| Paper | Title | Page |
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| THPA02 | Two-dimensional Effects on the Behavior of the CSR Force In a Bunch Compression Chicane | 469 |
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Funding: This work was supported by U.S. DOE under Contract No. DE-AC05-06OR23177. The endeavor to reach higher brightness of electron bunches in the design of future FEL is seriously challenged by the CSR effect in magnetic bends. Extensive studies on the CSR effects have shown that the 1D approximation of the CSR force is valid for a wide parameter regime. However, as the bunch gets increasingly compressed in the compression process, the behavior of the CSR interaction force will be influenced by the evolution of the 2D bunch distribution. Here we explore this 2D effect using semi-analytical and numerical study of the retarded potentials for an evolving 4D Gaussian phase space distribution with initial energy chirp. We will present results of our systematic exploration of this two-dimensional effect. We will display the interesting dependence of the 2D CSR force on the initial horizontal emittance and uncorrelated energy spread around minimum bunch length, and show the comparison of these results with their 1D counterpart. Physical interpretation will also be discussed. |
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| THPA06 | Emittance for Different Bunch Charges at the Upgraded PITZ Facility | 473 |
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| Optimizations of electron sources for short-wavelength Free Electron Laser (FELs) at the Photo Injector Test facility at DESY, location Zeuthen (PITZ) have been continued with a new radio frequency (RF) gun cavity, a new post-accelerating Cut Disk Structure (CDS) booster cavity and several upgraded diagnostic components. The new booster cavity allows stable operation with higher acceleration and longer pulse trains than the operation with the previous TESLA type cavity. Electron beams with a maximum mean momentum of about 25 MeV/c can be produced with the setup described in this paper. Together with the upgraded RF system for the gun and the new CDS booster cavity, the electron beam stability was significantly improved. A large fraction of the measurement program in 2010-2011was devoted to study the dependence of the transverse projected emittance on the bunch charge. Measurement results using this upgraded facility are reported and discussed. | ||
| THPA07 | A Multichannel Wavelength Resolved Coherent Radiation Detector for Bunch Profile Monitoring at FLASH | 477 |
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| Measuring the wavelength integrated intensity of coherent radiation in the micrometer to millimeter regime (THz radiation) is a widespread method to monitor the compression process in FEL linacs. While these devices give valuable information about the overall bunch length, they don't provide any information on the longitudinal structure and shape of the bunches. In this paper, we present a real time bunch profile monitor based on wavelength resolved THz detection. An in-vacuum spectrometer with four dispersive gratings and parallel read out of 120 individual wavelength bins provides detailed information shot-to-shot information on the bunch shape. The device can be operated in short (4-40 μm) and long range (40-400 μm) mode to cover the entire longitudinal phase space for compressed bunches of the FLASH linac. It is used as online monitoring device just as for bunch profile measurements during machine development. It's sensitivity down to the few micrometer scale allows to study very short features of the bunch profile as well as microbunching phenomena in this regime. | ||
| THPA08 | An Option of High Charge Operation for the European XFEL | 481 |
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| The 1.3 GHz superconducting accelerator developed in the framework of TESLA and the European XFEL project holds potential to accelerate high charge electron beams. This feature has been successfully demonstrated during the first run of the free electron laser at the TESLA Test Facility with lasing driven by electron bunches with a charge of up to 4 nC. Currently DESY and the European XFEL GmbH perform revision of the baseline parameters for the electron beam. In this report we discuss a potential option of operation of the European XFEL driven by high charge (1 nC to 3 nC) electron beams. We present the results of the production and characterization of high charge electron bunches. Experiments have been performed at PITZ and demonstrated good properties of the electron beam in terms of emittance. Simulations of the radiation properties of SASE FELs show that application of high charge electron beams will open up the possibility to generate radiation pulse energies up to a few hundred milli-Joule level. | ||
| THPA10 | RF Photo Gun Stability Measurement at PITZ | 485 |
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| High stability of the RF photo gun is one of the necessary conditions for the successful operation of linac based free electron lasers. Fluctuations of the RF launch phase have significant influence on the beam quality. Investigation on the dependence of different gun parameters and selection of optimal conditions are required to achieve high RF gun phase stability. Measurements of the gun RF phase stability are based on beam charge and momentum monitoring downstream of the gun. The stability of the RF gun phase for different operating conditions has been measured at the Photo Injector Test facility at DESY in Zeuthen (PITZ) and the results will be presented. | ||
