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| TUAAU01 |
High Power FEL Developments – A Review
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- G. Neil
Jefferson Lab, Newport News, Virginia
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High power FELs have continued to make significant progress in the last few years. Power advances are taking advantage of the energy recovering linac technology on both superconducting and room temperature machines. In general, the limiting technology has been the injector current capability but there are a number of other technical factors which must be considered to successfully develop a high average power Free Electron Laser. With a number of groups poised to develop 100 mA ERLs, many with FELs, the importance of resolving limiting issues is becoming more critical. The Recuperator at Novosibirsk has the record current of 22 mA and has produced over 400 W of FEL power. Work is underway to extend the power and performance of this pioneering machine. Meanwhile, at Jefferson Lab, the Upgrade FEL achieved 14.3 kW of output while recirculating 8 mA. Numerous efforts are underway to increase the average brightness capabilities injectors: Brookhaven, Los Alamos, and Berkeley National Labs, Cornell University, Advanced Energy Systems, Daresbury Lab, KEK, and FZ Dresden among others have significant injector development programs underway. This talk will review the status of high average power FELs around the world and discuss the technical developments underway in injectors, optics, and other areas to achieve yet higher performance.
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Slides
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| TUAAU02 |
Electron Outcoupling Scheme for the Novosibirsk FEL
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- O. A. Shevchenko, V. G. Tcheskidov, N. Vinokurov, A. N. Matveenko
BINP SB RAS, Novosibirsk
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One of the main problems of contemporary high power FELs is the mirror heating. One of the possible solutions of this problem is the use of electron outcoupling*. In this case the mirrors of optical resonator are not transparent and the coherent radiation from an additional undulator in the FEL magnetic system is used. To provide the output of this radiation the electron beam in the auxiliary undulator is deflected from the optical resonator axis. To save bunching it is preferable to use the achromatic deflecting bend. The project of electron outcoupling for the Novosibirsk FEL is described. Simulation results are presented.
* N. G. Gavrilov et al., NIM A304 (1991) 63-65
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Slides
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| TUAAU03 |
A Comparison of Short Rayleigh Range FEL Performance with Simulations
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- J. Blau, D. T. Burggraff, W. B. Colson, P. P. Crooker, J. Sans Aguilar
NPS, Monterey, California
- P. E. Evtushenko, G. Neil, M. D. Shinn, S. V. Benson
Jefferson Lab, Newport News, Virginia
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Previous three-dimensiontal simulations of Free-electron laser (FEL) oscillators showed that FEL gain doesn't fall off with Rayleigh range as predicted by one-dimensional simulations*. They also predict that the angular tolerance for the mirrors is much large than simplistic theory predicts. Using the IR Upgrade laser at Jefferson Lab lasing at 935 nm we have studied the performance of an FEL with very short Rayleigh range. We also looked at the angular sensitivity for several different Rayleigh ranges. We find that, even for large Rayleigh ranges, the angular sensitivity is much less than one might expect. The relative angle of the electron beam and optical mode can change by more than the 1/·102 divergence without reducing the laser gain. This is the first demonstration that 3-dimensional effects qualitatively change the performance of an FEL oscillator. We find very good agreement between simulations and measured gain. Surprisingly the gain continues to rise as the Rayleigh range is shortened and continues to grow even when the resonator becomes geometrically unstable. The same behavior is seen in both the experiment and simulations.
* W. B. Colson et al., "Short Rayleigh length free electron lasers",Physical Review Special Topics: Accelerators and Beams 9, 030703, 2006
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Slides
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| TUAAU05 |
Modelling Mirror Aberrations in FEL Oscillators Using OPC
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207 |
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- K.-J. Boller, J. G. Karssenberg, P. J.M. van der Slot
Mesa+, Enschede
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Thermal distortion in mirrors used in high average power FEL oscillators, like the JLAB FEL and the 4GLS VUV-FEL, will influence the mode quality and affect the FEL performance. In order to quantify these effects, these distortions needs to be characterised. Mirror aberrations are generally described using Zernike polynomials and also in case of thermal distortions, it has been shown that these polynomials can be used to describe the mirror distortion*. The Optical Propagation Code (OPC)** is a general optical propagation package in the paraxial approximation, that works together with gain codes like Medusa and Genesis 1.3 to model FEL oscillators. We have extended OPC to include phase masks, that can either be generated by an external program or internally using Zernike polynomials. This allows OPC to model mirror aberrations. We will present a few examples, illustrating the capabilities of OPC.
* Nucl. Instrum. Meth. A407 (1998)401** J. Appl. Phys. 100, 093106 (2006)
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Slides
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| TUPPH001 |
Positron Source Based on laser Compton Scattering Gamma Ray
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- S. Amano, S. Miyamoto, T. Mochizuki
NewSUBARU/SPring-8, Laboratory of Advanced Science and Technology for Industry (LASTI), Hyogo
- K. Imasaki, D. Li
ILT, Suita, Osaka
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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.
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| TUPPH002 |
High Order Mode Analyses for the Rossendorf SRF Gun
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228 |
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- D. Janssen
FZD, Dresden
- V. Volkov
BINP SB RAS, Novosibirsk
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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.
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| TUPPH006 |
FEL Potential of the High Current ERLs at BNL
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232 |
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- I. Ben-Zvi, V. Litvinenko, E. Pozdeyev, D. Kayran
BNL, Upton, Long Island, New York
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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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