible laser generated either by nonlinear optical material or the _lon-linearity of the FEL itself. The FEL output, in 10.4 bandwidth is 1 mJ per pulse, resulting in an average power of 10 watts, The availability of radiation with these characteiqstics would open up new opportunities in photochemistry, biology and rlonlinear optics, as discussed in

RF electron guns with a strained superlattice GaAs cathode are expected to generate polarized electron beams of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode's surface and lower cathode temperature. We plan to install a bulk GaAs:Cs in a SRF gun to evaluate the performance of both the gun and the cathode in this environment. The status of this project is: In our 1.3 GHz ½ cell SRF gun, the vacuum can be maintained at nearly 10 -12 Torr because of cryo-pumping at 2K. With conventional activation of bulk GaAs, we obtained a QE of 10% at 532 nm, with lifetime of more than 3 days in the preparation chamber and have shown that it can survive in transport from the preparation chamber to the gun. The beam line has been assembled and we are exploring the best conditions for baking the cathode under vacuum. We report here the progress of our test of the GaAs cathode in the SRF gun. ____________________________________________

Brookhaven National Laboratory Accelerator Test Facility is a laser-electron linear accelerator complex designed to provide high brightness beams for testing of advanced acceleration concepts and high power pulsed photon sources. Results of electron beam parameters attained during the commissioning of the nominally 45 MeV energy machine are presented.

Starting from a three-wave interaction system of equations for free-electron lasers in the framework of a quantum fluid model, we show that these equations satisfy the Sine-Gordon equation. The full solution in space and in time of this set of equations are numerically obtained.

We derive expressions for the coupling coefficients for electromagnetic four-wave mixing in the non-linear quantum vacuum. An experimental setup for detection of elastic photon-photon scattering is suggested, where three incoming laser pulses collide and generate a fourth wave with a new frequency and direction of propagation. An expression for the number of scattered photons is derived and, using beam parameters for the Astra Gemini system at the Rutherford Appleton Laboratory, it is found that the signal can reach detectable levels. Problems with shot-to-shot reproducibility are reviewed, and the magnitude of the noise arising from competing scattering processes is estimated. It is found that detection of elastic photon-photon scattering may for the first time be achieved.

High availability and reliability are among the most desirable features of control systems in modern High-Energy Physics (HEP) and other big-scale scientific experiments. One of the recent developments that has influenced this field was the emergence of the Advanced Telecommunications Computing Architecture (ATCA). Designed for the telecommunications industry it has been successfully applied in other domains such as accelerator control systems. A good example is the application of ATCA standard for the design of Low Level RF (LLRF) control system for the X-Ray Free Electron Laser (XFEL) being developed in Deutsches Elektronen Synchrotron (DESY). Reliability and availability requirements for such a device play a crucial role among other parameters. Thus, the ATCA standard, with fivenines availability, is considered one of the best candidates for this system. This article focuses on the central management unit of every ATCA board, namely the Intelligent Platform Management Controller (IPMC), developed for the LLRF ATCA Carrier Board (CB). It also argues that it is possible to create a fully functional IPMC using base specifications only which is a much more economical solution than acquiring such products from various vendors dealing with ATCA-related products. The solution presented here fully complies with all the most recent revisions of specifications that are required for an ATCA board to properly operate in an ATCA shelf, communicate with the redundant Shelf Manager (ShM) and host Advanced Mezzanine Cards (AMCs). Full Electronic-Keying (EK) functionality is present on the LLRF CB supporting such protocols as PCI Express (PCIe), Gigabit Ethernet (GbE) and proprietary Low Latency Links (LLL) making it possible to route connections between all the boards in the system. The IPMC solution presented here is mainly hardware independent as proper code organization allowed to separate low-level device drivers and high-level application logic dealing with the ATCA standard, which makes it portable to new carrier board designs.

