• A. Nause, E. Dyunin, A. Gover
  University of Tel-Aviv, Faculty of Engineering, Tel-Aviv

The possibility to control optical frequency current shot-noise by longitudinal collective interaction in an electron beams was suggested recently, based on an extended 1D (single Langmuir mode) model.[1] This model predicts the possibility to reduce the beam current-noise below the classical shot-noise level. 3D simulations in GPT were executed in order to verify the predicted current shot noise reduction. It was verified numerically that minimal current shot-noise is attainable in a drift length of quarter wavelength oscillation. However the attainment of the effect requires proper setting of the beam geometrical and current density parameters to avoid interference of higher order Langmuir modes.[2] The parameters range of which the single mode model is valid and the deterioration effects out of this range were determined. Parameters for future experiments are suggested. This process may be applicable for controlling microbunching instabilities and FEL coherence enhancement.

[1] A. Gover, PRL 102, 154801 (2009).
[2] M. Venturini, Phys. Rev. ST Accel. Beams 11, 034401(2008).

• E. Allaria
  ELETTRA, Basovizza
• X. Dao
  SLAC, Menlo Park, California
• G. De Ninno
  University of Nova Gorica, Nova Gorica

Recently, the second FEL line of the FERMI FEL has been modified in order to extend its tuning range down to 3 nm. In order to reach such a short wavelength starting from the UV seed laser the FERMI FEL-2 system relies on a double cascade of high gain harmonic generation. In this work we study the possibility of using the present FEL-2 layout with minor modifications to demonstrate the feasibility of the recently proposed echo-enabled harmonic generation (EEHG). The final aim is to cover the expected spectral range of FEL-2 with a single cascade. The performance of the EEHG in FERMI FEL-2 is estimated by means of start-to-end FEL simulations.

• L. Giannessi, M. Labat
  ENEA C.R. Frascati, Frascati (Roma)
• A. Bacci
  Istituto Nazionale di Fisica Nucleare, Milano
• B. Spataro
  INFN/LNF, Frascati (Roma)

We propose an experiment of self seeding at SPARC. The experiment would be done at visible/UV wavelengths where high reflectivity mirrors at normal incidence are available and its implementation would require only minor modifications of the existing SPARC layout. The new FEL configuration might significantly extend the SPARC FEL wavelength range of operation and would present several advantages as a higher brightness in wavelength tunable conditions together with a reduction of the demands in terms electron beam peak current and beam quality.

• V. Petrillo
  Universita' degli Studi di Milano, Milano
• A. Bacci, L. Serafini
  Istituto Nazionale di Fisica Nucleare, Milano
• M. Boscolo, M. Ferrario, C. Vaccarezza
  INFN/LNF, Frascati (Roma)
• G. Dattoli, L. Giannessi, M. Labat, P.L. Ottaviani, C. Ronsivalle
  ENEA C.R. Frascati, Frascati (Roma)
• S. Pagnutti
  ENEA-Bologna, Bologna
• L. Palumbo
  Rome University La Sapienza, Roma
• M. Serluca
  INFN-Roma, Roma

We describe a possible experiment aimed at generating sub-picosecond high brightness electron bunches with the SPARC photoinjector, which produce optical single spike radiation pulses in the regime of self-amplified spontaneous emission. The main purpose of the experiment is the production of short electron bunches as long as few SASE cooperation lengths by means of the Velocity Bunching technique. The measure of the properties of the electron beam, the determination of shape and spectrum of the radiation pulse and the validation of the single spike scaling laws will be analysed in order to foresee future operations at shorter wavelength with SPARX. We present in this paper start-to-end simulations of the beam production and FEL performance, statistical analysis and behaviour on the harmonics. The experience gained from this experiment will help in the configuration of the VUV and X-ray FEL SPARX to obtain FEL pulses below 10 fs.

• S. Reiche, R. Abela, H.-H. Braun, B. Patterson, M. Pedrozzi
  PSI, Villigen

The X-ray FEL facility SwissFEL, currently planned at the Paul Scherrer Institut, is primarily based on the SASE operation of a hard (1-7 Å) and soft (7-70 Å) X-ray beamline. However the soft X-ray FEL beamline is foreseen to allow for seeding down to 1 nm. The intrinsic shot noise in the electron bunch demands excellent state-of-the-art seeding sources and strategies. This presentation discusses various seeding options for the PSI-XFEL and evaluates them regarding performance and risk of implementation.

• S. Reiche, R. Abela, B. Beutner, H.-H. Braun, B. Patterson, M. Pedrozzi
  PSI, Villigen

The Paul Scherrer Institute is currently proposing a X-ray Free-electron Laser facility operating in the wavelength range of 0.1 to 7 nm. The overall design aims for a compact layout and relies on a low emittance electron beam and short period undulator. As an initial step, a 250 MeV is currently under construction to demonstrate a high brightness electron beam sufficient for operating the SwissFEL. An extension of the 250 MeV injector is under construction to test additional key components for the SwissFEL. Those are prototypes of the in-vacuum undulator modules as well as the proof-of-principle demonstration of echo-enabled harmonic generation as a possible seeding option for the SwissFEL at 1 nm. The combination of seeding and prototype undulator module allows for saturation of the FEL at 50 nm and first experiments with FEL radiation at the PSI.

