FEL2011 - Table of Session: MOPC (FEL Theory and New Concepts)

Paper	Title	Page
MOPC01	Compact THz Radiation Source Based on a Photocathode RF Gun	92
	S. Liu Shanghai Jiao Tong University, Shanghai, People's Republic of China J. Urakawa KEK, Ibaraki, Japan
	Terahertz (THz) science and technology have already become the research highlight at present. In this paper, we put forward a proposal to generate THz radiation at tens of MW peak power. Due to the ultrafast laser and the high accelerating field of photocathode RF gun, we can generate and accelerate electron beam to several MeV, of which the bunch length is less than sub-ps. When the short electron bunches are injected into the wiggler, THz radiation based on Coherent Synchrotron Radiation could be achieved with tens of MW peak power. The whole THz FEL facility can be scaled to the size of a tabletop.

MOPC02	Improvement of Termination Field of Bulk HTSC Staggered Array Undulator	96
	N. Kimura, M. A. Bakr, Y.W. Choi, H. Imon, K. Ishida, T. Kii, R. Kinjo, K. Komai, K. Masuda, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, K. Yoshida Kyoto University, Institute for Advanced Energy, Kyoto, Japan
	We have proposed a bulk High Temperature Superconductor Staggered Array Undulator (Bulk HTSC SAU) to achieve higher undulator field, shorter period, and variable K-value without changing gap[1]. The purpose of this study is to revise the controversial point, that bulk HTSC SAU generates strong wicked magnetic field on its terminations, which scatters electron beam. Therefore we studied a new method to correct the field. We developed a physical model which based on Bean model to deal with the bulk superconducting material and then constructed a simulation code. By using the calculation results, we developed the correction method by adding bulk material on the edge of undulator. Measurement of the magnetic field of a prototype of bulk HTSC SAU with this method has been performed. We confirm that the numerical calculation well describe the experimental results. In this conference, numerical and experimental results of our end field termination method will be presented. [1] R. Kinjyo, T. Kii, H. Zen, K Higashimura, K Masuda, K. Nagasaki, H. Ohgaki, Y.U. Jeong "Bulk High-TC Super Conductor Staggered Array Undulator" Proceedings of FEL2008

MOPC03	Modeling of the Quiet Start Algorithm in the Framework of the Correlation Function Theory	99
	O.A. Shevchenko, N. Vinokurov BINP SB RAS, Novosibirsk, Russia
	To suppress initial beam current fluctuations at the fundamental harmonic the macroparticle based FEL simulation codes use the quiet start algorithm. This algorithm should be valid at linear stage but there is no simple method to check whether it gives correct results at saturation. The regular approach to the start-up from noise problem should be based on the correlation function equation. In this paper we show that the quiet start algorithm can be naturally described in the framework of the correlation function theory. For this purpose one just needs to assume nonzero correlations in the initial particle distribution. This approach gives the possibility to compare simulation results for the system with reduced number of particles and artificially suppressed initial fluctuations with the case of real system with large number of particles.

MOPC04	The Effects of Jitters on Coherent X-ray Radiation Using a Modulation Compression Scheme	103
	J. Qiang LBNL, Berkeley, California, USA J. Wu SLAC, Menlo Park, California, USA
	Modulation compression scheme based on a chirped beam, laser modulator and laser chirper, and two bunch compressors was proposed recently to generate coherent multi-color atto-second X-ray radiation [1]. In this paper, we will present studies of effects of the initial longitudinal beam chirp jitter, time synchronization jitter between the electron beam and the laser chirper, and the laser chirper amplitude jitter on the final coherent X-ray radiation. [1]Ji Qiang and Juhao Wu, “Generation multi-color attosecond X-ray radiation through modulation compression,” arXiv:1102.4806v1.