Short-wavelength free-electron lasers are now well established as essential and unrivalled sources of ultrabright coherent X-ray radiation. One of the key characteristics of these intense X-ray pulses is their expected few-femtosecond duration. No measurement has succeeded so far in directly determining the temporal structure or even the duration of these ultrashort pulses in the few-femtosecond range. Here, by deploying the so-called streaking spectroscopy technique at the Linac Coherent Light Source, we demonstrate a non-invasive scheme for temporal characterization of X-ray pulses with sub-femtosecond resolution. This method is independent of photon energy, decoupled from machine parameters, and provides an upper bound on the X-ray pulse duration. We measured the duration of the shortest X-ray pulses currently available to be on average no longer than 4.4 fs. Analysing the pulse substructure indicates a small percentage of the free-electron laser pulses consisting of individual high-intensity spikes to be on the order of hundreds of attoseconds. ince the first discovery of X-rays as a means for the measurement of crystal structures 1 , three-dimensional imaging techniques with X-rays for the investigation of the spatial composition of crystalline materials and biological specimens have steadily been refined to reach their current nanoscale resolution. With the advent of free-electron lasers 2-5 (FELs) operating on the self-amplified spontaneous emission-SASE-principle 6 , sources of high-intensity femtosecond X-ray pulses are now available. Combining high spatial resolution and ultrashort duration, these pulses open the door to full four-dimensional 'movies' that convey simultaneous information on atomic structure and function. The implementation of these femtosecond X-ray pulses as a reliable tool for fourdimensional characterization with ultrafast temporal and atomic spatial resolution, as demonstrated by some pioneering experiments with synchrotron radiation 7 or electrons , requires exact knowledge of the duration and temporal structure of individual X-ray pulses in the interaction region. Generally, this is not just a crucial requirement for time-resolved measurements ; the precise assessment of peak intensities also forms the fundamental basis for any nonlinear studies as well as successful single-shot diffraction experiments on non-repetitive and non-reproducible structures, like those demonstrated with individual biomolecules, membrane proteins or viruses . Modern SASE FELs are able to produce coherent extreme ultraviolet (XUV) and X-ray 5,19 radiation with sufficient intensities for single-shot or pump-probe measurements. The Linac Coherent Light Source 5 (LCLS) has the additional advantage of being easily tuned in photon energy as well as in average pulse duration. For our investigations of the shortest possible X-ray pulses, the LCLS was working in the so-called 'low-charge mode', producing X-ray pulses expected to be of sub-10 fs duration 20 . Due to the SASE process, the underlying temporal structure of the emitted pulses is stochastic, which means that each subsequent X-ray pulse is inherently different from the last one 21 . In addition, FEL pulses suffer from intrinsic timing jitter introduced by the electron accelerator with respect to a measurement device in the lab frame. As a consequence, a single-shot measurement is required for the determination of the time structure of consecutive SASE X-ray pulses. The X-ray pulse duration can be indirectly inferred from measurements on the electron bunch length before stimulated emission of X-ray Bremsstrahlung in the undulator. Although this method is capable of resolving electron bunch lengths as short as 25 fs (ref. 5), studies of fundamental ionization processes and recent two-colour cross-correlation measurements on longer X-ray pulses (>40 fs) have revealed a substantial deviation of the actual X-ray pulse duration from the measured electron bunch length . Another cutting-edge approach involves measuring the time-resolved electron beam energy loss and energy spread induced by the FEL process, with a transverse radiofrequency deflector located after the undulator 23 . However, all these measurements

Approximately 70% of commercial industries worldwide use electron accelerator technology for various irradiation processes. The advantages of irradiation processes compared to thermal and chemical processes are higher output levels, reduced energy consumption, less environmental pollution, and producing superior product quality and having unique characteristics that cannot be imitated by other methods. Research Center for Accelerator Technology (PRTA), BRIN, Indonesia is developing standing wave LINAC (SWL) for food irradiation applications at S-band frequencies (±2856 MHz), electron energy of 6-18 MeV, and an average beam power of 20 kW. This paper aims to model, simulate, and analyze the klystron modulator in the RF linear accelerator (LINAC). The klystron modulator is the main component of the RF LINAC, which functions to supply klystron power with the order of megawatt peak DC, so that the klystron can amplify the low-level RF signal from the RF driver into a high-power RF signal with a power of 2-6 MW peak. The klystron modulator modeling is carried out based on mathematical modeling, then simulated using LTspice to analyze the system performance of the klystron modulator. The results of the klystron modulator modeling simulation show stable system performance and dynamic response. So that it meets the specifications of the 6-18 MeV SWL LINAC being developed by PRTA-BRIN.

In this paper we discuss the harmonic undulator optical klystron free electron laser to enhance intensity and gain of free electron laser. Inclusion of betatron oscillation of electron while entering the undulator magnets gives extra perturbation which reduces its intensity and gain in free electron laser at several harmonics. In this we have enhanced our intensity and gain with the help of a harmonic undulator optical klystron scheme and compare the results with that of a standard optical klystron free electron laser.

The SPARC project foresees the realization of a high brightness photo-injector to produce a 150-200 MeV electron beam to drive 500 nm FEL experiments in various configurations, a Thomson backscattering source and a plasma accelerator experiment (these last two ones jointly with the project PLASMONX). The SPARC photoinjector is also the test facility for the recently approved VUV FEL project named SPARX. The second stage of the commissioning, that is currently underway, foresees a detailed analysis of the beam matching with the linac in order to confirm the theoretically prediction of emittance compensation based on the "invariant envelope" matching and the demonstration of the "velocity bunching" technique in the linac. SASE, SEEDING and Single Spike experiments are foreseen by the end of the current year. In this contribution we report the experimental results obtained so far and the scientific program for the near future.

