FEL Theory and New Concepts
Paper Title Page
MOOAI1
 Tribute to Pascal Elleaume  
 
  • M.-E. Couprie
    SOLEIL, Gif-sur-Yvette, France
  • M.-E. Couprie
    CEA/DSM, Gif-sur-Yvette, France
  • J.-M. Ortega
    LCP/CLIO, Orsay, Cedex, France
  
  Tribute to Pascal Elleaume  
slides icon Slides MOOAI1 [9.432 MB]  
 
MOOBI1
 Numerical Methods for FEL Simulations  
 
  • S. Reiche
    Paul Scherrer Institut, Villigen, Switzerland
  
  The coupled system of radiation interacting with a co-propagating electron beam within an undulator of an FEL exhibits many degrees of freedom. Only in an idealized and simplified model the FEL equations can be solved analytically and a more complete description requires numerical methods. This presentation gives an overview about the basic algorithms, used in most FEL codes, to model a particle beam with up to 1 billion particles and a co-propagating radiation field with an Angstrom resolution in a Free-electron Laser up to several hundreds of meter long.  
slides icon Slides MOOBI1 [2.425 MB]  
 
MOPB05 Smith-Purcell Radiation with Negative-index Material 20
 
  • D. Li, K. Imasaki
    ILT, Suita, Osaka, Japan
  • M.R. Asakawa
    Kansai University, Osaka, Japan
  • M. Hangyo, K. Takano
    ILE Osaka, Suita, Japan
  • S. Miyamoto
    LASTI, Hyogo, Japan
  • Y. Tsunawaki
    OSU, Daito, Osaka, Japan
  • Z. Yang
    UESTC, Chengdu, Sichuan, People's Republic of China
  
  Smith-Purcell radiation from an electric line charge that moves, at constant speed, parallel to a grating made of metamaterial with negative index is analyzed. Through theoretical analysis and computations, we show that the Smith-Purcell radiation is stronger from a grating of negative-index material, than positive-index material and perfect conductor. Also, we found the radiation strongly depends on the values of permeability and permittivity.  
 
MOPB06 Smith-Purcell Free Electron Laser with Bragg Reflector 24
 
  • D. Li, K. Imasaki
    ILT, Suita, Osaka, Japan
  • M.R. Asakawa
    Kansai University, Osaka, Japan
  • M. Hangyo
    ILE Osaka, Suita, Japan
  • S. Miyamoto
    LASTI, Hyogo, Japan
  • Y. Tsunawaki
    OSU, Daito, Osaka, Japan
  • Z. Yang
    UESTC, Chengdu, Sichuan, People's Republic of China
  
  Grating with Bragg reflectors for the Smith-Purcell free-electron laser is proposed to improve the reflection coefficient, resulting in enhancing the interaction of the surface wave with the electron beam and, consequently, relax the requirements to the electron beam. With the help of particle-in-cell simulations, it has been shown that, the usage of Bragg reflectors may improve the growth rate, shorten the time for the device to reach saturation and lower the start current for the operation of a Smith-Purcell free-electron laser.  
 
MOPB07 Soft X-ray Free-electron Laser with a 10-time Reduced Size 28
 
  • F.H. Chao, C.H. Chen, K.Y. Huang, Y.-C. Huang
    NTHU, Hsinchu, Taiwan
  
  We present a 30-m long soft x-ray FEL consisting of a 5-MeV photoinjector, a 150 MeV linac, a magnetic chicane compressor, and a 3-m long undulator. We propose to employ both the 3rd and the 4th harmonics of a Nd laser at 355 and 266 nm, respectively, to illuminate the cathode of the photoinjector. Owing to the beating of the two lasers, the emitted electron beam could be modulated at 282 THz. The electrons are further accelerated to 150 MeV and, after acceleration, compressed by 33 times in a magnetic chicane. The temporal compression of the electron macropulse increases the electron bunching frequency to 9.3 PHz, corresponding to a soft x-ray wavelength of 32.2 nm. We adopt a solenoid-derived staggered array undulator* with a 3 m length, 5 mm undulator period, and 1.2 mm gap. With a solenoid field of 10 kG, we estimate an undulator parameter of 0.4 and a corresponding radiation wavelength of 32.2 nm for a 150 MeV driving beam. With 3.3 kA peak current, 0.03% energy spread, 2 mm-mrad emittance, and 80-micron beam radius at the undulator entrance, the GENESIS code predicts 0.2 GW radiation power from the 3 m long undulator for an initial bunching factor of merely 10 ppm.
* Y.C. Huang, H.C. Wang, R.H. Pantell, and J. Feinstein, "A staggered-array wiggler for far infrared, free-electron laser operation," IEEE J. Quantum Electronics 30 (1994) 1289. 		 
 
MOPB08 Studies for Polarization Control at LCLS 31
 
  • E. Allaria, Y.T. Ding, P. Emma, Z. Huang, H.-D. Nuhn, M. Rowen, J.J. Welch, J. Wu
    SLAC, Menlo Park, California, USA
  
  In order to improve the capabilities of LCLS to meet more of the user requirements it has been proposed to implement a method to produce circularly polarized coherent radiation in the LCLS free electron laser. In this work we will present the results of a new set of studies and simulations that have been done for adding polarization control to LCLS using circularly polarizing undulators. Attention has been focused mainly on the use of variable gap APPLE-II undulators to be used at the end of a long SASE radiator that is based on the standard planar LCLS undulators. Issues like polarization contamination from the planar polarized light, polarization fluctuation and the choice of undulator configuration have been studied.  
 
