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| TUPPH002 | Development of Frequency-Resolved Optical Gating for Measurement of Correlation between Time and Frequency of Chirped FEL | 308 |
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| A femtosecond infrared-chirped FEL is an effective way of dissociating molecules without the intramolecular vibrational redistribution. At Japan Atomic Energy Agency (JAEA), an energy recovery linac (ERL) has been investigated to produce high power FEL at far-infrared region. Normally the long-pulse electron beam is operated by the ERL; therefore the high-power chirped pulse can be generated. Until now, the amount of chirp in the pulse was measured to be f/f0 = 14% with the wavelength of 23 μm and the pulse width of 320 fs at FWHM. However the correlation between time and frequency in the chirped pulse was not measured. In order to measure the correlation between time and frequency in the chirped pulse directly, we have started to construct an FEL transport system and the frequency-resolved optical grating in new experimental room. The chirped pulse is guided to the experimental room by a 22-m vacuum duct which avoids the absorption of infrared radiation by water vapor. The optical focusing systems are located at the entrance and exit of the vacuum duct. Now we are measuring basic parameters of the chirped pulse (beam size, power and so on) in the experimental room. | ||
| TUPPH005 | Beam Current Doubling of JAEA ERL-FEL | 312 |
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| An energy-recovery linac (ERL) for a high-power free-electron laser (FEL) R&D program is in progress at Japan Atomic Energy Agency (JAEA). The first energy-recovery operation and FEL lasing was demonstrated in 2002 by remodeling the original superconducting linac. In the first demonstration, the accelerated beam current was same as the original linac. One of the benefits of the ERL is that the accelerating beam current can be easily increase by changing micro-pulse repetition rate without increasing the main linac RF source. After the first demonstration, the e-gun, the injector RF source, the low-level RF controller, and the operation system were improved for the beam current doubling. The doubled beam acceleration and FEL lasing have been successfully achieved with 10mA of beam current and 0.7kW of FEL power. | ||
| TUPPH006 | Performance of a Conventional Analog Phi-A Type Low-Level RF Controller | 316 |
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| For an FEL application and an ERL light source, high-stability of accelerator RF amplitude and phase is required. A low-level RF controller (LLC) of the JAEA-ERL has been improved to ensure high-stability accelerating RF field. The LLC is a conventional analog phi-A type controller with following functions: the feedback gain, loop-offset phase and time constant can be varied during operation to obtain optimum parameters for the high-stability RF field, all the circuits are contained in a temperature controlled oven. The LLC performance is tested for a 499.8MHz superconducting cavity and a 1300MHz copper cavity. The phase and amplitude stabilities of the 499.8MHz superconducting cavity within a 1ms macro-pulse are 0.0055deg-rms and 7.64×10-5, respectively. For the 1300MHz copper cavity, pulse mode and CW mode were tested. In the case of pulse mode, the phase and amplitude stabilities are 0.011deg-rms and 7.64×10-5, respectively. In the case of CW mode, the phase and amplitude stabilities are 0.011deg-rms and 6.68×10-5, respectively. | ||
| TUPPH007 | JAEA Photocathode DC-Gun for an ERL Injector | 319 |
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| ERL light source and FEL require an electron beam of large current and small emittance. In order to realize an electron gun satisfying such requirements, we started developments of a photocathode DC-gun and a new-type NEA-photocathode. The DC-gun consists of a chamber to activate NEA-surface, a 250keV acceleration chamber, and a mode-locked Ti:Sapphire laser. Since extreme high vacuum is essential to obtain a long-life photocathode, we adopt a load-lock system for transporting a photocathode between the chambers, each of which is equipped with an NEG pump. Up to now, we fabricated an electrodes chamber and a high voltage terminal of 250kV and we succeeded in a 250kV high voltage test. We also have suggested a superlattice photocathode as a new-type photocathode with higher performance than an existing technology. Up to now, we fabricated photocathode samples by molecular beam epitaxy and measured quantum efficiency after NEA-surface activation. | ||
| MOPPH032 | Analysis of FEL Oscillations in a Perfectly Synchronized Optical Cavity | 107 |
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We analyze free electron laser (FEL) oscillations in a perfectly synchronized optical cavity by solving the one dimensional FEL equations. The radiation stored in the cavity is shown to finally evolve into an intense few-cycle optical pulse in the high gain and low loss regime. The evolution of the leading slope of the optical pulse, which is defined from the front edge toward the primary peak, is found to play an important role in generating the intense few-cycle pulse. The phase space evolution of electrons on the second pass which interact with the leading slope of a SASE output pulse is obtained in a perturbation method similar to that used in our previous study for a SASE FEL*. The resulting analytical solution of the leading slope in the 2nd pass is shown to be approximated by that of a SASE FEL with FEL parameter greater than rho. The same perturbation method can thus be used to the subsequent passes. The peak amplitude and the pulse length at saturation are found to scale with the electron beam density and optical cavity loss. Those scalings accounts for the intense few-cycle FEL pulses observed in a high power FEL.
* N. Nishimori, Phys. Rev. ST-AB 8, 100701 (2005). |
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| TUAAU03 | FEL Oscillation with a High Extraction Efficiency at JAEA ERL FEL | 265 |
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One of challenges that high power FEL oscillators with energy recovery linac (ERL) are facing is to increase the extraction FEL efficiency as high as possible. The high efficiency oscillation relaxes the total beam current needed for high power lasing and makes the FEL optical pulse length shorter, which is useful for various applications. A Bates type recovery loop with energy acceptance well in excess of 10% allows an ERL FEL at Jefferson Lab to operate with a high FEL efficiency*. A triple bend achromat loop with energy acceptance of 7% has been used in an ERL FEL at Japan Atomic Energy Agency (JAEA)**. Recently we have achieved the efficiency exceeding 2%, which accompanies large energy spread beyond the energy acceptance of the loop, by doubling the electron bunch repetition rate***. The optical pulse can now interact with a fresh electron bunch every round trip, while it overlapped with an injected electron every two round trips before the doubling of the bunch repetition. This talk will summarize our recent development of a high power FEL with a high extraction efficiency at JAEA ERL FEL.
* S. Benson et al., in proceedings of the FEL2004, (2004) 229. ** R. Hajima et al., Nucl. Instr. and Meth. A445 (2000) 384. *** R. Nagai et al., in these proceedings. |
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