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TUP001 | THz Photo-Injector FEM Based on Spontaneous Coherent Emission from a Bunch of Negative-Mass Electrons | 317 |
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The use of short dense electron bunches produced form a photo-injector gun is attractive for realization of a THz FEL based on spontaneous coherent emission from such bunches. This type of emission is realized, when the axial length of bunches is shorter that the wavelength of the radiated wave. Therefore, the length of the operating region of such a FEL is strictly limited by degradation (an increase in the axial size) of the e-bunch caused by both the Coulomb repulsion and the velocity spread. The use of the regime of the 'negative mass' can be a way to provide stabilization of the axial size of e-bunches. Such a regime is realized in a magnetostatic undulator with a guiding homogeneous axial magnetic field. If the electron cyclotron frequency (corresponding to the guiding magnetic field) exceeds the bounce-frequency of electron oscillations in the periodic undulator field, then the abnormal dependence of the axial velocity of electrons on their energy takes place (an increase in the energy leads to a decrease in the axial velocity). In such regime, axial Coulomb repulsion of the electrons leads to their mutual attraction which slows down bunch degradation. The use of this regime results in a substantial increase in the length of the spontaneous coherent emission, and, therefore, in an increase in both the duration and the power of the output radiation pulse.
The work was supported by the Russian Scientific Foundation (RSCF), Project no. 14-19-01723 |
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TUP002 | Further Studies of Undulator Tapering in X-Ray FELs | 321 |
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We further the studies of the model-based optimization of tapered free-electron lasers presented in a recent publication [Phys. Rev. ST Accel. Beams 18, 040702 (2015)]. Departing from the ideal case, wherein the taper profile is a smooth and continuous function, we consider the more realistic case, with individual undulator segments separated by break sections. Using the simulation code GENESIS, we apply our taper optimization method to a case, which closely resembles the FLASH2 facility in Hamburg, Germany. By comparing steady-state and time-dependent simulations, we examine how time-dependent effects alter the optimal taper scenario. From the simulation results, we also deduce that the "traditional" empirical method, whereby the intermediate radiation power is maximized after closing every undulator gap, does not necessarily produce the highest final power at the exit of the undulator line. | ||
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TUP003 | Threshold of a Mirror-less Photonic Free Electron Laser Oscillator Pumped by One or More Electron Beams | 327 |
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Funding: This research is supported by the Dutch Technology Foundation STW, which is part of the Netherlands Organisation for Scientific Research, and which is partly funded by the Ministry of Economic Affairs Transmitting electrons through a photonic crystal can result in stimulated emission and the generation of coherent Cerenkov radiation. Here we consider a photonic-crystal slab consisting of a two-dimensional, periodic array of bars inside a rectangular waveguide. By appropriately tapering the bars at both ends of the slab, we numerically show that an electromagnetic wave can be transmitted through the waveguide filled with the photonic-crystal slab with close to zero reflection. Furthermore, the photonic-crystal slab allows transmission of electrons in the form of one or more beams. By appropriately designing the photonic-crystal slab, we obtain a backward wave interaction at low electron-beam energy of around 15 kV, that results in distributed feedback of the radiation on the electrons without any external mirrors being present. Here we discuss the dynamics of the laser oscillator near threshold and numerically show that the threshold current can be distributed over multiple electron beams, resulting in a lower current per beam. |
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TUP004 | Three-dimensional, Time-dependent Simulation of Free-Electron Lasers | 331 |
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Minerva is a simulation code that models the interaction of electrons with an optical field inside an undulator. Minerva uses a modal expansion for the optical field and the full Newton-Lorentz force equation to track the particles through the optical and magnetic fields. To allow propagation of the optical field outside the undulator and interact with optical elements, MINERVA interfaces with the optical propagation code OPC to mode, for example, FEL oscillators. As there exists a large variety of FELs ranging from long-wavelength oscillators to soft and hard X-ray FELs that are either seeded or starting from noise, a simulation code, such as Minerva, should be capable of modelling this huge variety of FEL configurations. Here we present a validation of the Minerva code against experimental data for various FEL configurations, ranging from long wavelength FEL oscillators to hard X-ray SASE FEL. | ||
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TUP005 | A Mirror-Less, Multi-Beam Photonic Free-Electron Laser Oscillator Pumped Far Beyond Threshold | 334 |
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Funding: This research is supported by the Dutch Technology Foundation STW, which is part of the Netherlands Organisation for Scientific Research, and which is partly funded by the Ministry of Economic Affairs In a photonic free-electron laser electrons are transmitted through a photonic crystal in the form of one or multiple electron beams to generate coherent Cerenkov radiation. Here we consider a photonic-crystal slab consisting of a two-dimensional, periodic array of bars inside a rectangular waveguide, with both ends tapered to provide complete transmission of an electromagnetic wave. By appropriately designing the photonic-crystal slab, we obtain a backward wave interaction at low electron beam energy of around 15 kV, that results in distributed feedback of the radiation on the electrons without any external mirrors being present. Here we numerically study the dynamics of the laser oscillator when pumped far beyond threshold with one or multiple electron beams. We show that using multiple beams with the same total current provide better suppression of higher-order modes and can produce more output power, compared to the laser pumped by a single beam of the same total current. |
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TUP006 | Quantum Nature of Electrons in Classical X-ray FELs | 338 |
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X-ray FELs built to date are well described by the classical theory. This theory in its simplest form is expressed as a system of pendulum equations for electrons coupled to the electromagnetic field. The FEL interaction requires bunching of the electrons on a scale less than radiation wavelength. The progress in the development of FELs and the need to reach even shorter laser radiation wavelength with low energy electrons require that the quantum characteristic of the FEL interaction to be properly considered. Quantum theories have been already proposed by a number of authors. These theories, however, have been developed for regimes that are not relevant for modern/planned X-ray FELs. Here, we focus on quantum effects in modern/future X-ray FELs and stop treating an electron as a point-particle. This results in quantum reduction of the bunching! Starting with the analysis of the free space dispersion for the electron wave packet, we will present a modified 1D FEL theory that takes into account the quantum uncertainty of the electron position in X-ray FELs. This theory allows for a unified classification of FELs with respect to the wave nature of an electron that shows a planned FEL at Los Alamos National Lab to be most affected. The Genesis simulation code has been modified in order to include quantum reduction of the bunching that lead to interesting results. LA-UR-15-26276 | ||
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TUP007 | High Fidelity Start-to-end Numerical Particle Simulations and Performance Studies for LCLS-II | 342 |
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High fidelity numerical particle simulations that leverage a number of accelerator and FEL codes have been used to analyze the LCLS-II FEL performance. Together, the physics models that are included in these codes have been crucial in identifying, understanding, and mitigating a number of potential hazards that can adversely affect the FEL performance, some of which are discussed in papers submitted to this conference[*, **]. Here, we present a broad overview of the LCLS-II FEL performance, based on these start-to-end simulations, for both the soft X-ray and hard X-ray undulators including both SASE and self-seeded operational modes.