MOPC05	HGHG Scheme for FLASH II	107
	A. Meseck, R. Mitzner HZB, Berlin, Germany W. Decking, B. Faatz, M. Scholz DESY, Hamburg, Germany
	FLASH II is a major extension of the existing FLASH facility at DESY. It has been proposed in collaboration with the HZB. FLASH II is a seeded FEL in the parameter range of FLASH. The final layout of the undulator section of FLASH II allows for different seeding schemes. So that seeding with an HHG source as well as seeding in cascaded HGHG scheme and several combination of these schemes are possible. However, for the shortest wavelengths down to 4 nm the cascaded HGHG scheme will be utilized. It consists of two frequency up conversion stages utilizing a Ti:Sa laser based seeding source in UVU range. We present and discuss start-to-end simulation studies for the shortest wavelength generated in the HGHG cascade of FLASH II.

MOPC06	X-Ray FELs Based on ERL Facilities	111
	A. Meseck HZB, Berlin, Germany G.H. Hoffstaetter, F. Löhl, C.E. Mayes CLASSE, Ithaca, New York, USA
	The characteristic high repetition rate and the high spectral brightness of the electron beams delivered by ERLs have led to a large number of ERL based proposals for hard X-ray sources including X-ray FELs. FEL oscillators, including those proposed for hard X-rays, require comparatively low peak currents and are particularly suitable for ERLs. However single-pass FELs in SASE or seeded mode do not seem out of reach when bunch-compression schemes for higher peak currents are utilized. Using the proposed Cornell ERL as an example, we present and discuss oscillator and single-pass FEL schemes which provide extremely high spectral-brightness ultra-short X-ray pulses for experiments.

MOPC09	Use of Re-Acceleration and Tapering in High Gain Free Electron Lasers to Enhance Power and Energy Extraction	115
	R. Dusad, G. Travish UCLA, Los Angeles, USA
	In high gain Free Electron Lasers (FELs), it is possible to use undulator tapering to increase power and energy extraction beyond saturation. For some applications, however, tapering is not sufficient or results in excessively long structures. Here we the study use of tapered undulators interrupted by short accelerator sections to increase the power extracted per unit length. Re-acceleration restores nominal energy to the beam with minimal disruption to bunching, and allows repeated use of a single taper profile. We show that for suitable parameter sets this approach can perform better than ideal tapering alone, and may serve to greatly improve and simplify high peak and average power FELs. Based on these findings, we propose a first experiment to test the re-acceleration with tapering concept.

MOPC10	Numerical Investigation of Longitudinal Coherence in a Linear Tapered SASE FEL	118
	H.T. Li, Q.K. Jia USTC/NSRL, Hefei, Anhui, People's Republic of China
	One goal of the several FEL facilities operating in soft X-ray range, is the production of high-gain narrow-bandwidth FEL. In this report, the performance of radiation power and longitudinal cohence is studied for x-ray FEL generated through several different methods, including tapered，inverse-tapered and step-tapered undulator, and the SASE-FEL applying distributed optical klystron. Three–dimensional simulation demonstrate that these methods all can increase the FEL power and improve the time and spectrum structure with their own parameter optimization. In particular, FEL generated from toothed undulaor is studied. It is shown that the longitudinal cohence is improved and a series of several fettosecond pulses at gigawatt power levels at a wavelength of 1.5 nm is generated.

MOPC12	Coherent Synchrotron Radiation and Bunch Compression Studies in the Emittance Exchange Beamline at the Fermilab A0 Photoinjector	121
	J.C.T. Thangaraj, M.D. Church, H.T. Edwards, A.S. Johnson, A.H. Lumpkin, J. Ruan, J.K. Santucci, Y.-E. Sun, R.M. Thurman-Keup Fermilab, Batavia, USA T.J. Maxwell, P. Piot Northern Illinois University, DeKalb, Illinois, USA
	One of goals of the Fermilab A0 photoinjector is to investigate experimentally the transverse to longitudinal emittance exchange principle. Coherent synchrotron radiation in the emittance exchange line could limit short pulse operation of the emittance exchanger. In this paper, we present experimental and simulation study of the coherent synchroton radiation (CSR) in the emittance exchange line at A0 photoinjector. We also show how EEX can be used to compress a bunch by adding chirp to the incoming beam.

