FEL2011 - List of Keywords (bunching)

Paper	Title	Other Keywords	Page
MOPB07	Soft X-ray Free-electron Laser with a 10-time Reduced Size	electron, undulator, FEL, laser	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.

MOPB17	Harmonic Generation for a Hard X-ray FEL	electron, undulator, FEL, emittance	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	laser, undulator, FEL, factory	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)	FEL, scattering, emittance, undulator	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	FEL, laser, radiation, damping	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	storage-ring, radiation, simulation, laser	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.

MOPB30	The Effects of Betatron Motion on the Preservation of FEL Microbunching	electron, betatron, emittance, undulator	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.

TUOA2	Collective and Individual Aspects of Fluctuations in Relativistic Electron Beams for Free Electron Lasers	plasma, electron, FEL, free-electron-laser	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 TUOA2 [0.361 MB]

TUPA01	Tunable THz-pulse-train Photoinjector	laser, electron, beat-wave, acceleration	187
	Y.-C. Huang, F.H. Chao, C.H. Chen, H.H. Chen, K.Y. Huang NTHU, Hsinchu, Taiwan
	Funding: This work is jointly supported by the National Science Council, under Contract NSC97-2112-M-007-018-MY2; the National Synchrotron Radiation Research Center,under Project 955LRF01N. A THz-pulse-train photoinjector is under construction at the High-energy OPtics and Electronics (HOPE) Laboratory at National Tsinghua University, Taiwan. This photoinjector is believed to be useful for generating high-power THz radiation, as well as for driving or loading a plasma-wave accelerator. A THz laser beat wave with full tunability in its beat frequency is employed to induce the emission of the THz electron pulses from the photoinjector. We show in our study that such a photoinjector is capable of generating periodically bunched MeV electrons with a bunching factor larger than 0.1 at THz frequencies for a total amount of 1 nC charges in a 10-ps time duration. We will also present a driver laser technology that can tune the electron bunch frequency with ease and help the growth of the high harmonics in the bunching spectrum of accelerated electrons. Experimental progress on this photoinjector will be reported in the conference.

TUPA11	Saturation Effect on VUV Coherent Harmonic Generation at UVSOR-II	laser, electron, simulation, FEL	212
	T. Tanikawa PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France M. Adachi, M. Katoh, J. Yamazaki, H. Zen UVSOR, Okazaki, Japan M. Hosaka, Y. Taira, N. Yamamoto Nagoya University, Nagoya, Japan
	Light source by using a laser seeding technique are under development at the UVSOR-II electron storage ring. In the past experiments, we have succeeded in generating coherent harmonics (CHs) in deep ultraviolet (UV) and vacuum UV (VUV) region, and also in generating CH with variable polarizations in deep UV [1]. In previous conferences, we reported an introduction of new-constructed spectrometer for VUV and results of spectra measurement, undulator gap dependencies, and injection laser power dependencies on VUV CHs [2]. This time we have successfully observed saturation on CHs intensities and have found some interesting phenomena, which are the necessary power of injection laser to achieve the saturation of CHG is different in different harmonic orders, and the CH intensity is oscillated in deep saturated regime. In this conference, we will discuss the results of some systematic measurements and those analytical and particle tracking simulations. [1] M. Labat, et al., Phys. Rev. Lett. 101 (2008) 164803 [2] T. Tanikawa, et al., Prc. 1st Int. Particle Accelerator Conf., Kyoto, 2010. [3] T. Tanikawa, et al., Appl. Phys. Express 3 (2010) 122702

TUPA25	EEHG Seeding Design for SwissFEL	laser, electron, FEL, emittance	251
	E. Prat, S. Reiche Paul Scherrer Institut, Villigen, Switzerland
	The SwissFEL facility, planned at the Paul Scherrer Institute, is based on the SASE operation of a hard (1-7 Å) and a soft (7-70 Å) X-ray FEL beamline. In addition, seeding is foreseen for the soft X-ray beamline, down to a wavelength of 1 nm. The Echo-Enabled Harmonic Generation (EEHG) scheme, which utilizes a rather complex manipulation of the longitudinal phase space distribution of the electron beam to generate high harmonic density modulation, is presently considered the first choice for seeding at SwissFEL. However, EEHG is highly demanding and complex at 1 nm, therefore other strategies like High-Harmonic Generation (HHG) and self-seeding are also evaluated. This paper presents the current status of the seeding design for SwissFEL based on EEHG.