* M. Venturini, et al., The microbunching instability and LCLS-II lattice design: lessons learned, FEL'15 ** Z. Zhang, et al., Microbunching-induced sidebands in a seeded free-electron laser, FEL'15 |
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TUP008 | High-Gain FEL in the Space-Charge Dominated Raman Limit | 347 |
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While FEL technology has reached the EUV and X-ray regime at existing machines such as LCLS and SACLA, the scale of these projects is often impractical for research and industrial applications. Sub-millimeter period undulators can reduce the size of a high-gain EUV FEL, but will impose stringent conditions on the electron beam. In particular, a high-gain EUV FEL based on undulators with a sub-millimeter period will require electron beam currents upwards of 1 kA at energies below 100 MeV. Coupled with the small gap of such undulators and their low undulator strengths, K < 0.1, these beam parameters bring longitudinal space-charge effects to the foreground of the FEL process. When the wavelength of plasma oscillations in the electron beam becomes comparable to the gain-length, the 1D theoretical FEL model transitions from the Compton to the Raman limit. In this work, we investigate the behavior of the FEL's gain-length and efficiency in these two limits. The starting point for the analysis was the one-dimensional FEL theory including space-charge forces. The derived results were compared to numerical results of Genesis 1.3 simulations. This theoretical model predicts that in the Raman limit, the gain-length scales as the beam current to the -1/4th power while the efficiency plateaus to a constant. | ||
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TUP009 | Coherent Thomson Scattering Using the PEHG | 351 |
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Electron beam is density modulated by the phase-merging effect to obtain ultra-short longitudinal structures in the phase space. Coherent radiations are then generated by the coherent Thomson scattering between the phase-merged beam and a long wavelength laser pulse. | ||
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TUP010 | Recent Progress in Upgrade of the High-Intensity THz-FEL at Osaka University | 354 |
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We are upgrading the THz-FEL at Osaka University for its applications to high intensity THz sciences, which originally generated the high intensity FEL with the macropulse energy up to 3.7 mJ and the micropulse energy up to ~10 uJ at a wavelength around 70 um. To increase the micropulse energy, charge in electron bunches is increased four time higher and the bunch intervals are expanded four times longer to maintain the average current in the linac unchanged. In the new operation mode, the macropulse energy increases up to 26 mJ and the micropulse energy to ~0.2 mJ, which is 20 times higher than the energy previously obtained in the conventional mode. We have developed a solid-state switch for the klystron modulator to highly stabilize the klystron voltage, so that the output power of the FEL becomes stable. We are conducting basic studies on FEL for further improvement of its performance, including measurement of power evolution from start-up to saturation, time structures of FEL micropulses measured with a Michelson interferometer, and time structures of macropulses measured with a Schottky diode detector. We will report results of these studies on the THz-FEL at Osaka University. | ||
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TUP011 | Performance and Tolerance Studies of the X-Ray Production for the X-Band FEL Collaboration | 359 |
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The X-band FEL collaboration is currently designing an X-ray free-electron laser based on X-band acceleration technology. This paper reports on the recent progress on the design of the undulator part of this machine including simulations of the X-ray production process. The basic parameters have been chosen and a beam transport system has been designed, considering strong and weak focusing of quadrupole and undulator magnets. Simulations of the X-ray production process have been carried out with realistic input beam distributions from particle tracking studies of the linac design team. The expectable X-ray properties for SASE and seeded FEL operation have been investigated and also undulator taper options have been studied. | ||
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TUP012 | Plans for an EEHG-based Short-Pulse Facility at the DELTA Storage Ring | 363 |
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Funding: Work supported by DFG, BMBF, FZ Jülich, and by the Federal State NRW. The 1.5-GeV synchrotron light source DELTA, operated by the TU Dortmund University, comprises a short-pulse facility based on the coherent harmonic generation (CHG) technique, which allows for the generation of radiation pulses with wavelengths down to 50 nm and a duration of 50 fs. In order to reach even shorter wavelengths, the present setup will be modified to employ the echo-enabled harmonic generation (EEHG) and femtoslicing techniques. In this paper, recent developments including an improved lattice design and a concept for the new vacuum chambers will be presented. |
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TUP013 | The X-Band FEL Collaboration | 368 |
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The X-band FEL collaboration is currently designing an X-ray free-electron laser based on X-band acceleration technology. Due to the higher accelerating gradients achievable with X-band technology, a X-band normal conducting linac can be shorter and therefore potentially cost efficient than what is achievable with lower frequency structures. This cost reduction of future FEL facilities addresses the growing demand of the user community for coherent X-rays. The X-band FEL collaboration consists of 12 institutes and universities that jointly work on the preparation of design reports for the specific FEL projects. In this paper, we report on the on-going activities, the basic parameter choice, and the integrated simulation results. We also outline the interest of the X-band FEL collaboration to use the electron linac CALIFES at CERN to test FEL concepts and technologies relevant for the X-band FEL collaboration. | ||