MOPC13	Terahertz-Wave Spectrophotometry – Experiments of Compton Backscattering of Continuous-spectrum Coherent Transition Radiation	125
	N. Sei AIST, Tsukuba, Ibaraki, Japan T. Takahashi Kyoto University, Research Reactor Institute, Osaka, Japan
	Funding: This study was financially supported by the Sumitomo foundation. We have studied a terahertz-wave spectrophotometry by using Compton backscattering of coherent radiations at the Kyoto University Research Reactor Institute. In the terahertz-wave spectrophotometry, the characteristics of the continuous-spectrum THz waves are converted into those of the other wavelengths which are easily measured by colliding the THz waves with a relativistic electron beam. Such the continuous-spectrum light beam by Compton backscattering is known in a field of astrophysics. We achieved to observe a continuous-spectrum visible beam resulting from Compton backscattering using coherent transition radiations from an L-band electron linear accelerator. The measured spectrum of the Compton backscattered photons was similar to that calculated from the spectrum of coherent transition radiation. In the presentation, the experimental results of terahertz-wave spectrophotometry will be explained in detail. N. Sei and T. Takahashi, Appl. Phys. Express 3 (2010) 052401.

MOPC14	Infrared Single Spike Pulses Generation Using a Short Period Superconducting Tape Undulator at APEX	129
	D. Filippetto, C. F. Papadopoulos, G. Penn, S. Prestemon, F. Sannibale LBNL, Berkeley, California, USA C. Pellegrini UCLA, Los Angeles, California, USA M. Yoon POSTECH, Pohang, Kyungbuk, Republic of Korea
	Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231 We report on the possibility of constructing an infrared FEL by combining a novel design super-conducting undulator developed at LBNL with the high brightness beam from the APEX injector facility at the Lawrence Berkeley National Laboratory. Calculations show that the resulting FEL is expected to deliver a saturated power of about a MW within a 4 m undulator length when operating in Self-Amplified-Spontaneus-Emission mode, with a single-spike of coherent radiation at 2 μm wavelength. The sub-cm undulator periods, associated with the relatively low energy of the APEX beam (20-25 MeV), forces the FEL to operate in a regime with unusual and interesting characteristics. The alternative option of laser seeding the FEL is also examined, showing the potential to reduce the saturation length even further.

MOPC19	Pre-modulated Electron Bunch Sequence	133
	D. Wang, L.X. Yan TUB, Beijing, People's Republic of China
	We modulate electron bunch sequence of 0.1 ~ 1nC total charge, after photocathode RF acceleration of 68 ~120MV / m, 3m long travelling-wave accelerating tube for the overall velocity compression. PARMELA simulation results prove that the bunch of high relativity can reach high charge and have short longitude rms length, less than 1ps of each single bunch and picoseconds interval at the accelerating tube exit. Taking use of the pre-modulated bunch sequence, we can do further research in CTR, CSR and FEL radiation.

MOPC21	Comparison of Growth Rates of Two-Stream Free Electron Lasers (TSFEL) with Planar Wiggler Magnet and AC Electrical Wiggler Pumps	136
	N. Mahdizadeh Islamic Azad University, Sabzevar Branch, Sabzevar, Iran F.M. Aghamir University of Tehran, Tehran, Iran
	Funding: Sabzevar Branch, Islamic Azad University A Comparison between growth rates of a Two Stream Free Electron Laser (TSFEL) with a planar wiggler pump and ac electrical wiggler pump has been presented. With the aid of fluid theory, dispersion relations are derived and their characteristics have been numerically analyzed. In this analysis, the longitudinal component of the stress tensor has been retained for beam temperature consideration. Similarities and differences in dispersion relations and growth rate have, also, been presented.