MOPB15 Numerical Simulation of CAEP Compact FEL THz Source 35
 
  • L.J. Chen, Q.K. Jia
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  • M. Li, X. Yang
    CAEP/IAE, Mianyang, Sichuan, People's Republic of China
  
  Free Election Laser Terahertz source is a good choice for THz source, whose wavelength is tunable. Using 1D FEL stimulation code FELO, we simulate the output characteristic of China Academy of Engineering Physics (CAEP) FEL THz, which is a waveguide FEL oscillator. The beam qualitys’ influence on the operation of FEL, such as energy dispersion, emittance and beam current, have been studied to designate a set of beam parameters. Besides, the output performance of FEL at different output coupling ratio is analyzed. The cavity detuning is discussed too. Meanwhile the influence of the position of the undulator in the cavity on the FEL performance is also studied.  
 
MOPB16 New Tunable DUV Light Source for Seeding Free-electron Lasers 38
 
  • N.Y. Joly, W. Chang, P. Hölzer, J. Nold, P.St.J. Russell, J.C. Travers
    Max Planck Institute for the Science of Light, Erlangen, Germany
  • M.-E. Couprie, M. Labat
    SOLEIL, Gif-sur-Yvette, France
  
  Seeding of single-pass free-electron lasers is a promising approach for improving the temporal coherence compared to self-amplified spontaneous emission [1], at the same time reducing the saturation length and reinforcing the harmonic level. Convention lasers or harmonics generated in gas are usually used as coherent seeds [1]. However such sources require complicated set-up and have limited tuneability. Here, we suggest the use of a newly discovered and efficient source of UV light, continuously tunable from 120 nm to 320 nm. The extremely compact and simple set-up consists of 20 cm of hollow-core photonic crystal fibre filled with a noble gas at variable pressure up to a few tens of bar and pumped by ~1 μJ 30 fs pulses at 800 nm [2]. The process relies on a favourable sequence of linear and nonlinear effects: low pressure-tunable dispersion, pulse compression due to a combination of self-phase-modulation and anomalous dispersion, self-steepening and dispersive wave generation. Tunable diffraction-limited DUV pulses of ~50 nJ and fs duration are generated. Seeding of FEL is discussed.
[1] G. Lambert et al., Nature Physics 4, 296-300 (2008)
[2] N. Joly et al., accepted in PRL 		 
 
MOPB17 Harmonic Generation for a Hard X-ray FEL 41
 
  • Q.R. Marksteiner, K. Bishofberger, B.E. Carlsten, L.D. Duffy, N.A. Yampolsky
    LANL, Los Alamos, New Mexico, USA
  
  Funding: We gratefully acknowledge the support of the US Department of Energy through the LANL LDRD Propgram for this work.
The proposed MaRIE XFEL at Los Alamos National Laboratory will generate ¼ Å, longitudinally coherent x-rays with a 20 GeV electron beam. A masked emittance exchanger can be used to generate coherent electron bunching at nm wavelengths. This masked emittance exchanger must be at 1 GeV in the accelerator, in order to mitigate debunching from incoherent synchrotron radiation (ISR). After this, the harmonic content must be stepped up by a factor of 200 in frequency and the electrons must be accelerated to 20 GeV. The nonlinear debunching effects in the accelerator from emittance must be mitigated by keeping the beam transversely large. There are several schemes to step the coherent bunching up to higher harmonics, all which require modulator and dispersive sections [1]. Echo-Enhanced Harmonic Generation, which requires large dispersion, must be incorporated at low energies, where ISR is reduced. Here we compare the usefulness of different harmonic generation schemes, and examine the possibility of placing successive harmonic generation sections at energies lower than 20 GeV in the accelerator line, with the accelerator sections in between used to introduce dispersion to the beam.
[1] Phys. Rev. E 71, 046501 (2005), etc. 		 
 
MOPB19 Using Laser Harmonics to Increase Bunching Factor in EEHG 45
 
  • G.V. Stupakov
    SLAC, Menlo Park, California, USA
  • M.S. Zolotorev
    LBNL, Berkeley, California, USA
  
  Funding: This work was supported by U.S. DOE Contracts No. DE-AC02-76SF00515 and DE-AC02-05CH11231
Echo-enabled harmonic generation (EEHG) is one of most promising approaches to seeding of soft x-ray FELs. It allows one to obtain beam bunching at high harmonics (of order of 100) of the laser frequency at a level of a few percent. In this paper we demonstrate that using the second and third harmonics of the laser radiation one can substantially increase the beam bunching: for a cold beam one can obtain values approaching 0.4 in the range of harmonic numbers 100~200. Such bunching factors are close to those achieved at saturation in the FEL process, which means that one can eliminate the lasing process and use coherent radiation of the pre-bunched beam in the undulator-radiator as a bright source of x-rays. We also discuss an option of using nonlinear dispersive elements to increase the bunching factor. 		 
 
MOPB20 Effect of Coulomb Collisions on Echo-Enabled Harmonic Generation (EEHG) 49
 
  • G.V. Stupakov
    SLAC, Menlo Park, California, USA
  
  Funding: Work supported by U.S. DOE Contract No. DE-AC02-76SF00515.
Echo-enabled harmonic generation (EEHG) for FEL seeding uses two undulator-modulators and two chicanes to introduce a fine structure into the beam longitudinal phase space which, at the end of the system, transforms into high harmonic modulation of the beam current. As a result of this phase space manipulation, after the first chicane, the energy distribution function becomes a rapidly modulated function of energy, with the scale of the modulation of the order of the initial energy spread of the beam divided by the EEHG harmonic number. Small-angle Coulomb collisions between the particles of the beam (also known as intrabeam scattering) tend to smear out this modulation and hence to suppress the beam bunching. In this paper we calculate the EEHG bunching factor with account of the collisions and derive a simple scaling relation for the strength of the effect. Our estimates show that collisions become a limiting factor in EEGH seeding for harmonic numbers roughly exceeding 100. 		 
 