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TUP014 | Beam Commissioning and Initial Measurements on the MAX IV 3 GeV Linac | 375 |
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The linear accelerator at the MAX IV facility in Lund, Sweden, was constructed for injection and top up of the two storage rings and as a high brightness driver for the Short Pulse Facility. It is also prepared to be used as an injector for a possible future Free Electron Laser. Installation of the linac was completed and beam commissioning started in the early fall of 2014. In this paper we present the progress during the first phase of commissioning along with results from initial measurements of optics, emittance, beam energy and charge. | ||
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TUP015 | Status of the ALICE IR-FEL: from ERL Demonstrator to User Facility | 379 |
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The ALICE (Accelerators and Lasers In Combined Experiments) accelerator at STFC Daresbury Laboratory in the UK was conceived in 2003 and constructed as a short-term Energy Recovery Linac demonstrator to develop the underpinning technology and expertise required for a proposed 600MeV ERL-based FEL facility. In this paper we present an update on the performance and status of ALICE which now operates as a funded IR-FEL user facility. We discuss the challenges of evolving a short-term demonstrator into a stable, reliable user facility and present a summary of the current scientific programme. | ||
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TUP017 | HPC Simulation Suite for Future FELs | 384 |
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A new HPC simulation suite, intended to aid in both the investigation of novel FEL physics and the design of new FEL facilities, is described. The integrated start-to-end suite, currently under development, incorporates both plasma (VSim) and linac (ELEGANT, ASTRA) accelerator codes, and will include the 3D unaveraged FEL code Puffin to probe novel FEL effects. | ||
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TUP019 | Time Locking Options for the Soft X-Ray Beamline of SwissFEL | 388 |
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SwissFEL is an FEL facility presently under construction at the Paul Scherrer institute that will serve two beamlines: Aramis, a hard X-ray beamline which is in construction phase and will provide FEL radiation in 2017 with a wavelength between 0.1 and 0.7 nm; and Athos, a soft X-ray beamline which is in design phase and it is expected to offer FEL light in 2021 for radiation wavelengths between 0.7 and 7 nm. A passive synchronization of the FEL signal to a laser source is fundamental for key experiments at Athos, such as the time-resolved resonant inelastic X-ray scattering (RIXS) experiments. In this paper we explore different options to achieve this time synchronization by means of energy modulating the electron beam with an external laser. | ||
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TUP020 | Recent Study in iSASE | 393 |
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The Improved Self-Amplified Spontaneous Radiation (iSASE) scheme has potential to reduce SASE FEL bandwidth. This is achieved by repeatedly delaying the electrons with respect to the radiation pulse using phase shifters in the undulator break sections. It has been shown that the strength, locations and sequences of phase shifters are important to the iSASE performance. Particle swarm optimization algorithm is used to explore the phase shifters configuration space globally. | ||
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TUP021 | Fundamental Limitations of the SASE FEL Photon Beam Pointing Stability | 397 |
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The radiation from SASE FEL has always limited value of the degree of transverse coherence. Two effects define the spatial coherence of the radiation: the mode competition effect, and the effect of poor longitudinal coherence. For the diffraction limited case we deal mainly with the effect of the poor longitudinal coherence leading to significant degradation of the spatial coherence in the post-saturation regime. When transverse size of the electron beam significantly exceeds diffraction limit, the mode competition effect does not provide the selection of the fundamental FEL mode, and spatial coherence degrades due to contribution of the higher azimuthal modes. Another consequence of this effect are fluctuations of the spot size and pointing stability of the photon beam. These fluctuations are fundamental and originate from the shot noise in the electron beam. The effect of pointing instability becomes more pronouncing for shorter wavelengths. Our study is devoted to the fundamental analysis of the effect and description of possible means for improving the degree of transverse coherence and the pointing stability. | ||
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TUP022 | Measurement of Spatial Displacement of X-rays in Crystals for Self-Seeding Applications | 405 |
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Free-electron laser (FEL) radiation arises from shot noise in the electron bunch, which is amplified along the undulator section and results in X-ray pulses consisting of many longitudinal modes [1]. The output bandwidth of FELs can be decreased by seeding the FEL process with longitudinally coherent radiation. In the hard x-ray region, there are no suitable external sources. This obstacle can be overcome by self-seeding. The X-ray beam is separated from the electrons using a magnetic chicane, and then monochromatized. The monochromatized X-rays serve as a narrowband seed, after recombination with the electron bunch, along the downstream undulators. This scheme generates longitudinally coherent FEL pulses.[2] have proposed monochromatization based on Forward Bragg Diffraction (FBD), which introduces a delay of the narrowband X-rays pulse of the order of femtoseconds that can be matched to the delay of the electron bunch due to the chicane. Unfortunately, the FBD process produces a small transverse displacement of the X-ray beam, which results in the loss of efficiency of the seeding process [3]. Preliminary results from an experiment performed at Cornell High Energy Synchrotron Source seem to confirm the predicted transverse displacement, which is therefore to be taken into account in the design of self-seeding infrastructure for optimizing the FEL performance.
