|Characterization of Partially Coherent Ultrashort FEL Pulses
|Temporal metrology is a major need for free-electron lasers. However, the lack of longitudinal coherence, that is shot-to-shot fluctuations, of these sources has prevented so far the full amplitude and phase temporal characterization of FEL pulses. To sort out this issue, we propose a solution inspired from attosecond metrology, where XUV pulse measurement techniques already exist, and from coherent diffraction imaging, where numerical solutions have been developed for processing partially coherent diffraction patterns. The experimental protocole implies the measurement of photoelectron spectra obtained through XUV-laser photoionisation. The spectra are then processed with an algorithm in order to retrieve the partially coherent FEL pulse. When applied to SASE FELs, the technique gives access to the full statistics of the emitted pulses. With seeded-FELs, the pulse shape becomes stable from shot-to-shot, but an XUV-laser time jitter remains. In that case, the technique enables the joint measurement of the FEL pulse shape (in amplitude and phase) and of the laser/FEL jitter envelope. The concept has been validated with numerical simulations in the context of the LUNEX5 FEL project.
|Quantum FEL II: Many-electron Theory
|We investigate the emergence of the quantum regime of the FEL when many electrons interact simultaneously with the wiggler and the laser field. We find the Quantum FEL as the limit where only two momentum states are populated by the electrons. Moreover, we obtain exponential gain-per-pass and start-up from vacuum.
|Quantum FEL I: Multi-mode Theory
|The quantum regime of the FEL in a single-mode, single-particle approximation is characterized by a two-level behaviour of the center-of-mass motion of the electrons. We extend this model to include all modes of the radiation field and analyze the effect of spontaneous emission. In particular, we investigate this scattering mechanism to derive experimental conditions for realizing an FEL in the quantum regime.
|Two-color Free-electron Laser via Two Orthogonal Undulators
|An amplifier Free electron Laser (FEL) including two orthogonal polarized undulators with different periods and field intensities is able to emit two color radiations with different frequency and polarization while the total length of device does not change respect to usual single color FELs. The wavelengths of two different colors can be changed by choosing different periods, while variation in the magnetic strengths can be used to modify the gain lengths.
|Spectral Limits and Frequency Sum-rule of Current and Radiation Noise Measurement
Funding: This research was supported by a grant from the United States-Israel Binational Science Foundation(BSF), Jerusalem, ISRAEL
The current noise spectrum of an electron beam is generally considered white and expressed by the shot-noise formula (eI0). It is possible to control the spectral energy of a random electron beam current by longitudinal space charge microdynamics and dispersive transport. Both noise suppression (relative to eI0)[1,2] and noise enhancement have been demonstrated, exhibiting sub/super-Poissonian particle distribution statistics, respectively. We present a general theory for the current noise of an e-beam and its radiation emission in the entire spectrum. The measurable current noise spectrum is not white. It is cut-off at high frequencies, limited by the measurement length and the beam axial momentum spread (fundamentally limited by quantum uncertainty). We show that under certain conditions the current noise spectrum satisfies a frequency sum-rule: exhibiting noise enhancement in one part of the spectrum when suppressed at another part and vice versa. The spontaneous emission (radiation noise) into a single radiation mode or single direction in any scheme (OTR, Undulator etc.) is sub-radiant when the beam current is sub-Poissonian and vice versa, but the sum-rule does not apply.
|An Analysis of Optimum Out-coupling Fraction for Maximum Output Power in Oscillator FEL
|The effect of the out-coupling fraction on the output power in oscillator FEL is analyzed. The formulas of the optimum out-coupling fraction and the corresponding maximum output power are given. They are dependent on the initial small signal gain and the passive loss rate of the light in the optical cavity. The initial comparison show that the result given by the formula agree well with the results in references.
|A Simple Method for Generating a Few Femtosecond Pulses in Seeded FELs
Funding: Work supported by Major State Basic Research Development Program of China (2011CB808301) and the Fundamental Research Funds for the Central Universities of China (WK2310000045)
We propose a simple method to generate a few femtosecond pulses in seeded FELs. We use a longitudinal energy-chirped electron beam passing through a dogleg where transverse dispersion will generate a horizontal energy chirp, then in the modulator, a seed laser with narrow beam radius will only modulate the centre part of electron beam and short pulses in high harmonics will be generated in the radiator. Using a representative realistic set of parameters, we show that 30 nm XUV pulse with duration of 8 femtoseconds (FWHM) and peak power of GW level can be generated from a 180 nm UV seed laser with beam waist of 75 m.
|Numerical Simulation of a Super-radiant THz Source Driven by Femtosecond Electron Bunches
Funding: We would like to acknowledge the financial support from the Swedish FEL center.
Pulsed THz FELs are typically driven by rf Linacs which produce intense electron bunches with a duration of a few picoseconds or even shorter. When the bunch duration is less than a picosecond, the wavelength of the THz light is greater than the bunch length and the FEL operates in the super-radiant (SR) regime*. In the report, we summarize our studies performed for an SR source operating in the THz frequency range. In particular, we focus on an open-type planar undulator comprising no guiding structure. Using a numerical code that supports 3D modeling of the SR dynamics as well as statistical properties of electron bunches, we analyze influence of electron bunch parameters on generated THz radiation and reveal some surprising results. More specifically, for the considered undulator configuration, we predict degradation in the angular divergence and spectral broadening of the generated radiation as the electron bunch emittance decreases. We also demonstrate how electron bunch broadening associated with the electron energy spread can eventually be suppressed.
* R. Chulkov, V. Goryashko, and V. Zhaunerchyk, Report III of the series of reports by the Swedish FEL Center and FREIA Group, http://www.diva-portal.org/smash/get/diva2:699684/FULLTEXT01.pdf.
|Poster TUP012 [1.553 MB]
|X-Ray Smith-Purcell Radiation from a Beam Skimming a Grating Surface
Smith-Purcell radiation as a base of Free Electron Lasers is actively studied experimentally and by simulating. Usually the beam is supposed to move at some distance above the target. In practice the distance is tried to decrease so that the beam passes very close to the target surface. Experimental data contains the information about grating heating. The authors of article* suggested the cause of the heating is that the beam skims the grating surface. Developing the method used in**,*** we give the analytical description of the X-Ray radiation arising when the beam of charge particles moves parallel above the periodical target, but the part of the beam crosses the target. The radiation arising is the superposition of Smith-Purcell radiation and transition radiation from the grating. This radiation determines the process of beam bunching and following gain of radiation.
*H.L.Andrews et al,Phys. Rev. ST AB 12 (2009) 080703
**A.A.Tishchenko, A.P.Potylitsyn, M.N.Strikhanov, Phys. Rev. E 70 (2004) 066501
***D.Yu.Sergeeva, A.A.Tishchenko, M.N.Strikhanov, NIM B 309 (2013) 189
|Forward X-Ray and Ultraviolet Smith-Purcell Radiation for FEL
The scheme of Free Electron Lasers based on Smith-Purcell effect is well known to describe the process of interaction between an electron beam and evanescent wave, which bunches this beam. In this work we concentrate on the process of generation of the radiation propagating at small angles. In terms of approach described in detail in*,**, we investigate the Smith-Purcell radiation at oblique incidence of a single charged particle for X-Ray and UV frequency region. This forward radiation propagates through all the region of the beam moving and provides more close interaction between the beam and the radiation, than usual surface waves existing in FELs. Spectral and angular characteristics of the forward radiation are discussed from point of view its role in Smith-Purcell based FELs.