MOPB21 Seeded Radiation Sources with Sawtooth Waveforms 53
 
  • D.F. Ratner
    Stanford University, Stanford, California, USA
  • A. Chao
    SLAC, Menlo Park, California, USA
  
  Despite the recent success of SASE-based FELs, there is still considerable interest in driving coherent radiation sources with external seeding. Seeding schemes, such as HGHG and EEHG, can increase longitudinal coherence, decrease saturation lengths, and improve performance of tapering, polarization control and other FEL features. Typically, seeding schemes start with a simple sinusoidal modulation, which is manipulated to provide bunching at a high harmonic of the original wavelength. In this paper, we consider variations starting with a sawtooth modulation. The sawtooth creates a clean phase space structure, providing a maximal bunching factor without the need for an FEL interaction. While a pure sawtooth modulation is a theoretical construct, it is possible to approach the waveform by combining two or more of the composite wavelengths. We give examples of sawtooth seeding for HGHG, EEHG and other schemes including compressed seeding, steady state microbunching, and reversible seeding. Finally, we note that the sawtooth modulation may aid in suppression of the microbunching instability.  
 
MOPB23 Reversible Seeding in Storage Rings 57
 
  • D.F. Ratner
    Stanford University, Stanford, California, USA
  • A. Chao
    SLAC, Menlo Park, California, USA
  
  We propose to generate steady-state microbunching in a storage ring by implementing a reversible seeding scheme. High gain harmonic generation (HGHG) and echo-enhanced harmonic generation (EEHG) are two promising methods for microbunching linac electron beams. Because both schemes increase the energy spread of the seeded beam, they cannot drive a coherent radiator turn-by-turn in a storage ring. However, reversing the seeding process following the radiator minimizes the impact on the electron beam and may allow coherent radiation at or near the storage ring repetition rate. In this paper we describe the general idea and outline a proof-of-principle experiment.  
 
MOPB25 Improvement of the Crossed Undulator Design for Effective Circular Polarization 61
 
  • G. Geloni
    European XFEL GmbH, Hamburg, Germany
  • V. Kocharyan, E. Saldin
    DESY, Hamburg, Germany
  
  The production of X-ray radiation with a high degree of circular polarization constitutes an important goal at XFEL facilities. A simple scheme to obtain circular polarization control with crossed undulators has been proposed so far. In its simplest configuration the crossed undulators consist of pair of short planar undulators in crossed position separated by an electromagnetic phase shifter. An advantage of this configuration is a fast helicity switching. A drawback is that a high degree of circular polarization (over 90%) can only be achieved for lengths of the insertion devices significantly shorter than the gain length, i.e. at output power significantly lower than the saturation power level. Here we propose to use a setup with two or more crossed undulators separated by phase shifters. This cascade crossed undulator scheme is distinguished, in performance, by a fast helicity switching, a high degree of circular polarization (over 95%) and a high output power level, comparable with the saturation power level in the baseline undulator at fundamental wavelength. We present feasibility study and exemplifications for the LCLS baseline in the soft X-ray regime.  
 
MOPB26 Self-seeded Operation of the LCLS Hard X-ray FEL in the Long-bunch Mode of Operation 65
 
  • G. Geloni
    European XFEL GmbH, Hamburg, Germany
  • V. Kocharyan, E. Saldin
    DESY, Hamburg, Germany
  
  Self-seeding options for the LCLS baseline were recently investigated using a scheme which relies on a single-crystal monochromator in Bragg-transmission geometry. The LCLS low-charge (0.02 nC) mode of operation was considered in order to demonstrate the feasibility of the proposed scheme. The wakefield effects from the linac and from the undulator vacuum chamber are much reduced at such low charge, and can be ignored. In this paper we extend our previous investigations to the case of the LCLS mode of operation with nominal charge. Based on the LCLS start-to-end simulation for an electron beam charge of 0.25 nC, and accounting for the wakefields from the undulator vacuum chamber we demonstrate that the same simplest self-seeding system (two undulators with a single-crystal monochromator in between) is appropriate not only for short (few femtosecond) bunches, but for longer bunches too.  
 
MOPB27 Circular Polarization Control for the LCLS Baseline in the Soft X-ray Regime 69
 
  • G. Geloni
    European XFEL GmbH, Hamburg, Germany
  • V. Kocharyan, E. Saldin
    DESY, Hamburg, Germany
  
  Several schemes have been discussed to obtain soft-polarization control in the context of the LCLS. We propose a novel method to generate 10 GW level power at the fundamental harmonic with 99% degree of circular polarization from the LCLS baseline. Its merits are low cost, simplicity and easy implementation. As in previously proposed methods, the microbunching of the planar undulator is used here as well. After the baseline undulator, the electron beam is sent through a 40 m long straight section, and subsequently through a short helical (APPLE II) radiator. The microbunching is easily preserved, and intense coherent radiation is emitted in the helical radiator. The background radiation from the baseline undulator can be suppressed by letting radiation and electrons through horizontal and vertical slits upstream the helical radiator, where the radiation spot size is about ten times larger than the electron bunch transverse size. Thin Be foils for the slits will preserve from electron losses. Other facilities e.g. LCLS II or the European XFEL may benefit from this work as well, due to availability of sufficiently long free space at the end of undulator tunnel.  
 
