FEL2015 - Classification: Advanced Concepts and Techniques

Paper	Title	Page
MOP067	Transverse Emittance-Preserving Transfer Line and Arc Compressor for High Brightness Electron Sources	191
	S. Di Mitri, M. Cornacchia, S. Spampinati Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy S. Spampinati Cockcroft Institute, Warrington, Cheshire, United Kingdom
	Minimizing transverse emittance is essential in single- or few-passes accelerators designed to deliver high brightness electron beams. Emission of coherent synchrotron radiation (CSR) is an important factor of emittance degradation. We have demonstrated, with analytical and experimental results, that this perturbation may be cancelled by imposing certain conditions on the electron optics when the bunch length is constant along the line. This scheme of CSR suppression is then enlarged, analytically and numerically, to cover the case of varying bunch length in a periodic arc compressor. The proposed solution hold the promise of cost-saving of compact transfer lines with large bending angles, and new schemes for beam longitudinal gymnastics both in recirculating and in single-pass accelerators driving free electron lasers. S. Di Mitri, M. Cornacchia, S. Spampinati, Phys. Rev. Letters, 110, 014801 (2013) ** S. Di Mitri, M. Cornacchia, Europhys. Letters, 109, 62002 (2015)
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MOP068	First Simulation Results on Free Electron Laser Radiation in Displaced Phase-combined Undulators	196
	N.S. Mirian UVSOR, Okazaki, Japan E. Salehi AUT, Tehran, Iran
	This report deals with self amplified spontaneous emission free electron laser (FEL) amplifier where the FEL emission is obtained from displaced phase combined undulators. Magnetic field of this adjustment methods in three dimensions is presented. The electron dynamics is investigated. The simulation method and results are explained. The radiation properties of the fundamental resonance and third harmonic through the phase combined undulators are compared with the normal undulator with the same undulator deflection parameter
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MOP070	Harmonic Generation in Two Orthogonal Undulators	200
	N.S. Mirian UVSOR, Okazaki, Japan
	In this report, the harmonic generation in two orthogonal undulators is under discussion. There is a possibility of generation of the even and odd harmonics as well as no-integer harmonics in two orthogonal undulators. By considering the first order of electron velocity, the total energy radiated per unit solid angle per unit frequency interval for a single electron traveling along the undulators is derived. Also a numerical simulation of one-dimensional non-averaged equations is conducted to present the self amplified spontaneous emission of harmonic generation in two orthogonal undulators.
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MOP071	Carrier-Envelope-Phase Stable Linearly and Circularly Polarized Attosecond Pulse Sources	205
	Z. Tibai, G. Almási, Zs. Csiha-Nagy, J.A. Fülöp, J. Hebling University of Pecs, Pécs, Hungary J.A. Fülöp, Gy. Tóth MTA-PTE High-Field Terahertz Research Group, Pecs, Hungary
	Recently, we proposed a robust method for producing waveform-controlled attosecond pulses in the EUV spectral range.* In our scheme the relativistic electron beam, provided by a LINAC, is sent through a modulator undulator where a TW-power laser beam is superimposed on it in order to generate nanobunches. The nanobunched electron beam passes through a single- or few-period radiator undulator (RU). The waveform of the generated attosecond pulses closely resembles the longitudinal distribution of the magnetic field. According to our calculations, at 20 nm (60 nm) wavelength carrier-envelope-phase (CEP) stable pulses with 23 nJ (80 nJ) energy, 80 as (240 as) duration, and 31 mrad (13 mrad) CEP fluctuation (standard deviation) can be achieved at K=0.5. More than 500 nJ energy is predicted at longer wavelengths and larger K. The energy fluctuation of the EUV pulse is 2.5 times higher than that of the laser. By using a helical RU, even circularly polarized attosecond pulses with 30/300 nJ energy can be generated, depending on the wavelength. To the best of our knowledge, no other presently available technique enables the generation of arbitrary-waveform, CEP-controlled attosecond pulses. The predicted pulse energies are sufficiently high to be used as pump pulses in attosecond pump-probe measurements. * Z. Tibai et al., Phys. Rev. Lett. 113, 104801 (2014).
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MOP074	Efficiency Enhancement of a Harmonic Lasing Free-Electron Laser	209
	N.S. Mirian UVSOR, Okazaki, Japan B. Maraghechi, E. Salehi AUT, Tehran, Iran
	The harmonic lasing free-electron laser amplifier, in which two wigglers is employed in order for the fundamental resonance of the second wiggler to coincide with the third harmonic of the first wiggler to generate ultraviolet radiation, is studied. A set of coupled nonlinear first-order differential equations describing the nonlinear evolution of the system, for a long electron bunch, is solved numerically by CYRUS code. Thermal effects in the form of longitudinal velocity spread are also investigated. The second wiggler field decreases linearly and nonlinearly at the point where the radiation of the third harmonic saturates to enhance the efficiency. The optimum starting point and the slope of the tapering of the amplitude of the wiggler are found by a successive run of the code. It is found that tapering can increase the saturated power of the third harmonic considerably.
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MOP075	Three-dimensional Simulation of a Harmonic Lasing Free-Electron Laser Amplifier	213
	E. Salehi, B. Maraghechi AUT, Tehran, Iran N.S. Mirian UVSOR, Okazaki, Japan