• S. Reiche, H.-H. Braun, Y. Kim, M. Pedrozzi
  PSI, Villigen

The Paul Scherrer Institut is proposing an X-ray FEL facility, providing a wavelength range between 1 Angstrom to 7 nm. The major mode of operation is SASE with a supplemental seeding option for wavelength down to 1 nm. In addition a low charge operation of about 10 pC is considered to achieve single spike operation in the soft X-ray regime and thus overcoming the limitation of seeding sources at that wavelength. This presentation discusses the basic operation as well expected stability of the performance in energy and spectral power.

• P.K. Mishra
  University of Ottawa, Ottawa, Ontario

The full dispersion relation obtained for free-electron laser using helical wiggler circularly polarized magnetic field and an axial guide magnetic field using particle trajectories, their interaction with electric field by method of characteristics making the treatments quite general is reduced to Raman regime approximations in case of tenuous electron beam. The temporal and convective growth rates have been compared between full dispersion relation and Raman dispersion relation in microwave region. Results show the maximum of temporal growth in full dispersion relation and Raman dispersion relation is at the same locations. Whereas the maximum of convective growth rate in full dispersion relation is slightly deviated with respect to the Raman dispersion relation. The growth rates in Raman regime in both the cases are enhanced with respect to full dispersion relation for the same plasma frequency and cavity parameters.

• J.T. Donohue
  CENBG, Gradignan
• J. Gardelle
  CESTA, Le Barp

The results of the CESTA experiment that used a flat, wide, and intense beam to produce coherent Smith-Purcell radiation are compared with 2-D and 3-D simulations performed with the PIC code "MAGIC". The comparison provides considerable support to the paradigm proposed a few years ago by Andrews and Brau.

• I. Zagorodnov, M. Dohlus
  DESY, Hamburg

We present a fully three dimensional time-domain simulation code for free-electron lasers. Compared to the existing codes, we have implemented different numerical schemes for tracking and field calculations. The equations of motion of the particles are integrated with a leap-frog scheme. The parabolic field equation is resolved with implicit Neumann finite difference scheme based on azimuthal expansion. Additionally we have implemented the open boundary condition with the help of perfectly matched layer for parabolic equation. The last feature allows for a mesh only in the bunch vicinity. The implemented field solver is accurate and fast. We test the accuracy of the code with different numerical tests and apply the code to estimate the expected properties of the radiation in FLASH facility with 3rd harmonic module.

• J. Hussain
  RGPV, Bhopal
• V. Gupta
  KCB Technical Academy, Indore
• G. Mishra
  Devi Ahilya University, Indore

In the recent past harmonic undulators[1-4] are proposed for enhancced free electron laser radiation at higher harmonics. In this paper we include the important influence of beam energy spread on harmonic undulator radiation. A two-peak electron beam energy distribution[5]is considered to enhance the spectrum broadening and gain reduction in the harmonic undulator free electron laser.

[1] Jeeva Khan Hussain, Vikesh Gupta, G.Mishra, IL Nuovo Cimento B, In Press 2009.
[2] G. Mishra, Mona Gehlot, Jeeva Khan Hussain, Journal of Modern Optics, In Press 2009.
[3] G. Mishra, Mona Gehlot, Jeeva Khan Hussain, Nuclear Instruments and Methods in Phy. Res. A, In Press 2009.
[4] V. Gupta, G. Mishra, Nuclear Instruments and Methods in Phy. Res. A, vol.574(2007)p-150
[5] F.Ciocci, G.Dattoli, Nuclear Instruments and Methods in Phy. Res. B71(1992)p-339

• S. Tripathi, G. Mishra
  Devi Ahilya University, Indore
• V. Gupta
  KCB Technical Academy, Indore
• J. Hussain
  RGPV, Bhopal

A new three frequency undulator has been proposed.[1] The authors assume that the electron moves on axis in a three harmonic undulator structure. Let us consider the case of the fundamental. The intensity at this frequency will be further enhanced by the contribution from the modulation at sum-difference frequencies. The fundamental intensity will be raised. For the next odd harmonics of the fundamental, there will be contributions from the harmonic field components to produce an enhanced intensity at the third odd harmonics. At this frequency there will be further contributions from the sum-frequency. However the intensity contributions from the sum-difference frequency will be small in comparison to the primary odd harmonics and the net result is that the third harmonic intensity will be raised . Thus the three frequency works in a similar way to that of the harmonic undulator scheme. In this paper we calculate the three frequency undulator radiation and discuss the feasibility of free electron laser operation with this undulator scheme.