*A.P.Potylitsyn, M.I.Ryazanov, M.N.Strikhanov, A.A.Tishchenko, Diffraction Radiation from Relativistic Particles, Springer, 2011
**D.Yu.Sergeeva, A.A.Tishchenko, M.N.Strikhanov, NIM B 309 (2013) 189
|Radiation and Interaction of Layers in Quasi-plane Electron Bunches Moving in Undulators
|The model of radiating planes (1D radiating gas) consisting of electrons that oscillate and travel with a relativistic translational velocity allows one to develop a simple general theory describing a number of important effects of radiation in a undulator for dense electron bunches formed in photoinjector accelerators. Having based on this method and taking into account both Coulomb and radiation interactions of the planes with an arbitrary density, particle velocity distribution and energy chirp we have found analytically and numerically efficiency and frequency spectrum for coherent spontaneous radiation, including conditions for generation of minimum narrow and very broadband spectra. The developed theory has been applied for estimation of a powerful terahertz radiation source with a moderate energy of electrons.
|Quasi-optical Theory of Terahertz Superradiance from an Extended Electron Bunch
Funding: This study was supported by the Russian Foundation for Basic Research (project no. 14-08-01180) and the Dynasty Foundation.
We consider superradiance of an extended relativistic electron bunch moving over a periodically corrugated surface for the generation of multi-megawatt terahertz pulses*. To study the above process we have developed a three-dimensional, self-consistent, quasi-optical theory of Cherenkov stimulated emission which includes a description of the formation of evanescent waves near the corrugated surface and its excitation by RF current induced in the electron bunch. Results obtained in the framework of a quasi-optical model were confirmed by direct CST STUDIO PIC simulations. There is a possibility of advancement towards still shorter wavelengths (infrared and optical), which can be achieved by decreasing the period of the diffraction gratings and increasing the density and energy of the particles in the electron bunches. Increase of coupling impedance can be obtained by using inclined incidence of electron bunch on corrugated surface (clinotron configuration).
Ginzburg N.S et al. Phys. Rev. Lett. 2013. V.110, Iss.18. 184801.
|Using Lorentz Transformations for Simulations of Wiggler Superradiance from the Picosecond Electron Bunches
Funding: This work was supported by Russian Foundation for Basic Research under Grant No 12-02-01152.
In this paper we present a theoretical analysis of superradiance (SR) from picosecond electron bunches wiggling in periodical undulator field based both on the method of averaged ponderomotive force and on a direct numerical PIC (particle-in-cell) simulation. Within both approaches the analysis takes place in the reference frame co-moving with electrons which allows simplifying the procedure of simulation significantly due to the fact that all the spatial scales including the radiation wavelength, the length of the beam and the length of the pump field pacet into which the undulator field is transformed are of the same order. We show that in the reference frame the SR effect can be interpreted as a formation of the distributed Bragg mirror in the bulk of the electron beam which is effectively reflecting (scattering) the pump wave. A possibility of generation of multimegawatt pulses in terahertz and far infrared wave ranges is demonstrated.
|Sensitivity Study of a Tapered Free-Electron Laser
|The output power of a free-electron laser (FEL) can be greatly enhanced by tapering the undulator line. In this work, a sensitivity study of a tapered FEL is presented. The study is conducted using the numerical simulation code GENESIS and a taper optimization method. Starting from a possible case for the future X-ray FEL at the MAX IV Laboratory in Lund, Sweden, a number of parameters are varied systematically and the impact on the FEL power is investigated. These parameters include the electron beam's initial energy, current, emittance, energy spread, as well as the seed radiation power.
|Update on the FEL Code Genesis 1.3
|The widely used time-dependent code Genesis 1.3 has been modified to address new needs of users worldwide. The existing limitation of tracking isolated slices of the FEL beam has been overcome by keeping the entire electron beam in memory, which is tracked as a whole through the undulator. This modification allows for additional features such as allowing particles to migrate into other slices or applying self-consistent wakefield and space charge models.
|MINERVA, a New Code to Model Free-Electron Lasers
|Simulation codes modelling the interaction of electrons with an optical field inside an undulator are an essential tool for understanding and designing free-electron lasers (FELs). As there exists a large variety of FELs ranging from long-wavelength oscillators using partial wave guiding to soft and hard x-ray FELs that are either seeded or starting from noise, a simulation code should be capable of modelling this huge variety of FEL configurations. A new code under development, named MINERVA, will be capable of modelling such a large variety of FELs. The code uses a modal expansion for the optical field, e.g., a Gaussian expansion for free-space propagation, and an expansion in waveguide modes for propagation at long wavelengths, or a combination of the two for partial guiding at THz frequencies. MINERVA uses the full Newton-Lorentz force equation to track the particles through the optical and magnetic fields. To allow propagation of the optical field outside the undulator and interact with optical elements, MINERVA interfaces with the optical propagation code OPC to model oscillators. Here we describe the main features of MINERVA and give various examples of its capabilities.
|Recent Updates to the Optical Propagation Code OPC
Funding: This research is supported in part by Office of Naval Research Global, grant number N62909-10-1-7151
In order to understand and design free-electron lasers (FELs), simulation codes modeling the interaction of electrons with a co-propagating optical field in the magnetic field of an undulator are essential. However, propagation of the optical field outside the undulator is equally important for evaluation of the optical field at the location of the application or to model FEL oscillators. The optical propagation code OPC provides such capabilities and can interface with FEL gain codes like GENESIS 1.3, MEDUSA and MINERVA. Here we present recent additions and modifications to the code that (i) improves the speed of the code and (ii) extends the modeling capabilities. These include amongst other, inline diagnostics that results in considerable faster runtimes, the ability to convert from free-space modes to guided modes (currently only cylindrical waveguides), and the possibility to determine the spectrum at each transverse location. The latter opens the possibility to include dispersion in the optical propagation. Finally, work is underway to support HDF5 to remain compatible with the upcoming new release of GENESIS 1.3.
|The Implementation of 3D Undulator Fields in the Unaveraged FEL Simulation Code Puffin
Funding: We acknowledge STFC MoA 4132361; ARCHIE-WeSt HPC, EPSRC grant EP/K000586/1; John von Neumann Institute for Computing (NIC) on JUROPA at Jlich Supercomputing Centre (JSC), under project HHH20
The FEL simulation code Puffin is modified to include 3D magnetic undulator fields. Puffin, having previously used a 1D undulator field, is modified to accommodate general 3D magnetic fields. Both plane and curved pole undulators have been implemented. The electron motion for both agrees with analytic predictions.
|Modeling CSR in a Vacuum Chamber by Partial Fourier Analysis and the Discontinuous Galerkin Method
Funding: Work supported by DOE contracts DE-FG-99ER41104 and DE-AC03-76SF00515.
We continue our study of CSR* from a bunch on an arbitrary curved orbit in a plane, which used a Fourier transform in s-ct. The vacuum chamber has rectangular cross section with possibly varying horizontal width. We use the slowly varying amplitude approximation, and invoke a Fourier expansion in the vertical coordinate y, which meets the boundary conditions on the top and bottom plates and makes contact with the Bessel equation of the frequency domain treatment. The fields are defined by a PDE in s and x, first order in s, which is discretized in x by finite differences (FD) or the discontinuous Galerkin method (DG). We compare results of FD and DG, and also compare to our earlier calculations in 3D (paraxial) which did not use the Fourier series in y*,**. This approach provides more transparency in the physical description, and when only a few y-modes are needed, provides a large reduction in computation time.