	Three-dimensional simulation of harmonic lasing Free-electron laser is represented in the steady-state regime. Here, the third harmonic of the first wiggler is adjusted at the fundamental resonance of the second wiggler by reducing the magnetic field strength of the second wiggler. The hyperbolic wave equations can be transformed into parabolic diffusion equations by using the slowly varying envelope approximation. A set of coupled nonlinear first-order differential equations describing the nonlinear evolution of the system is solved numerically by CYRUS3D code. This set of equations describes self-consistently the longitudinal spatial dependence of the radiation waists, curvatures, and amplitudes together with the evaluation of the electron beam. Thermal effects in the form of longitudinal velocity spread are also investigated. In order to reduce the length of the wiggler, the prebunched electron beam is considered.
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MOP076	Free-Electron Laser Driven by a 500 MeV Laser Plasma Accelerator Beam	217
	W. Qin, J.E. Chen, S. Huang, K.X. Liu, X.Q. Yan, L. Zeng PKU, Beijing, People's Republic of China Y. Ding, Z. Huang SLAC, Menlo Park, California, USA
	A laser plasma accelerator is under construction at Peking University and several hundred MeV electron beams are expected. In this paper we discuss applying a 500 MeV beam with 1% relative energy spread to FEL. Bunch decompression method is considered to deal with the large energy spread of the beam. Emittance growth induced by large divergence and energy spread in electron beam transport has been treated with the chromatic matching manipulation. Simulation shows that 100 MW level, 6.3 fs , 0.008 bandwidth output can be obtained for 30 nm FEL. TGU method with assumed matched beam is also discussed as a comparison.
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TUP074	Results from the Nocibur Experiment at Brookhaven National Laboratory's Accelerator Test Facility	540
	N.S. Sudar, J.P. Duris, I.I. Gadjev, P. Musumeci UCLA, Los Angeles, USA M. Babzien, M.G. Fedurin, K. Kusche, I. Pogorelsky, M.N. Polyanskiy, C. Swinson BNL, Upton, Long Island, New York, USA
	Conversion efficiencies of electrical to optical power in a Free Electron Laser are typically limited by their Pierce parameter, ρ ~0.1%. Introducing strong undulator tapering can increase this efficiency greatly, with simulations showing possible conversion efficiencies of ~40%. Recent experiments performed with the Rubicon Inverse Free Electron Laser have demonstrated acceleration gradients of ~ 100 MeV/m and high particle trapping efficiency by coupling a pre-bunched electron beam to a high power CO2 laser pulse in a strongly tapered helical undulator. By reversing the undulator period tapering and re-optimizing the field strength along the Rubicon undulator, we obtain an Inverse Free Electron Laser decelerator, which we have aptly renamed Nocibur. This tapering profile is chosen so that the change in beam energy defined by the ponderomotive decelerating gradient matches the change in resonant energy defined by the undulator parameters, allowing the conversion of a large fraction of the electron beam power into coherent narrow-band radiation. We discuss this mechanism as well as results from a recent experiment performed with the Nocibur undulator at Brookhaven National Laboratory's Accelerator Test Facility.
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TUP079	Laser Wakefield Acceleration by using a Laser Produced Aluminium Plasma	543
	J. Kim, Y.H. Hwangbo, S.G. Jeon KERI, Changwon, Republic of Korea K.N. Kim, S. H. Park, W.J. Ryu, N. Vinokurov KAERI, Daejon, Republic of Korea
	In laser wakefield accelerator, usually a gas target is used to generate plasma medium. With this gas target, the pressure of the system cannot be keep as low as possible for electron beam application such as seeding the storage ring. To reduce this vacuum problem in LWFA, a plasma generated from solid Al target was used as plasma medium. A fundamental beam from the Q-switched ns pump laser in the Ti:sapphire power amplifier was used to generate a plasma from solid Al target. The plasma density was controlled by changing the distance between the main laser pulse for electron acceleration and the solid target. The plasma density was measured by the interferometer. The measured density indicates that the average charge of the ion in pre-plasma was 4.4. The main pulse ionized the Al plasma up to Al XII which means that the ionization injection could be used as an injection scheme. A 28 TW fs laser was used to accelerate the electron. A quasi-monochromatic electron was generated. The peak energy was 70 MeV and energy spread was 15 %. The divergence of the beam was 12 mrad in horizontal direction and 6 mrad in vertical direction.
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TUP080	Terahertz Source Utilizing Resonant Coherent Diffraction Radiation at KEK ERL Test Accelerator	547
	Y. Honda, A. Aryshev, M. Shevelev, M. Shimada KEK, Ibaraki, Japan
	An energy recovery linac test accelerator, cERL, has been developing at KEK. It can produce a high repetition rate short bunched electron beam in a continuous operation mode. We propose to develop a high power THz radiation source at the return loop of the cERL. Coherent diffraction radiation of THz regime is emitted when an electron bunch passes through a conductive mirror with a beam hole at the center. If we form an optical cavity using two mirrors facing each other and the cavity length coincides with the bunch repetition rate, the coherent diffraction radiation of multiple bunches adds up coherently in the cavity. By extracting the power through transmission of one of the mirrors, we can realize a high power and high efficiency THz source. We discuss performance of the source assuming the beam parameters of cERL.
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WEC01	A Concept for a Plasma Wakefield Accelerator Driven FEL
	M.J. Hogan SLAC, Menlo Park, California, USA