MOPB28 Gas-filled Cell as a Narrow Bandwidth Bandpass Filter in the VUV Wavelength Range 73
 
  • G. Geloni
    European XFEL GmbH, Hamburg, Germany
  • V. Kocharyan, E. Saldin
    DESY, Hamburg, Germany
  
  We propose a method for spectrally filtering radiation in the VUV wavelength range by means of a monochromator constituted by a cell filled with a resonantly absorbing rare gas. Around particular wavelengths, the gas exhibits narrow-bandwidth absorbing resonances following the Fano profile. Within the photon energy range 60-65 eV, the correlation index of the Fano profiles for the photo-ionization spectra in He is equal to unity, meaning that the minimum of the cross-section is exactly zero. For sufficiently large column density in the gas cell, the spectrum of the incoming radiation will be attenuated by the background cross-section of many orders of magnitude, except for those wavelengths close to the point where the cross-section is zero. Remarkable advantages of a gas monochromator based on this principle are simplicity, efficiency and narrow-bandwidth. A gas monochromator installed in the experimental hall of a VUV SASE FEL facility would enable the delivery of a single-mode VUV laser beam. The design is identical to that of existing gas attenuator systems for VUV or X-ray FELs. We present feasibility study and exemplifications for the FLASH facility in the VUV regime.  
 
MOPB29 Generation of Doublet Spectral Lines at Self-seeded X-ray FELs 77
 
  • G. Geloni
    European XFEL GmbH, Hamburg, Germany
  • V. Kocharyan, E. Saldin
    DESY, Hamburg, Germany
  
  We propose to extend our recently proposed single-crystal monochromatization setup to the case when two or more crystals are arranged in a series to spectrally filter the SASE radiation at two or more closely-spaced wavelengths within the FEL gain band. This allows for the production of doublet or multiplet spectral lines. We present simulation results for the LCLS baseline operating at two closely spaced wavelengths. We show that we can produce fully coherent radiation shared between two longitudinal modes. Mode spacing can be easily tuned within the FEL gain band. The proposed scheme allows for a modulation of the electron bunch at optical frequencies without a seed quantum laser. In fact, the XFEL output intensity contains an oscillating "mode-beat" component whose frequency is related to the frequency difference between the pair of longitudinal modes considered. At saturation one obtains FEL-induced optical modulations of energy loss and energy spread in the electron bunch, which can be converted into density modulation with a weak chicane behind the baseline undulator. Powerful coherent radiation, synchronized with the X-ray pulses, can then be generated with an OTR station.  
 
MOPB30 The Effects of Betatron Motion on the Preservation of FEL Microbunching 81
 
  • G. Geloni
    European XFEL GmbH, Hamburg, Germany
  • V. Kocharyan, E. Saldin
    DESY, Hamburg, Germany
  
  In some options for circular polarization control at X-ray FELs, a helical radiator is placed a few ten meters distance behind the baseline undulator. If the microbunch structure induced in the baseline (planar) undulator can be preserved, intense coherent radiation is emitted in the helical radiator. The effects of betatron motion on the preservation ofμbunching in such in-line schemes should be accounting for. In this paper we present a comprehensive study of these effects. It is shown that one can work out an analytical expression for the debunching of an electron beam moving in a FODO lattice, strictly valid in the asymptote for a FODO cell much shorter than the betatron function. Further on, numerical studies can be used to demonstrate that the validity of such analytical expression goes beyond the above-mentioned asymptote, and can be used in much more a general context. Finally, a comparison with Genesis simulations is given.  
 
MOPB31 Self-seeding Scheme with Gas Monochromator for Narrow-Bandwidth Soft X-Ray 85
 
  • G. Geloni
    European XFEL GmbH, Hamburg, Germany
  • V. Kocharyan, E. Saldin
    DESY, Hamburg, Germany
  
  We propose an extension of our recently-proposed single-crystal self-seeding scheme to the soft X-ray range using a cell filled with resonantly absorbing gas as monochromator. The transmittance spectrum in the gas exhibits an absorbing resonance with narrow bandwidth. Then, similarly to the hard X-ray case, the temporal waveform of the transmitted radiation pulse is characterized by a long monochromatic wake, whose power is much larger than the equivalent shot noise power in the electron bunch. The monochromatic wake of the radiation pulse is combined with the delayed electron bunch and amplified in the second undulator. The proposed setup is extremely simple, and composed of as few as two simple elements: a gas cell, to be filled with noble gas, and a short magnetic chicane. The installation of the magnetic chicane does not perturb the undulator focusing system and does not interfere with the baseline mode of operation.  
 
MOPB32 System Trade Analysis for an FEL Facility 89
 
  • M.W. Reinsch, B. Austin, J.N. Corlett, L.R. Doolittle, G. Penn, D. Prosnitz, J. Qiang, A. Sessler, M. Venturini, J.S. Wurtele
    LBNL, Berkeley, California, USA
  
  Designing an FEL from scratch requires the design team to balance multiple science needs, FEL and accelerator physics constraints and engineering limitations. STAFF (System Trade Analysis for an FEL Facility) enables the user to rapidly explore a large range of Linac and FEL design options. The model utilzes analytical models such as the Ming Xie formulas when appropriate and look-up tables when necessary to maintain speed, flexibility and extensiblity. STAFF allows for physics models for FEL harmonics, wake fields, cavity higher-order modes and aspects of linac particle dynamics. The code will permit the user to study error tolerances and multiple beamlines so as to explore the full capabilities of an entire user facility. This makes it possible to optimize the integrated system in terms of performance metrics such as photons/pulse, photons/sec and tunability range while ensuring that unrealistic requirements are not put on either the electron beam quality, undulator field/gap requirements or other system elements. This paper will describe preliminary results from STAFF as applied to a CW FEL soft X-ray facility.  
 