* See FEL13 Proceedings MOPSO06: http://accelconf.web.cern.ch/AccelConf/FEL2013/papers/mopso06.pdf
** See PRST-AB 7 054403 (2004) and Jpn. J. Appl. Phys. 51 016401 (2012).
|Simple Quantum Mechanical Derivation of FEL Gain
Funding: This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences under contract No. DE-AC02-06CH11357
A quantum mechanical derivation of FEL gain in low gain regime is presented. Although nothing new and probably well known to experts, the derivation given here uses two basic principles of physics: (1) energy conservation and (2) the fact that the matrix elements of the photon creation a+ or annihilation operator a between two states of photon number n1 and n2 is proportional to the square root of n1, which is the greater of n1 and n2. The simplicity of this derivation may have some pedagogical value.
|TW X-ray Free Electron Laser Optimisation by Transverse Pulse Shaping
|We study the dependence of the peak power of a 1.5 Angstrom TW, tapered X-ray free-electron laser on the transverse electron density distribution. Multidimensional optimization schemes for TW hard X-Ray free electron lasers are applied to the cases of transversely uniform and parabolic electron beam distributions and compared to a Gaussian distribution. The optimizations are performed for a 200 m undulator and a resonant wavelength of 1.5 Angstrom using the fully 3-dimensional FEL particle code GENESIS. The study shows that the flatter transverse electron distributions enhance optical guiding in the tapered section of the undulator and increase the maximum radiation power from a maximum of 1.56 TW for a transversely Gaussian beam to 2.26 TW for the parabolic case and 2.63 TW for the uniform case. Spectral data also shows a 30-70 % reduction in energy deposited in the sidebands for the uniform and parabolic beams compared with a Gaussian.
|Transverse Coherence Properties of a TGU-based FEL
|The use of a transverse gradient undulator (TGU) is considered an attractive option for FELs driven by electron beams with a relatively large energy spread. In this scheme, a dispersion is introduced in the beam while the undulator poles are inclined so that the undulator field acquires a linear dependence upon the transverse position in the direction of dispersion. By suitably selecting the dispersion and the field gradient, the energy spread effect can be significantly mitigated, thus avoiding a drastic reduction in the FEL gain. However, adding the dispersion typically leads to electron beams with large aspect ratios. As a result, the presence of higher-order modes in the output FEL radiation can become significant. To investigate this effect, we study the properties of the higher-order eigenmodes of a TGU-based, high-gain FEL, using both a simplified, analytically-solvable model and a variational technique. This formalism is then used to provide an estimate of the degree of transverse coherence for a representative soft X-ray, TGU FEL example.
|Initial Value Problem for an FEL Driven by an Asymmetric Electron Beam
|FEL configurations in which the driving electron beam is not axially symmetric (round) are important in the study of novel concepts (such as TGU-based FELs) but also become relevant when one wishes to explore the degree to which the deviation from symmetry-inevitable in practical cases-affects the performance of more conventional FEL schemes. In this paper, we present a technique for solving the initial value problem of such an asymmetric FEL. Extending an earlier treatment of ours, we start from a self-consistent, fully 3D, evolution equation for the complex amplitude of the electric field of the FEL radiation, which is then solved by expanding the radiation amplitude in terms of a set of orthogonal transverse modes. The numerical results from such an analysis are in good agreement with simulation and provide a full description of the radiation in the linear regime. Moreover, when the electron beam sizes are constant, this approach can be used to verify the predictions of the standard eigenmode formalism.
|Mode Contents Analysis of a Tapered Free Electron Laser
|For the ultimate use for the scientific experiments, the free electron laser (FEL) will propagate for long distance, much longer than the Rayleigh range, after exiting the undu- lator. To characterize the FEL for this purpose, we study the electromagnetic field mode components of the FEL photon beam. With the mode decomposition, the transverse coher- ence can be analyzed all along. The FEL here in this paper is a highly tapered one evolving through the exponential growth and then the post-saturation taper. Modes contents are analyzed for electron bunch with three different types of transverse distribution: flattop, Gaussian, and parabolic. The tapered FEL simulation is performed with Genesis code. The FEL photon beam transverse electric field is decom- posed with Gaussian-Laguerre polynomials. The evolutions of spot size, source location, and the portion of the power in the fundamental mode are discussed here. The approach can be applicable to various kind scheme of FEL.
|Improved Self Amplified Spontaneous Emission (iSASE) is a scheme that reduces FEL bandwidth by increasing phase slippage between the electron bunch and radiation field. This is achieved by repeatedly delaying electrons using phase shifters between undulator sections. Genesis code is modified to facilitate this simulation. With this simulation code, the iSASE bandwidth reduction mechanism is studied in detail. A Temporal correlation function is introduced to describe the similarity between the new grown field from bunching factor and the amplified shifted field. This correlation function indicates the efficiency of iSASE process.
|Mode Component Evolution and Coherence Analysis in Terawatt Tapered FEL
|A fast and robust algorithm is developed to decompose FEL radiation field transverse distribution into a set of orthonormal basis. Laguerre Gaussian and Hermite Gaussian can be used in the analysis. The information of mode components strength and Gaussian beam parameters allows users in downstream better utilize FEL. With this method, physics of mode components evolution from starting stage, to linear regime and post saturation are studied with detail. With these decomposed modes, correlation function can be computed with less complexity. Eigenmodes of the FEL system can be solved using this method.
|FEL Code Comparison for the Production of Harmonics via Harmonic Lasing
|Harmonic lasing offers an attractive option to significantly extend the photon energy range of FEL beamlines. Here, the fundamental FEL radiation is suppressed by various combinations of phase shifters, attenuators, and detuned undulators while the radiation at a desired harmonic is allowed to grow linearly. The support of numerical simulations is extensively used in evaluating the performance of this scheme. This paper compares the results of harmonic growth in the harmonic lasing scheme using three FEL codes: FAST, GENESIS, and GINGER.
|FEL Simulation and Performance Studies for LCLS-II
|The design and performance of the LCLS-II free-electron laser beamlines are presented using start-to-end numerical particle simulations. The particular beamline geometries were chosen to cover a large photon energy tuning range with x-ray pulse length and bandwidth flexibility. Results for self-amplified spontaneous emission and self-seeded operational modes are described in detail for both hard and soft x-ray beamlines in the baseline design.
|Broadly Tunable Free-Electron Laser for Four-wave Mixing Experiments with Soft X-ray Pulses
|This paper examines a FEL design for the production of three soft x-ray pulses from a single electron beam suitable for four-wave mixing experiments. Independent control of the wavelength, timing and angle of incidence of the three ultra-short, ultra-intense pulses with exquisite synchronization is critical. A process of selective amplification where a chirped electron beam and a tapered undulator are used to isolate the gain region to only a short fraction of the electron beam is explored in detail. Numerical particle simulations are used to demonstrate the essential features of this scheme in the context of the LCLS-II design study.
|A New 4D Model of Short-pulse FEL Oscillators
Funding: This work has been supported by the Office of Naval Research and the High Energy Laser Joint Technology Office.
At the Naval Postgraduate School, we have recently developed a new 4D (x,y,z,t) model for FEL oscillators where the pulse length is comparable to the slippage distance. The model follows multiple transverse and longitudinal optical modes over many passes through a resonator, including the effects of diffraction, pulse slippage and desynchronism. The code is parallelized to run on a cluster computer, and the resonator optics are self-contained, so no external optics program is necessary. The mirrors and the electron beam can be shifted or tilted off-axis to study misalignment effects. This new model is useful for studying the combined effects of longitudinal and transverse modes, the trapped particle instability, and the development of sidebands. The model is currently being validated by comparison to analytic formulas and other FEL codes, as well as existing and proposed FEL experiments. Results of these studies and examples of various effects that this new model can be used to understand will be presented.
|Investigation of Reverse Taper to Optimize the Degree of Polarization for the Delta Undulator at the LCLS
Funding: U.S. Department of Energy under contract No. DE-AC02-76SF00515
A 3.2 m adjustable phase Delta undulator* will soon be installed on the last girder of the LCLS undulator line. The Delta undulator will act as an afterburner terminating the 33 undulator line, providing arbitrary polarization control to users. Two important figures of merit for users will be the degree of polarization and the x-ray yield. In anticipation of this installation, machine development time at the LCLS was devoted to maximizing the final undulator x-ray contrast and yield with a standard canted pole undulator acting as a stand in for the Delta undulator. Following the recent suggestion** that a reverse taper (dK/dz > 0) in the main undulator line could suppress linearly polarized light generated before an afterburner while still producing the requisite microbunching, we report on a reverse taper study at the LCLS wherein a yield contrast of 15 was measured along the afterburner. We also present 1D simulations comparing the reverse taper technique to other schemes.