[1] J.S. Wark et al., J. Apply. Crystallogr. 32, 692 (1999) [2] G. Geloni et al., DESY report 10-053 (2010). [3] Y. Shvyd'ko et al., Phys. Rev. ST Accel. Beams 15, 100702 (2012) |
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Poster TUP022 [5.503 MB] | |
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TUP023 | A Modified Self-Seeded X-ray FEL Scheme Towards Shorter Wavelengths | 409 |
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We present a modified self-seeded FEL scheme for harmonic generation. Different from classical HGHG scheme whose seed laser is a conventional laser with longer wavelength, this scheme first uses a regular self-seeding monochromator to generate a seed laser, followed by a HGHG configuration to produce shorter-wavelength radiations. As an example, we perform start-to-end simulations to demonstrate the second and third harmonic FELs from a soft x-ray self-seeding case at the fundumental wavelength of 1.72 nm. The harmonic performance results will be discussed. | ||
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TUP025 | Studies of Undulator Tapering for the CLARA FEL | 412 |
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Undulator tapering is a well-known method for enhancing the performance of free-electron lasers [1]. It works by keeping the resonant wavelength constant, despite variation in the electron beam energy. Both the energy-extraction efficiency and the spectral brightness of the FEL can be improved using this technique. In this paper we present recent studies of undulator tapering for the CLARA FEL in both SASE and seeded modes. The methods used to optimise the taper profile are described, and the properties of the final FEL pulses are compared.
[1] N.M. Kroll, P.L. Morton, M.N. Rosenbluth, J. Quantum Electronics 17, 8 (1981). |
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Poster TUP025 [0.919 MB] | |
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TUP026 | Measurment Uncertainties in Gas-Based Monitors for High Repetition Rate X-Ray FEL Operations | 417 |
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Funding: Portions of this research were carried out at the LCLS at the SLAC National Accelerator Laboratory. LCLS is an User Facility operated for the US DOE Office of Science by Stanford University. Thermodynamic simulations using a finite difference method were carried out to investigate the measurement uncertainties in gas-based X-ray FEL diagnostic monitors under high repetition rate operations such as planned for the future LCLS-II soft and hard X-ray FEL's. For monitors using relatively high gas pressures for obtaining sufficient signals, the absorbed thermal power becomes non-negligible as repetition rate increases while keeping pulse energy constant. The fluctuations in the absorbed power were shown to induce significant measurements uncertainties, especially in the single-pulse mode. The magnitude of this thermal effect depends nonlinearly on the absorbed power and can be minimized by using a more efficient detection scheme in which the gas pressure can be set sufficiently low |
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TUP027 | Facility Upgrades for the High Harmonic Echo Program at SLAC's NLCTA | 422 |
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The Echo program currently underway at SLAC's NLCTA test accelerator aims to use Echo-Enabled Harmonic Generation (EEHG) to produce considerable bunching in the electron beam at high harmonics of a 2.4um seed laser. The production of such high harmonics in the EUV wavelength range necessitates an efficient radiator and associated light diagnostics to accurately characterize and tune the echo effect. We have installed and commissioned the Visible to Infrared SASE Amplifier (VISA) undulator, a strong focusing two meter long planar undulator of Halbach array design with 1.8cm period length. To characterize the output radiation, we have designed, built, and calibrated a grazing incidence EUV spectrometer which operates between 12-120nm with resolution sufficient to resolve individual harmonics. An absolute wavelength calibration is achieved by using both EEHG and High Gain Harmonic Generation (HGHG) signals from the undulator. | ||
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TUP028 | DESIGN OF THE MID-INFRARED FEL OSCILLATOR IN CHINA | 427 |
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In 2014, Xiamen University and other three research organizations received the approval to realize an infrared free electron laser (IR-FEL) for fundamental of energy chemistry. The IR-FEL covers the spectral range of 2.5-200 μm and will be built in NSRL. Two FEL oscillators driven by one Linac will be used to generate mid- infrared and far-infrared lasers. In this article we describe the design studies for the mid-infrared FEL oscillator. | ||
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TUP029 | Single Picosecond THz Pulse Extraction from the FEL Macropulse using a Laser Activating Semiconductor Reflective Switch | 430 |
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The THz-FEL at the Institute of Scientific and Industrial Research, Osaka University can generate high-intensity THz pulses or FEL macropulses, which comprise approximately 100 micropulses at 37 ns intervals in the 27 MHz mode or 400 micropulses at 9.2 ns intervals in the 108 MHz mode. The maximum macropulse energy in the 27 MHz mode reaches 26 mJ at a frequency of 4.5 THz and the micropulse energy is estimated to be 0.2 mJ. To open new areas of studies with high intensity THz radiation for user experiments, we are developing a single pulse extraction system from the pulse train using a laser activating semiconductor reflective switch. We have succeeded in extracting a single THz pulse, duration of which is estimated to be less than 20 ps, from the FEL macropulse using a gallium arsenide wafer for the switch. We will report on the THz pulse extraction system and its performance. | ||
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TUP030 | Time Dependent Study for an X-ray FEL Oscillator at LCLS-II | 433 |
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The LCLS-II with its high repetition rate and high quality beam will be capable of driving an X-ray free electron laser oscillator at higher harmonics in the hard X-ray regime (0.1 nm). The oscillator consists of a low loss X-ray crystal cavity using diamond Bragg crystals with meV bandwidth. The expected average spectral flux has been estimated to be at least two orders of magnitude greater than present synchrotron-based sources with highly stable, coherent pulses of duration 1 ps or less for applications in Mössbauer spectroscopy and inelastic x-ray scattering. A more detailed study of the start up of a fifth-harmonic X-ray FEL oscillator at LCLS-II will be presented with full, time-dependent simulations. | ||
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Poster TUP030 [0.619 MB] | |
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TUP032 | Numerical Studies of the Influence of the Electron Bunch Arrival Time Jitter on the Gain Process of an XFEL-Oscillator for the European XFEL | 436 |
