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| MOPPH046 | Operation of Near-infrared FEL at Nihon University | electron, coupling, linac, undulator | 114 | |||||
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The near-infrared FEL at Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University has been operated for a variety of scientific applications since 2003. The stability of the FEL power was improved appreciably by the advanced stability of the 125 MeV electron linac. Currently fundamental FEL wavelength ranges from 1 to 6 microns, which is restricted by the electron energy and the optical devices. The higher harmonics in the visible region is also available. The maximum macropulse output energy of 60 mJ/pulse has been obtained at a wavelength of 1725 nm. The short FEL resonator at LEBRA causes relatively high optical energy density on the surface of the resonator mirrors; present copper-based Ag mirrors in use at LEBRA are not durable enough for long term operation. As an alternative way of generating intense harmonics in the visible to near-UV region, second and third harmonic generation by means of non-linear optical devices has been tested for the FELs around 1.5 microns as input fundamental photons.
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| WEPPH018 | A High Brightness X-band Split Photoinjector Concept and Related Technological Challenges | gun, emittance, brightness, electron | 370 | |||||
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Future light sources based on high gain free electron lasers, require the production, acceleration and transport up to the undulator entrance of high brightness (low emittance, high peak current) electron bunches. Wake fields effects in accelerating sections and in magnetic bunch compressors typically contribute to emittance degradation, hence the photo-injector design and its operation is the leading edge for high quality beam production. The state of the art photoinjector beam brightness can be in principle brought above the 1015 A/m2 threshold with an X-band gun and a proper emittance compensation scheme. We discuss in this paper an optimized design of a split X-band photoinjector, a convenient matching scheme with the downstream linac, based on the SPARC project experience, and the further technological developments required to reach such an appealing goal.
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| WEPPH023 | Beam Properties from S-band Energy Compensated Thermionic RF Gun and Linac for KU-FEL | electron, emittance, gun, free-electron-laser | 386 | |||||
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Energy degradation arising from back-bombardment effect was quite serious problem for using a thermionic RF gun as injector of FEL device. Thus we have developed energy compensation technique, which keeps cavity voltage as constant by controlling input RF power to the RF gun. We have successfully extracted electron beam with constant energy from the thermionic RF gun with the energy compensation technique*. However, PFN tuning of the Klystron modulator and time-varying beamloading would affect macro-pulse properties; energy spread, emittance, phase mismatch between RF gun and accelerator, etc. Thus we have estimated effects to the beam properties by using the 1D thermal conduction model** and PARMERA, and also evaluated these properties experimentally. The estimated and measured results were not so serious for KU-FEL system. We will discuss the comparison between the experimental results and the calculation results in this conference.
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* N. Okawachi, et al., Proc. of the FEL 2006, pp.664-667 (2006)** T. Kii, et al., Nucl. Instr. and Meth. A 483 310-314 (2002) |
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| WEPPH033 | Stabilization of a Klystron Voltage at 100 PPM Level for PAL XFEL | controls, feedback, target, power-supply | 424 | |||||
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The PAL XFEL needs a stable electron beam. The stable charging of PFN (pulse forming network) of a klystron-modulator is essential to provide the stable acceleration field for an electron beam. For PAL XFEL, stabilization of klystron voltage pulses at 100 PPM level is required. Short-term stability is determined by a minimum resolution of a charging system. Long-term stability is determined by a thermal stability due to the temperature drift. This paper shows details of hardware R&D and test results to achieve the target stability.
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| WEPPH051 | Development of a Beam Current Transformer for the X-FEL Project in SPring-8 | electron, dumping, damping, controls | 464 | |||||
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The SCSS prototype accelerator has been constructed at SPring-8. The output signal of the current transformer (CT) for measuring an electron beam current in SCSS prototype accelerator has a few megahertz noise emitted from the thyratron of klystron modulator, a ringing signal caused by the weak field of the electron beam. The long period undulation of an electrical ground level at the CT output also occurred by a large electric current generated by the klystron modulator, and flown into the ground. As a result, it is difficult to measure the beam current correctly. Therefore, we devised a new CT monitor in order to improve the problem as mentioned above. The improvement points are below. The thyratron noise was reduced by contacting between the ground of the CT case and the outer surface of a CT signal cable. The ringing signal was suppressed by intercalating dumping resistance material into the space between the case and the ferrite core of CT. We think that the undulation of ground level could be common mode noise and devised how to modulate the undulation. In this paper, we introduce the improvement points, and the obtained waveform of the CT signal as result.
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| FRAAU04 | Re-Commissioning of the Far-Infrared Free Electron Laser for Stable and High Power Operation after the Renewal of the L-Band Linac at ISIR, Osaka University | linac, wiggler, electron, controls | 521 | |||||
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We have been developing a far-infrared FEL since late 1980s based on the 40 MeV, L-band electron linac at the Institute of Scientific and Industrial Research (ISIR), Osaka University. The first lasing was obtained at 32~40 um in 1994 and since then we progressively modified the FEL system and continued experiment in between to expand the wavelength region toward the longer wavelength. We finally obtained lasing at 150 um in 1998. We could not obtain power saturation because the macropulse duration is 2 us, though the RF pulse is 4 us long, due to a long filling time of the acceleration tube of the L-band linac and the number of amplification times is limited to 50 only. The linac was constructed approximately 30 years ago and it was not suitable for stable and high power operation of FEL, so that we suspended the development of the FEL. In 2002, we had an opportunity to remodel the linac largely for higher stability and reproducibility of operation. We also added a new operation mode for FEL in which the macropulse duration can be extended to 8 us. I took time to remodel the linac and commission it, but finally the operation mode for FEL is being commissioned and we are resuming the FEL again after the long suspension. We will report the progress and the current status of the re-commissioning of the FEL.
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Slides
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