* Nuhn, H.-D., Anderson, S., Bowden, G., Ding, Y., Gassner, G., et al., (2013).
** Schneidmiller, E. A. and Yurkov, M. V., Phys. Rev. ST Accel. Beams 16, 110702 (2013).
|Observation of Smith-Purcell Radiation at 32 GHz from a Multi-channel Grating with Sidewalls
|In a demonstration experiment at 5 GHz, we found copious emission of coherent Smith-Purcell (SP) radiation at the fundamental frequency of the evanescent surface wave, when the grating had sidewalls. Reaching higher frequencies requires a reduction in the size of the grating, which leads to a considerable reduction in power. To partially compensate this, we suggested superposing several copies of the reduced grating in parallel. A test of this concept has been performed with a seven-channel grating, at a frequency near 32 GHz. The SP radiation signals were observed directly with a fast oscilloscope. Power levels were of order 5 kW, in fair agreement with three-dimensional simulations made using the code "MAGIC".
|Flying RF Undulator
|A new concept for the room-temperature rf undulator, designed to produce coherent X-ray radiation by means of a relatively low-energy electron beam and pulsed mm-wavelength radiation, is proposed. The “flying” undulator is a high-power short rf pulse co-propagating together with a relativistic electron bunch in a helically corrugated waveguide. The electrons wiggle in the rf field of the -1st spatial harmonic with the phase velocity directed in the opposite direction in respect to the bunch velocity, so that particles can irradiate high-frequency Compton’s photons. A high group velocity (close to the speed of light) ensures long cooperative motion of the particles and the co-propagating rf pulse. This work is supported by the Russian Foundation for Basic Research (Projects 14-08-00803 and 14-02-00691).
|Poster TUP040 [0.189 MB]
|High Efficiency Lasing with a Strongly Tapered Undulator
Funding: This work was supported by DOE grant DE-FG02-92ER40693, Defense of Threat Reduction Agency award HDTRA1-10-1-0073 and University of California Office of the President award 09-LR-04-117055-MUSP.
Typical electrical to optical energy conversion efficiencies for FELs are limited by the Pierce parameter to 10-3 or smaller. Undulator tapering schemes have enabled extraction of as much as 1 or 2% of the electron energy. Recently, the UCLA BNL helical inverse free electron laser (IFEL) experiment at ATF demonstrated energy doubling and acceleration of 30% of an electron beam from 52 to 93 MeV with a modest 1011 W power CO2 laser pulse. By reversing and retuning the undulator, the electrons may be violently decelerated, thereby transferring energy from the beam to the laser pulse. Simulations show that by sending a 1 kA, 70 MeV electron beam and 100 GW laser into a prebuncher and the reversed undulator, 41% of the electron beam energy should be converted to radiation, allowing the laser pulse power to grow to 127 GW.
|IFEL Driven Micro-Electro-Mechanical System Free Electron Laser
|The Free Electron Laser has provided modern science with a tunable source of high frequency, high power, coherent radiation. To date, short wavelength FEL's have required large amounts of space in order to achieve the necessary beam energy to drive the FEL process and to reach saturation of the output radiation power. By utilizing new methods for beam acceleration as well as new undulator technology, we can decrease the space required to build these machines. In this paper, we investigate a scheme by which a tabletop XUV FEL might be realized. Utilizing the Rubicon Inverse Free Electron Laser (IFEL) at BNL together with micro-electro-mechanical system (MEMS) undulator technology being developed at UCLA, we propose a design for a compact XUV FEL.
|Terahertz FEL based on Photoinjector Beam in RF Undulator
|Photoinjectors, which can produce picosecond electron bunches of MeV-level, are attractive for THz generation. Fortunately, a long distance to reach scattering power saturation in FEL is not necessary, if bunch length is shorter than the produced THz half-wavelength. However, the energy of several MeVs does not allow providing long traveling of the flying bunch without longitudinal divergence. That is why, we suggest using specific RF undulator in a form of the normal wave in the helical waveguide at 3 cm wavelength. The mentioned wave has the -1st space harmonic with transverse fields and negative phase velocity (responsible for particle wiggling). This wave has also the 0th harmonic with longitudinal field and positive phase velocity equal to bunch velocity. Due to the synchronous 0th harmonic one can channel low-energy bunches (due to longitudinal focusing field) as far as several meters distance. One might also inject electron bunches in slightly accelerating field, in this case the output THz pulse obtain nearly linear frequency modulation. Such long THz pulses with the mentioned modulation of the frequency can be effectively compressed by pair of diffraction gratings.
|Poster TUP046 [2.914 MB]
|Chirped Pulse Superradiant Free-electron Laser
Funding: This work is supported by Ministry of Science and Technology under Contract NSC 102-2112-M-007-002-MY3
When a short electron bunch traverses an undulator and radiates a wavelength significantly longer than the bunch length, the electrons quickly loses energy through so-called superradiance and generate a negatively chirped radiation frequency at the output. In this paper, we develop a theory to describe this chirped-pulse radiation and numerically demonstrate pulse compression by using a quadratic phase filter. As a design example at THz, a photoinjector/linac system generates a 15 MeV electron bunch containing 15-pC charge in a 60-fs duration. The electrons radiate a chirped pulse at 2.5 THz from a 1.5 m long undulator with a period of 5.6 cm and undulator parameter of 1.7. By using a grating pair, the output THz field can be compressed from 27 to 3 cycles. As another example at EUV, a future dielectric laser accelerator  is assumed to generate a 100 MeV electron bunch containing 75-fC charge in 1-nm long length. The electrons radiate a chirped EUV pulse at 13.5 nm from a 15.8 cm long dielectric laser undulator  with a period of 1.05 mm and undulator field of 3.3 T. By using a quadratic phase filter as a pulse compressor, the peak power of the EUV radiation is increased from 0.7 to 10 kW.
*Y.C. Huang and R.L. Byer, Appl. Phys. Lett. 69 (15), (1996) 2185-2177.
**T. Plettner, R. L. Byer., Phys. Rev. ST Accel. Beams 11, (2008) 030704.
|Thoughts on the New Technologies for Compact FEL Devices
|The possibility to merge different solutions exploiting wave undulators, laser plasma acceleration and other schemes, allows the design of compact Free Electron Laser (FEL) sources operating in the extreme UV-X-ray region of the spectrum. Newly developed high peak power lasers have opened indeed effective possibilities of driving coherent light sources operating with laser plasma accelerated beams and wave undulators. We combine different ideas including also the concept of sheared beam configuration to achieve compact and reliable FEL devices. We finally comment on the perspective use of Radio Frequency (RF) undulators, which seems to be fairly good candidates for opening a new technological strategy for the design of FEL oscillators, including bi-harmonic and multi-frequency operation.
|Storage Ring XFEL with Longitudinal Focusing
|In present work we investigate the possibility of running a high gain FEL on a storage ring using a longitudinally focusing insertion to compress bunches passing an undulator. If integrated into a storage ring similar to PETRA III such device could potentially produce continuous ∼1ps pulses of photons in the nm range with peak pulse powers of tens of GW. Even without operating in FEL saturation mode the longitudinal focusing can provide means to increase the brightness and shorten the photon pulse length
|Coherent Radiation Sources Driven by Superconducting Spoke Accelerators
Funding: This work has been supported by the Office of Naval Research and the High Energy Laser Joint Technology Office.