TUPA30	Multi-stage Bunch Compression at the Japanese X-ray Free Electron Laser SACLA	cavity, electron, linac, laser	259
	K. Togawa, T. Hara, H. Tanaka RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
	The Japanese x-ray free electron laser facility, named as SACLA (Spring-8 Angstrom Compact free electron LAser), was constructed at SPring-8 site. After finishing installation of all accelerator components, beam commissioning started on February 21, 2011. In order to produce a high-quality electron beam with extremely low-emittance and high-peak current, SACLA adopts multi-stage bunch compression scheme that uses an injector velocity bunching system and following three magnetic bunch compressors. A design bunch compression factor reaches to 3000, namely the peak current of 1 A at the CeB6 thermionic gun increases up to 3 kA at the exit of the final bunch compressor at 1.4 GeV. A longitudinal bunch profile was measured using a transverse beam deflector cavity that was located at the exit of the final bunch compressor. After step-by-step beam commissioning from the injector, we have accomplished a peak current of 3 kA and a short bunch length less than 100 fs. In this conference, we will report the commissioning of the multi-stage bunch compression system at SACLA.

TUPB10	Echo Seeding Experiment at FLASH	laser, undulator, electron, FEL	279
	K.E. Hacker, S. Khan DELTA, Dortmund, Germany G. Angelova Hamberg, V.G. Ziemann Uppsala University, Uppsala, Sweden A. Azima Uni HH, Hamburg, Germany P. Salén, P. van der Meulen FYSIKUM, AlbaNova, Stockholm University, Stockholm, Sweden H. Schlarb DESY, Hamburg, Germany
	Using the two perpendicularly oriented undulators and chicanes developed for an optical replica synthesizer (ORS) experiment together with the sFLASH 800 nm seed laser, radiator undulators and diagnostics, an echo seeding experiment will be conducted at FLASH in January 2012. For this experiment, the 800 nm laser pulse will be transported with a new, 12 meter long, in-vacuum laser transport line. On an in-vacuum optical breadboard, the 800 nm pulse will then be tripled in beta-BBO nonlinear crystals. The laser pulse will then be split longitudinally using a birefringent alpha BBO crystal into two pulses with orthogonal polarization states corresponding to the orthogonal orientations of the ORS undulators. These pulses will be focused to a 400 μm waist between the undulators with a Galileo telescope and steered with 4 motorized mirrors onto the electron beam axis in the ORS undulator section. The hardware layout and simulations of the echo seeding parameters will be described.

TUPB14	Design Studies for Cascaded HGHG and EESHG Experiments Based on SDUV-FEL	laser, radiation, FEL, electron	291
	C. Feng, J.H. Chen, H.X. Deng, Q. Gu, D. Wang, M. Zhang, Z.T. Zhao SINAP, Shanghai, People's Republic of China
	Funding: This work was supported by the National Natural Science Foundation of China (Grant No. 10935011). As a test facility for modern FEL R&D, The Shanghai deep ultra-violent FEL (SDUV-FEL) is now under upgrading for the cascading two stage of HGHG experiment. It is found that this upgraded facility will be also well suited for the echo-enabled staged harmonic generation (EESHG) scheme demonstration. With help of 3D simulation codes, design studies on the FEL physics for both these two schemes based on the upgraded SDUV-FEL is presented in this paper.

WEPB02	Study of Highly Isochronous Beamlines for FEL Seeding	FEL, quadrupole, undulator, laser	391
	C. Sun, H. Nishimura, G. Penn, M.W. Reinsch, D. Robin, F. Sannibale, C. Steier, W. Wan LBNL, Berkeley, California, USA
	Recently seeding schemes, such as ECHO for short (nm) wavelength FELs, have been proposed. These schemes require that the nm level longitudinal bunch structure be preserved over distance of several meters. This poses a challenge for the beamline design. In this paper we present our studies of several solutions for beamlines that are nearly isochronous.

THPA33	Bunch Length Measurement Based on the Beam Position Monitor	pick-up, simulation, electron, FEL	555
	J. Wang, M. Li, H.B. Wang, D. Wu CAEP/IAE, Mianyang, Sichuan, People's Republic of China
	BPM (Beam Position Monitor) is the most basic instrument of the beam dynamics. The signal of the BPM consist more information of the beam apart from the beam position. By processing and analyzing of the BPM signal, the information of the bunch length can be got. It's a challenge to use this method when the energy is low (<30 MeV) and the bunch length is especially short(10 ps rms). In this paper, the BPM system which can be used to measure the bunch length is discussed. And the method of the signal processing and analyzing is given.