| THPA12 | Beam Energy Measurements in the FLASH Injector using Synchrotron Radiation and Bunch Arrival Monitors | 489 |
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| The high beam energy stability required for stable operation of linac-driven free-electron lasers demands for precise cavity RF field regulation. This is in particular true for the accelerator modules at low beam energies which are used to induce an energy correlation on the electron beam for longitudinal bunch compression in magnetic chicanes. At FLASH, a major upgrade of the injector has taken place in the shutdown 2009/2010 including the installation of a 3rd harmonic accelerating module, exchange of modulators and re-cabling and temperature stabilization of the low-level RF electronics. Several beam-based techniques have been developed recently which can be used to monitor the beam energy with high precision or as fast feedbacks for the RF regulation. In this paper, we report on bunch-resolved energy measurements recorded independently with a synchrotron radiation monitor and two bunch arrival monitors. Good agreement between the monitors was found and the measurement data are compared with the results from RF detection. | ||
| THPA13 | A 54.167MHz Laser Wire System for Free Electron Laser in CAEP | 493 |
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| The laser wire (LW) method has been demonstrated as an effective non-interceptive technique for measuring transverse electron beam size of CW FELs and ERLs. To measure the beam size of a CW DC gun, which is built as an electron source of THz FEL in China Academy of Engineering Physics (CAEP), a high repetition LW system is proposed. The first proposed system is going to be installed at the exit of the DC gun, where the energy of electron beam is extremely low. In this paper, the LW system adapted to the FEL beam parameters is discussed, and the main parameters are given. | ||
| THPA14 | Upgrade of the Optical Synchronization System for FLASH II | 496 |
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| The optical synchronization system at FLASH has been in operation since 2008. Due to continuous improvement and several upgrades it has become an integral part of the machine operation and of pump-probe experiments as both rely on its performance. In summer 2013, a second FEL section, called FLASH II, which is using the same accelerator as FLASH will start its operation to increase the number of user experiments and to test new seeding schemes. This also requires a major extension of the synchronization system since new clients have to be supplied with a 10 fs-stable timing signal. Six additional stabilized fiber links and the according end stations like bunch arrival time monitors and laser synchronization setups will be installed. | ||
| THPA15 | Simulation Studies of Generating Ultra Short Pulses at PITZ | 499 |
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| Generation of the ultra short electron bunches (<10fs bunch length) which have a small transverse phase space volume and relatively small energy spread is of great interest. Such bunches are required for fully coherent (transversally and longitudinally) FEL radiation (single spike lasing) and for plasma acceleration experiments. The Photo Injector Test Facility at DESY in Zeuthen has already demonstrated the possibility to generate and characterize high quality electron beams for a wide range of bunch charges. Currently electron bunches have a typical length of several ps. To study the possibility of producing short electron bunches at PITZ many beam dynamics simulations have been performed for 1pC bunch charge using the ASTRA code. The current PITZ beam line is supposed to be extended by a small magnet chicane. Several temporal profiles of the cathode laser pulse have been used for the simulations to produce ultra-short electron bunches with small transverse sizes. The results of the beam dynamics simulations are presented and discussed. | ||
| THPA17 | Study of the Back-bombardment Effect in the ITC-Rf Gun for t-ACTS Project at Tohoku University | 503 |
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A specially designed thermionic RF gun which consists of two independently tunable cells [1] (ITC) is used to produce sub-picoseconds electron pulses as the source for coherent terahertz radiation at Tohoku University. Simulations of particle motion show that the back-bombardment effect on the LaB6 cathode surface is serious and should be controlled carefully. Using EGS5 [2] the power deposition of the back-bombardment inside the cathode can be calculated by using the information of back-streaming electrons derived from GPT [3] simulation, and further used to evaluate the temperature increase on the cathode surface by numerically solving a 2-dimentional equation for heat conduction. In the 2D model, the back-streaming electrons are treated as external heat source as well as the cathode heater that heats the cathode from its side along with thermal radiation from its surface. In addition, some methods will be proposed to reduce the back-bombardment effect and we will also compare the simulation results with experimental data.