	Funding: Work supported in part by the U.S. Department of Energy under contract number DE-AC02-76SF00515. Plasma wakefield accelerators have received much attention for their ability to boost the energy of electrons by several GeV in a space of a few centimeters to a meter. In addition, the compact size of the accelerating wakefield in the plasma favors beams with femtosecond duration, small size and ultimately small emittance. The plasma accelerator community is studying multiple methods to inject electrons into the plasma wake and produce high brightness beams. By leveraging the high-rep rate beam drivers made possible by superconducting RF technology and ideas for controlled injection into the plasma wake, a meter scale plasma could serve as both and energy and brightness transformer, producing beams that surpass the state of the art and open new avenues for XFEL development. In this talk I will summarize the status of plasma wakefield accelerator research, present a concept for a plasma wakefield accelerator driven XFEL and discuss the outlook for the next few years.
	Slides WEC01 [34.737 MB]
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WEC02	High Gradient IFEL Acceleration and Deceleration in Strongly Tapered Undulators
	J.P. Duris, P. Musumeci UCLA, Los Angeles, California, USA
	Efficient coupling of relativistic electron beams with high power radiation lies at the heart of advanced accelerator and light source research and development. Recent inverse free electron laser experiments using strongly tapered undulators have demonstrated high-gradient acceleration of >50% of injected electrons, producing beams of high-quality. By accommodating the evolving radiation field in the design of the undulator tapering, a large fraction of energy may be transferred between the electrons and laser, enabling compact, high-current GeV accelerators and various wavelength light-sources of unprecedented peak powers.
	Slides WEC02 [5.405 MB]
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WEC03	Generating Intense Fully Coherent Soft X-Ray Radiation Based on a Laser-Plasma Accelerator
	C. Feng, H.X. Deng, Z.T. Zhao SINAP, Shanghai, People's Republic of China D. Xiang Shanghai Jiao Tong University, Shanghai, People's Republic of China
	Funding: This work is supported by the National Natural Science Foundation of China (11475250, 11175240, 11275253, and 11322550). Laser-plasma based accelerator has the potential to dramatically reduce the size and cost of future x-ray light sources to the university-laboratory scale. However, the large energy spread of the laser-plasma accelerated electron beam may hinder the way for short wavelength free-electron laser generation. In this paper, we propose a novel method for directly imprinting strong coherent micro-bunching on the electron beam with large intrinsic energy spread by using a wavefront-tilted conventional optical laser beam and a weak dipole magnet. Theoretical analysis and numerical simulations demonstrate that this technique can be used for the generation of fully coherent femtosecond soft x-ray radiation at gigawatts level with a very short undulator.
	Slides WEC03 [3.405 MB]
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WEC04	Subradiant Spontaneous Undulator Emission through Collective Suppression of Shot Noise
	D.F. Ratner, E. Hemsing, A. Marinelli SLAC, Menlo Park, California, USA A. Gover University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel A. Nause UCLA, Los Angeles, USA
	The phenomenon of Dicke's subradiance, in which the collective properties of a system suppress radiation, has received broad interest in atomic physics, but can also be applied to relativistic electron beams. The resulting "quiet" beam generates less spontaneous undulator radiation than emitted even by a random shot noise beam. Quiet beams could have diverse accelerator applications, including lowering power requirements for seeded FELs. Here we present recent experimental observations at the Next Linear Collider Test Accelerator and discuss prospects for pushing the phenomenon to X-ray wavelengths.
	Slides WEC04 [2.935 MB]
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WEP075	Femtosecond X-ray Pulse Generation with an Energy Chirped Electron Beam	722
	C. Emma, C. Pellegrini UCLA, Los Angeles, USA Y. Ding, Z. Huang, A.A. Lutman, G. Marcus, A. Marinelli, C. Pellegrini SLAC, Menlo Park, California, USA
	We study the generation of short (sub 10 fs) pulses in the X-ray spectral region using an energy chirped electron beam in a Self Amplified Spontaneous Emission Free Electron Laser (SASE FEL) and a self-seeding monochromator [1]-[2]. The monochromator filters a small bandwidth, short duration pulse from the frequency chirped SASE spectrum. This pulse is used to seed a small fraction of the long chirped beam, hence a short pulse with narrow bandwidth is amplified in the following undulators. We present start-to-end simulation results for LCLS operating in the soft X-ray self-seeded mode with an energy chirp of 1% over 30 fs and a bunch charge of 150pC. We demonstrate the potential to generate ~5 fs pulses with a bandwidth ~0.3eV. We also assess the possibility of further shortening the pulse by utilizing one more chicane after the self-seeding stage and shifting the radiation pulse to a 'fresh' part of the electron beam. Experimental study on this short pulse seeding mode has been planned at the LCLS.
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WEP076	Tapering Studies for TW Level X-ray FELs with a Superconducting Undulator and Built-in Focusing	726
	C. Emma UCLA, Los Angeles, USA K. Fang, C. Pellegrini, J. Wu SLAC, Menlo Park, California, USA