MOPC01 Compact THz Radiation Source Based on a Photocathode RF Gun 92
 
  • S. Liu
    Shanghai Jiao Tong University, Shanghai, People's Republic of China
  • J. Urakawa
    KEK, Ibaraki, Japan
  
  Terahertz (THz) science and technology have already become the research highlight at present. In this paper, we put forward a proposal to generate THz radiation at tens of MW peak power. Due to the ultrafast laser and the high accelerating field of photocathode RF gun, we can generate and accelerate electron beam to several MeV, of which the bunch length is less than sub-ps. When the short electron bunches are injected into the wiggler, THz radiation based on Coherent Synchrotron Radiation could be achieved with tens of MW peak power. The whole THz FEL facility can be scaled to the size of a tabletop.  
 
MOPC02 Improvement of Termination Field of Bulk HTSC Staggered Array Undulator 96
 
  • N. Kimura, M. A. Bakr, Y.W. Choi, H. Imon, K. Ishida, T. Kii, R. Kinjo, K. Komai, K. Masuda, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, K. Yoshida
    Kyoto University, Institute for Advanced Energy, Kyoto, Japan
  
  We have proposed a bulk High Temperature Superconductor Staggered Array Undulator (Bulk HTSC SAU) to achieve higher undulator field, shorter period, and variable K-value without changing gap[1]. The purpose of this study is to revise the controversial point, that bulk HTSC SAU generates strong wicked magnetic field on its terminations, which scatters electron beam. Therefore we studied a new method to correct the field. We developed a physical model which based on Bean model to deal with the bulk superconducting material and then constructed a simulation code. By using the calculation results, we developed the correction method by adding bulk material on the edge of undulator. Measurement of the magnetic field of a prototype of bulk HTSC SAU with this method has been performed. We confirm that the numerical calculation well describe the experimental results. In this conference, numerical and experimental results of our end field termination method will be presented.
[1] R. Kinjyo, T. Kii, H. Zen, K Higashimura, K Masuda, K. Nagasaki, H. Ohgaki, Y.U. Jeong "Bulk High-TC Super Conductor Staggered Array Undulator" Proceedings of FEL2008 		 
 
MOPC03 Modeling of the Quiet Start Algorithm in the Framework of the Correlation Function Theory 99
 
  • O.A. Shevchenko, N. Vinokurov
    BINP SB RAS, Novosibirsk, Russia
  
  To suppress initial beam current fluctuations at the fundamental harmonic the macroparticle based FEL simulation codes use the quiet start algorithm. This algorithm should be valid at linear stage but there is no simple method to check whether it gives correct results at saturation. The regular approach to the start-up from noise problem should be based on the correlation function equation. In this paper we show that the quiet start algorithm can be naturally described in the framework of the correlation function theory. For this purpose one just needs to assume nonzero correlations in the initial particle distribution. This approach gives the possibility to compare simulation results for the system with reduced number of particles and artificially suppressed initial fluctuations with the case of real system with large number of particles.  
 
MOPC04 The Effects of Jitters on Coherent X-ray Radiation Using a Modulation Compression Scheme 103
 
  • J. Qiang
    LBNL, Berkeley, California, USA
  • J. Wu
    SLAC, Menlo Park, California, USA
  
  Modulation compression scheme based on a chirped beam, laser modulator and laser chirper, and two bunch compressors was proposed recently to generate coherent multi-color atto-second X-ray radiation [1]. In this paper, we will present studies of effects of the initial longitudinal beam chirp jitter, time synchronization jitter between the electron beam and the laser chirper, and the laser chirper amplitude jitter on the final coherent X-ray radiation.
[1]Ji Qiang and Juhao Wu, “Generation multi-color attosecond X-ray radiation through modulation compression,” arXiv:1102.4806v1. 		 
 
MOPC05 HGHG Scheme for FLASH II 107
 
  • A. Meseck, R. Mitzner
    HZB, Berlin, Germany
  • W. Decking, B. Faatz, M. Scholz
    DESY, Hamburg, Germany
  
  FLASH II is a major extension of the existing FLASH facility at DESY. It has been proposed in collaboration with the HZB. FLASH II is a seeded FEL in the parameter range of FLASH. The final layout of the undulator section of FLASH II allows for different seeding schemes. So that seeding with an HHG source as well as seeding in cascaded HGHG scheme and several combination of these schemes are possible. However, for the shortest wavelengths down to 4 nm the cascaded HGHG scheme will be utilized. It consists of two frequency up conversion stages utilizing a Ti:Sa laser based seeding source in UVU range. We present and discuss start-to-end simulation studies for the shortest wavelength generated in the HGHG cascade of FLASH II.  
 
MOPC06 X-Ray FELs Based on ERL Facilities 111
 
  • A. Meseck
    HZB, Berlin, Germany
  • G.H. Hoffstaetter, F. Löhl, C.E. Mayes
    CLASSE, Ithaca, New York, USA
  
  The characteristic high repetition rate and the high spectral brightness of the electron beams delivered by ERLs have led to a large number of ERL based proposals for hard X-ray sources including X-ray FELs. FEL oscillators, including those proposed for hard X-rays, require comparatively low peak currents and are particularly suitable for ERLs. However single-pass FELs in SASE or seeded mode do not seem out of reach when bunch-compression schemes for higher peak currents are utilized. Using the proposed Cornell ERL as an example, we present and discuss oscillator and single-pass FEL schemes which provide extremely high spectral-brightness ultra-short X-ray pulses for experiments.  
 