[1] V.I.R. Niculescu et al. Rom Journ. Phy. Vol.53, Nos.5-6, P.775-780 (2008)

• V. Gupta
  KCB Technical Academy, Indore
• J. Hussain
  RGPV, Bhopal
• G. Mishra
  Devi Ahilya University, Indore

In the recent past, variable polarized undulators and variable polarized harmonic undulator [1-4] are proposed. The scheme consists of two identical linearly polarized magnets with high permeability shims in the gap of the undulator magnets. In this paper we include the important effects of beam energy spread on the variable polarized harmonic undulator radiation and discuss free electron laser gain. We have considered both single and two peak gaussian beam energy distribution to calculate intensity and gain reduction. We show that the variable polarized harmonic undulator scheme compensates the undesired effects of the beam energy spread in comparison to the standard variable polarized undulator free electron laser.

[1] G. Dattoli, L. Bucci, Nuclear Instruments and Methods in Phy. Res. A, vol.450(2000)p-479.
[2] G. Dattoli, L. Bucci, Optics Comm., vol.177(2000)p-323.
[3] V. Gupta, G. Mishra, Nuclear Instruments and Methods in Phy. Res. A, vol.574(2007)p-150.
[4] G. Mishra, Mona Gehlot, Jeeva Khan Hussain, Nuclear Instruments and Methods in Phy. Res. A, In Press 2009.

• B. Maraghechi, M.H. Rouhani
  AUT, Tehran

Three-dimensional simulation of harmonic up conversion in free electron laser amplifier operating simultaneously with two cold electron beams of different energies is presented in steady-state regime. By using slowly varying envelope approximation, the hyperbolic wave equations can be transformed into parabolic diffusion equations. By applying the source-dependent expansion to these equations, electromagnetic fields are represented in terms of the Hermit Gaussian modes. The electron dynamics is described by the fully three dimensional Lorentz force equation in the presence of a realistic planar magnetostatic wiggler and electromagnetic fields. A set of coupled nonlinear first order differential equations is derived and solved numerically. This set of equation describes self consistently the longitudinal spatial dependence of radiation waists, curvatures, and amplitudes together with the evolution of the electron beam.

• B. Maraghechi, M.H. Rouhani
  AUT, Tehran

One dimensional simulation of Raman free electron laser amplifier with planar wiggler and ion channel guiding is presented. Using Maxwell’s equations and full Lorentz force equation of motion for electron beam, a set of coupled nonlinear differential equations is derived in slowly varying amplitude and wave number approximation and solved numerically. This set of equation describes self consistently the longitudinal dependence of radiation amplitudes, wave numbers, growth rates, space charge amplitudes, and wave numbers together with the evolution of the electron beam. Because of using non-wiggler averaged equation of motion, it is possible to treat the injection of the beam into the wiggler. The electron beam is assumed cold, propagates with a relativistic velocity, ions are assumed immobile and slippage is ignored. The effect of prebunching on saturation can be added to this code. Therefore no driving signal is needed. Ion channel density is varied and the results for group I and II orbits were compared with the absence of ion channel. In contrast to the axial magnetic field, this type of guiding does not produce any drifting motion.

• Yu. Lurie, Y. Pinhasi
  Ariel University Center of Samaria, Faculty of Engineering, Ariel

In pulsed beam free-electron devices, longitudinal space-charge fields result in collective effects leading to expansion of short electron pulses along their trajectory. This effect restricts application of intense ultra-short electron pulses, and requests a careful theoretical description. In the present work, longitudinal space-charge fields are considered in the framework of a three-dimensional, space-frequency approach. The basic equations of the model, originally obtained as a solution of the wave equations for the electromagnetic field in an uniform waveguide, are shown to satisfy also Gauss's law. Longitudinal electric field was found in the model analytically for a point-like charge, moving along a waveguide with a constant velocity. This enables consideration and comparison of different components of the resulted longitudinal electric field, such as forward and backward going waves, near and under cut-off frequencies, and so on. Possible simplifications in evaluations of longitudinal space-charge fields in the model are discussed.

• Y. Pinhasi, Yu. Lurie
  Ariel University Center of Samaria, Faculty of Engineering, Ariel

Free-electron lasers (FELs) and masers, utilize distributed interaction between an electron beam and the electromagnetic field. Our space-frequency theory [*] is extended to consider collective effects emerging while ultra short electron pulses are propagating in the interaction region. The total electromagnetic field (radiation and space-charge) is presented in the frequency domain as an expansion in terms of transverse eigen-modes. The mutual interaction between the electron beam and the electromagnetic field is fully described by a set of coupled equations, expressing the evolution of mode amplitudes and electron beam dynamics. The model is used for the study of radiation excitation in pulsed beam free-electron lasers operating in millimeter wavelengths and Tera-Hertz frequencies. The approach is applied in a numerical particle code WB3D, simulating wide-band interaction of a free-electron laser operating in the linear and non-linear regimes, and is utilized to study spontaneous and super-radiant emissions radiated by a an electron bunch at the sub-millimeter regime, taking into account three dimensional space-charge effects playing a role in such ultra short bunches.