	Funding: U.S. Department of Energy DE-SC0009983. Tapering optimization schemes for TeraWatt (TW) level X-ray Free Electron Lasers (FELs) are critically sensitive to the length of individual undulator and break sections. Break sections can be considerably shortened if the focusing quadrupole field is superimposed on the undulator field increasing the filling factor and the overall extraction efficiency of the tapered FEL. Furthermore, distributed focusing reduces the FODO length and allows one to use smaller beta functions. This reduces particle de-trapping due to betatron motion from the radial tails of the electron beam. We present numerical calculations of the tapering optimization for such an undulator using the three dimensional time dependent code GENESIS. Time dependent simulations show that 8 keV photons can be produced with over 3 TW peak power in a 100m long undulator. We also analyze in detail the time dependent effects leading to power saturation in the taper region. The impact of the synchrotron sideband growth on particle detrapping and taper saturation is discussed. We show that the optimal taper profile obtained from time independent simulation does not yield the maximum extraction efficiency when multi-frequency effects are included. A discussion of how to incorporate these effects in a revised model is presented.
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WEP078	Advances on the LUNEX5 and COXINEL Projects	730
	M.-E. Couprie, C. Benabderrahmane, P. Berteaud, C. Bourassin-Bouchet, F. Bouvet, J.D. Bozek, F. Briquez, L. Cassinari, L. Chapuis, J. Da Silva, J. Daillant, D. Dennetière, Y. Dietrich, M. Diop, J.P. Duval, M.E. El Ajjouri, T.K. El Ajjouri, C. Herbeaux, N. Hubert, M. Khojoyan, M. Labat, N. Leclercq, A. Lestrade, A. Loulergue, J. Lüning, P. Marchand, O. Marcouillé, J.L. Marlats, F. Marteau, C. Miron, P. Morin, A. Nadji, R. Nagaoka, F. Polack, F. Ribeiro, J.P. Ricaud, P. Rommeluère, P. Roy, G. Sharma, K.T. Tavakoli, M. Thomasset, M. Tilmont, M.-A. Tordeux, M. Valléau, J. Vétéran, W. Yang, D. Zerbib SOLEIL, Gif-sur-Yvette, France S. Bielawski, M. Le Parquier PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France X. Davoine CEA/DAM/DIF, Arpajon, France N. Delerue, M. El Khaldi, W. Kaabi, F. Wicek LAL, Orsay, France G. Devanz, C. Madec CEA/IRFU, Gif-sur-Yvette, France A. Dubois CCPMR, Paris, France C. Evain, C. Szwaj PhLAM/CERLA, Villeneuve d'Ascq, France D. Garzella CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette, France G. Lambert, V. Malka, A. Rousse, C. Thaury LOA, Palaiseau, France A. Mosnier CEA/DSM/IRFU, France E. Roussel Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
	Funding: ERC COXINEL 340015 LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) aims at investigating compact and advanced Free Electron Laser (FEL). It comprises one one hand a 400 MeV superconducting linac for studies of advanced FEL schemes, high repetition rate operation (10 kHz), multi-FEL lines, and one the other hand a Laser Wake Field Accelerator (LWFA) for its qualification by a FEL application, an undulator line enabling advanced seeding and pilot user applications in the 40-4 nm spectral range. Following the CDR completion, different R&D programs were launched, as for instance on FEL pulse duration measurement, high repetition rate electro-optical sampling. The COXINEL ERC Advanced Grant aims at demonstrating LWFA based FEL amplification, thanks to a proper electron beam manipulation, with a test experiment under preparation. As a specific hardware is also under development such as a cryo-ready 3 m long undulator of 15 mm period is under development.
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WEP079	Inclusion of Advanced Fields and Boundary Conditions in the Analytic Theory for High Gain FELs	735
	P. Niknejadi, J. Madey University of Hawaii, Honolulu,, USA
	The efforts in realizing x-ray free electron lasers (FELs) and enhancing their performance has stimulated remarkable theoretical developments and experimental advances in the field. Yet, the successful operation of x-ray FELs based on the self-amplified spontaneous emission (SASE) principle which has made them a powerful new tool, has beckoned our attention for better understanding a comprehensive physical basis of the theory that has the potential to improve the temporal structure and spectral optimization of these sources. We have previously explained the advantages of including the coherent radiation reaction force as a part of the solution to the boundary value problem for FELs that radiate into "free space" (SASE FELs) and discussed how the advanced field of the absorber can interact with the radiating particles at the time of emission.(, ) Here we present the outline of our theoretical approach which follows from eigenmode analysis of optical guiding in FELs. We will also discuss in some detail the experimental setup that could verify and/or further our understanding of the the underlying physics of these devices. P. Niknejadi et al., Phys. Rev. D 91 096006 (2015) ** P. Niknejadi and J.M.J. Madey, in Proceedings of Free Electron Laser Conference, JACoW, Basel, Switzerland (2014)
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WEP082	High-Power Ultrashort Terahertz Pulses generated by a Multi-foil Radiator with Laser-Accelerated Electron Pulses	739
	J.S. Jo, B.A. Gudkov, Y.U. Jeong, H.N. Kim, K.N. Kim, K. Lee, S.V. Miginsky, S. H. Park, W.J. Ryu, N. Vinokurov KAERI, Daejon, Republic of Korea B.A. Gudkov, S.V. Miginsky, N. Vinokurov BINP SB RAS, Novosibirsk, Russia
	Terahertz (THz) wave is an attractive source for a variety of research including imaging, spectroscopy, security, etc. We proposed a new scheme of high-power and ultrashort THz generation by using the coherent transition radiation from a cone-shaped multi-foil radiator [] and a rectangle-shaped multi-foil radiator. To perform the proof-of-principle of the multi-foil THz radiator, we used 80~100 MeV electron bunches from laser-plasma acceleration. While a cone-shaped multi-foil radiator has a circular polarization with a conic wave, we made a rectangle-shaped multi-foil radiator that has a linear polarization in a plane-like wave, which can be used more widely for various applications. We can easily control the power of multi-foil radiator by adjusting the number of foils. We compare the THz power ratio between 1 sheet and multi sheets using cooled bolometer. We will measure the pulse duration and bandwidth of the THz wave from the multi-foil radiators in a single-shot by using electro-optic sampling and cross-correlation method. Phys. Rev. Lett. 110, 064805.
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Paper