MOPC22	Nonlinear Analyses in Two-stream Free-Electron Laser with Helical Wiggler Pump	138
	N. Mahdizadeh Islamic Azad University, Sabzevar Branch, Sabzevar, Iran F.M. Aghamir University of Tehran, Tehran, Iran A. Raghavi PNUM, Mashhad, Iran
	Funding: Sabzevar Branch, Islamic Azad University The analysis of a Two-Stream Free Electron Laser (TSFEL) with a helical wiggler pump is presented. The power and the signal growth rate are calculated. A set of coupled nonlinear differential equations for slowly varying amplitudes and phases is obtained through the substitution of vector and scalar potentials into the Maxwell-Poisson equations. The electron orbit equations are derived by Lorentz force equation. The obtained equations for fields and ensemble of electrons are solved numerically. The power and growth rate of TSFEL are compared with those of conventional FEL. It has been found that the TSFEL reaches the saturation regime in a longer axial distance in comparison to the conventional FEL and the growth rate of the TSFEL is somewhat lower than conventional FEL.

MOPC27	Small Signal Gain for Two Stream FEL	141
	A. Raghavi PNUM, Mashhad, Iran N. Mahdizadeh Islamic Azad University, Sabzevar Branch, Sabzevar, Iran
	The problem of wave-particle interaction in the small signal gain regime for the tow-stream free electron laser is considered using a relativistic moving frame. The equation of motion in this frame is solved by means of a non-relativistic Hamiltonian. Small signal gain (SSG) for the laser is derived in both moving and laboratory frames.

MOPC28	Fine Tuning of the K-parameter of Two Segments of the European XFEL Undulator Systems	144
	Y. Li, J. Pflüger European XFEL GmbH, Hamburg, Germany E. Gluskin ANL, Argonne, USA N. Vinokurov BINP SB RAS, Novosibirsk, Russia
	For large and segmented undulator systems as needed for the European XFEL a non-destructive, in situ, radiation diagnostics method would strongly compliment e-beam diagnostics. If such method would allow to fine tune the K parameter of individual undulator segments with an accuracy set by the Pierce parameter ρ, which is on the order of 2~3×10^-4, this would provide a very helpful tool for FEL commissioning. This paper provides a first analysis of a strategy of tuning the K parameter of two adjacent undulator segments. The spontaneous, monochromatized, on axis intensity is analyzed as a function of the phase delay set by the phase shifter in between. It makes use of diagnostic equipment which will be available at the European XFEL anyway. First results are demonstrated and limitations will be discussed.

Paper

Title

Page

Compact THz Radiation Source Based on a Photocathode RF Gun

92

S. Liu
Shanghai Jiao Tong University, Shanghai, People's Republic of China
J. Urakawa
KEK, Ibaraki, Japan

Terahertz (THz) science and technology have already become the research highlight at present. In this paper, we put forward a proposal to generate THz radiation at tens of MW peak power. Due to the ultrafast laser and the high accelerating field of photocathode RF gun, we can generate and accelerate electron beam to several MeV, of which the bunch length is less than sub-ps. When the short electron bunches are injected into the wiggler, THz radiation based on Coherent Synchrotron Radiation could be achieved with tens of MW peak power. The whole THz FEL facility can be scaled to the size of a tabletop.

MOPC02

Improvement of Termination Field of Bulk HTSC Staggered Array Undulator

96

N. Kimura, M. A. Bakr, Y.W. Choi, H. Imon, K. Ishida, T. Kii, R. Kinjo, K. Komai, K. Masuda, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, K. Yoshida
Kyoto University, Institute for Advanced Energy, Kyoto, Japan

We have proposed a bulk High Temperature Superconductor Staggered Array Undulator (Bulk HTSC SAU) to achieve higher undulator field, shorter period, and variable K-value without changing gap[1]. The purpose of this study is to revise the controversial point, that bulk HTSC SAU generates strong wicked magnetic field on its terminations, which scatters electron beam. Therefore we studied a new method to correct the field. We developed a physical model which based on Bean model to deal with the bulk superconducting material and then constructed a simulation code. By using the calculation results, we developed the correction method by adding bulk material on the edge of undulator. Measurement of the magnetic field of a prototype of bulk HTSC SAU with this method has been performed. We confirm that the numerical calculation well describe the experimental results. In this conference, numerical and experimental results of our end field termination method will be presented.
[1] R. Kinjyo, T. Kii, H. Zen, K Higashimura, K Masuda, K. Nagasaki, H. Ohgaki, Y.U. Jeong "Bulk High-TC Super Conductor Staggered Array Undulator" Proceedings of FEL2008