MOPC09 Use of Re-Acceleration and Tapering in High Gain Free Electron Lasers to Enhance Power and Energy Extraction 115
 
  • R. Dusad, G. Travish
    UCLA, Los Angeles, USA
  
  In high gain Free Electron Lasers (FELs), it is possible to use undulator tapering to increase power and energy extraction beyond saturation. For some applications, however, tapering is not sufficient or results in excessively long structures. Here we the study use of tapered undulators interrupted by short accelerator sections to increase the power extracted per unit length. Re-acceleration restores nominal energy to the beam with minimal disruption to bunching, and allows repeated use of a single taper profile. We show that for suitable parameter sets this approach can perform better than ideal tapering alone, and may serve to greatly improve and simplify high peak and average power FELs. Based on these findings, we propose a first experiment to test the re-acceleration with tapering concept.  
 
MOPC10 Numerical Investigation of Longitudinal Coherence in a Linear Tapered SASE FEL 118
 
  • H.T. Li, Q.K. Jia
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  
  One goal of the several FEL facilities operating in soft X-ray range, is the production of high-gain narrow-bandwidth FEL. In this report, the performance of radiation power and longitudinal cohence is studied for x-ray FEL generated through several different methods, including tapered，inverse-tapered and step-tapered undulator, and the SASE-FEL applying distributed optical klystron. Three–dimensional simulation demonstrate that these methods all can increase the FEL power and improve the time and spectrum structure with their own parameter optimization. In particular, FEL generated from toothed undulaor is studied. It is shown that the longitudinal cohence is improved and a series of several fettosecond pulses at gigawatt power levels at a wavelength of 1.5 nm is generated.  
 
MOPC12 Coherent Synchrotron Radiation and Bunch Compression Studies in the Emittance Exchange Beamline at the Fermilab A0 Photoinjector 121
 
  • J.C.T. Thangaraj, M.D. Church, H.T. Edwards, A.S. Johnson, A.H. Lumpkin, J. Ruan, J.K. Santucci, Y.-E. Sun, R.M. Thurman-Keup
    Fermilab, Batavia, USA
  • T.J. Maxwell, P. Piot
    Northern Illinois University, DeKalb, Illinois, USA
  
  One of goals of the Fermilab A0 photoinjector is to investigate experimentally the transverse to longitudinal emittance exchange principle. Coherent synchrotron radiation in the emittance exchange line could limit short pulse operation of the emittance exchanger. In this paper, we present experimental and simulation study of the coherent synchroton radiation (CSR) in the emittance exchange line at A0 photoinjector. We also show how EEX can be used to compress a bunch by adding chirp to the incoming beam.  
 
MOPC13 Terahertz-Wave Spectrophotometry – Experiments of Compton Backscattering of Continuous-spectrum Coherent Transition Radiation 125
 
  • N. Sei
    AIST, Tsukuba, Ibaraki, Japan
  • T. Takahashi
    Kyoto University, Research Reactor Institute, Osaka, Japan
  
  Funding: This study was financially supported by the Sumitomo foundation.
We have studied a terahertz-wave spectrophotometry by using Compton backscattering of coherent radiations at the Kyoto University Research Reactor Institute. In the terahertz-wave spectrophotometry, the characteristics of the continuous-spectrum THz waves are converted into those of the other wavelengths which are easily measured by colliding the THz waves with a relativistic electron beam. Such the continuous-spectrum light beam by Compton backscattering is known in a field of astrophysics. We achieved to observe a continuous-spectrum visible beam resulting from Compton backscattering using coherent transition radiations from an L-band electron linear accelerator*. The measured spectrum of the Compton backscattered photons was similar to that calculated from the spectrum of coherent transition radiation. In the presentation, the experimental results of terahertz-wave spectrophotometry will be explained in detail.
* N. Sei and T. Takahashi, Appl. Phys. Express 3 (2010) 052401. 		 
 
MOPC14 Infrared Single Spike Pulses Generation Using a Short Period Superconducting Tape Undulator at APEX 129
 
  • D. Filippetto, C. F. Papadopoulos, G. Penn, S. Prestemon, F. Sannibale
    LBNL, Berkeley, California, USA
  • C. Pellegrini
    UCLA, Los Angeles, California, USA
  • M. Yoon
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  
  Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
We report on the possibility of constructing an infrared FEL by combining a novel design super-conducting undulator developed at LBNL with the high brightness beam from the APEX injector facility at the Lawrence Berkeley National Laboratory. Calculations show that the resulting FEL is expected to deliver a saturated power of about a MW within a 4 m undulator length when operating in Self-Amplified-Spontaneus-Emission mode, with a single-spike of coherent radiation at 2 μm wavelength. The sub-cm undulator periods, associated with the relatively low energy of the APEX beam (20-25 MeV), forces the FEL to operate in a regime with unusual and interesting characteristics. The alternative option of laser seeding the FEL is also examined, showing the potential to reduce the saturation length even further. 		 
 
MOPC19 Pre-modulated Electron Bunch Sequence 133
 
  • D. Wang, L.X. Yan
    TUB, Beijing, People's Republic of China
  
  We modulate electron bunch sequence of 0.1 ~ 1nC total charge, after photocathode RF acceleration of 68 ~120MV / m, 3m long travelling-wave accelerating tube for the overall velocity compression. PARMELA simulation results prove that the bunch of high relativity can reach high charge and have short longitude rms length, less than 1ps of each single bunch and picoseconds interval at the accelerating tube exit. Taking use of the pre-modulated bunch sequence, we can do further research in CTR, CSR and FEL radiation.  
 
MOPC21 Comparison of Growth Rates of Two-Stream Free Electron Lasers (TSFEL) with Planar Wiggler Magnet and AC Electrical Wiggler Pumps 136
 
  • N. Mahdizadeh
    Islamic Azad University, Sabzevar Branch, Sabzevar, Iran
  • F.M. Aghamir
    University of Tehran, Tehran, Iran
  
  Funding: Sabzevar Branch, Islamic Azad University
A Comparison between growth rates of a Two Stream Free Electron Laser (TSFEL) with a planar wiggler pump and ac electrical wiggler pump has been presented. With the aid of fluid theory, dispersion relations are derived and their characteristics have been numerically analyzed. In this analysis, the longitudinal component of the stress tensor has been retained for beam temperature consideration. Similarities and differences in dispersion relations and growth rate have, also, been presented. 		 
 