[1] H. Hama et al., New J. Phys. 8 (2006) 292 [2] Electron Gamma Shower, http://rcwww.kek.jp/research/egs/egs5.html [3] General Particle Tracer, http://www.pulsar.nl/gpt |
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| THPA18 | Operation of the FLASH Photoinjector Laser System | 507 |
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| The photoinjector of FLASH uses an RF gun equipped with caesium telluride photocathodes illuminated by appropriate UV laser pulses as a source of ultra-bright electron beams. The superconducting accelerator of FLASH is able to accelerate thousands of electron bunches per second in burst mode. This puts special demands on the design of the electron source, especially the laser system. The fully diode pumped laser system is based on Nd:YLF and produces a train of 2400 UV pulses in a burst of 0.8 ms length with a repetition rate of 5 Hz and 800 pulses with 10 Hz. The single pulse energy is up to 25 μJ per pulse at 262 nm. The laser uses a pulsed oscillator synchronized to the master RF with a stability of better than 200 fs in arrival time at the RF gun. Special care has been taken to produce a uniform and stable pulse train in terms of pulse energy, shape, and phase. Since FLASH is a free-electron laser user facility, the laser is designed to operate for more than 8000 h per year without operator intervention and little maintenance. We report on operational experience with the new system brought in operation in spring 2010. | ||
| THPA19 | Photocathodes at FLASH | 511 |
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| For several years now, caesium telluride photocathodes are successfully used in the photoinjector of the free electron laser FLASH at DESY, Germany. They show a high quantum efficiency and long lifetime. The injector produces routinely thousand of bunches per second with a single bunch charge in the range of 0.1 to 1.5 nC. Recent results on lifetime, quantum efficiency, darkcurrent, and operating experience is reported. At DESY, a new preparation system has been set-up. First cathodes have been produced and tested successfully. | ||
| THPA21 | Commissioning of a Streak Camera for Laser Characterization at NML | 515 |
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| A streak camera will be used for longitudinal profile measurement of a drive laser for the superconducting radio frequency photoinjector test facility at Fermilab. We are evaluating both a Photek intensified CCD camera and a Hamamatsu cooled CCD camera as the readout camera option for the Hamamatsu C5680 streak camera unit with a synchroscan sweep unit. Trade on low signal sensitivity and spatial resolution for the two lens-coupled options are being evaluated. In addition, an ultrashort laser pulse from a Ti:sapphire laser is used to measure the temporal resolution for both configurations. | ||
| THPA23 | Investigations on Thermal Emittance at PITZ | 519 |
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| The main aim of the Photo-Injector Test Facility at DESY, location Zeuthen (PITZ) is to develop and test an FEL photo-injector system capable of producing high charge electron bunches of lowest possible transverse emittance, which has a fundamental impact on FEL performance. Recent measurement results at PITZ showed a fairly small electron beam transverse projected emittance [1] which increased interest in the thermal emittance and its contribution to the overall electron beam emittance budget. Therefore thermal emittance was investigated at PITZ. Results of these studies are presented and discussed. | ||
| THPA24 | Development of Pr2Fe14B Cryogenic Undulator CPMU at SOLEIL | 523 |
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| Short period, high field undulators can enable short wavelength FEL at low beam energy, with decreased gain length, thus allowing much more compact and less costly FEL systems. A R&D programme for the construction of a 2 m long 18 mm period CPMU is under progress at SOLEIL. The use of PrFeB which features a 1.35 T remanence (Br) at room temperature enables to increase the peak magnetic field at 5.5 mm minimum gap, from 1.04 T at room temperature to 1.15 T at a cryogenic temperature of 77 K. For FELs, we can reach higher magnetic field of 1.91 T at lower gap of 3 mm. Pr was chosen instead of Nd magnetic material, because of the no appearance of the SRT phenomenon. Different corrections were performed first at room temperature to adjust the phase error, the electron trajectory and to reduce the multipolar components. The mounting inside the vacuum chamber enables the fitting of a dedicated magnetic measurement bench to check the magnetic performance of the undulator at low temperature. The results of the magnetic measurements at low temperature and the comparison with the measurement at room temperature are reported. A U18 CPMU will be used in LUNEX5 project at SOLEIL. | ||
