| Paper | Title | Page |
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| TUPPH001 | Positron Source Based on laser Compton Scattering Gamma Ray | |
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| Positron generation from a laser Compton scattering gamma ray is presented. When the gamma ray bombards a target, the positron is generated due to the reaction of pair production, and it can be applied as the positon source of a collider. In our experiment, a 17 MeV gamma ray is produced in the way of laser Compton scattering and it induces positrons and electrons in a Pb target. The positron flux and energy spectrum were measured. | ||
| TUPPH002 | High Order Mode Analyses for the Rossendorf SRF Gun | 228 |
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| High Order Modes (HOM) excited by the beam in a superconducting RF gun (SRF gun) could destroy the quality of the electron beam. This problem is studied on the base of frequency domain description by considering of the equivalent RLC circuit contour for each HOM, periodical excited by a pulsed current source. Expression for the voltage, the field amplitude and the phase of the excited HOM has been obtained. The equations for the coupling impedances of monopole TM-HOM and TE-HOM in the RF gun cavity has been derived. In this calculation the change of the particle velocity due to acceleration is taken into account. Resonance frequencies, coupling impedances, unloaded and external quality factors, excitation voltages and field distributions for each HOM including trapped HOM are calculated for Rossendorf SRF gun up to the frequency of 7.5 GHz, using the complex field solver CLANS. The dependence of the calculated parameters from a cavity deformation has been studied. The influence of the seven most dangerous HOM on the beam quality has been estimated by particle tracking using the ASTRA code. | ||
| TUPPH006 | FEL Potential of the High Current ERLs at BNL | 232 |
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An ampere class 20 MeV superconducting Energy Recovery Linac (ERL) is under construction at Brookhaven National Laboratory (BNL)* for testing concepts for high-energy electron cooling and electron-ion colliders. This ERL prototype will be used as a test bed to study issues relevant for very high current ERLs. High average current and high performance of electron beam with some additional components make this ERL an excellent driver for high power far infrared Free Electron Laser (FEL). A possibility for future up-grade to a two-pass ERL is considered. We present the status and our plans for construction and commissioning of the ERL. We discus a FEL potential based on electron beam provided by BNL ERL.
* Litvinenko, V. N. et al. High current energy recovery linac at BNL. Proc. 26th International Free Electron Laser Conference and 11th FEL Users Workshop (FEL 2004). |
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| TUPPH007 | Spatial Coherence Measurement of UVSOR-II Free Electron Laser | |
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| The well defined phase relationship of coherent radiation is wished for a large number of experiments. The advent of very small emittance electron beams allowed improvement of the transverse coherence of the undulators radiation and lead to extensive use of modern synchrotron facilities in the visible to x-ray domain. Nevertheless, Free Electron Lasers (in particular in the seeded Coherent Harmonic Generation (CHG) scheme) may offer additional capabilities such as shorter pulse duration, smaller spectral bandwidth, higher peak power and improved transverse coherence. Transverse coherence of the third Coherent Harmonic has been studied on the UVSOR-II storage ring (Japan) at 600 MeV, using a 2.5 mJ, 1 kHz, 1.2 ps Ti:Sa laser at 800 nm wavelength with the double slit method. The improvement of the transverse coherence of the FEL radiation compared to spontaneous emission is shown via the visibility of the interference pattern resulting from double slits. The experimental results are compared to analytical calculations as well as to 3D FEL and wavefront propagation simulations performed with SRW. | ||
| TUPPH008 | Beam Dynamics Studies on the UVSOR-II Free Electron Laser | 236 |
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| In the Coherent Harmonic Generation Free Electron Laser configuration, an external laser source is seeded inside a first undulator. The interaction between the electron beam and this seed induces energy modulation of the bunch, further converted into a density modulation, producing coherent radiation in a second undulator. The energy modulation enhances the energy spread of the electron bunch, converted by the machine optics into a modification of its longitudinal distribution. In the case of a storage ring FEL, the electrons are re-circulating: the same bunch keeps interacting with the seeded laser, and relaxation of the distribution is only allowed in between two laser injections. Such specific dynamics has been studied on the CHG FEL of UVSOR-II storage ring (Japan). The electron beam stored at 600 MeV is seeded using a 2.5 mJ, 1 kHz, 1.2 ps Ti:Sa laser at 800 nm wavelength, allowing radiation at 266 nm (third harmonic). A Streak Camera is used to record the evolution of the longitudinal profiles as a function of the repetition rate and average power of the seeding laser, leading to bunch lengthening and distortion dynamical analysis. It appeared that because the heating induced by the interaction remains local, the refreshment process of the electronic distribution is modified. The experimental results are compared to simulations using SYNC. | ||
| TUPPH009 | SASE FEL Simulations for the European XFEL with the Codes Simplex and Genesis | |
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| Numerical simulation studies of the FEL process have been carried out for the European XFEL project. The impact of the undulator lattice quadrupole magnets misalignments on the FEL performance has been investigated using the FEL simulation codes SIMPLEX and GENESIS. The choice of the optimal beta function for the undulator has been investigated as well. The problem of the reduction of the number of quadrupole magnets in the undulator lattice is considered. | ||
| TUPPH010 | Gamma Laser on the Base of Diffraction Scattering an Intense 4.3 GeV Electron Beam on a Crystal | |
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| Difficulties of creating gamma lasers are generally known. Difficulties of creating gamma lasers are generally known. However such gamma laser as a phenomenon of nature has unexpectedly manifested in our experiments on the Yerevan synchrotron. A nonlinear increase in gamma ray emission depending on the electron beam intensity had been shown in the foregoing. New striking results will be presented, among them: swelling a gamma beam profile or growth of the spatial coherent length of electron-photon interaction in crystal and tending produced photons to coalescence at their interaction with substance. New data give evidence: gamma laser takes place when electron beam touches the crystal. | ||