MOPC03

Modeling of the Quiet Start Algorithm in the Framework of the Correlation Function Theory

99

O.A. Shevchenko, N. Vinokurov
BINP SB RAS, Novosibirsk, Russia

To suppress initial beam current fluctuations at the fundamental harmonic the macroparticle based FEL simulation codes use the quiet start algorithm. This algorithm should be valid at linear stage but there is no simple method to check whether it gives correct results at saturation. The regular approach to the start-up from noise problem should be based on the correlation function equation. In this paper we show that the quiet start algorithm can be naturally described in the framework of the correlation function theory. For this purpose one just needs to assume nonzero correlations in the initial particle distribution. This approach gives the possibility to compare simulation results for the system with reduced number of particles and artificially suppressed initial fluctuations with the case of real system with large number of particles.

MOPC04

The Effects of Jitters on Coherent X-ray Radiation Using a Modulation Compression Scheme

103

J. Qiang
LBNL, Berkeley, California, USA
J. Wu
SLAC, Menlo Park, California, USA

Modulation compression scheme based on a chirped beam, laser modulator and laser chirper, and two bunch compressors was proposed recently to generate coherent multi-color atto-second X-ray radiation [1]. In this paper, we will present studies of effects of the initial longitudinal beam chirp jitter, time synchronization jitter between the electron beam and the laser chirper, and the laser chirper amplitude jitter on the final coherent X-ray radiation.
[1]Ji Qiang and Juhao Wu, “Generation multi-color attosecond X-ray radiation through modulation compression,” arXiv:1102.4806v1.

MOPC05

HGHG Scheme for FLASH II

107

A. Meseck, R. Mitzner
HZB, Berlin, Germany
W. Decking, B. Faatz, M. Scholz
DESY, Hamburg, Germany

FLASH II is a major extension of the existing FLASH facility at DESY. It has been proposed in collaboration with the HZB. FLASH II is a seeded FEL in the parameter range of FLASH. The final layout of the undulator section of FLASH II allows for different seeding schemes. So that seeding with an HHG source as well as seeding in cascaded HGHG scheme and several combination of these schemes are possible. However, for the shortest wavelengths down to 4 nm the cascaded HGHG scheme will be utilized. It consists of two frequency up conversion stages utilizing a Ti:Sa laser based seeding source in UVU range. We present and discuss start-to-end simulation studies for the shortest wavelength generated in the HGHG cascade of FLASH II.

MOPC06

X-Ray FELs Based on ERL Facilities

111

A. Meseck
HZB, Berlin, Germany
G.H. Hoffstaetter, F. Löhl, C.E. Mayes
CLASSE, Ithaca, New York, USA

The characteristic high repetition rate and the high spectral brightness of the electron beams delivered by ERLs have led to a large number of ERL based proposals for hard X-ray sources including X-ray FELs. FEL oscillators, including those proposed for hard X-rays, require comparatively low peak currents and are particularly suitable for ERLs. However single-pass FELs in SASE or seeded mode do not seem out of reach when bunch-compression schemes for higher peak currents are utilized. Using the proposed Cornell ERL as an example, we present and discuss oscillator and single-pass FEL schemes which provide extremely high spectral-brightness ultra-short X-ray pulses for experiments.

MOPC09

Use of Re-Acceleration and Tapering in High Gain Free Electron Lasers to Enhance Power and Energy Extraction

115

R. Dusad, G. Travish
UCLA, Los Angeles, USA

In high gain Free Electron Lasers (FELs), it is possible to use undulator tapering to increase power and energy extraction beyond saturation. For some applications, however, tapering is not sufficient or results in excessively long structures. Here we the study use of tapered undulators interrupted by short accelerator sections to increase the power extracted per unit length. Re-acceleration restores nominal energy to the beam with minimal disruption to bunching, and allows repeated use of a single taper profile. We show that for suitable parameter sets this approach can perform better than ideal tapering alone, and may serve to greatly improve and simplify high peak and average power FELs. Based on these findings, we propose a first experiment to test the re-acceleration with tapering concept.