| THPA25 | Standard Electron Beam Diagnostics for the European XFEL | 527 |
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| The European XFEL under construction in Hamburg needs to control the electron beam parameters for reliable machine and FEL operation. Due to the flexible bunch pattern, a minimum bunch spacing of 222 ns and large beam charge range a high dynamic range of the monitors is necessary. Furthermore the high average beam power enforces an elaborated machine protection system. This paper presents an overview of the planned standard electron beam diagnostics. The status of the main systems is presented, as well as the results from prototype tests with beam at FLASH. | ||
| THPA26 | Feedback Strategies for Bunch Arrival Time Stabilization at FLASH Towards 10 fs | 531 |
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| Highly precise regulation of accelerator RF fields is a prerequisite for a stable and reproducible photon generation at Free Electron Lasers such as FLASH. Due to major improvements of the RF field controls during 2010 and 2011 the FEL performance and the beam stability was significantly improved. In order to facilitate femtosecond precision pump-probe and seeding experiments at FLASH a combination of RF and beam based feedback loops are used. In this paper, we present the achieved stabilization of the arrival time and the pulse compression at FLASH using intra-pulse train feedbacks. Current limitations and future steps toward sub-10fs rms jitter are discussed. | ||
| THPA28 | Lasing of Near Infrared FEL with the Burst-mode Beam at LEBRA | 535 |
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| Improvement of the electron beam injector system in the linac at the Laboratory for Electron Beam Research and Application (LEBRA) of Nihon University made possible to accelerate the burst-mode beam extracted from the conventional DC triode electron gun. The electron beam with the pulse width less than 1ns and the period of 44.8ns, which corresponds to the round-trip time in the FEL optical resonator, has been extracted by using a high-speed grid pulser (Kentec Inc.). Taking into account of the electron beam pulse width, sequence of two or three FEL pulses with the accelerating RF period was possible. In the lasing experiment a single FEL pulse or a row of two FEL pulses was observed using a streak camera. By the adjustment of the timing of the high-speed grid pulse generated in synchronous with the accelerating RF, lasing of a single FEL pulse in the single short beam pulse has been observed at an FEL wavelength of approximately 1800nm. The result suggests that a single FEL pulse with 44.8ns period is available in the wavelength range from 1600 to 6000nm at the LEBRA FEL system. | ||
| THPA29 | Performance of the RF Cavity BPM at XFEL/SPring-8 “SACLA” | 539 |
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| We have developed an rf cavity beam position monitor (RF-BPM) for the XFEL facility at SPring-8, “SACLA”. The demanded position resolution of the BPM is less than 1 μm, because an electron beam and X-rays must be overlapped with 4 μm precision in the undulator section. To achieve this requirement, we employed a C-band RF-BPM that has a resonant frequency of 4760 MHz. The RF-BPM has a TM110 dipole mode resonator for position detection and a TM010 monopole mode resonator for phase reference and charge normalization. Rf signals from the RF-BPM are detected by IQ (In-phase and Quadrature) demodulators and the detected signals are recorded by 238 MHz waveform digitizers. The position resolution was confirmed to be 0.2 μm by using a 250 MeV electron beam at the SCSS test accelerator. Then, 57 RF-BPMs were produced and installed into SACLA. The beam tuning of SACLA started in February 2011 and the RF-BPM system has been working well. We report the basic performance such as a resonant frequency, a Q factor, machining accuracy etc. for each cavity and the achieved position resolution of the RF-BPM system. | ||
| THPA30 | First Results with Tomographic Reconstruction of the Transverse Phase Space at PITZ | 543 |
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| The development of high brightness electron sources capable to drive FELs like FLASH and European XFEL is a major objective of the Photo-Injector Test Facility at DESY in Zeuthen, PITZ. A key parameter used to define the beam quality at PITZ is the transverse phase-space density distribution and its evolution along the beamline. Complementary to the standard phase-space measurement setup constituting slit-scan stations, a module for tomographic diagnostics has been commissioned in 2010/2011. It consists of four observation screens separated by FODO cells and an upstream matching section. The expected advantages of the tomography method are the possibility to measure both transverse planes simultaneously and an improved resolution for low charges and short pulse trains. The fundamental challenges are related to strong space-charge forces at low beam momentum of only 25~MeV/c at PITZ at the moment. Such a constraint presents an obstacle to obtain beam envelope parameters well-matched to the optics of the FODO lattice. This contribution presents the first practical experience with the phase-space tomography module. | ||