MOPC22 Nonlinear Analyses in Two-stream Free-Electron Laser with Helical Wiggler Pump 138
 
  • N. Mahdizadeh
    Islamic Azad University, Sabzevar Branch, Sabzevar, Iran
  • F.M. Aghamir
    University of Tehran, Tehran, Iran
  • A. Raghavi
    PNUM, Mashhad, Iran
  
  Funding: Sabzevar Branch, Islamic Azad University
The analysis of a Two-Stream Free Electron Laser (TSFEL) with a helical wiggler pump is presented. The power and the signal growth rate are calculated. A set of coupled nonlinear differential equations for slowly varying amplitudes and phases is obtained through the substitution of vector and scalar potentials into the Maxwell-Poisson equations. The electron orbit equations are derived by Lorentz force equation. The obtained equations for fields and ensemble of electrons are solved numerically. The power and growth rate of TSFEL are compared with those of conventional FEL. It has been found that the TSFEL reaches the saturation regime in a longer axial distance in comparison to the conventional FEL and the growth rate of the TSFEL is somewhat lower than conventional FEL. 		 
 
MOPC27 Small Signal Gain for Two Stream FEL 141
 
  • A. Raghavi
    PNUM, Mashhad, Iran
  • N. Mahdizadeh
    Islamic Azad University, Sabzevar Branch, Sabzevar, Iran
  
  The problem of wave-particle interaction in the small signal gain regime for the tow-stream free electron laser is considered using a relativistic moving frame. The equation of motion in this frame is solved by means of a non-relativistic Hamiltonian. Small signal gain (SSG) for the laser is derived in both moving and laboratory frames.  
 
MOPC28 Fine Tuning of the K-parameter of Two Segments of the European XFEL Undulator Systems 144
 
  • Y. Li, J. Pflüger
    European XFEL GmbH, Hamburg, Germany
  • E. Gluskin
    ANL, Argonne, USA
  • N. Vinokurov
    BINP SB RAS, Novosibirsk, Russia
  
  For large and segmented undulator systems as needed for the European XFEL a non-destructive, in situ, radiation diagnostics method would strongly compliment e-beam diagnostics. If such method would allow to fine tune the K parameter of individual undulator segments with an accuracy set by the Pierce parameter ρ, which is on the order of 2~3×10-4, this would provide a very helpful tool for FEL commissioning. This paper provides a first analysis of a strategy of tuning the K parameter of two adjacent undulator segments. The spontaneous, monochromatized, on axis intensity is analyzed as a function of the phase delay set by the phase shifter in between. It makes use of diagnostic equipment which will be available at the European XFEL anyway. First results are demonstrated and limitations will be discussed.  
 
MOTUI1
 Simple Physics for Marvelous Radiation Device: A Tutorial for FEL Theory  
 
  • K.-J. Kim
    ANL, Argonne, USA
  
  Funding: Work supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
Principles behind a free-electron laser (FEL) will be explained in terms of simple physics. Characteristics of several varieties of FEL devices–amplifier, oscillator, and harmonic generator–will be delineated. The high-performance frontier in short wavelength, time resolution, and coherence will be discussed. Wild speculation for the future will be entertained. 		 
slides icon Slides MOTUI1 [2.832 MB]  
 
TUOAI1 Hard X-ray Self-seeding for XFELs: Towards Coherent FEL Pulses 148
 
  • G. Geloni
    European XFEL GmbH, Hamburg, Germany
  • V. Kocharyan, E. Saldin
    DESY, Hamburg, Germany
  
  Start-up from shot noise limits the longitudinal coherence of typical SASE XFEL pulses. Self-seeding schemes provide an elegant solution to this problem. However, their applicability to the baseline of already working or designed XFELs is subject to constraints, including minimal changes to the baseline design and possibility to recover the baseline mode of operation. Here we discuss a recently proposed single-bunch self-seeding scheme for hard X-rays. The physical principles of this scheme can be extended to soft X-rays as well. The method is based on a particular kind of monochromator, which relies on the use of a single crystal in Bragg-transmission geometry. In its simplest configuration, the setup consists of an input undulator and an output undulator separated by such monochromator. Several, more advanced configurations can be considered. For example, for high repetition rates of the X-ray pulses, or when a high spectral purity of the output radiation is requested, the simplest two-undulator configuration is not optimal: three or more undulators separated by monochromators can then be used. Exemplifications, based on facilities working or under construction will be discussed.  
slides icon Slides TUOAI1 [2.818 MB]  
 
TUOA2 Collective and Individual Aspects of Fluctuations in Relativistic Electron Beams for Free Electron Lasers 156
 
  • K.-J. Kim, R.R. Lindberg
    ANL, Argonne, USA
  
  Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
Fluctuations in highly bright, relativistic electron beam for free electron lasers (FELs) exhibit both collective as well as individual particle aspects[1]. If the collective part characterized by plasma oscillation dominate, then it might be feasible to suppress the shot noise[2]. To study these issues, we solve the 1-D coupled Poisson-Klimontovich equations by the Laplace transform technique. We find the density fluctuations to be a linear combination of the collective plasma oscillation and the random motion of Debye-screened dressed particles[3]. The relative magnitude ξ of the random to the collective part can be computed explicitly. For the LCLS case, we find that ξ is about unity for electron beams just prior to the λ = 1.5 Å FEL, and about 1% for the beam at 135 MeV at λ = 1 μm. The “position noise” (bunching factor) could be reduced to about ξ by a quarter of plasma oscillation. However, this leads to an increase in the “momentum noise”, which contributes significantly to the growth of the self-amplified spontaneous emission.
[1] D. Pines, D. Bohm, Phys. Rev.,85,338 (1952)
[2] A. Gover, E. Dyunin, Phys. Rev.Letters, 102,154801 (2009)
[3] S. Ichimaru, Basic Principles of Plasma Physics, The Benjamin/Cummins Pub. Co. (1973) 		 
slides icon Slides TUOA2 [0.361 MB]  
 