| TUPPH011 | Analytical Studies of Transverse Coherence Properties of X-ray FELs | 240 |
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| We describe analytically the process of formation of transverse coherence in X-ray SASE FELs. | ||
| TUPPH012 | Compact X-ray Free-Electron-Laser Based on an Optical Undulator | 244 |
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| The interaction between a very high brightness electron beam and a relativistically intense optical laser pulse produces X rays via coherent Thomson back scattering with FEL collective amplification. The phenomenon is, however, very selective, so that the characteristics of both electron and laser beam must satisfy tight requirements in terms of beam current, emittance, energy spread and laser amplitude stability within the pulse. The three-dimensional equations governing the radiation phenomena have been studied in both linear and non linear regime and solved numerically for the particularly interesting values of wavelengths of 1 Ang, 1 nm and 12 nm. The performance of the collective Thomson source has been compared with that of an equivalent static undulator. A set of scaling laws ruling the phenomenon is also presented. The possibility of using an electron beam produced via LWFA in the bubble regime is investigated. | ||
| TUPPH013 | Production of Ultra-short Radiation Pulses in Frequency Doubler | 248 |
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Typically beam formation system of driver linac for SASE FEL produces electron beams with small local energy spread. This feature opens up extra possibilities for implementation of different FEL schemes. One of them is an effective frequency doubler*. It consists of an undulator tuned to the fundamental harmonic, dispersion section, and undulator tuned to the second harmonic. The first stage is a conventional soft X-ray SASE FEL. Its gain is controlled in such a way that the maximum energy modulation of the electron beam at the XFEL exit is about equal to the local energy spread, but still far away from saturation. When electron bunch passes through dispersion section this energy modulation leads to effective compression of the particles. Then bunched electron beam enters the 2nd harmonic undulator, and produces the radiation at the 2nd harmonic. Recently SASE FEL FLASH in Hamburg demonstrated unique mode of operation generating sub-10-fs radiation pulses**. In this paper we study an option of frequency doubler for FLASH operating in the femtosecond mode of operation.
* J. Feldhaus et al., NIM A 528 (2004) 471.** W. Ackermann et al., "Operation of a free electron laser from the extreme ultraviolet to the water window", Nature Photonics, in press. |
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| TUPPH014 | Generation of X-ray FEL Light Using Laser Wakefield Accelerated Electron Beams | 252 |
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| We consider a new class of high gain FELs based on femtosecond electron bunches with extra high current density produced by Laser Wake Field Acceleration (LWFA). The FELs of this kind can be used for generation of high power femtosecond x-ray pulses. We present the results of simulations of FEL operation with some reasonable beam parameters which will be obtained in future. We focus our attention on the advantages which can be gained from the unique possibility of the use of femtosecond hundred-kiloamperes bunches, generated by LWFA. We also consider the impact of the relatively poor electron beam properties on FEL characteristics. | ||
| TUPPH015 | Diffraction Effects in the Coherent Transition Radiation Bunch Length Diagnostics | 256 |
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| Diffraction effects in the Coherent Transition Radiation (CTR) bunch length diagnostics were considered for the A0 Photoinjector and the ILC injection module. The effects can cause a noticeable distortion of the measured CTR spectra dependently on the experimental setup and the bunch parameters. The distortion results in the the errors of the bunch length determination. Presented calculations show possible errors in determination of the bunch length in assumed experiments based on the CTR spectra measurements at A0 Photo injector and the ILC injection module. | ||
| TUPPH018 | Development of Ultra-short Pulse, Single Coherent Spike for SASE X-ray FELs | |
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| There is a large interest in the production of high power, ultra-short, one femtoseconds or less, coherent X-ray pulses, for atomic physics and other applications. However the present design of X-ray SASE FELs leads to an X-ray pulse about 100 times longer. Several methods to reduce the bunch length to the 10-1 fs region have been proposed. These methods are based on electron bunch manipulation to cut the lasing part of the bunch to a fraction of the total length, thus reducing the X-ray pulse length. We are considering here a different method, using ultra-short, very low charge electron bunches, with a length of the order or shorter than the FEL cooperation length. In this case the X-ray pulse length after amplification in the undulator is a few times the electron bunch length. Our simulations show that in an LCLS-like case we can obtain coherent, Fourier transform limited, X-ray pulses, consisting of a single spike, with a FWHM of about 0.1 um, corresponding to about 300 as, a peak power of about 5 GW, and an intensity of about 10 uJ. | ||
| TUPPH019 | Simulations for the LCLS Injector | 260 |
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| The commissioning of the LCLS Injector has started this year. The electron beam quality for producing high power SASE X-rays is very challenging to reach. In this paper, we will describe comparisons between simulations made with multi-particle tracking code and electron beam measurements performed on the LCLS injector. | ||
| TUPPH020 | Quiet Start Method in small signal HGHG FEL Simulation | 264 |
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| Quiet start scheme is broadly utilized in Self Amplified Spontaneous Radiation (SASE)FEL simulations, which is proven to be correct and efficient. Nevertheless, due to the energy modulation and dispersion section, the High Gain Harmonic Generation (HGHG) FEL simulation will not be improved by the traditional quiet start method. A new approach is presented to largely decrease the number of macro-partilces per slice that can be implemented in both time-independent and time-dependent simulation, accordingly expedites the high order harmonic cascade simulation or other small signal HGHG cases. |