* Y. Pinhasi, Yu. Lurie, A. Yahalom: “Space-frequency model of ultra wide-band interactions in millimeter wave masers”, Phys. Rev. E 71, (2005), 036503- 1-8

• W. Liu, W.-H. Huang, C.-X. Tang, D. Wu
  TUB, Beijing

The THz wave has some unique characteristics resulting in varieties of applications to medical and industrial imaging, biomedical research and material science,etc. The various schemes for generating the THz waves have been employed. At the present time, an intense interest has been raised in the Smith-Purcell devices, for which is a promising alternative in development of a tunable, compact, powerful of THz radiation source. In this paper, the radiation characteristics of terahertz (THz) Smith-Purcell radiation generated from the ultrashort electron beam are analyzed with the help of three-dimensional particle-in-cell simulation, the radiation power and energy are obtained the PIC simulation. The radiation characteristics generated from train bunches are compared with that of single bunch. The formation factors including the longitudinal and transverse are calculated. Through this study, we observe that the radiation power is enhanced and the band width can be adjusted with the train bunches.

• T.-Y. Lee, M.S. Chae, J. Choi, H.-S. Kang, M. Kim
  PAL, Pohang, Kyungbuk
• I.S. Ko
  POSTECH, Pohang, Kyungbuk

This paper discusses feasibility of a compact XFEL in the future. It gives theoretical argument how a compact XFEL can be possible. For that purpose, a method of energy scaling is developed. It is shown that an extremely low emittance electron gun is an essential element for the realization of a compact XFEL.

• B. Beutner
  PSI, Villigen

The planned SwissFEL facility will supply coherent, ultra-bright, and ultra-short XFEL photon beams covering a wide wavelength range from 0.1 nm to 7 nm, with nominal beam emittances in the range from 0.18 to 0.43 mm mrad. At the 250 MeV Injector test facility for the SwissFEL the beam quality will be studied to confirm the feasibility of the XFEL requirements. In order to understand and optimise the electron beam, precise measurements of the beam properties are essential. The diagnostics setup consists of various quadrupoles for phase advance scans and a 3.5-cell FODO lattice. Included in the diagnostic setup is a transverse deflecting RF structure for longitudinal resolved measurements. In this paper the techniques for emittance and Twiss parameter reconstruction are discussed. The focus is on transport matrix inversion and tomographic phase space reconstruction using the maximum entropy algorithm. The layout of the diagnostic section, the electron optics setup, and the strategy for measurements of the emittance are presented. Data on the systematic error concerning beam size measurement errors and beam energy uncertainties complete this summary.

• L.T. Campbell, R. Martin, B.W.J. McNeil
  USTRAT/SUPA, Glasgow

A new un-averaged 3D numerical model has been developed that will allow investigation of previously unexplored FEL physics. Previous 1D models have allowed exploration of the effects of amplification of coherent spontaneous emission and non-localised electron dynamics (see e.g. [1] and refs. therein.) A 3D model was also developed based upon a mixed finite element\Fourier method [2]. However, due to some limitations in the parallel routines, this restricted somewhat the FEL systems the model could describe. A significantly modified version of this model is presented here which does not require a finite element description and uses only transforms in Fourier space. This allows more effective and consistent data organization across multiple parallel processors enabling larger, more complex FEL systems to be studied. Furthermore, unlike the previous 3D model which uses commercially produced numerical packages, the new simulation code uses only open-source routines which will ultimately allow it to be freely available (open-source.)

[1] BWJ McNeil, GRM Robb & MW Poole, MPPB060, PAC, Portland, USA, 2003
[2] C.K.W. Nam, P. Aitken, & B.W.J. McNeil, MOPPH025, FEL Conference, Korea, 2008

• S.I. Bajlekov, S.M. Hooker
  University of Oxford, Clarendon Laboratory, Oxford
• R. Bartolini
  Diamond, Oxfordshire

Ultrashort electron bunches from laser-driven plasma accelerators hold promise as drivers for short-wavelength free electron lasers*. While full 3-D FEL simulation techniques have been successful in simulating lasing at present-day facilities, the novel sources investigated here are likely to violate a number of widely-held assumptions. For instance the HHG seed radiation, as well as the radiation generated by the bunch, do not conform to the slowly-varying envelope approximation (SVEA) on which the majority of codes are based. Additionally, the longitudinal macroparticle binning precludes the full physics of the system from being modeled. In order to more completely simulate the arising sub-wavelength effect we have developed an unaveraged 1-D time-dependent code without the SVEA. We highlight some of the additional features that these new systems present through analytical and numerical analyses. We discuss the regimes in which these effects become important, and investigate how they may be used to enhance the lasing process. Finally we outline a framework for full 3-D simulation of a short-wavelength FEL driven by a laser-plasma accelerator.