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The superconducting linac of the European XFEL Laboratory in Hamburg will produce electron bunch trains with a time structure that allow in principle the operation of an XFELO (X-ray FEL-Oscillator). The electron bunches of the European XFEL have an expected length between 2 and 180 fs (FWHM) with an expected arrival time jitter of about 30 fs (RMS). A jitter of the electron bunch arrival time leads to a detuning between the electron and photon pulse. Since an XFEL-Oscillator relies on a spatial overlap of electron and photon pulse, the influence of a lack of longitudinal overlap is studied. The simulations are performed for different bunch lengths and levels of arrival time jitter. The results of a simulation are presented where angular, transversal and arrival time jitter are taken into account simultaneously, assuming parameters expected for the European XFEL Linac. | ||
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TUP034 | New Ellipsoidal Photocathode Laser Pulses at the Upgraded PITZ Facility | 439 |
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High brightness electron sources for free electron lasers like FLASH and the European XFEL are developed, optimized and characterized at the Photo Injector Test facility at DESY in Zeuthen (PITZ). Last year the facility was significantly upgraded with a new prototype photocathode laser capable of producing homogeneous ellipsoidal pulses. Previous simulations have shown that the corresponding pulses produce high brightness electron bunches with minimized emittance. Furthermore, a new normal conducting RF gun cavity was installed with a modified two-window waveguide RF feed layout for stability and reliability tests, as required for the European XFEL. Other relevant additions to the facility include beamline modifications for improved electron beam transport through the PITZ accelerator, refinement of both the cooling and RF systems for improved parameter stability, and preparations for the installation of a plasma cell. This paper describes the facility upgrades and reports on the operational experience with the new components. | ||
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Poster TUP034 [1.211 MB] | |
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TUP035 | Operation of a Slit Emittance Meter in the MAX IV Gun Test Stand | 444 |
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The MAX IV facility in Lund, Sweden is currently under commissioning. There are two guns in the current MAX IV injector, one thermionic gun for storage ring injection and one photocathode gun for the Short Pulse Facility. There is a possibility of extending the facility to include a Free Electron Laser. To investigate how the beam from the injector can be improved and how to match it to the future requirements for a FEL, the emittance meter from SPARC has been recommissioned at the MAX IV gun test stand. In this paper we report on the progress of this work and results from the first measurements. | ||
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TUP036 | Initial Commissioning Results of the MAX IV Injector | 448 |
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The MAX IV facility in Lund, Sweden is currently under commissioning. In the MAX IV injector there are two guns, one thermionic gun for storage ring injection and one photocathode gun for the Short Pulse Facility. The commissioning of the injector and the LINAC has been ongoing for the last year and ring commissioning is due to start shortly. In this paper we will present the results from beam performance experiments for the injector at the current stage of commissioning. | ||
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TUP038 | Construction of the EU-XFEL Laser Heater | 452 |
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Funding: We thank the Swedish research council under Project number DNR-828-2008-1093 for financial support. Installation of the laser heater for the EU-XFEL is completed and first commissioning runs are imminent. We discuss the installation of the key elements and provide an outlook of the commissioning phase. |
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TUP040 | Simulation and Design of Low Emittance RF Electron Gun | 455 |
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Funding: This work has been supported by the CMU Junior Research Fellowship Program and the Department of Physics and Materials Science, Faculty of Science, Chiang Mai University. Generation of high-brightness electron beam is one of the most critical issues in development of advanced electron accelerators and light sources. At the Plasma and Beam Physics (PBP) Research Facility, Chiang Mai University, a low emittance RF electron gun is under the development. This RF-gun is planned to be used as an electron source for a future IR/THz FEL facility. An extra resonant cavity is added to the modified design of the existing PBP-CMU RF-gun in order to reduce the transverse sliced emittance. This cell is coupled to the main full-cell via a side-coupling cavity. The electromagnetic field distributions inside the cavities are simulated by using the CST Microwave Studio 2012. Then, beam dynamic simulations utilizing the program PARMELA are performed. Both RF and beam dynamic simulation results are reported and discussed in this contribution. The authors would like to acknowledge the financial support to participate this conference by the Department of Physics and Materials Science and the Graduate School, Chiang Mai University. |
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Poster TUP040 [2.140 MB] | |
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TUP041 | Simultaneous Operation of Three Laser Systems at the FLASH Photoinjector | 459 |
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The free-electron laser facility FLASH at DESY (Hamburg, Germany) operates two undulator beamlines simultaneously. Both undulator beamlines are driven by a common linear superconducting accelerator with a beam energy of up to 1.25 GeV. The superconducting technology allows the acceleration of trains of several hundred microsecond spaced bunches with a repetition rate of 10 Hz. A fast kickers-septum system is installed to distribute one part of the electron bunch train to FLASH1 and the other part to FLASH2 keeping the full 10 Hz repetition rate for both beamlines. In order to deliver different beam properties to each beamline, the FLASH photoinjector uses two independent laser systems to generate different bunch pattern and bunch charges. One laser serves the FLASH1 beamline, the other the FLASH2 beamline. A third laser with adjus ö laser pulse duration is used to generate ultra-short bunches for single spike lasing. | ||
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TUP042 | Lifetime of Cs2Te Cathodes Operated at the FLASH Facility | 464 |
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The injector of the free-electron laser facility FLASH at DESY (Hamburg, Germany) uses Cs2Te photocathodes. We report on the lifetime, quantum efficiency (QE), and darkcurrent of photocathodes operated at FLASH during the last year. Cathode 618.3 has been operated for a record of 439 days with a stable QE in the order of 3%. The fresh cathode 73.3 shows an enhancement of emitted electrons for a few microseconds of a 1 MHz pulse train. | ||