TUOA3
 Three-dimensional Kinetic Theory of Longitudinal Space-charge Interactions in a Thermal Relativistic Electron Beam  
 
  • A. Marinelli, E. Hemsing, J.B. Rosenzweig
    UCLA, Los Angeles, California, USA
  
  We develop an analytical model of space-charge interactions leading to longitudinal plasma oscillations and space-charge induced microbunching amplification. Our theory is based on a modal description of space-charge waves which includes energy spread, emittance, betatron motion and geometrical effects due to the finite size of the beam. In analogy with the three-dimensional theory of free-electron lasers, we derive a dispersion relation for the space-charge oscillation modes that can be expressed in terms of four dimensionless parameters. We find approximate variational solutions as well as numerical solutions with a discretization method. Finally we we apply this model to the optimization of a longitudinal space-charge amplification experiment.  
slides icon Slides TUOA3 [3.254 MB]  
 
TUOA4 Toward TW-level, Hard X-ray Pulses at LCLS 160
 
  • W.M. Fawley, J.C. Frisch, Z. Huang, Y. Jiao, H.-D. Nuhn, C. Pellegrini, J. Wu
    SLAC, Menlo Park, California, USA
  • S. Reiche
    Paul Scherrer Institut, Villigen, Switzerland
  
  Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515.
Coherent diffraction imaging of complex molecules, like proteins, requires a large number of hard X-ray photons, ~10+13/pulse, within a time ~10 fs or less. This is equivalent to a peak power of about one TW, much larger than that currently generated by LCLS or other proposed X-ray FELs. We study the feasibility of producing such pulses from LCLS and the proposed LCLS-II, employing a configuration beginning with a SASE amplifier, followed by a "self-seeding" crystal monochromator [1], and finishing with a long tapered undulator. Results suggest that TW-level output power at 8 keV is possible, with a total undulator length below 200 m. We use a 40 pC electron bunch charge, normalized transverse emittance of 0.2-mm-mrad, peak current of 4 kA, and electron energy about 14 GeV. We present a tapering strategy that extends the original "resonant particle" formalism by optimizing the transport lattice to maximize optical guiding and enhance net energy extraction. We also discuss the transverse and longitudinal coherence properties of the output radiation pulse. Fluctuation of such a tapered FEL is studied with realistic jitter measured at LCLS and with start-to-end simulation. 		 
slides icon Slides TUOA4 [9.357 MB]  
 
WEOA2 SASE FEL Pulse Duration Analysis from Spectral Correlation Function 318
 
  • A.A. Lutman, Y.T. Ding, Y. Feng, Z. Huang, J. Krzywinski, M. Messerschmidt, J. Wu
    SLAC, Menlo Park, California, USA
  
  Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515.
A new method to measure the X-rays pulse duration through the analysis of the statistical properties of the SASE FEL spectra has been developed. The information on the pulse duration is contained in the correlation function of the intensity spectra measured after a spectrometer. The spectral correlation function is derived analytically for different profile shapes in the exponential growth regime and issues like spectral central frequency jitter and shot by shot statistical gain are addressed. Numerical simulations will show that the method is applicable also in saturation regime and that both pulse duration and spectrometer resolution can be recovered from the spectral correlation function. The method has been experimentally demonstrated at LCLS, measuring the soft X-rays pulse durations for different electron bunch lengths, and the evolution of the pulse durations for different undulator distances. Shorter pulse durations down to 13 fs FWHM have been measured using the slotted foil. 		 
slides icon Slides WEOA2 [0.758 MB]  
 
WETUI1
 Electromagnetic Radiation in Accelerator Physics  
 
  • G.V. Stupakov
    SLAC, Menlo Park, California, USA
  
  Funding: Work supported by U.S. DOE Contract No. DE-AC02-76SF00515.
In this tutorial I will focus on several topics which are sometimes neglected, or shadowed, in textbooks, but are essential for a deeper understanding of radiation processes in accelerator physics. They include the notions of longitudinal and transverse formation lengths in the process of radiation, coherent versus incoherent radiation, effect of correlations of particles' positions on radiation, fluctuations of the spectrum, and radiative reaction forces. Importance of these concepts is illustrated with analysis of synchrotron, undulator and transition radiation. I try to avoid complicated equations throughout the lecture relying instead on order of magnitude estimates. 		 
slides icon Slides WETUI1 [4.507 MB]  
 
THOA4 Three Bunch Compressor Scheme for SASE FEL 447
 
  • H.-S. Kang, I.S. Ko, S.H. Nam
    PAL, Pohang, Kyungbuk, Republic of Korea
  • M.-H. Cho, C.H. Yi
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  
  The bend angle of dipoles in bunch compressor needs to be small enough to reduce the emittance increase due to CSR, which requires a larger energy chirp at the preceding RF linac. Correlated energy spread is not reduced below FEL parameter after the following RF linac because of the small number of accelerating sections as in the PAL XFEL design. Three bunch compressor scheme can make it possible to minimize the CSR induced emittnace growth as well as reduce the correlated energy spread below FEL parameter.  
slides icon Slides THOA4 [1.467 MB]