The NPS FEL Group and Niowave are collaborating to design several FEL systems using superconducting spoke RF cavities. Accelerators reaching electron beam energies of 2MeV to 75MeV with milliamps of average current are considered to drive FELs using a short ten period undulator, approximately 30cm long. The coherent radiation ranges from THz to infrared depending on the electron beam energy. In the 2MeV accelerator, the radiation process can be super-radiant due to the long millimeter wavelength, while the 40MeV accelerator generates infrared wavelengths in a conventional FEL oscillator configuration. An intermediate 8MeV accelerator powers an FEL oscillator with short picosecond pulses providing a kilowatt of THz power in a compact source. Compton backscattering is described to generator incoherent, but monochromatic x-rays for medical applications.
|Short-period Undulators based on Laser-driven Wakefields in Plasma Channels
Funding: Work supported by the U.S. DOE under Contract No.DE-AC02-05CH11231.
We present a novel type of short-period undulator based on controlling the focusing forces on a beam in a plasma wave excited by an intense laser pulse undergoing centroid oscillations in a plasma channel. The period of such a plasma undulator is proportional to the Rayleigh length of the laser pulse and can be sub-mm with an effective undulator strength parameter of order unity. The undulator period can further be controlled and reduced by beating laser modes, or using multiple colors, in the plasma channel. We present analytic expressions for the electron trajectories in the plasma undulator. Analytic work is compared to numerical modeling. Examples are presented of short-period laser-driven plasma undulators based on available laser and plasma channel parameters.
|Status of Electron Beam Slicing Project at NSLS-II, BNL
|The Electron Beam Slicing (e-beam slicing) at NSLS-II, Brookhaven National Laboratory, supported by the Laboratory Directed Research and Development (LDRD) Program, is focused on the development of the new method to generate ultra-short x-ray pulses using focused short low energy (∼20 MeV) electron bunches to create short slices of electrons from the circulating electron bunches in a synchrotron radiation storage ring. The e-beam slicing activities are staged in 3 main phases. In Phases 0, the theory of e-beam slicing is developed, the low energy linac compressor is simulation designed, the radiation separation between the satellite and core is analyzed by simulation and the properties of the e-beam slicing system are discussed and compared with other ultra-short x- ray sources. Phase 0 has completed successfully, Phase 1 is under way. This paper presents an update on the status of Phase 0.
|Electron Beam De-chirping in a Plasma
|Beam-driven plasma wakefield acceleration (PWFA) is a promising and evolving technique for next-generation, compact light sources. By propagating a dense drive-beam through a plasma, expelled plasma electrons can excite wakefields supporting electric fields in excess of 10 GV/m. Like in a conventional radio-frequency cavity, the acceleration strongly depends on the injection phase with respect to the wakefield. Different injection schemes have been proposed recently, all having in common a significant time-energy correlation, the so-called energy-chirp. These energy-chirps typically lead to energy bandwidths of up to 10% in PWFA, hampering efficient beam transport and eventually any kind of free-electron laser (FEL) application. Analogous to short-range wakefields generated by electron beams in a resistive beam pipe, the wakefields generated by the electron beam in a plasma can be used to compensate the initial energy-chirp. Here we present the idea of electron beam de-chirping in a plasma and show the conditions for optimal de-chirping with simultaneous beam quality preservation. This is the basis for efficient beam transport and thus paves the way for FELs utilizing PWFA.
|Development of Compact THz-FEL System at Kyoto University
|We are developing a compact accelerator based terahertz (THz) radiation source by free-electron laser (FEL) at the Institute of Advanced Energy, Kyoto University. The system consists of a 1.6 cell BNL type photocathode RF-gun, a focusing solenoid magnet, a magnetic bunch compressor, focusing quadrupoles and an undulator. The system generates an ultra-short electron pulse in a few hundred femtoseconds shorter than radiation wavelength, resulting in super-radiant emission from the undulator. The target radiation wavelength is 100 to 300 μm. A tracking simulation and optimization are performed by using PARMELA and General Particle Tracer (GPT) code. The FEL radiations are analyzed by a 1 dimensional FEL theory. The design parameters, simulation results and status are reported and discussed in this paper.
|Compact FEL Facilities for the Next Generation EUV Lithography
|Recently, for highly cost-effective productivity, chip manufacturers such as Samsung, Hynix, and Intel have been developing a next generation extreme ultraviolet (EUV) lithography technology. Due to the current low average power limitation, however, a new light source with a shorter wavelength of around 13.5 nm and a sufficient average photon beam power higher than 1 kW is strongly requested for the EUV lithography. In 2014, we had several meetings on the EUV lithography with Korean major chip manufactures. In this paper, we report manufactures' requirements and concerns on FEL based light source for the EUV lithography. In addition, we also describe possible compact FEL facilities for the next generation EUV lithography.
|Potential Photochemical Applications of the Free Electron Laser Irradiation Technique in Living Organisms
In 2001, the Laboratory for Electron Beam Research and Application (LEBRA) achieved the first lasing of 0.9–6.5 microns near-infrared free electron lasers (FELs), in which higher harmonics were generated by using nonlinear optical crystals. Following this breakthrough, we have paid considerable attention to LEBRA-FEL’s potential for investigating photochemical reactions in living organisms. We have established a micro-irradiation technique using an optical fiber connected to a fine tapered glass rod of <5 microns in diameter, enabling FEL irradiation of a single cell and even the inner organelles of live cells. We then verified that visible LEBRA-FEL light can control the germination of lettuce seeds, a well-known photochemical reaction, and determined that red light (660 nm FEL) promotes germination and far-red light (740 nm FEL) inhibits it. Here, we summarize the efficiency of various visible wavelengths of LEBRA-FEL light, ranging from 0.4–0.8 microns, for regulating photoreactions in lettuce seeds and we also summarize the efficiency of infrared wavelengths up to 20 microns, which can be generated by combined use of the LEBRA-FEL and the Kyoto University FEL.
We thank the staff of Prof. T. Morii (Institute of Advanced Energy, Kyoto Univ.) for helpful assistance.
|Observation of Time-Resolved Phase Change in Polymer Films using a Mid-Infrared FEL
The operation wavelength of FEL at Kyoto University is 5-20μm with a macropulse duration of 1.5μs, micropulse duration of 0.6ps, and wavelength stability of <1.3% . Using frequency conversion we can obtain the single-shot spectra of mid-IR FEL . Toward the time-resolved (TR) study we have installed the plasma mirror to shorten the macropulse duration from μs to ns . Polymers are interesting candidates for the TR study in the mid-IR region. Some of the well-known polymers are polystyrene (PS), polyethylene (PE), etc. PS exists only in an amorphous phase, while PE exists in both amorphous and crystal phases. In this study we undertake the TR study of PE films. We melt the PE film with ns laser pulses at 532 nm, and probe the following dynamics using the mid-IR FEL. To increase the absorption efficiency at 532 nm, we fabricate the PE film doped with gold nanoparticles. As a result of melting the sharp absorption peaks of PE turns to the broad peak, indicating the phase change from crystal to amorphous. This way, we can observe the phase change of PE films in a TR manner with the mid-IR FEL, which is not possible with other commonly used devices such as FTIR.
 Qin et al., Opt. Lett. 38, 1068 (2013).
 Wang, Nakajima, Zen, Kii, Ohgaki, Opt. Lett. 37, 5148 (2012).
 Wang, Nakajima, Zen, Kii, Ohgaki, Appl. Phys. Lett. 103, 191105 (2013).
|Narrow Linewidth, Chirp-Control and Radiation Extraction Optimization in an Electrostatic Accelerator FEL Oscillator
|In recent years the electrostatic accelerator FEL based in Ariel has undergone many upgrades. By varying the accelerating potential the resonator allows lasing between 95-110 GHz. It is now possible to remotely control the output reflectivity of the resonator and thereby vary both the power built up in the resonator and that emitted. This has allowed fine control over the power for different user experiments. A voltage ramping device has been installed at the resonator/wiggler to correct drops in voltage which occur due to electrons striking the walls of the beam line. This has allowed stable pulses of just over 50 μs with a chirp rate of ~80 kHz/μs.
|Scanning Problems of FLARE, a THz-FEL Waveguide
Funding: FLARE is part of the NCAS project funded through the “Big Facilities” programme of the Netherlands Organisation for Scientific Research (NWO).