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TUP043 | PAL-XFEL Cavity BPM Prototype Beam Test at ITF | 468 |
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To achieve sub-micrometer resolution, PAL-XFEL undulator section will use X-band Cavity beam position monitor (BPM) systems. The prototype cavity BPM pick-up was designed and fabricated to test the performance of the cavity BPM system. The fabricated prototype cavity BPM pick-up was installed at Pohang Accelerator Laboratory injector test facility (PAL ITF) for the beam test. Under 200 pC beam charge condition, the signal properties of the cavity BPM pick-up were measured. Also, the dynamic range of the cavity BPM pick-up was measured by using the corrector magnet. In this paper, the design and beam test results of the prototype cavity BPM pick-up will be discussed. | ||
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Poster TUP043 [0.695 MB] | |
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TUP044 | Spark EL - Single Pass BPM | 471 |
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Monitoring and subsequent optimization of the electron linacs and beam transfers requires specific instrumentation for beam position data acquisition and processing. Spark EL is the newly developed prototype intended for position monitoring in single or multi bunch operation linacs and transfer lines. The motivation, processing principles and first results are presented. | ||
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TUP045 | MTCA.4 Phase Detector for Femtosecond-Precision Laser Synchronization | 474 |
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For time-resolved experiments at FELs such as the European XFEL an accurate synchronization of the machine is essential. The required femtosecond- level synchronization we plan to achieve with an optical synchronization system, in which an inherent part is the master laser oscillator (MLO) locked to the electrical reference. At DESY we develop a custom rear transition module in MTCA.4 standard, which will allow for different techniques of phase detection between the optical and the electrical signal, as well as locking to an optical reference using a cross-correlator. In this paper we present the current status of the development, including two basic solutions for the detection to an RF. One of the methods incorporates an external drift free detector based on the so-called MZI setup. The other one employs the currently used downconverter scheme with subsequent improvements. The module can serve for locking a variety of lasers with different repetition rates. | ||
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Poster TUP045 [4.010 MB] | |
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TUP049 | Prototype of the Improved Electro-Optical Unit for the Bunch Arrival Time Monitors at FLASH and the European XFEL | 478 |
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At today's free-electron lasers, high-resolution electron bunch arrival time measurements have become increasingly more important in fast feedback systems providing accurate timing stability for time-resolved pump-probe experiments and seeding schemes. At FLASH and the upcoming European XFEL a reliable and precise arrival time detection down to the femtosecond level has to cover a broad range of bunch charges, which may even change from 1 nC down to 20 pC within a bunch train. This is fulfilled by arrival time monitors which employ an electro-optical detection scheme by means of synchronised ultra-short laser pulses. At both facilities, the new bunch arrival time monitor has to cope with the special operation mode where the MHz repetition rate bunch train is separated into several segments for different SASE beam lines. Each of the segments will exhibit individual timing jitter characteristics since they are generated from different injector lasers and can be accelerated with individual energy gain settings. In this paper, we describe the recent improvements of the electro-optical unit developed for the bunch arrival time monitors to be installed in both facilities. | ||
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TUP050 | Extension of Existing Pulse Analysis Methods to High-Repetition Rate Operation: Studies of the "Time-Stretch Strategy" | 483 |
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Funding: ANR (2010-042301, DYNACO), LABEX CEMPI project (ANR-11-LABX-0007), ERC grant COXINEL (340015), GENCI TGCC/IDRIS (x2014057057,i2015057057). Many single-shot recording setups are based on the encoding of the information onto a laser pulse. This concerns in particular electro-optic sampling of bunch shapes, and VUV/X pulse monitors using transient reflectivity. The upgrade of these methods to high repetition rates presents challenging issues, that are due to the limited speed of the recording cameras. Recently [1], we demonstrated that multi-MHz repetition rates can be achieved using a relatively simple upgrade of existing setups, using the so-called "photonic time-stretch" technique. Here we present guidelines for the practical realization in the case of electro-optic sampling. We also present a performance analysis, and compare it to the spectral encoding case. The technique is potentially applicable to other cases where the information can be encoded on a chirped laser pulse, as, e.g., transient reflectivity diagnostics of XUV pulses. [1] Observing microscopic structures of a relativistic object using a time-stretch strategy, E. Roussel, C. Evain, M. Le Parquier, C. Szwaj, S. Bielawski, L. Manceron, J.-B. Brubach, M.-A. Tordeux, J.-P. Ricaud, L. Cassinari, M. Labat, M.-E Couprie, and P. Roy, Scientific Reports 5, 10330 (2015). |
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TUP053 | Real-World Considerations for Crossed-Polarized Undulator Radiation Conversion | 486 |
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Cross-polarized (X-POL) configurations are a means to produce circularly-polarized radiation output from purely planar-polarized undulators. Recent polarization results from both the FERMI FEL-1 [1] at XUV wavelengths and Shanghai DUV FEL [2] at visible wavelengths have confirmed that such configurations do work for single pass FELs. However, analysis of both FERMI and SINAP results indicate that the quantitative degree of planar to circular conversion can be significantly affected by several experimental details. Full conversion requires not only equal intensity of the two cross-polarized beams but also perfect overlap in space and time of their far-field amplitude and phase patterns. From both simple theoretical analysis and more detailed simulation modeling, we examine a number of possible factors that can degrade the net linear to circular conversion efficiency. In addition to the previous suggestions by Ferrari et al. of problems with unbalanced powers and transverse phase variation arising from different effective emission z locations for the two cross-polarized radiation pulses, we also consider separate degradation effects of imperfect downstream overlap of the two linearly-polarized beams arising from different emission tilt angles and mode sizes. We also discuss optimizing the conversion efficiency by aperturing the radiation pulses downstream of the undulators.
