| Paper | Title | Other Keywords | Page |
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| MOP004 | An Electron Linac Injector With a Hybrid Buncher Structure | linac, gun, electron, klystron | 55 |
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At present the Linac II at DESY consists of a 6A/150kV DC electron gun, a 400 MeV primary electron linac, a 800 MW positron converter, and a 450 MeV secondary electron/positron linac. To improve the maintainability of the system and to reduce operational risks the original 150kV diode gun will be replaced by a 100kV triode. Together with the gun the whole injection system will be upgraded and optimized for minimal load on the converter target and primary linac. The core of the new injector are a 5MeV standing wave/travelling wave hybrid structure and a magnetic energy filter. Simulations show that With 6A DC current up to 3.7A can be bunched into 20° of the 2.998 GHz RF. This phase range is narrow enough to fit after on-crest acceleration into the energy acceptance of the following accumulator ring PIA. |
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| MOP029 | S0-studies on ICHIRO 9-cell Cavities in Collaboration with KEK and Jlab | cavity, HOM, superconductivity, electron | 118 |
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In 2008, KEK and Jlab did the collaboration of S0-study on ICHIRO 9-cell #5 which has no end groups on beam tubes. As S0 tight loop test, surface treatments and vertical tests were repeated on ICHIRO#5 at both of Jlab and KEK. Maximum gradients of 36.5MV/m at Jlab and 33.7MV/m at KEK were achieved so far. In this year, 2010, KEK and Jlab started new S0-study collaboration on ICHIRO 9cell #7 which has full end groups on beam tubes. ICHIR#7 was already sent to Jlab and VT as received was done. We will report the results of tight loop tests at Jlab. |
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| MOP074 | High Power Evaluation of X-band High Power Loads | vacuum, klystron, ion, linac | 226 |
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Several types of X-band high power loads developed for several tens of MW range were designed, fabricated and used for high power tests at X-band facility of KEK. Some of them have been used for many years and some show possible deterioration of RF performance. Recently revised-design loads were made by CERN and the high power evaluation was performed at KEK. In this paper, the main requirements are recalled, together with the design features. The high power test results are analysed and presented. |
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| MOP075 | Breakdown Characteristics in DC Spark Experiments of Copper Focusing on Purity and Hardness | vacuum, linear-collider, collider, focusing | 229 |
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To investigate the breakdown characteristic related to the differences in purity and hardness, four types of oxygen-free copper (OFC) materials, usual class 1 OFC with/without diamond finish, 7-nine large-grain copper and 6-nine hot-isotropic-pressed copper, were tested with the DC spark test system at CERN. Measurements of beta, breakdown fields and breakdown probability are discussed followed by the surface inspection mostly with SEM on the tested materials. |
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| TUP010 | Test Results of Components for CW and Near-CW Operation of a Superconducting Linac | cavity, HOM, linac, SRF | 413 |
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The European XFEL will use superconducting TESLA cavities operating with 650 μs long bunch trains. With 220 ns bunch spacing and 10 Hz RF-pulse repetition rate up to 27000 high quality bunches/s will be delivered to insertion devices generating unprecedented high average brilliance photon beams at very short wavelength. While many experiments can take advantage of full bunch trains, others prefer an increased several μ-seconds intra pulse distance between bunches, or short bursts with kHz repetition rate. With the nominal RF-pulse structure these features will lead to a substantially reduced number of bunches per second and therefore to significantly lower average brilliance. We discuss here an R&D program aiming for a far future upgrade of the European XFEL; operation in the cw and/or near-cw mode. The program profits from the continuous improvement in performance of TESLA cavities, which allows for longer RF-pulses in comparison with the current design. We present test results of a SRF electron injector and a new RF-power source, and some modification of the HOM damping scheme, which will avoid the necessity of re-assembly of the XFEL accelerator for the upgraded operations. |
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| TUP096 | First Results of Slice Emittance Diagnostics with an Energy Chirped Beam at PITZ | emittance, laser, dipole, booster | 635 |
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Recent successes in existing linac based FEL facilities operation and improvements in future FEL designs became possible due to detailed research in high-brightness electron beam production. The Photo Injector Test facility in Zeuthen (PITZ) is the DESY center for electron source characterization and optimization. New slice emittance diagnostics was recently commissioned at PITZ. In the measurement approach a bunch is accelerated off-crest in the accelerating cavity downstream the gun, a part of the bunch is selected after a dipole with a slit perpendicular to the dispersive direction, and the transverse emittance of the bunch part is measured using a quadrupole or a slit scan. Test measurement results are presented for 1 nC charge, flat-top and Gaussian longitudinal laser shapes. |
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| TH304 | Linear Induction Accelerators at the Los Alamos National Laboratory DARHT Facility | target, electron, dipole, induction | 750 |
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The Dual-Axis Radiographic Hydrodynamic Test Facility (DARHT) at Los Alamos National Laboratory consists of two linear induction accelerators at right angles to each other. The First Axis, operating since 1999, produces a nominal 20-MeV, 2-kA single beam-pulse with 60-nsec width. In contrast, the DARHT Second Axis, operating since 2008, produces up to four pulses in a variable pulse format by slicing micro-pulses out of a longer 1.6-microseconds (flat-top) pulse of nominal beam-energy and -current of 17 MeV and 2 kA respectively. Bremsstrahlung radiation, shining on a hydro-dynamical experimental device, is produced by focusing the electron beam-pulses onto a high-Z target. Variable pulse-formats allow for adjustment of the pulse-to-pulse doses to record a time sequence of x-ray images of the explosively driven imploding mock device. In this talk, we present a sampling of the numerous physics and engineering challenges encountered and the solutions thereof that led to the present fully operational dual axes capability. First successful simultaneous use of both the axes for a hydrodynamic experiment was achieved in 2009. |