The (0.2 – 3) THz free-electron laser FLARE is equipped with a waveguide extending over the full cavity length. Therefore, the tuning gaps observed in the long-wavelength range of FELIX, FELBE and CLIO, which were attributed to mode-conversion at the waveguide free-space transitions, are avoided. Unfortunately, an even more severe scanning problem is observed and continuous tuning of the photon energy is up to this moment impossible. The origin of this problem is not yet understood and experiments to gain insight into the problem are ongoing. We have investigated the (coherent) spontaneous emission as a function of wavelength, the gain build-up in the vicinity of tuning gaps, and the operation at a micro-pulse repetition frequency at which only a single photon bunch circulates in the cavity. The latter is explored to investigate if the low-frequency mode (the slow wave) that can also build up in a wave-guided cavity and travels at lower group velocity than the electron bunches, interferes with the efficient power build-up of the desired high-frequency mode in the trailing bunches. Status and results of the experiments will be discussed.
|Poster TUP065 [4.287 MB]
|Facility for Coherent THz and FIR Radiation
|Linac based THz sources are increasingly becoming the method of choice for a variety of research fields, justifying the increasing demand for high repetition rate THz FEL facilities world wide. In particular, pump and probe experiments with THz and IR radiation are of major interest for the user community. In this paper, we propose a facility which accommodates an SRF-linac driven cw THz-FEL in combination with an IR undulator which utilizes the microbunched beam. The layout permits almost perfect synchronization between pump and probe pulse as well as nearly independently tunable THz and IR radiation.
|Poster TUP066 [1.655 MB]
|Influence of the Lower Frequency Branch on the Performance of a Waveguided THz FEL
Funding: We would like to acknowledge the financial support from Swedish Research Council and Swedish FEL Center.
The Terahertz (THz) frequency range is highly relevant in many applications ranging from medicine to security and communication. Among different available THz sources, free electron lasers (FELs) are the most powerful and versatile sources that provide tunable light in the whole THz region. THz FELs usually operate as oscillators and employ a waveguide to suppress diffraction losses. When a waveguide covers only a part of the optical cavity, substantial drops of the output power at certain wavelengths are observed *. The THz FEL FLARE operating in the wavelength range of 0.1-1.5 mm comprises a waveguide which covers the whole cavity length**. Surprisingly, the spectral gaps are still observed. To get insight into origin of the gaps, we perform numerical simulations taking into account both lower and higher resonant frequency branches, as well as interaction between 150 THz pulses that simultaneously propagate through the FLARE cavity. Simulations predict that the lower frequency branch can hamper amplification of the other branch and, thus, can lead to the spectral gaps.
* R. Prazerez et al. Phys. Rev. ST Accel. Beams 12, 010701 (2009)
** R. Chulkov et al. Multi-Mode Dynamics in a Short-Pulse THz FEL. Phys. Rev. ST Accel. Beams, to be published in 2014
|Poster TUP067 [1.457 MB]
|Cavity Length Change vs. Mirror Steering in a Ring Confocal Resonator
Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-84-ER40150, the Office of Naval Research, and the Joint Technology Office.
In principle, a ring confocal resonator allows for the use of a short Rayleigh length without the extreme sensi-tivity to mirror steering typical in a near-concentric reso-nator . One possible weakness of such a resonator is that the cavity length is no longer independent of the mirror steering. This is one of the strengths of a linear resonator. In this presentation, it is shown that, in a simple 2-dimensional corner cube type ring confocal resonator, the cavity length is, in fact, not dependent on the mirror steering to first order in the mirror angles. Thus the ring-confocal resonator might be a very easy-to-operate and stable resonator for short Rayleigh range operation in FEL oscillators
 Stephen Benson, George Neil, Michelle Shinn, Laser and Beam Control Technologies, Santanu Basu, James Riker, Editors, Proceedings of SPIE Vol. 4632 (2002).
|Numerical Calculation of Diffraction Loss for Characterisation of a Partial Waveguide FEL Resonator
|Waveguide is widely used in long wavelength Free-Electron Lasers to reduce diffraction losses. In this paper the amplitude and phase transverse distribution of light emission produced in a partial-waveguide FEL resonator is calculated by Fresnel principle. To acquire high power out-coupled and optimize resonator structure of HUST THz-FEL, the characterisation of reflecting mirror is discussed to reduce diffraction loss.
|Regenerative Laser Undulator X-ray Free-Electron Laser (ReLUX-FEL)
We present a new high-gain x-ray FEL concept based on a nearly co-propagating sheared laser undulator  and regenerative amplification [2,3] of a single x-ray pulse via successive interactions between a single electron bunch and the same laser undulator pulse. This new x-ray FEL configuration is called the Regenerative Laser Undulator X-ray FEL which uses a relativistic electron beam crossing a sheared TW laser beam at small angles. The generated x-ray pulse follows a zigzag path between Bragg reflectors and repetitively interacts with the laser and electron pulses. Between interactions, the electron bunch is advanced longitudinally to maintain its overlap with the x-ray pulse. The laser pulse follows a different path that includes an optical delay to synchronize it with the electron and x-ray pulses. The laser wave-front tilt and width are designed to increase the interaction time to provide many oscillation cycles. We present a ReLUX-FEL that can produce coherent 12-keV photons with 2 GeV electron beams. Time-independent Genesis simulations show that with 3 kA peak current and an FEL rho of 0.0007, the ReLUX-FEL saturates after 12 interactions.
 J.E. Lawler et al., J. Phys. D: Appl. Phys. 46 (2013) 325501.
 D.C. Nguyen et al., NIMA 429 (1999) 125.
 Z. Huang et al., PRL 96 (2006) 144801
|Poster TUP071 [0.618 MB]
|Present Status of Coherent Electron Cooling Proof-of-principle Experiment
Funding: Work supported by Stony Brook University and by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
The status of FEL-based Coherent Electron Cooling Proof-of-principle Experiment at BNL is presented. The experimental set-up is comprised of a 2 MeV CW SRF electron gun and 20 MeV CW SRF linac and 8-m long helical FEL amplifier. The status of the accelerator commissioning, and progress in the construction of the helical undulator at Budker INP, is also reported
|High Power Operation of the THz FEL at ISIR, Osaka University
|The THz FEL at Osaka University is based on the L-band linac that provides a multi-bunch electron beam with an 8 us duration in the energy range from 12.5 to 20 MeV. Although the RF frequency of the linac is 1.3 GHz, the bunch intervals are expanded to 9.2 ns for the FEL using a sub-harmonic buncher system that operates at 108 MHz, to enhance the bunch charge to 1 nC/bunch. The FEL covers the wavelength range from 30 to 150 um, and maximum energies of the macropulse and the micropulse are 3.7 mJ and 11 uJ, respectively, at ~70 um measured at an experimental station. To enhance the FEL power further, the electron beam current cannot be increased simply because the beam loading in the acceleration tube is too high. To solve this problem, we have developed a 27 MHz grid pulser for the thermionic electron gun that makes the bunch intervals 4 times longer and increases charge of the bunch 4 times higher whereas the beam loading is the same as that in the 108 MHz mode. In this new operation mode, where a single FEL pulse lases in the cavity, we have succeeded in obtaining the micropulse energy exceeding 100 uJ at a wavelength of 68 um.
|High Power Coupled FEL Oscillators for the Generation of High Repetition Rate Ultrashort Mid-IR Pulses
100-200 MeV range ERL-FELs generating few cycle short, high intensity mid-IR pulses with tens of MHz repetition rates might become attractive tools in various strong field applications. In a recent study  a mode locked coupled FEL oscillator scheme has been presented to produce multi-mJ level, ultra-short (<10 cycles) pulses tunable within the entire IR region. In this work an improved coupled FEL oscillator scheme is described. The coupled system operates unidirectionally (feedback in the reverse direction less than 10-8 level). The various operational regimes of the system are discussed. Some of the conclusions stated in  have been revised.