[1] E. Ferrari et al., Paper THA02, Proc. FEL2013 (2013). [2] H. Deng et al., Phys. Rev. ST Accel. Beams 17, 020704 (2014). |
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TUP055 | Technical Overview of Bunch Compressor System for PAL XFEL | 490 |
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Pohang Accelerator Laboratory(PAL) is developing a SASE X-ray Free Electron Laser based on 10 GeV linear accelerator. Bunch compressor (BC) systems are developed to be used for the linear accelerator tunnel. It consists of three(BC1, BC2, BC3H) hard X-ray line and one(BC3S) soft X-ray line. BC systems are composed of four dipole magnets, three quadrupole magnet, BPM and collimator. The support system is based on an asymmetric four-dipole magnet chicane in which asymmetry and variable R56. can be optimized. This flexibility is achieved by allowing the middle two dipole magnets to move transversely. In this paper, we describe the design of the stages used for precise movement of the bunch compressor magnets and associated diagnostics components. | ||
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TUP056 | Design Challenge and Strategy for the LCLS-II High Repetition Rate X-ray FEL Photon Stoppers | 493 |
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Funding: Portions of this research were carried out at the LCLS at the SLAC National Accelerator Laboratory. LCLS is an User Facility operated for the US DOE Office of Science by Stanford University. Future high repetition rate X-ray FELs such as the European XFEL and LCLS-II presents new challenges to photon diagnostics as well as essential beamline components. In addition to these devices having to sustain the high peak power of a single-pulse FEL radiation, they must also be capable of handling the enormous power density of tens to hundreds of watts over an area as small as 0.1 mm X mm. In this talk, I will discuss the potential impact of high power FEL operation on performance of a gas attenuator and the design challenges to beam intercepting components such as a collimator or stopper. |
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TUP057 | The Highly Adjustable Magnet Undulator | 499 |
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The highly adjustable magnet undulator is a concept aiming for flexibility and extensive tunability of undulator settings in the linear as well as the helical regime. I report about suggested layout, magnetic simulations. | ||
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TUP065 | Beam Dynamics Simulation for the Upgraded PITZ Photo Injector Applying Various Photocathode Laser Pulses | 501 |
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The Photo Injector Test facility PITZ at DESY, Zeuthen site, characterizes and optimizes high brightness electron sources for linac-based Free Electron Laser (FELs) with a specific focus on the requirements of FLASH and the European XFEL. X-ray FELs require high brightness electron beam in terms of high peak current, small transverse emittance and energy spread. Such high quality beams are mandatory for efficient SASE generation in a single pass through long undulators with narrow gaps. Photocathode laser pulse shaping is a powerful tool to optimize the photo injector performance. Recently, a new photocathode laser system capable of producing 3D quasi-ellipsoidal pulses has been installed at PITZ. It is foreseen to operate this new system in parallel to the nominal one that generates cylindrical pulses with various temporal profiles. A set of numerical simulations was performed to study and compare the beam dynamics of electron beams produced with 3D ellipsoidal laser profile with the typical cylindrically shaped (flat-top) profile. Different bunch charges from 20 pC up to several nC are considered, in order to find an optimum PITZ machine setup which will yield the lowest transverse emittance. we present and discuss the results of this comparison in the submission. | ||
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TUP066 | Benchmark of ELEGANT and IMPACT | 505 |
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The beam dynamics codes ELEGANT and IMAPCT have many users. We use these two codes for the design of LCLSII. Both codes use a 1D model for the coherent synchrotron radiation (CSR) in bend magnets. In addition, IMPACT has a 3D space-charge model, while ELEGANT uses a 1D model. To compare the two codes, especially the space-charge effects, we systematically benchmark the two codes with different physics aspects: wakefields, CSR and space-charge forces. | ||
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TUP067 | Effect of Hot Ions in LCLC-II | 508 |
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The ions in a linac, such as ERL, draw more attention recently. LCLSII has a long linac with 1MHz repetition rate. The ions, in general, are not deeply trapped due to the long bunch spacing. The effect of ion thermal energy becomes important in this regime. The beam dynamics with ions are studied numerically. There is a linear growth in amplitude, but not exponential growth as traditional fast ion instability. This instability set a maximum bunch-train length to limit the beam amplitude to fractional beam σ. Theoretical works are also done to compare the simulations. We also extend our works to different regimes where the motions of ions from stable to unstable. | ||
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TUP068 | Electron Beam Phase Space Tomographie at the European XFEL Injector | 515 |
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Transverse emittances as well as the energy spread and the peak current of the electron bunches are important parameters for high-gain free electron lasers such as the European XFEL. Investigations of the 6D phase space characterisation would give important indications to optimise the beam quality for SASE operation. The injector of the European XFEL includes, inter alia, a laser heater, a transverse deflecting cavity, a spectrometer, a diagnostic section with four OTR screens as well as several quadrupole magnets. In this paper, we will discuss the possibilities to characterise the 6D phase space of the electron beam in the injector of the Eurpean XFEL. | ||
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TUP069 | THz Based Phase-Space Manipulation in a Guided IFEL | 519 |
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Funding: This work has been supported by DOE grant DE-FG02-92ER40693, and NSF grant PHY-1415583. We propose a guided IFEL interaction driven by a broadband THz source to compress a relativistic electron bunch and synchronize it with an external laser pulse. A high field single-cycle THz pulse is group velocity-matched to the electron bunch inside a waveguide, allowing for a sustained interaction in a magnetic undulator. The THz pulse is generated via optical rectification from the external laser source, with peak field of up to 4.6 MV/m. We present measurements of the THz waveform before and after a parallel plate waveguide with varying aperture size and estimate the group velocity. We also present results from a preliminary 1-D multi-frequency simulation code we are developing to model the guided broadband IFEL interaction. Given a 6 MeV, 100 fs electron bunch with an initial 10-3 energy spread, as can be readily produced at the UCLA Pegasus laboratory, the simulations predict a phase space rotation of the bunch distribution that will reduce the initial timing jitter and compress the electron bunch by nearly an order of magnitude. |
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TUP070 | Energy Jitter Minimization at LCLS | 523 |