* Leemans et al., Nat. Phys. 2, 696 (2006); Gruner et al., Appl. Phys. B 86, 431 (2007).

• R.A. Bosch
  UW-Madison/SRC, Madison, Wisconsin
• R.J. Bosch
  Harvard School of Public Health, Boston

We derive the average and rms bunching for Poisson statistics. For a bunch with a large number of particles, the results are practically equivalent to a bunch with a fixed number of independent particles.

• Z. Huang, D.F. Ratner, G.V. Stupakov, D. Xiang
  SLAC, Menlo Park, California

We study effects of energy chirp on echo-enabled harmonic generation (EEHG). Analytical expressions are compared with numerical simulations for both harmonic and bunching factors. We also discuss the EEHG free-electron laser bandwidth increase due to an energy-modulated beam and its pulse length dependence on the electron energy chirp.

• G.V. Stupakov, Y.T. Ding, Z. Huang
  SLAC, Menlo Park, California

If the energy spread of a beam is larger then the Pierce parameter, the FEL gain length increases dramatically and the FEL output gets suppressed. We show that if the energy distribution of such a beam is modulated on a small scale, the gain length can be noticeably decreased. Such an energy modulation is generated by first modulating the beam energy with a laser via the mechanism of inverse FEL, and then sending it through a strong chicane. We show that this approach also works for the optical klystron enhancement scheme. Our analytical results are corroborated by numerical simulations.

• A. Gurinovich, V.G. Baryshevsky, N.A. Belous, V.A. Evdokimov, E.A. Gurnevich, P.V. Molchanov
  Belarussian State University, Scientific Research Institute of Nuclear Problems, Minsk

Electrodynamical properties of a crystal-like artificial periodic structure (photonic crystal) formed by a periodically strained metallic threads have been studied both theoretically [1] and experimentally [2]. In the present paper operation of Volume Free Electron Laser using a ''grid'' photonic crystal with variable period is considered. Theoretical analysis of properties of the photonic crystal built from metallic threads in a cylindrical resonator is accompanied with discussion of the experimental results. Dependence of radiation output on guiding magnetic field is analyzed. Radiation spectrum and polarization for different configurations of the photonic crystal are considered.

[1] V.G. Baryshevsky, A.A. Gurinovich, NIM B252 (2006) p.92
[2] V.G. Baryshevsky, N.A. Belous, A.A. Gurinovich, A.S. Lobko, P.V. Molchanov, V.I. Stolyarsky, Proc. of FEL2006, P.331.

• R. Bachelard, F. Briquez, M.-E. Couprie, A. Loulergue
  SOLEIL, Gif-sur-Yvette
• A. Ben Ismail, S. Corde, J. Faure, G. Lambert, O. Lundh, V. Malka, A. Rousse, K. Ta Phuoc
  LOA, Palaiseau
• G. De Ninno
  ELETTRA, Basovizza
• M. Labat
  ENEA C.R. Frascati, Frascati (Roma)

In the quest for compact FEL ultra-compact sources, a test experiment is under preparation, to couple an electron beam from a laser driven plasma accelerator, stable and tunable in energy, to an undulator. The electron beam is generated in the colliding laser pulses scheme, by focusing two short and intense laser pulse in an underdense plasma plume. The electron bunch has an energy tunable in up to a few hundreds MeV with 1% energy spread, a length 10 fs, a charge in the 10 pC range, while its radius and divergence are respectively 1μm and 3 mrad. As a first step toward a FEL experiment, the transport and radiation through an undulator of this short and compact electron beam is studied. The spontaneous emission through a 60 cm undulator in the 40-120 nm range is presented, and criteria to reach the threshold of Self-Amplified Spontaneous Emission are discussed.

• E. Saldin, E. Schneidmiller, V. Vogel, H. Weise, M.V. Yurkov
  DESY, Hamburg
• E. Syresin
  JINR, Dubna, Moscow Region

The driving engine of the Free Electron Laser in Hamburg (FLASH) is an L-band superconducting accelerator. It is designed to operate in a pulsed mode with 800 μs pulse duration and repetition rate of 10 Hz. Maximum accelerated current over macropulse is about 10 mA, and with the energy of electrons of 1 GeV average output power is about 72 kW. Expected power of the FEL radiation generated by FLASH is about 40 W. We show that FLASH technology holds great potential for increasing average power of the linear accelerator and increase of the transformation efficiency of the electron kinetic energy to the light. Thus, it will be possible to construct FLASH-like free electron laser operating at the wavelength of 13.5 nanometer with an average power in a kilowatt range. Such a source meets the requirements to the light source for the next generation lithography (NGL).