Title

Page

Transverse Emittance-Preserving Transfer Line and Arc Compressor for High Brightness Electron Sources

191

S. Di Mitri, M. Cornacchia, S. Spampinati
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
S. Spampinati
Cockcroft Institute, Warrington, Cheshire, United Kingdom

Minimizing transverse emittance is essential in single- or few-passes accelerators designed to deliver high brightness electron beams. Emission of coherent synchrotron radiation (CSR) is an important factor of emittance degradation. We have demonstrated, with analytical and experimental results, that this perturbation may be cancelled by imposing certain conditions on the electron optics when the bunch length is constant along the line*. This scheme of CSR suppression is then enlarged, analytically and numerically, to cover the case of varying bunch length in a periodic arc compressor**. The proposed solution hold the promise of cost-saving of compact transfer lines with large bending angles, and new schemes for beam longitudinal gymnastics both in recirculating and in single-pass accelerators driving free electron lasers.
* S. Di Mitri, M. Cornacchia, S. Spampinati, Phys. Rev. Letters, 110, 014801 (2013)
** S. Di Mitri, M. Cornacchia, Europhys. Letters, 109, 62002 (2015)

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MOP068

First Simulation Results on Free Electron Laser Radiation in Displaced Phase-combined Undulators

196

N.S. Mirian
UVSOR, Okazaki, Japan
E. Salehi
AUT, Tehran, Iran

This report deals with self amplified spontaneous emission free electron laser (FEL) amplifier where the FEL emission is obtained from displaced phase combined undulators. Magnetic field of this adjustment methods in three dimensions is presented. The electron dynamics is investigated. The simulation method and results are explained. The radiation properties of the fundamental resonance and third harmonic through the phase combined undulators are compared with the normal undulator with the same undulator deflection parameter

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MOP070

Harmonic Generation in Two Orthogonal Undulators

200

N.S. Mirian
UVSOR, Okazaki, Japan

In this report, the harmonic generation in two orthogonal undulators is under discussion. There is a possibility of generation of the even and odd harmonics as well as no-integer harmonics in two orthogonal undulators. By considering the first order of electron velocity, the total energy radiated per unit solid angle per unit frequency interval for a single electron traveling along the undulators is derived. Also a numerical simulation of one-dimensional non-averaged equations is conducted to present the self amplified spontaneous emission of harmonic generation in two orthogonal undulators.

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MOP071

Carrier-Envelope-Phase Stable Linearly and Circularly Polarized Attosecond Pulse Sources

205

Z. Tibai, G. Almási, Zs. Csiha-Nagy, J.A. Fülöp, J. Hebling
University of Pecs, Pécs, Hungary
J.A. Fülöp, Gy. Tóth
MTA-PTE High-Field Terahertz Research Group, Pecs, Hungary

Recently, we proposed a robust method for producing waveform-controlled attosecond pulses in the EUV spectral range.* In our scheme the relativistic electron beam, provided by a LINAC, is sent through a modulator undulator where a TW-power laser beam is superimposed on it in order to generate nanobunches. The nanobunched electron beam passes through a single- or few-period radiator undulator (RU). The waveform of the generated attosecond pulses closely resembles the longitudinal distribution of the magnetic field. According to our calculations, at 20 nm (60 nm) wavelength carrier-envelope-phase (CEP) stable pulses with 23 nJ (80 nJ) energy, 80 as (240 as) duration, and 31 mrad (13 mrad) CEP fluctuation (standard deviation) can be achieved at K=0.5. More than 500 nJ energy is predicted at longer wavelengths and larger K. The energy fluctuation of the EUV pulse is 2.5 times higher than that of the laser. By using a helical RU, even circularly polarized attosecond pulses with 30/300 nJ energy can be generated, depending on the wavelength. To the best of our knowledge, no other presently available technique enables the generation of arbitrary-waveform, CEP-controlled attosecond pulses. The predicted pulse energies are sufficiently high to be used as pump pulses in attosecond pump-probe measurements.
* Z. Tibai et al., Phys. Rev. Lett. 113, 104801 (2014).

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MOP074

Efficiency Enhancement of a Harmonic Lasing Free-Electron Laser

209

N.S. Mirian
UVSOR, Okazaki, Japan
B. Maraghechi, E. Salehi
AUT, Tehran, Iran

The harmonic lasing free-electron laser amplifier, in which two wigglers is employed in order for the fundamental resonance of the second wiggler to coincide with the third harmonic of the first wiggler to generate ultraviolet radiation, is studied. A set of coupled nonlinear first-order differential equations describing the nonlinear evolution of the system, for a long electron bunch, is solved numerically by CYRUS code. Thermal effects in the form of longitudinal velocity spread are also investigated. The second wiggler field decreases linearly and nonlinearly at the point where the radiation of the third harmonic saturates to enhance the efficiency. The optimum starting point and the slope of the tapering of the amplitude of the wiggler are found by a successive run of the code. It is found that tapering can increase the saturated power of the third harmonic considerably.

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MOP075

Three-dimensional Simulation of a Harmonic Lasing Free-Electron Laser Amplifier

213

E. Salehi, B. Maraghechi
AUT, Tehran, Iran
N.S. Mirian
UVSOR, Okazaki, Japan

Three-dimensional simulation of harmonic lasing Free-electron laser is represented in the steady-state regime. Here, the third harmonic of the first wiggler is adjusted at the fundamental resonance of the second wiggler by reducing the magnetic field strength of the second wiggler. The hyperbolic wave equations can be transformed into parabolic diffusion equations by using the slowly varying envelope approximation. A set of coupled nonlinear first-order differential equations describing the nonlinear evolution of the system is solved numerically by CYRUS3D code. This set of equations describes self-consistently the longitudinal spatial dependence of the radiation waists, curvatures, and amplitudes together with the evaluation of the electron beam. Thermal effects in the form of longitudinal velocity spread are also investigated. In order to reduce the length of the wiggler, the prebunched electron beam is considered.