The SPARC project foresees the realization of a free electron laser operating at 500 nm driven by a high brightness photo-injector at a beam energy of 150-200 MeV. The SPARC photoinjector is also the test and training facility for the recently approved VUV/soft X-ray FEL project named SPARX . The second stage of the commissioning, that is currently underway, foresees a detailed analysis of the beam matching with the linac in order to confirm the theoretically prediction of emittance compensation based on the "invariant envelope" matching, the demonstration of the "velocity bunching" technique in the linac and the characterisation of the spontaneous and stimulated radiation in the SPARC undulators. In this paper we report the experimental results obtained so far.

In this Letter we report the first experimental observation of the double emittance minimum effect in the beam dynamics of high-brightness electron beam generation by photoinjectors; this effect, as predicted by the theory, is crucial in achieving minimum emittance in photoinjectors aiming at producing electron beams for short wavelength single-pass free electron lasers. The experiment described in this Letter was performed at the SPARC photoinjector site, during the first stage of commissioning of the SPARC project. The experiment was made possible by a newly conceived device, called an emittance meter, which allows a detailed and unprecedented study of the emittance compensation process as the beam propagates along the beam pipe.

The IFUSP Microtron transport line guides the 5 MeV electron beam from the booster to the main microtron, where it can be accelerated up to 38 MeV in steps of 0.9 MeV. A few meters after leaving the main microtron, the beam is guided to the experimental hall, which is located 2.7 m below the accelerator room. The level translation is made by two 90 • bending magnets. In the experimental hall there is a switching magnet to drive the beam to two different experimental lines. Each of these lines has another 90 • bending magnet. These magnets were designed, constructed and characterized in house. In this work we present the analysis of the field distribution of these 90 • bending magnets. We also present a reproducibility analysis where the field distributions of two twin magnets are presented.

Since their discovery in 1898, x rays have tantalized scientists with their ability to see into solid objects. By the time synchrotron radiation was definitively observed almost a half-century later in 1947, the scientific use of x rays was well established. For example, they were, and continue to be, the principal probe of the positions of atoms in crystallized solids, from the comparatively simple structures in metals and semiconductors to the highly complex arrangements in biological molecules, such as proteins and DNA. By the early 1960s, the potential benefits of synchrotron radiation with its bright, wavelength-selectable beams of x rays were sufficiently apparent that significant attempts to harness it arose around the world. The subsequent growth of synchrotron radiation research has markedly expanded the scope of x-ray investigations. The result is a collection of spectroscopic, scattering, diffraction, and imaging tools that can probe in minute detail both the atomic and electronic structures of all manner of samples, large and extremely small, including gases, liquids, and non-crystalline and inhomogeneous solids.

The newly commissioned Orion laser system has been used to study dense plasmas created by combined short pulse laser heating and laser driven shock compression, using the ns and sub-ps laser beams available at the facility. The plasma density was systematically varied between 1 g/cc and 10 g/cc by using aluminum samples buried in plastic or diamond sheets. The aluminum was heated to electron temperatures between 500 eV and 700 eV allowing the plasma conditions to be diagnosed by K-shell emission spectroscopy. These were inferred from comparison with a variety of codes, including FLY and FLYCHK and from radiation-hydrodynamic simulations. Time-resolved X-ray emission was recorded using a spectrometer coupled to an X-ray streak camera, with additional time-integrated spectrometers recording onto image plate. The K-shell spectra show evidence of the lowering of the ionization potential, where the data are in reasonable agreement with FLY and FLYCHK when using the standard treatment proposed by Stewart and Pyatt. The data have also been compared to more sophisticated models and the results are presented.

We report the first experimental results on a high-gain harmonic-generation (HGHG) free-electron laser (FEL) operating in the ultraviolet. An 800 nm seed from a Ti-Sapphire laser has been used to produce saturated amplified output at the 266 nm third-harmonic. The results confirm the advantages of the HGHG FEL: stable central wavelength, narrow bandwidth and small pulse energy fluctuation. The harmonic output at 88 nm, which accompanies the 266 nm radiation, has been used in an ion pair imaging experiment in chemistry.

The slice transverse emittance of an electron beam is of critical significance for an x-ray FEL. In a photocathode RF gun, the slice transverse emittance is not only determined by the emission process, but also influenced strongly by the nonlinear space charge effect. In this paper, we study the slice transverse emittance evolution in a photocathode RF gun using a simple model that includes effects of RF acceleration, focusing, and space charge force. The results are compared with IMPACT-T space charge simulations and may be used to understand the development of the slice emittance in an RF gun. *

Dipole modes have been shown to be successful diagnostics for the beam position in superconducting accelerating cavities at the Free Electron Laser in Hamburg (FLASH) facility at DESY. By help of downmixing electronics the signals from the two higher order mode (HOM) couplers mounted on each cavity are monitored. The calibration, based on singular value decomposition, is more complicated than