• J. Grünert
  European X-ray Free Electron Laser Project Team, c/o DESY, Hamburg

The European XFEL will provide x-ray radiation with properties that challenge diagnostics. Especially its unique pulse train structure of up to 3000 pulses of 100 fs duration, each at only 200ns spacing between neighboring pulses, asks for new approaches to the characterization of these x-ray photons. Also, the highly intense peak power of 20 GW rules out many of the conventional techniques developed for 3rd generation SR sources. The intensity and position monitors will use the interaction of the photons with dilute gases, other online devices could also use parasitically available scattered light, while intrusive but removable detectors will be dedicated to commissioning and optimization before user runs. This is in particular the K-monochromator which ensures during the photon based undulator alignment that the magnetic gap and the phasing between modules are correctly adjusted. The paper presents an overview of the baseline components of the XFEL facility diagnostics system and the requirements to them which result from the extreme radiation conditions.

• X.J. Shu
  IAP, Beijing
• T.C. Peng
  Wuhan University, Wuhan

It is proposed that a chirped pulse can be amplified using a free-electron laser. Chirped pulse amplification (CPA) technology is one of the major ways to get high power and ultra short FEL pulse．Linear chirped pulse amplification at single pass FEL amplifier is studied through numerical simulations using our 1D time-dependent code GOFEL-P. The processes of chirped pulses with different chirped parameters being amplified by normal FEL amplifier or the FEL amplifier with energy-chirped beam are studied. The peak power and width of the final compressed pulse with different chirped parameters have been calculated. The results show that, the normal FEL amplifier can amplify the chirped pulse, the peak power of the final compressed pulse can reach 10s GW and the width of the pulse can be 10s fs with the parameters of TTF. In the case of using the energy-chirped beam to amplify chirped pulse, the gain bandwidth of the FEL amplifier will be wider and the chirped parameter will be larger. The peak power of the final compressed pulse can even reach near 10 times larger and the width of the pulse 10 times shorter than that with normal electron beam.

• G.L. Orlandi, B. Beutner, R. Ischebeck, V. Schlott, B. Steffen
  PSI, Villigen

Diagnostics with a transverse spatial resolution in the order or even higher than the intrinsic limit of the traditional OTR light spot imaging techniques is required for high energy and low emittance electron beams by FEL driver linac. High resolution measurements of the beam transverse size can be performed by moving the radiation detection from the space of the electron transverse coordinates to the Fourier conjugate space of the radiation angular distribution. The development of such a new diagnostic technique is related to the experimental investigation of the beam transverse size effects in the angular distribution of the OTR spectral intensity. The status of the experimental investigation of such a phenomenon at the SwissFEL project and the main features of such a new diagnostic technique will be presented.

• C.P. Hauri, R. Ganter
  PSI, Villigen

The SwissFEL requires an emittance in the range from 0.18 to 0.43 mm mrad. To achieve this ambitious goal we are developing a wavelength-tunable laser system providing powerful UV pulses with arbitrary temporal shape in the range of 3-10 ps. The system should allow exact matching of the photon energy to the work function of the cathode material and consequently the reduction of the thermal emittance. Transverse and longitudinal laser pulse shaping is foreseen to minimize nonlinear space charge forces in the electron bunch to maintain lowest emittance during acceleration. In this paper we present the design and concept of this novel laser system and show first experimental results.

• A. Oppelt, R. Abela, B. Beutner, B. Patterson, S. Reiche
  PSI, Villigen

A powerful THz source is being considered for THz-pump / X-ray probe experiments at the planned SwissFEL. The source should deliver half-cycle pulses of less than 1 ps duration with an energy of 100 μJ in a focal region of 1 mm². Design considerations and simulations for such a source fulfilling the challenging parameter combination will be presented.

• D.J. Dunning, N. Thompson
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
• B.W.J. McNeil
  USTRAT/SUPA, Glasgow
• P.H. Williams
  Cockcroft Institute, Warrington, Cheshire

Start-to-end modelling of a SASE mode-locked FEL amplifier scheme [1] is presented using a superconducting re-circulating linac design[2]. Locking of the modes is achieved by modulating the electron beam energy at the mode frequency spacing. Previous studies [3] have shown that in a High Harmonic Generation (HHG) seeded mode-coupled FEL amplifier scheme (no electron beam energy modulation), although the attosecond pulse train structure of the seed is amplified through to saturation, temporal broadening of the individual pulses occurs. An HHG seeded mode-locked FEL amplifier scheme is modelled and it is seen that the temporal spikes of the HHG seed must be correctly phase-matched with the electron beam energy modulation for successful operation. By using a filtered HHG seed, which removes the seed’s attosecond pulse train structure, no such phase matching is required. Despite the absence of an initial attosecond pulse structure, a modal structure develops and is subsequently amplified to generate an attosecond pulse train with the good temporal coherence properties of the seed, significantly shorter individual pulse widths and higher peak powers than may be achieved in the other schemes.