MOPC10

Numerical Investigation of Longitudinal Coherence in a Linear Tapered SASE FEL

118

H.T. Li, Q.K. Jia
USTC/NSRL, Hefei, Anhui, People's Republic of China

One goal of the several FEL facilities operating in soft X-ray range, is the production of high-gain narrow-bandwidth FEL. In this report, the performance of radiation power and longitudinal cohence is studied for x-ray FEL generated through several different methods, including tapered，inverse-tapered and step-tapered undulator, and the SASE-FEL applying distributed optical klystron. Three–dimensional simulation demonstrate that these methods all can increase the FEL power and improve the time and spectrum structure with their own parameter optimization. In particular, FEL generated from toothed undulaor is studied. It is shown that the longitudinal cohence is improved and a series of several fettosecond pulses at gigawatt power levels at a wavelength of 1.5 nm is generated.

MOPC12

Coherent Synchrotron Radiation and Bunch Compression Studies in the Emittance Exchange Beamline at the Fermilab A0 Photoinjector

121

J.C.T. Thangaraj, M.D. Church, H.T. Edwards, A.S. Johnson, A.H. Lumpkin, J. Ruan, J.K. Santucci, Y.-E. Sun, R.M. Thurman-Keup
Fermilab, Batavia, USA
T.J. Maxwell, P. Piot
Northern Illinois University, DeKalb, Illinois, USA

One of goals of the Fermilab A0 photoinjector is to investigate experimentally the transverse to longitudinal emittance exchange principle. Coherent synchrotron radiation in the emittance exchange line could limit short pulse operation of the emittance exchanger. In this paper, we present experimental and simulation study of the coherent synchroton radiation (CSR) in the emittance exchange line at A0 photoinjector. We also show how EEX can be used to compress a bunch by adding chirp to the incoming beam.

MOPC13

Terahertz-Wave Spectrophotometry – Experiments of Compton Backscattering of Continuous-spectrum Coherent Transition Radiation

125

N. Sei
AIST, Tsukuba, Ibaraki, Japan
T. Takahashi
Kyoto University, Research Reactor Institute, Osaka, Japan

Funding: This study was financially supported by the Sumitomo foundation.
We have studied a terahertz-wave spectrophotometry by using Compton backscattering of coherent radiations at the Kyoto University Research Reactor Institute. In the terahertz-wave spectrophotometry, the characteristics of the continuous-spectrum THz waves are converted into those of the other wavelengths which are easily measured by colliding the THz waves with a relativistic electron beam. Such the continuous-spectrum light beam by Compton backscattering is known in a field of astrophysics. We achieved to observe a continuous-spectrum visible beam resulting from Compton backscattering using coherent transition radiations from an L-band electron linear accelerator*. The measured spectrum of the Compton backscattered photons was similar to that calculated from the spectrum of coherent transition radiation. In the presentation, the experimental results of terahertz-wave spectrophotometry will be explained in detail.
* N. Sei and T. Takahashi, Appl. Phys. Express 3 (2010) 052401.

MOPC14

Infrared Single Spike Pulses Generation Using a Short Period Superconducting Tape Undulator at APEX

129

D. Filippetto, C. F. Papadopoulos, G. Penn, S. Prestemon, F. Sannibale
LBNL, Berkeley, California, USA
C. Pellegrini
UCLA, Los Angeles, California, USA
M. Yoon
POSTECH, Pohang, Kyungbuk, Republic of Korea

Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
We report on the possibility of constructing an infrared FEL by combining a novel design super-conducting undulator developed at LBNL with the high brightness beam from the APEX injector facility at the Lawrence Berkeley National Laboratory. Calculations show that the resulting FEL is expected to deliver a saturated power of about a MW within a 4 m undulator length when operating in Self-Amplified-Spontaneus-Emission mode, with a single-spike of coherent radiation at 2 μm wavelength. The sub-cm undulator periods, associated with the relatively low energy of the APEX beam (20-25 MeV), forces the FEL to operate in a regime with unusual and interesting characteristics. The alternative option of laser seeding the FEL is also examined, showing the potential to reduce the saturation length even further.