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MOP076

Free-Electron Laser Driven by a 500 MeV Laser Plasma Accelerator Beam

217

W. Qin, J.E. Chen, S. Huang, K.X. Liu, X.Q. Yan, L. Zeng
PKU, Beijing, People's Republic of China
Y. Ding, Z. Huang
SLAC, Menlo Park, California, USA

A laser plasma accelerator is under construction at Peking University and several hundred MeV electron beams are expected. In this paper we discuss applying a 500 MeV beam with 1% relative energy spread to FEL. Bunch decompression method is considered to deal with the large energy spread of the beam. Emittance growth induced by large divergence and energy spread in electron beam transport has been treated with the chromatic matching manipulation. Simulation shows that 100 MW level, 6.3 fs , 0.008 bandwidth output can be obtained for 30 nm FEL. TGU method with assumed matched beam is also discussed as a comparison.

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TUP074

Results from the Nocibur Experiment at Brookhaven National Laboratory's Accelerator Test Facility

540

N.S. Sudar, J.P. Duris, I.I. Gadjev, P. Musumeci
UCLA, Los Angeles, USA
M. Babzien, M.G. Fedurin, K. Kusche, I. Pogorelsky, M.N. Polyanskiy, C. Swinson
BNL, Upton, Long Island, New York, USA

Conversion efficiencies of electrical to optical power in a Free Electron Laser are typically limited by their Pierce parameter, ρ ~0.1%. Introducing strong undulator tapering can increase this efficiency greatly, with simulations showing possible conversion efficiencies of ~40%. Recent experiments performed with the Rubicon Inverse Free Electron Laser have demonstrated acceleration gradients of ~ 100 MeV/m and high particle trapping efficiency by coupling a pre-bunched electron beam to a high power CO2 laser pulse in a strongly tapered helical undulator. By reversing the undulator period tapering and re-optimizing the field strength along the Rubicon undulator, we obtain an Inverse Free Electron Laser decelerator, which we have aptly renamed Nocibur. This tapering profile is chosen so that the change in beam energy defined by the ponderomotive decelerating gradient matches the change in resonant energy defined by the undulator parameters, allowing the conversion of a large fraction of the electron beam power into coherent narrow-band radiation. We discuss this mechanism as well as results from a recent experiment performed with the Nocibur undulator at Brookhaven National Laboratory's Accelerator Test Facility.

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TUP079

Laser Wakefield Acceleration by using a Laser Produced Aluminium Plasma

543

J. Kim, Y.H. Hwangbo, S.G. Jeon
KERI, Changwon, Republic of Korea
K.N. Kim, S. H. Park, W.J. Ryu, N. Vinokurov
KAERI, Daejon, Republic of Korea

In laser wakefield accelerator, usually a gas target is used to generate plasma medium. With this gas target, the pressure of the system cannot be keep as low as possible for electron beam application such as seeding the storage ring. To reduce this vacuum problem in LWFA, a plasma generated from solid Al target was used as plasma medium. A fundamental beam from the Q-switched ns pump laser in the Ti:sapphire power amplifier was used to generate a plasma from solid Al target. The plasma density was controlled by changing the distance between the main laser pulse for electron acceleration and the solid target. The plasma density was measured by the interferometer. The measured density indicates that the average charge of the ion in pre-plasma was 4.4. The main pulse ionized the Al plasma up to Al XII which means that the ionization injection could be used as an injection scheme. A 28 TW fs laser was used to accelerate the electron. A quasi-monochromatic electron was generated. The peak energy was 70 MeV and energy spread was 15 %. The divergence of the beam was 12 mrad in horizontal direction and 6 mrad in vertical direction.

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TUP080

Terahertz Source Utilizing Resonant Coherent Diffraction Radiation at KEK ERL Test Accelerator

547

Y. Honda, A. Aryshev, M. Shevelev, M. Shimada
KEK, Ibaraki, Japan

An energy recovery linac test accelerator, cERL, has been developing at KEK. It can produce a high repetition rate short bunched electron beam in a continuous operation mode. We propose to develop a high power THz radiation source at the return loop of the cERL. Coherent diffraction radiation of THz regime is emitted when an electron bunch passes through a conductive mirror with a beam hole at the center. If we form an optical cavity using two mirrors facing each other and the cavity length coincides with the bunch repetition rate, the coherent diffraction radiation of multiple bunches adds up coherently in the cavity. By extracting the power through transmission of one of the mirrors, we can realize a high power and high efficiency THz source. We discuss performance of the source assuming the beam parameters of cERL.

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WEC01

A Concept for a Plasma Wakefield Accelerator Driven FEL

M.J. Hogan
SLAC, Menlo Park, California, USA

Funding: Work supported in part by the U.S. Department of Energy under contract number DE-AC02-76SF00515.
Plasma wakefield accelerators have received much attention for their ability to boost the energy of electrons by several GeV in a space of a few centimeters to a meter. In addition, the compact size of the accelerating wakefield in the plasma favors beams with femtosecond duration, small size and ultimately small emittance. The plasma accelerator community is studying multiple methods to inject electrons into the plasma wake and produce high brightness beams. By leveraging the high-rep rate beam drivers made possible by superconducting RF technology and ideas for controlled injection into the plasma wake, a meter scale plasma could serve as both and energy and brightness transformer, producing beams that surpass the state of the art and open new avenues for XFEL development. In this talk I will summarize the status of plasma wakefield accelerator research, present a concept for a plasma wakefield accelerator driven XFEL and discuss the outlook for the next few years.