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The energy jitters of the electron beam can affects the FEL in self-seeded modes if the jitter is large compared to the FEL parameter. We work in multiple ways to reduce the jitters, including hardware improvement, optimization linac set-up. This paper discusses the optimization of linac set-up. The solutions always suggest that we can largely reduce the energy jitter from a weak compression at BC1 and a stronger compression at BC2. Meanwhile a low beam energy at BC2 also reduce the energy jitter, which is confirmed by the experiment. The results can be explained by a simple model. Experimental results are also presented, demonstrating better than 20% and 40% relative energy jitter reduction for 13.6 and 4 GeV linac operation, respectively. | ||
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TUP071 | A FAST Particle Tracking Code | 530 |
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This paper presents a fast particle tracking (FPT) code for linac beam dynamics. It includes wake fields, coherent synchrotron radiation (CSR) and longitudinal space charge. We systematically benchmark the FPT with ELEGANT with different physics aspects: pure optics, wakefields, CSR and space-charge forces | ||
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TUP072 | Cathode Ion Bombardment in LCLS and LCLS-II RF Gun | 534 |
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This paper studies the ions bombardment on the cathode in the LCLS and LCLS-II gun. APEX gun is used here for LCLS-II, which will be operate at 1 MHz repetition rate. Therefore, It is important to estimate the ion bombardment. One specific PIC code is used track arbitrary particles (ions and electron here) in arbitrary 2D/3D electromagnetic field and solenoid field to estimate the possibility of ion bombardment. The LCLS gun has 1.6 cells while the LCLS-II gun (APEX gun) is a half-cell gun. The frequencies of the two guns are also quite different. These characters make the ion dynamics quite differently. We estimated the bombardment for various ion species and studied the effects RF pulse shape and RF phase | ||
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TUP074 | Results from the Nocibur Experiment at Brookhaven National Laboratory's Accelerator Test Facility | 540 |
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Conversion efficiencies of electrical to optical power in a Free Electron Laser are typically limited by their Pierce parameter, ρ ~0.1%. Introducing strong undulator tapering can increase this efficiency greatly, with simulations showing possible conversion efficiencies of ~40%. Recent experiments performed with the Rubicon Inverse Free Electron Laser have demonstrated acceleration gradients of ~ 100 MeV/m and high particle trapping efficiency by coupling a pre-bunched electron beam to a high power CO2 laser pulse in a strongly tapered helical undulator. By reversing the undulator period tapering and re-optimizing the field strength along the Rubicon undulator, we obtain an Inverse Free Electron Laser decelerator, which we have aptly renamed Nocibur. This tapering profile is chosen so that the change in beam energy defined by the ponderomotive decelerating gradient matches the change in resonant energy defined by the undulator parameters, allowing the conversion of a large fraction of the electron beam power into coherent narrow-band radiation. We discuss this mechanism as well as results from a recent experiment performed with the Nocibur undulator at Brookhaven National Laboratory's Accelerator Test Facility. | ||
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TUP079 | Laser Wakefield Acceleration by using a Laser Produced Aluminium Plasma | 543 |
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In laser wakefield accelerator, usually a gas target is used to generate plasma medium. With this gas target, the pressure of the system cannot be keep as low as possible for electron beam application such as seeding the storage ring. To reduce this vacuum problem in LWFA, a plasma generated from solid Al target was used as plasma medium. A fundamental beam from the Q-switched ns pump laser in the Ti:sapphire power amplifier was used to generate a plasma from solid Al target. The plasma density was controlled by changing the distance between the main laser pulse for electron acceleration and the solid target. The plasma density was measured by the interferometer. The measured density indicates that the average charge of the ion in pre-plasma was 4.4. The main pulse ionized the Al plasma up to Al XII which means that the ionization injection could be used as an injection scheme. A 28 TW fs laser was used to accelerate the electron. A quasi-monochromatic electron was generated. The peak energy was 70 MeV and energy spread was 15 %. The divergence of the beam was 12 mrad in horizontal direction and 6 mrad in vertical direction. | ||
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TUP080 | Terahertz Source Utilizing Resonant Coherent Diffraction Radiation at KEK ERL Test Accelerator | 547 |
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An energy recovery linac test accelerator, cERL, has been developing at KEK. It can produce a high repetition rate short bunched electron beam in a continuous operation mode. We propose to develop a high power THz radiation source at the return loop of the cERL. Coherent diffraction radiation of THz regime is emitted when an electron bunch passes through a conductive mirror with a beam hole at the center. If we form an optical cavity using two mirrors facing each other and the cavity length coincides with the bunch repetition rate, the coherent diffraction radiation of multiple bunches adds up coherently in the cavity. By extracting the power through transmission of one of the mirrors, we can realize a high power and high efficiency THz source. We discuss performance of the source assuming the beam parameters of cERL. | ||
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TUP085 | Lebra Free-Electron Laser Elicits Electrical Spikes from the Retina and Optic Nerve of the Slugs Limax Valentianus | 550 |
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Since 2001, the Laboratory for Electron Beam Research and Application (LEBRA) has been providing tunable free-electron lasers (FELs) encompassing the near-IR region and some of the mid-IR region (0.9-6 microns), and generating visible wavelengths up to 400 nm by means of nonlinear optical crystals. We are investigating the efficiency of LEBRA-FELs for triggering photoreactions in living organisms. Last year we described the effects of LEBRA-FELs in controlling the photoreaction of lettuce seeds; red FEL (660 nm) and far-red FEL (740 nm) activate and inhibit germination, respectively. Here we used LEBRA-FEL to illuminate the retina of slugs (Limax valentianus), and determined which FEL wavelengths generate electrical spikes from the retina-optic nerve. Blue FEL light (wavelength: 470 nm) efficiently produced electrical spikes from the retina. The results are consistent with a previous study, where a xenon arc lamp with interference filters was used to produce monochromatic visible light. We plan to extend the wavelengths to the near- and mid-IR regions of LEBRA-FEL. We summarize our current results for the use of FEL in investigating the electrophysiology of the retina of slugs.
We thank Mr. T. Kuwabara (a graduate of Departments of Physics, College of Science and Technolgy, Nihon University) for helpful assistance. |
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