| THPA31 | Commissioning of ITC-RF Gun for t-ACTS Project at Tohoku University | 547 |
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Funding: This work is partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (S), Contract #20226003. A test accelerator as the coherent terahertz source project (t-ACTS) is in progress at Tohoku University, in which an isochronous ring and a bunched free electron laser will provide the intense terahertz radiation by dint of the sub-picoseconds electron pulses [1, 2]. A thermionic RF gun with two independently-tunable cells (ITC), an alpha magnet and a 3 m accelerating structure are employed in the t-ACTS injector for the short pulse generation. Tracking simulations show that very short electron pulse less than 100 fs with a bunch charge of about 20 pC can be obtained by means of the velocity bunching scheme [2]. Although the usable amount of the extracted beam from the ITC-RF gun is quite small comparing with photo-injectors, there seem to be distinct features such as the better stability and the multi-bunch capability. High power RF processing for the gun has already been accomplished, and then the beam commissioning will be started soon. We will report results of beam commissioning of the ITC-RF gun and also present the current status of t-ACTS project. [1] H. Hama et al., New J. Phys. 8 (2006) 292, [2] H. Hama and M. Yasuda, Proc. of FEL2009, TUPC69, (2009) 394 [3] F. Miyahara et al., Proc. of IPAC'10, THPD094, (2010) 4509 |
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| THPA32 | Femtosecond Stable Laser-to-RF Phase Detection Using Optical Modulators | 551 |
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| Free-Electron Lasers like FLASH and the European XFEL require the synchronization of RF stations to the optical timing reference of the accelerator. For this purpose, a new technique to phase-lock RF sources to an optical pulse train has been invented. The new technique uses an opto-microwave coupling device together with an ultra-low phase-noise RF source operating at a frequency of 1.3 GHz. In our arrangement, the laser-to-RF phase detector is insensitive to amplitude fluctuations of the optical reference pulse train, which allows the detector to achieve femtosecond precision over long time periods. In this paper, we present the balanced laser-to-RF phase detection principle along with a tolerance study of the arrangement and first results from our prototype setup. | ||
| THPA33 | Bunch Length Measurement Based on the Beam Position Monitor | 555 |
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| BPM (Beam Position Monitor) is the most basic instrument of the beam dynamics. The signal of the BPM consist more information of the beam apart from the beam position. By processing and analyzing of the BPM signal, the information of the bunch length can be got. It's a challenge to use this method when the energy is low (<30 MeV) and the bunch length is especially short(10 ps rms). In this paper, the BPM system which can be used to measure the bunch length is discussed. And the method of the signal processing and analyzing is given. | ||
| THPA34 | Assessment of Thermionic Emission Properties and Back Bombardment Effects for LaB6 and CeB6 | 557 |
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| Back Bombardment (BB) effect limits wide usage of thermionic RF guns. BB effect induces not only ramping-up of a cathode’s temperature and beam current, but also degradation of cavity voltage and beam energy during the macropulse. In this research we are clarifying BB phenomenon and find out cathode material properties contribution on BB effect. Therefore, assessment of emission properties and comparison of BB effect in LaB6 and CeB6 are introduced. Emission properties for these materials are measured in temperature range between 1600 and 2100 K. Then, heating property of materials is investigated against BB effect by numerical calculation of stopping range and deposited heat. Finally, change in cathode temperate and corresponding change in current density during 6 μs pulse duration is determined. Experimental results estimates work functions at 1800 K for LaB6 and CeB6 were 2.8 and 2.75 eV respectively. Our simulation of BB effect shows that for a pulse of 6 μs duration, LaB6 cathode experiences a large change in temperature compared with CeB6. The change in current density is two times higher. The experimental and simulation results will be presented in the meeting | ||