[1] N.R. Thompson, B.W.J. McNeil, Phys. Rev. Lett. 100, 203901 (2008)
[2] P.H. Williams et al, WE5RF, 23rd PAC, Vancouver (2009)
[3] B.W.J. McNeil et al, MOCAU04, 30th Int. FEL Conf., Gyeongju (2008)

• F.E. Hannon, S.V. Benson, D. Douglas, P. Evtushenko, J.M. Klopf, G. Neil, C. Tennant, G.P. Williams, S. Zhang
  JLAB, Newport News, Virginia

Jefferson Laboratory is proposing to construct a next generation light source that capitalizes on the existing infrastructure of the Energy Recovery Linac (ERL) based Free Electron Laser (FEL) that has been operational since 1998. The new user facility, called JLAMP, will feature a two-pass superconducting linac to accelerate electron bunches to 600MeV with the possibility of energy recovery. The photon source will be a seeded amplifier FEL that covers the 10 to 100eV energy range, capable of providing up to seven orders of magnitude increase in average brightness over existing sources. At longer wavelengths the device will also have the option of operating as a high gain resonator for users who desire a higher repetition rate. The design options and technical challenges associated with the development of the JLAMP machine are presented here.

• M.P. Anania, D. Clark, R.C. Issac, D.A. Jaroszynski, A. J. W. Reitsma, G.H. Welsh, S.M. Wiggins
  USTRAT/SUPA, Glasgow
• J.A. Clarke, M.W. Poole, B.J.A. Shepherd
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
• M.J. de Loos, S.B. van der Geer
  Pulsar Physics, Eindhoven

Recent progress in developing laser-plasma accelerators is raising the possibility of a compact coherent radiation source that could be housed in a medium sized university department. Beam properties from laser-plasma accelerators have been traditionally considered as not being of sufficient quality to produce amplification. Our work shows that this is not the case. Here we present a study of the beam characteristics of a laser-plasma accelerator. We also highlight the latest results on the ALPHA-X compact FEL. We show how the beam properties of the ALPHA-X beam line have been optimized in order to drive a FEL. We discuss the implementation of a focussing system consisting of a triplet of permanent magnet quadrupoles and a triplet of electromagnetic quadrupoles. The design of these devices has been carried out using the GPT (General Particle Tracer "*") code, which considers space charge effects and allows a realistic estimate of electron beam properties along the beam line. The latest measurements of energy spread and emittance will be presented. Currently we have measured energy spreads less than 0.7% and, using a pepper pot, put an upper limit on the emittance of 5 pi mm mrad.

"*" S.B. van der Geer and M.J. de Loos, “General Particle Tracer code: design, implementation and application” (2001);

• G. Penn, A. Zholents
  LBNL, Berkeley, California

Attosecond X-ray pulses are an invaluable probe for the study of electronic and structural changes during chemical reactions. The wide bandwidth of these pulses is comparable to that of the valence electronic states, and is well suited to probing valence electron excitations using core electron transitions. We investigate a method for creating two synchronized, attosecond soft X-ray pulses in a free electron laser, through optical manipulation of electrons located in two distinct sections of the electron bunch. Each X-ray pulse can have energy of the order of 100 nJ and pulse width of the order of 250 attoseconds. The central frequency of each X-ray pulse can be independently tuned to separate core electron transition frequencies of specific atoms in the molecule. The time interval between the two attosecond pulses is tunable from a few femtoseconds to a few hundred femtoseconds with a precision better than 100 attoseconds.

• C.R. Prokop, P. Piot
  Northern Illinois University, DeKalb, Illinois
• M.C. Lin, P. Stoltz
  Tech-X, Boulder, Colorado

Terahertz (THz) radiation occupies a very large portion of the electromagnetic spectrum and has generated much recent interest due to its ability to penetrate deep into many organic materials without the damage associated with ionizing radiation such as X-rays. One path for generating copious amount of tunable narrow-band THz radiation is based on the Smith-Purcell free-electron laser (SPFEL) effect first proposed by Walsh. In this paper we present the design and start-to-end simulation of a compact SPFEL. The device is based on a low energy (20-40 keV) electron accelerator capable of producing sheet electron beams needed to enhance the SPFEL interaction. The beam tracking simulations are carried with a quasistatic particle-in-cell program (Astra from DESY) while the beam dynamics and electromagnetics of the SPFEL interaction is modeled using a finite-difference time-domain electromagnetic solver (VORPAL from Tech-X Corporation).