Slides WEC01 [34.737 MB]

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WEC02

High Gradient IFEL Acceleration and Deceleration in Strongly Tapered Undulators

J.P. Duris, P. Musumeci
UCLA, Los Angeles, California, USA

Efficient coupling of relativistic electron beams with high power radiation lies at the heart of advanced accelerator and light source research and development. Recent inverse free electron laser experiments using strongly tapered undulators have demonstrated high-gradient acceleration of >50% of injected electrons, producing beams of high-quality. By accommodating the evolving radiation field in the design of the undulator tapering, a large fraction of energy may be transferred between the electrons and laser, enabling compact, high-current GeV accelerators and various wavelength light-sources of unprecedented peak powers.

Slides WEC02 [5.405 MB]

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WEC03

Generating Intense Fully Coherent Soft X-Ray Radiation Based on a Laser-Plasma Accelerator

C. Feng, H.X. Deng, Z.T. Zhao
SINAP, Shanghai, People's Republic of China
D. Xiang
Shanghai Jiao Tong University, Shanghai, People's Republic of China

Funding: This work is supported by the National Natural Science Foundation of China (11475250, 11175240, 11275253, and 11322550).
Laser-plasma based accelerator has the potential to dramatically reduce the size and cost of future x-ray light sources to the university-laboratory scale. However, the large energy spread of the laser-plasma accelerated electron beam may hinder the way for short wavelength free-electron laser generation. In this paper, we propose a novel method for directly imprinting strong coherent micro-bunching on the electron beam with large intrinsic energy spread by using a wavefront-tilted conventional optical laser beam and a weak dipole magnet. Theoretical analysis and numerical simulations demonstrate that this technique can be used for the generation of fully coherent femtosecond soft x-ray radiation at gigawatts level with a very short undulator.

Slides WEC03 [3.405 MB]

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WEC04

Subradiant Spontaneous Undulator Emission through Collective Suppression of Shot Noise

D.F. Ratner, E. Hemsing, A. Marinelli
SLAC, Menlo Park, California, USA
A. Gover
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
A. Nause
UCLA, Los Angeles, USA

The phenomenon of Dicke's subradiance, in which the collective properties of a system suppress radiation, has received broad interest in atomic physics, but can also be applied to relativistic electron beams. The resulting "quiet" beam generates less spontaneous undulator radiation than emitted even by a random shot noise beam. Quiet beams could have diverse accelerator applications, including lowering power requirements for seeded FELs. Here we present recent experimental observations at the Next Linear Collider Test Accelerator and discuss prospects for pushing the phenomenon to X-ray wavelengths.

Slides WEC04 [2.935 MB]

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WEP075

Femtosecond X-ray Pulse Generation with an Energy Chirped Electron Beam

722

C. Emma, C. Pellegrini
UCLA, Los Angeles, USA
Y. Ding, Z. Huang, A.A. Lutman, G. Marcus, A. Marinelli, C. Pellegrini
SLAC, Menlo Park, California, USA

We study the generation of short (sub 10 fs) pulses in the X-ray spectral region using an energy chirped electron beam in a Self Amplified Spontaneous Emission Free Electron Laser (SASE FEL) and a self-seeding monochromator [1]-[2]. The monochromator filters a small bandwidth, short duration pulse from the frequency chirped SASE spectrum. This pulse is used to seed a small fraction of the long chirped beam, hence a short pulse with narrow bandwidth is amplified in the following undulators. We present start-to-end simulation results for LCLS operating in the soft X-ray self-seeded mode with an energy chirp of 1% over 30 fs and a bunch charge of 150pC. We demonstrate the potential to generate ~5 fs pulses with a bandwidth ~0.3eV. We also assess the possibility of further shortening the pulse by utilizing one more chicane after the self-seeding stage and shifting the radiation pulse to a 'fresh' part of the electron beam. Experimental study on this short pulse seeding mode has been planned at the LCLS.

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WEP076

Tapering Studies for TW Level X-ray FELs with a Superconducting Undulator and Built-in Focusing

726

C. Emma
UCLA, Los Angeles, USA
K. Fang, C. Pellegrini, J. Wu
SLAC, Menlo Park, California, USA

Funding: U.S. Department of Energy DE-SC0009983.
Tapering optimization schemes for TeraWatt (TW) level X-ray Free Electron Lasers (FELs) are critically sensitive to the length of individual undulator and break sections. Break sections can be considerably shortened if the focusing quadrupole field is superimposed on the undulator field increasing the filling factor and the overall extraction efficiency of the tapered FEL. Furthermore, distributed focusing reduces the FODO length and allows one to use smaller beta functions. This reduces particle de-trapping due to betatron motion from the radial tails of the electron beam. We present numerical calculations of the tapering optimization for such an undulator using the three dimensional time dependent code GENESIS. Time dependent simulations show that 8 keV photons can be produced with over 3 TW peak power in a 100m long undulator. We also analyze in detail the time dependent effects leading to power saturation in the taper region. The impact of the synchrotron sideband growth on particle detrapping and taper saturation is discussed. We show that the optimal taper profile obtained from time independent simulation does not yield the maximum extraction efficiency when multi-frequency effects are included. A discussion of how to incorporate these effects in a revised model is presented.