Paper

Title

Other Keywords

Page

MOPB07

Soft X-ray Free-electron Laser with a 10-time Reduced Size

electron, undulator, FEL, laser

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.

MOPB17

Harmonic Generation for a Hard X-ray FEL

electron, undulator, FEL, emittance

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

laser, undulator, FEL, factory

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)

FEL, scattering, emittance, undulator

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

FEL, laser, radiation, damping

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

storage-ring, radiation, simulation, laser

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.

MOPB30

The Effects of Betatron Motion on the Preservation of FEL Microbunching

electron, betatron, emittance, undulator

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.

TUOA2

Collective and Individual Aspects of Fluctuations in Relativistic Electron Beams for Free Electron Lasers

plasma, electron, FEL, free-electron-laser

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 TUOA2 [0.361 MB]

TUPA01

Tunable THz-pulse-train Photoinjector

laser, electron, beat-wave, acceleration

187

Y.-C. Huang, F.H. Chao, C.H. Chen, H.H. Chen, K.Y. Huang
NTHU, Hsinchu, Taiwan

Funding: This work is jointly supported by the National Science Council, under Contract NSC97-2112-M-007-018-MY2; the National Synchrotron Radiation Research Center,under Project 955LRF01N.
A THz-pulse-train photoinjector is under construction at the High-energy OPtics and Electronics (HOPE) Laboratory at National Tsinghua University, Taiwan. This photoinjector is believed to be useful for generating high-power THz radiation, as well as for driving or loading a plasma-wave accelerator. A THz laser beat wave with full tunability in its beat frequency is employed to induce the emission of the THz electron pulses from the photoinjector. We show in our study that such a photoinjector is capable of generating periodically bunched MeV electrons with a bunching factor larger than 0.1 at THz frequencies for a total amount of 1 nC charges in a 10-ps time duration. We will also present a driver laser technology that can tune the electron bunch frequency with ease and help the growth of the high harmonics in the bunching spectrum of accelerated electrons. Experimental progress on this photoinjector will be reported in the conference.

TUPA11

Saturation Effect on VUV Coherent Harmonic Generation at UVSOR-II

laser, electron, simulation, FEL

212

T. Tanikawa
PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France
M. Adachi, M. Katoh, J. Yamazaki, H. Zen
UVSOR, Okazaki, Japan
M. Hosaka, Y. Taira, N. Yamamoto
Nagoya University, Nagoya, Japan

Light source by using a laser seeding technique are under development at the UVSOR-II electron storage ring. In the past experiments, we have succeeded in generating coherent harmonics (CHs) in deep ultraviolet (UV) and vacuum UV (VUV) region, and also in generating CH with variable polarizations in deep UV [1]. In previous conferences, we reported an introduction of new-constructed spectrometer for VUV and results of spectra measurement, undulator gap dependencies, and injection laser power dependencies on VUV CHs [2]. This time we have successfully observed saturation on CHs intensities and have found some interesting phenomena, which are the necessary power of injection laser to achieve the saturation of CHG is different in different harmonic orders, and the CH intensity is oscillated in deep saturated regime. In this conference, we will discuss the results of some systematic measurements and those analytical and particle tracking simulations.
[1] M. Labat, et al., Phys. Rev. Lett. 101 (2008) 164803
[2] T. Tanikawa, et al., Prc. 1st Int. Particle Accelerator Conf., Kyoto, 2010.
[3] T. Tanikawa, et al., Appl. Phys. Express 3 (2010) 122702

TUPA25

EEHG Seeding Design for SwissFEL

laser, electron, FEL, emittance

251

E. Prat, S. Reiche
Paul Scherrer Institut, Villigen, Switzerland

The SwissFEL facility, planned at the Paul Scherrer Institute, is based on the SASE operation of a hard (1-7 Å) and a soft (7-70 Å) X-ray FEL beamline. In addition, seeding is foreseen for the soft X-ray beamline, down to a wavelength of 1 nm. The Echo-Enabled Harmonic Generation (EEHG) scheme, which utilizes a rather complex manipulation of the longitudinal phase space distribution of the electron beam to generate high harmonic density modulation, is presently considered the first choice for seeding at SwissFEL. However, EEHG is highly demanding and complex at 1 nm, therefore other strategies like High-Harmonic Generation (HHG) and self-seeding are also evaluated. This paper presents the current status of the seeding design for SwissFEL based on EEHG.