• F.V. Hartemann, F. Albert, G.G. Anderson, S.G. Anderson, C.P.J. Barty, A.J. Bayramian, S.M. Betts, T.S. Chu, R.R. Cross, C.A. Ebbers, S.E. Fisher, D.J. Gibson, R.A. Marsh, D.P. McNabb, M. J. Messerly, K.L. O'Neill, M. Shverdin, C. Siders
  LLNL, Livermore, California
• E.N. Jongewaard, T.O. Raubenheimer, S.G. Tantawi, A.E. Vlieks
  SLAC, Menlo Park, California
• A. Ladran
  LBNL, Berkeley, California
• V. A. Semenov
  UCB, Berkeley, California

Recent progress in accelerator physics and laser technology have enabled the development of a new class of gamma-ray light sources based on Compton scattering between a high-brightness, relativistic electron beam and a high intensity laser pulse produced via chirped-pulse amplification (CPA). In this talk, the current state-of-the-art will be reviewed, along with important applications, including nuclear resonance fluorescence. The design of a precision gamma-ray source will also be discussed, along with the key technologies chosen for the project: X-band linac and photo-injector, photo-cathode laser pulse shaping, and hyper-dispersion CPA.

• E. Hemsing, A. Marinelli, P. Musumeci, J.B. Rosenzweig, D. Schiller
  UCLA, Los Angeles

An electron beam that is subject to the typical FEL microbunching instability is microbunched longitudinally in both density and velocity, according to the shape of the ponderomotive phase bucket. Higher-order three-dimensional microbunching geometries can be created if the e-beam interacts either with a more complicated resonant field structure, or at higher harmonics of the fundamental resonance. At harmonics inside a helical wiggler, the e-beam interacting with an axisymmetric gaussian laser field becomes microbunched into a helix, or combination of twisted helices, depending on the harmonic number. The twisted e-beam can then be used to emit coherent light with orbital angular momentum in a downstream radiator. An experimental effort to explore the principles of this interaction is discussed.

• D. Xiang, Z. Huang, G.V. Stupakov
  SLAC, Menlo Park, California
• D.F. Ratner
  Stanford University, Stanford, California

We propose and analyze a scheme to achieve a seeded hard x-ray source based on a two-stage echo-enabled harmonic generation (EEHG) FEL. In the scheme a 180 nm seed laser covering the whole bunch is first used to modulate the beam when beam energy is 2 GeV. After passing through a strong chicane complicated fine structures are introduced into the phase space. The beam is again modulated by a short 180 nm laser that only covers the rear part of the beam and then accelerated to 6 GeV. A weak chicane is then used to convert the energy modulation to density modulation. The density-modulated beam is sent through a radiator to generate intense 6 nm radiation which will be time-delayed to interact with the front fresh part of the bunch. Finally we generate in the beam density modulation at the 1199th harmonic of the seed laser. We will discuss the issues related to the realization of the seeded hard x-ray FEL.

• D. Xiang, Z. Huang, G.V. Stupakov
  SLAC, Menlo Park, California

We propose a scheme that combines the echo-enabled harmonic generation technique with the bunch compression and allows one to generate harmonic numbers of a few hundred in a microbunched beam through up-conversion of the frequency of an ultraviolet seed laser. A few-cycle intense laser is used to generate the required energy chirp in the beam for bunch compression and for selection of an attosecond x-ray pulse. Sending this beam through a short undulator results in an intense isolated attosecond x-ray pulse. Using a representative realistic set of parameters, we show that 1 nm x-ray pulse with peak power of a few hundred MW and duration as short as 20 attoseconds (FWHM) can be generated from a 200 nm ultraviolet seed laser. The proposed scheme may enable the study of electronic dynamics with a resolution beyond the atomic unit of time (∼24 attoseconds) and may open a new regime of ultrafast sciences.

• D.F. Ratner
  Stanford University, Stanford, California
• A. Chao, Z. Huang
  SLAC, Menlo Park, California

We propose a single-stage scheme to produce coherent soft X-ray radiation directly from a UV seed laser. Seeding an electron bunch prior to compression simultaneously shortens the laser wavelength and increases the modulation amplitude. The final X-ray wavelength is tunable by controlling the compression factor with the RF phase. Photocathode beams with large energy spreads require corresponding large modulation amplitudes, leading to strong over-bunching during compression in the first chicane. We introduce a second chicane to unwind and restore the bunching. We also show that transportation of fine compressed modulation structure is feasible due to recompression in the second chicane.

• V. Litvinenko, V. Yakimenko
  BNL, Upton, Long Island, New York

We propose a demonstration experiment at Accelerator Test Facility at BNL on suppression of spontaneous undulator radiation from an electron beam. We describe the method, the proposed layout and possible schedule.

• S.D. Webb, V. Litvinenko
  BNL, Upton, Long Island, New York

FEL-based coherent electron cooling offers a new avenue to achieve high luminosities in high energy colliders such as RHIC, LHC, and eRHIC. Traditional FEL treatments treat the FEL as an amplifier of optical waves with specific initial conditions, and obtain the resulting field. This new approach requires knowledge of the phase space distribution of the electron cloud in the FEL. We present 1D analytical results for the phase space distribution of an electron cloud with an arbitrary initial current profile, and discuss approaches of expanding to 3D results.