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WEP078

Advances on the LUNEX5 and COXINEL Projects

730

M.-E. Couprie, C. Benabderrahmane, P. Berteaud, C. Bourassin-Bouchet, F. Bouvet, J.D. Bozek, F. Briquez, L. Cassinari, L. Chapuis, J. Da Silva, J. Daillant, D. Dennetière, Y. Dietrich, M. Diop, J.P. Duval, M.E. El Ajjouri, T.K. El Ajjouri, C. Herbeaux, N. Hubert, M. Khojoyan, M. Labat, N. Leclercq, A. Lestrade, A. Loulergue, J. Lüning, P. Marchand, O. Marcouillé, J.L. Marlats, F. Marteau, C. Miron, P. Morin, A. Nadji, R. Nagaoka, F. Polack, F. Ribeiro, J.P. Ricaud, P. Rommeluère, P. Roy, G. Sharma, K.T. Tavakoli, M. Thomasset, M. Tilmont, M.-A. Tordeux, M. Valléau, J. Vétéran, W. Yang, D. Zerbib
SOLEIL, Gif-sur-Yvette, France
S. Bielawski, M. Le Parquier
PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France
X. Davoine
CEA/DAM/DIF, Arpajon, France
N. Delerue, M. El Khaldi, W. Kaabi, F. Wicek
LAL, Orsay, France
G. Devanz, C. Madec
CEA/IRFU, Gif-sur-Yvette, France
A. Dubois
CCPMR, Paris, France
C. Evain, C. Szwaj
PhLAM/CERLA, Villeneuve d'Ascq, France
D. Garzella
CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette, France
G. Lambert, V. Malka, A. Rousse, C. Thaury
LOA, Palaiseau, France
A. Mosnier
CEA/DSM/IRFU, France
E. Roussel
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy

Funding: ERC COXINEL 340015
LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) aims at investigating compact and advanced Free Electron Laser (FEL). It comprises one one hand a 400 MeV superconducting linac for studies of advanced FEL schemes, high repetition rate operation (10 kHz), multi-FEL lines, and one the other hand a Laser Wake Field Accelerator (LWFA) for its qualification by a FEL application, an undulator line enabling advanced seeding and pilot user applications in the 40-4 nm spectral range. Following the CDR completion, different R&D programs were launched, as for instance on FEL pulse duration measurement, high repetition rate electro-optical sampling. The COXINEL ERC Advanced Grant aims at demonstrating LWFA based FEL amplification, thanks to a proper electron beam manipulation, with a test experiment under preparation. As a specific hardware is also under development such as a cryo-ready 3 m long undulator of 15 mm period is under development.

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WEP079

Inclusion of Advanced Fields and Boundary Conditions in the Analytic Theory for High Gain FELs

735

P. Niknejadi, J. Madey
University of Hawaii, Honolulu,, USA

The efforts in realizing x-ray free electron lasers (FELs) and enhancing their performance has stimulated remarkable theoretical developments and experimental advances in the field. Yet, the successful operation of x-ray FELs based on the self-amplified spontaneous emission (SASE) principle which has made them a powerful new tool, has beckoned our attention for better understanding a comprehensive physical basis of the theory that has the potential to improve the temporal structure and spectral optimization of these sources. We have previously explained the advantages of including the coherent radiation reaction force as a part of the solution to the boundary value problem for FELs that radiate into "free space" (SASE FELs) and discussed how the advanced field of the absorber can interact with the radiating particles at the time of emission.(*, **) Here we present the outline of our theoretical approach which follows from eigenmode analysis of optical guiding in FELs. We will also discuss in some detail the experimental setup that could verify and/or further our understanding of the the underlying physics of these devices.
* P. Niknejadi et al., Phys. Rev. D 91 096006 (2015)
** P. Niknejadi and J.M.J. Madey, in Proceedings of Free Electron Laser Conference, JACoW, Basel, Switzerland (2014)

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WEP082

High-Power Ultrashort Terahertz Pulses generated by a Multi-foil Radiator with Laser-Accelerated Electron Pulses

739

J.S. Jo, B.A. Gudkov, Y.U. Jeong, H.N. Kim, K.N. Kim, K. Lee, S.V. Miginsky, S. H. Park, W.J. Ryu, N. Vinokurov
KAERI, Daejon, Republic of Korea
B.A. Gudkov, S.V. Miginsky, N. Vinokurov
BINP SB RAS, Novosibirsk, Russia

Terahertz (THz) wave is an attractive source for a variety of research including imaging, spectroscopy, security, etc. We proposed a new scheme of high-power and ultrashort THz generation by using the coherent transition radiation from a cone-shaped multi-foil radiator [*] and a rectangle-shaped multi-foil radiator. To perform the proof-of-principle of the multi-foil THz radiator, we used 80~100 MeV electron bunches from laser-plasma acceleration. While a cone-shaped multi-foil radiator has a circular polarization with a conic wave, we made a rectangle-shaped multi-foil radiator that has a linear polarization in a plane-like wave, which can be used more widely for various applications. We can easily control the power of multi-foil radiator by adjusting the number of foils. We compare the THz power ratio between 1 sheet and multi sheets using cooled bolometer. We will measure the pulse duration and bandwidth of the THz wave from the multi-foil radiators in a single-shot by using electro-optic sampling and cross-correlation method.
* Phys. Rev. Lett. 110, 064805.

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