 M. Tecimer, PRST-AB 15, 020703 (2012).
|Commissioning Status of the ASTA Facility at Fermilab
Funding: Work at Fermilab supported by Fermi Research Alliance, LLC under Contract No. DE-AC02- 07CH11359 with the United States Department of Energy.
Early commissioning results and status of the Advanced Superconducting Test Accelerator (ASTA) at Fermilab will be described. The ASTA facility consists of an L-band rf photocathode (PC) gun, two superconducting L-band rf booster cavities, transport lines, and an 8-cavity TESLA style cryomodule. Early results include first photoelectrons from the Cs2Te photocathode and operations at 3-5 MeV from the rf PC gun. The beam line with one 4-dipole chicane, extensive diagnostics, and 50-MeV spectrometer are being installed. The base beam profile imaging stations have been equipped with both YAG:Ce scintillators and optical transition radiation (OTR) screens, optical transport, and with 5 Mpix digital CCD cameras using Gig-E readout. A set of rf BPMs, wall current monitors, and toroids are also being implemented. Transport of OTR to a C5680 Hamamatsu streak camera is also planned for longitudinal profile information at the picosecond level. Downstream of this location is the 8-cavity cryomodule in which most cavities have been operated at the targeted 31.5 MV/m gradient. Initial beam measurements at 20 MeV and updated cryomodule results will be presented as available.
|In Service of Accelerator Stewardship: The BNL Accelerator Test Facility and its Upgrade
Funding: Work done under the auspices of the US Department of Energy, Office of High Energy Physics
The Brookhaven Accelerator Test Facility (ATF) pioneered the principles of Accelerator Stewardship and served the Advanced Accelerator Concepts community as a users’ facility for over two decades. Over this time, the ATF provided facilities and expert support free of charge for users from academia, industry and national labs with a unique combination of high-brightness electron beams and high power lasers synchronized with the electron beam as well as diverse beam instrumentation and control software. There are over 30 scientists who did all or part of their graduate degree work using the ATF. The Accelerator Stewardship is now a formal program at the Office of High Energy Physics (OHEP), and the ATF has been awarded a transformational upgrade by OHEP, the ATF-II, that will lead in a short time to a dramatic increase in the capabilities of the facility. The Stewardship mission and the ATF-II will be the subject of this presentation.
|Characteristics of Transported Terahertz-wave Coherent Synchrotron Radiation at LEBRA
Funding: This work has been supported in part under the Visiting Researcher's Program of the Research Reactor Institute, Kyoto University, and ZE Research Program ZE25B-7, Kyoto University.
Nihon University and National Institute of Advanced Industrial Science and Technology have jointly developed terahertz-wave coherent synchrotron radiation (CSR) at Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University since 2011. We have already observed intense terahertz-wave radiation from a bending magnet located above an undulator dedicated for an infrared free-electron laser (FEL), and confirmed it to be CSR [*]. Moreover, we have transported the CSR to an experimental room, which is next to the accelerator room across a shield wall, using an infrared FEL beamline. The transported CSR beam can be applied to two-dimensional imaging and spectroscopy experiments. In this presentation, characteristics of the CSR beam and applications for the CSR beam at LEBRA will be reported.
* N. Sei et al., “Observation of intense terahertz-wave coherent synchrotron radiation at LEBRA”, J. Phys. D, 46 (2013) 045104.
|A Swedish Compact Linac-based THz/X-ray Source at FREIA
|THz radiation enables probing and controlling low-energy excitations in matter such as molecular rotations, DNA dynamics, spin waves and Cooper pairs. In view of growing interest to the THz radiation, the Swedish FEL Center and FREIA Laboratory are working on the conceptual design of a compact multicolor photon source for multidisciplinary research. We present the design of such a source driven by high-brightness electron bunches produced by a superconducting linear accelerator. A THz source is envisioned as an FEL oscillator since this enables not only generation of THz pulses with a bandwidth down to 0.01% (with inter-pulse locking technique) but also generation of short pulses with several cycles in duration by detuning the resonator. For pump-probe experiments, the THz source will be complemented with an X-ray source. One of the most promising options is the inverse Compton scattering of quantum laser pulses from electron bunches. Such an X-ray source will operate in water window with output intensity comparable to a second generation synchrotron. The envisioned THz/X-ray source is compact with a cost comparable to the cost of one beamline at a synchrotron.
|Towards an X-ray FEL at the MAX IV Laboratory
|The design of the 3 GeV linac for the MAX IV facility was done to provide the ability to host a future FEL in the hard X-ray as well as in the soft X-ray range. The linear accelerator, with its two bunch compressors, is now under commissioning. Through the years increasing details for the actual FEL have been discussed and presented. In parallel a steering group for the science case for a Swedish FEL has worked and engaged a large number of Swedish user groups. These two paths are now converging into a joint project to develop the concept of an FEL at MAX IV. We will report on the paths to FEL performance based on the 3 GeV injector, FEL design considerations, the scientific preparation of the project, the linac commissioning and the strategy and priorities.
|Configuration and Status of the Israeli THz Free Electron Laser
Funding: This project is funded in part by Israel Ministry of Defense.
A THz FEL is being built in Ariel University. This project is a collaboration between Ariel University, and Tel Aviv University. Upon completion it is intended to become a user facility. The FEL is based on a compact photo cathode gun (60 cm) that will generate an electron beam at energies of 4.5 - 6.5 MeV. The pulses are planned to be of 300 pico Coulomb for a single pulse, and of up to 1.5 nano Coulomb for a train of pulses. The FEL is designed to emit radiation between 1 and 5 THz. It is planned to operate in the super radiance regime. The configuration of the entire system will be presented, as well as theoretical and numerical results for the anticipated output of the FEL, which is in excess of 150 KW instantaneous power. The bunching of the electron bean will be achieved by mixing two laser beams on the photo-cathode. The compression of the beam will be achieved be introducing an energy chierp to the beam and passing it through a helical chicane. We plan on compressing the single pulse to less than 150 femto seconds. The status of the project at the time of the conference will be presented.
|Poster TUP081 [3.276 MB]
|Coherent Harmonic Generation at the DELTA Storage Ring: Towards User Operation
Funding: Work supported by DFG, BMBF, FZ Jülich, and by the Land NRW.