MOPC19

Pre-modulated Electron Bunch Sequence

133

D. Wang, L.X. Yan
TUB, Beijing, People's Republic of China

We modulate electron bunch sequence of 0.1 ~ 1nC total charge, after photocathode RF acceleration of 68 ~120MV / m, 3m long travelling-wave accelerating tube for the overall velocity compression. PARMELA simulation results prove that the bunch of high relativity can reach high charge and have short longitude rms length, less than 1ps of each single bunch and picoseconds interval at the accelerating tube exit. Taking use of the pre-modulated bunch sequence, we can do further research in CTR, CSR and FEL radiation.

MOPC21

Comparison of Growth Rates of Two-Stream Free Electron Lasers (TSFEL) with Planar Wiggler Magnet and AC Electrical Wiggler Pumps

136

N. Mahdizadeh
Islamic Azad University, Sabzevar Branch, Sabzevar, Iran
F.M. Aghamir
University of Tehran, Tehran, Iran

Funding: Sabzevar Branch, Islamic Azad University
A Comparison between growth rates of a Two Stream Free Electron Laser (TSFEL) with a planar wiggler pump and ac electrical wiggler pump has been presented. With the aid of fluid theory, dispersion relations are derived and their characteristics have been numerically analyzed. In this analysis, the longitudinal component of the stress tensor has been retained for beam temperature consideration. Similarities and differences in dispersion relations and growth rate have, also, been presented.

MOPC22

Nonlinear Analyses in Two-stream Free-Electron Laser with Helical Wiggler Pump

138

N. Mahdizadeh
Islamic Azad University, Sabzevar Branch, Sabzevar, Iran
F.M. Aghamir
University of Tehran, Tehran, Iran
A. Raghavi
PNUM, Mashhad, Iran

Funding: Sabzevar Branch, Islamic Azad University
The analysis of a Two-Stream Free Electron Laser (TSFEL) with a helical wiggler pump is presented. The power and the signal growth rate are calculated. A set of coupled nonlinear differential equations for slowly varying amplitudes and phases is obtained through the substitution of vector and scalar potentials into the Maxwell-Poisson equations. The electron orbit equations are derived by Lorentz force equation. The obtained equations for fields and ensemble of electrons are solved numerically. The power and growth rate of TSFEL are compared with those of conventional FEL. It has been found that the TSFEL reaches the saturation regime in a longer axial distance in comparison to the conventional FEL and the growth rate of the TSFEL is somewhat lower than conventional FEL.

MOPC27

Small Signal Gain for Two Stream FEL

141

A. Raghavi
PNUM, Mashhad, Iran
N. Mahdizadeh
Islamic Azad University, Sabzevar Branch, Sabzevar, Iran

The problem of wave-particle interaction in the small signal gain regime for the tow-stream free electron laser is considered using a relativistic moving frame. The equation of motion in this frame is solved by means of a non-relativistic Hamiltonian. Small signal gain (SSG) for the laser is derived in both moving and laboratory frames.

MOPC28

Fine Tuning of the K-parameter of Two Segments of the European XFEL Undulator Systems

144

Y. Li, J. Pflüger
European XFEL GmbH, Hamburg, Germany
E. Gluskin
ANL, Argonne, USA
N. Vinokurov
BINP SB RAS, Novosibirsk, Russia

For large and segmented undulator systems as needed for the European XFEL a non-destructive, in situ, radiation diagnostics method would strongly compliment e-beam diagnostics. If such method would allow to fine tune the K parameter of individual undulator segments with an accuracy set by the Pierce parameter ρ, which is on the order of 2~3×10^-4, this would provide a very helpful tool for FEL commissioning. This paper provides a first analysis of a strategy of tuning the K parameter of two adjacent undulator segments. The spontaneous, monochromatized, on axis intensity is analyzed as a function of the phase delay set by the phase shifter in between. It makes use of diagnostic equipment which will be available at the European XFEL anyway. First results are demonstrated and limitations will be discussed.