TUPA30

Multi-stage Bunch Compression at the Japanese X-ray Free Electron Laser SACLA

cavity, electron, linac, laser

259

K. Togawa, T. Hara, H. Tanaka
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan

The Japanese x-ray free electron laser facility, named as SACLA (Spring-8 Angstrom Compact free electron LAser), was constructed at SPring-8 site. After finishing installation of all accelerator components, beam commissioning started on February 21, 2011. In order to produce a high-quality electron beam with extremely low-emittance and high-peak current, SACLA adopts multi-stage bunch compression scheme that uses an injector velocity bunching system and following three magnetic bunch compressors. A design bunch compression factor reaches to 3000, namely the peak current of 1 A at the CeB6 thermionic gun increases up to 3 kA at the exit of the final bunch compressor at 1.4 GeV. A longitudinal bunch profile was measured using a transverse beam deflector cavity that was located at the exit of the final bunch compressor. After step-by-step beam commissioning from the injector, we have accomplished a peak current of 3 kA and a short bunch length less than 100 fs. In this conference, we will report the commissioning of the multi-stage bunch compression system at SACLA.

TUPB10

Echo Seeding Experiment at FLASH

laser, undulator, electron, FEL

279

K.E. Hacker, S. Khan
DELTA, Dortmund, Germany
G. Angelova Hamberg, V.G. Ziemann
Uppsala University, Uppsala, Sweden
A. Azima
Uni HH, Hamburg, Germany
P. Salén, P. van der Meulen
FYSIKUM, AlbaNova, Stockholm University, Stockholm, Sweden
H. Schlarb
DESY, Hamburg, Germany

Using the two perpendicularly oriented undulators and chicanes developed for an optical replica synthesizer (ORS) experiment together with the sFLASH 800 nm seed laser, radiator undulators and diagnostics, an echo seeding experiment will be conducted at FLASH in January 2012. For this experiment, the 800 nm laser pulse will be transported with a new, 12 meter long, in-vacuum laser transport line. On an in-vacuum optical breadboard, the 800 nm pulse will then be tripled in beta-BBO nonlinear crystals. The laser pulse will then be split longitudinally using a birefringent alpha BBO crystal into two pulses with orthogonal polarization states corresponding to the orthogonal orientations of the ORS undulators. These pulses will be focused to a 400 μm waist between the undulators with a Galileo telescope and steered with 4 motorized mirrors onto the electron beam axis in the ORS undulator section. The hardware layout and simulations of the echo seeding parameters will be described.

TUPB14

Design Studies for Cascaded HGHG and EESHG Experiments Based on SDUV-FEL

laser, radiation, FEL, electron

291

C. Feng, J.H. Chen, H.X. Deng, Q. Gu, D. Wang, M. Zhang, Z.T. Zhao
SINAP, Shanghai, People's Republic of China

Funding: This work was supported by the National Natural Science Foundation of China (Grant No. 10935011).
As a test facility for modern FEL R&D, The Shanghai deep ultra-violent FEL (SDUV-FEL) is now under upgrading for the cascading two stage of HGHG experiment. It is found that this upgraded facility will be also well suited for the echo-enabled staged harmonic generation (EESHG) scheme demonstration. With help of 3D simulation codes, design studies on the FEL physics for both these two schemes based on the upgraded SDUV-FEL is presented in this paper.

WEPB02

Study of Highly Isochronous Beamlines for FEL Seeding

FEL, quadrupole, undulator, laser

391

C. Sun, H. Nishimura, G. Penn, M.W. Reinsch, D. Robin, F. Sannibale, C. Steier, W. Wan
LBNL, Berkeley, California, USA

Recently seeding schemes, such as ECHO for short (nm) wavelength FELs, have been proposed. These schemes require that the nm level longitudinal bunch structure be preserved over distance of several meters. This poses a challenge for the beamline design. In this paper we present our studies of several solutions for beamlines that are nearly isochronous.

THPA33

Bunch Length Measurement Based on the Beam Position Monitor

pick-up, simulation, electron, FEL

555

J. Wang, M. Li, H.B. Wang, D. Wu
CAEP/IAE, Mianyang, Sichuan, People's Republic of China

BPM (Beam Position Monitor) is the most basic instrument of the beam dynamics. The signal of the BPM consist more information of the beam apart from the beam position. By processing and analyzing of the BPM signal, the information of the bunch length can be got. It's a challenge to use this method when the energy is low (<30 MeV) and the bunch length is especially short(10 ps rms). In this paper, the BPM system which can be used to measure the bunch length is discussed. And the method of the signal processing and analyzing is given.