At DELTA, a 1.5-GeV synchrotron light source at the TU Dortmund University, a short-pulse facility based on Coherent Harmonic Generation (CHG) is in operation and shall soon be used for pump-probe experiments. Due to the interaction of ultrashort laser pulses with electron bunches in an undulator, CHG provides short and coherent pulses at harmonics of the laser wavelength. In this paper, recent progress towards user operation, pulse characterization studies such as transverse and longitudinal coherence measurements as well as CHG in the presence of an RF phase modulation are presented.
|ALPHA – The THz Radiation Source based on AREAL
|Advanced Research Electron Accelerator Laboratory (AREAL) based on photo cathode RF gun is under construction at the CANDLE. The basic aim of this new facility is to generate sub-picosecond duration electron bunches with an extremely small beam emittance and energies up to 50 MeV. One of the promising directions of the facility development is the creation of ALPHA (Amplified Light Pulse for High-end Applications) experimental stations with coherent radiation source in THz region based on the concept of both conventional undulator and novel radiation sources. The status of the AREAL facility, the main features and outlooks for the ALPHA station are presented in this work.
|Laser-Plasma Acceleration in Hamburg
Plasma-based accelerators promise ultra-compact sources of highly relativistic electron beams, especially suited for driving novel x-ray light sources. The stability and reproducability of laser-plasma generated beams however, is still not comparable to conventional machines. Within the LAOLA Collaboration, the University of Hamburg and DESY work closely together to combine university research with the expertise of a large and well-established accelerator facility. We will discuss the experimental programm and plasma-related activities in Hamburg, with a special focus on the recently commissioned 200 TW laser ANGUS. Integrated in the REGAE facility, it drives two beamlines to study external injection of electron into a plasma stage, as well as plasma-driven undulator radiation. present the recently commissioned 200 TW laser ANGUS and the experimental program in Hamburg. One of the pilot applications of a plasma accelerator is a compact FEL. As an outlook, I will discuss the concepts and experimental strategies towards a first proof-of-concept FEL experiment using plasma-driven electron beam available today.
on behalf of the LAOLA Collaboration
|FERMI Status Report
|FERMI, the seeded FEL located at the Elettra laboratory in Trieste, Italy, is now in regular operation for users with its first FEL line, FEL-1, which covers the wavelength range between 100 and 20 nm. We will give an overview of the typical operating modes of the facility for users and we will report on the status of beamlines and experimental stations. Three beamlines are now opened for users, three more are in construction. Meanwhile, the second FEL line of FERMI, FEL-2, a HGHG double stage cascade covering the wavelength range 20 to 4 nm is still under commissioning; we will report on the latest results in particular at the shortest wavelength, 4 nm in the fundamental.
|Experiment Preparation Towards a Demonstration of Laser Plasma Based Free Electron Laser Amplification
|One direction towards compact Free Electron Laser is to replace the conventional linac by a laser plasma driven beam, provided proper electron beam manipulation to handle the value of the energy spread and of the divergence. Applying seeding techniques also enables to reduce the required undulator length. Rapidly developing Laser Wakefield Accelerators (LWFA) are already able to generate synchrotron radiation. With the presently achieved electron divergence and energy spread an adequate beam manipulation through the transport to the undulator is needed for FEL amplification. A test experiment for the demonstration of FEL amplification with a LWFA is under preparation in the frame of the COXINEL ERC contract in the more general context of LUNEX5. Electron beam transport follows different steps with strong focusing thanks to variable strength permanent magnet quadrupoles, demixing chicane with conventional dipoles, and a second set of quadrupoles for further focusing in the undulator. Progress on the equipment preparation and expected performance are described.
|The Status of LUNEX5 Project
|LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) aims at investigating the production of short, intense, coherent Free Electron Laser (FEL) pulses in the 40-4 nm spectral range. It comprises a 400 MeV superconducting Linear Accelerator for high repetition rate operation (10 kHz), multi-FEL lines and adapted for studies of advanced FEL schemes, a 0.4 - 1 GeV Laser Wake Field Accelerator (LWFA) for its qualification by a FEL application, a single undulator line enabling seeding with High order Harmonic in Gas and echo configurations and pilot user applications. Concerning the superconducting linac, the electron beam dynamics has been modified from a scheme using a third harmonic linearizer and a compression chicane to dog-leg coupled to sextupoles. Besides, the choice of the gun is under revision for fulfilling to 10 kHz repetition rate. Following transport theoretical studies of longitudinal and transverse manipulation of a LWFA electron beam enabling to provide theoretical amplification, a test experiment is under preparation in collaboration with the Laboratoire d’Optique Appliquée towards an experimental demonstration.
|Free Electron Lasers in 2014
Funding: This work has been supported by the Office of Naval Research and the High Energy Laser Joint Technology Office.
Thirty-eight years after the first operation of the short wavelength free electron laser (FEL) at Stanford University, there continue to be many important experiments, proposed experiments, and user facilities around the world. Properties of FELs in the infrared, visible, UV, and x-ray wavelength regimes are tabulated and discussed.
|The Turkish Accelerator and Radiation Laboratory in Ankara (TARLA) Project
Funding: Work is supported by Ministry of Development of Turkey with Grand No: DPT2006K-120470
The Turkish Accelerator and Radiation Laboratory in Ankara (TARLA) which is proposed as a first facility of Turkish Accelerator Center (TAC) Project will operate two Infra-Red Free Electron Lasers (IR-FEL) covering the range of 3-250 microns. The facility will consist of an injector fed by a thermionic triode gun with two-stage RF bunch compression, two superconducting accelerating modules operating at continuous wave (CW) mode and two independent optical resonator systems with different undulator period lengths. The electron beam will also be used to generate Bremsstrahlung radiation. The facility aims to be first user laboratory in the region of Turkey in which both electromagnetic radiation and particles will be used. In this paper, we discuss design goals of the project and present status and road map of the project.
|Developments in the CLARA FEL Test Facility Accelerator Design and Simulations
|We present recent developments in the accelerator design of CLARA (Compact Linear Accelerator for Research and Applications), the proposed UK FEL test facility at Daresbury Laboratory. These comprise a revised front-end to ensure integration with the existing VELA line, simulations of a magnetically compressed ultra-short mode and a post-FEL diagnostics section. We also present first considerations on the inclusion of final acceleration using X-band structures.
|A Beam Test of Corrugated Structure for Passive Linearizer
|A dechirper which is a vacuum chamber of two corrugated, metallic plates with adjustable gap was successfully tested at Pohang, in August 2013. Another beam test was carried out to test the same structure to see if the corrugated plates may work as a linearizer. The test result will be presented together with the simulation result.
|Design of a Compact Light Source Accelerator Facility at IUAC, Delhi
Funding: * The project is supported jointly by Board of Research in Nuclear Sciences and Inter University Accelerator Center
The demand for a light source with high brightness and short pulse length from the researchers in the field of physical, chemical, biological and medical sciences is growing in India. To cater to the experimental needs of multidisciplinary sciences, a project to develop a compact Light Source at Inter University Accelerator Centre (IUAC) has been taken up. In the first phase of the project, prebunched  electron beam of ~ 8 MeV will be produced by a photocathode RF gun and coherent THz radiation will be produced by a short undulator magnet. In the second phase, the energy of the electron beam will be increased up to 50 MeV by two sets of superconducting niobium resonators. The coherent IR radiation will be produced by using an undulator magnet (conventional method) and X-rays by Inverse Compton Scattering. To increase the average brightness of the electromagnetic radiation, fabrication of superconducting RF gun is going to be started in a parallel development. In this paper the detailed design of the LSI accelerator complex as well as construction timetable will be presented. The physical principles of THz generation and major accelerator subsystems will be discussed.
 S. Liu & J.Urakawa, Proc. of FEL 2011, page-92
|Fast, Multi-band Photon Detectors based on Quantum Well Devices for Beam-monitoring in New Generation Light Sources
|In order to monitor the photon-beam position for both diagnostics and calibration purposes, we have investigated the possibility to use InGaAs/InAlAs Quantum Well (QW) devices as position-sensitive photon detectors for Free-Electron Laser (FEL) or Synchrotron Radiation (SR). Owing to their direct, low-energy band gap and high electron mobility, such QW devices may be used also at Room Temperature (RT) as fast multi-band sensors for photons ranging from visible light to hard X-rays. Moreover, internal charge-amplification mechanism can be applied for very low signal levels, while the high carrier mobility allows the design of very fast photon detectors with sub-nanosecond response times. Segmented QW sensors have been preliminary tested with 100-fs-wide UV laser pulses and X-ray SR. The reported results indicate that these devices respond with 100-ps rise-times to ultra-fast UV laser pulses. Besides, X-ray tests have shown that these detectors are sensitive to beam position and exhibit a good efficiency in the collection of photo-generated carriers.