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| THP010 | Exploiting New Electrochemical Understanding of Niobium Electropolishing for Improved Performance of SRF Cavities for CEBAF | cavity, niobium, controls, impedance | 779 |
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Recent incorporation of analytic electrochemistry into the development of protocols for electropolishing niobium SRF cavities has yielded new insights for optimizing this process for consistent, high-performance results. Use of reference electrodes in the electrolyte, electrochemical impedance spectroscopy (EIS), rotating disk electrodes (RDE), and controlled sample temperatures has greatly clarified the process dynamics over the empirical understanding developed via years of practice. Minimizing rf losses at high operational gradients is very valuable for CW linacs. Jefferson Lab is applying these new insights to the low-loss 7-cell cavity design developed for the CEBAF 12 GeV Upgrade. Together with controlled cleaning and assembly techniques to guard against field-emission causing particulates, the resulting process is yielding consistent cavity performance that exceeds project requirements. Cavity tests show BCS-limited Q well above 30 MV/m. Detailed process data, interpretation, and resulting rf performance data will be presented. |
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| THP032 | Status of the EP Simulations and Facilities for the SPL | cavity, simulation, controls, niobium | 824 |
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CERN is assembling a new vertical electropolishing facility in order to process several niobium cavities of beta 1 and beta 0.65 in the context of the HP-SPL R&D programme. Electrochemical simulations are being used in order to define the optimal cathode geometry to process the cavities in a vertical position. Macroscopic properties of fluid dynamics like the Reynolds number and thermodynamics linked to the power dissipated in the process are taken into account to dimension the main system components. All the materials from the different equipments must be compatible with all chemicals within the required working temperature and pressure. To provide safe operating conditions when handling chemicals or processing cavities, specific safety and protection equipment is also foreseen. |
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| THP033 | Superconducting Sputtered Nb/Cu QWR for the HIE-ISOLDE Project at CERN | cavity, plasma, niobium, linac | 827 |
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For the foreseen intensity and energy upgrade of the ISOLDE complex at CERN (HIE-ISOLDE project) a new superconducting LINAC based on sputtered Nb/Cu Quarter Wave Resonators (QWRs) of two different beta families will be installed in the next three to five years. A prototype cavity of the higher beta family is currently being developed. In this paper we will discuss the latest developments on the sputtering technique for this kind of cavity geometry. First cold RF measurements will be reported. |
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| THP056 | Development of a 300-Kv Solid State Modulator for an Argonne XFELO Injector* | gun, controls, high-voltage, power-supply | 881 |
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A solid state Marx-based pulsed voltage supply is being developed at Argonne National Laboratory (ANL) with the capability of providing 300-kV pulses with 0.5-μs rise time, 1-μs fall time, 2-μs pulse flat top, and up to 10-Hz repetition rate. The supply is designed to operate a direct current (DC) thermionic prototype gun producing ≈ 0.1-μm beam emittance, a part of the ANL x-ray free-electron laser oscillator (XFELO) injector feasibility studies. The pulsed supply utilizes isolated gate bipolar transistor (IGBT) devices. Stage switching allows this supply to quickly charge the 200-pF gun capacitance and maintain 300-mA gun current during the pulse flat top. A second string of IGBT switches charges the stage capacitors and acts as a 'crowbar' to quickly remove high voltage from the gun at the pulse's fall time or during load arcing. We present an overview of the design and development of the XFELO injector DC gun pulsed power supply. * Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH1137. |
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| THP058 | Power Supply System for Klystron in J-PARC Linac | linac, klystron, proton, status | 887 |
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This report will describe the present status of the power supply systems (PS systems) for the klystrons in the J-PARC (Japan Proton Accelerator Research Complex) linac. The technical specification, the operating experience, and the upgrade plan, of the PS systems will be presented in this report. Now the energy of the J-PARC linac is 181MeV, and the linac includes twenty 324MHz klystrons. In 2012, the energy will be upgraded to 400MeV, and the linac will include twenty 324MHz klystrons and twenty-five 972MHz klystrons. The klystrons are the modulating-anode types. The PS systems include the High voltage DC power supplies (DCPSs) and the anode-modulators. One DCPS drives one or four klystrons, and one anode-modulator drives one klystron. |
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| THP061 | Towards a Modulator for the XFEL RF Stations: Test Results of the Prototype from Thomson Multimedia | klystron, site, controls, linac | 893 |
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The European XFEL, an X-ray free electron laser, is planned as an European project with a strong connection to the DESY research center in Hamburg. Construction started in summer 2007 and commissioning will begin in 2014. The LINAC of the XFEL will incorporate 27 RF stations to supply the RF power required by the superconducting cavities. In order to generate this power (10MW at 1.3GHz) HV pulse modulators are required. Each modulator has to supply 12kV pulses at 1.6kA for 1.7ms pulse duration and at 10Hz nominal repetition rate. The repetition rate can be increased to 30Hz keeping the average power of the 10Hz operation. Although experience exists for FLASH with modulators constructed and built by one company two additional companies have been selected and contracted to design and to build additional prototypes of modulators according to the XFEL requirements. A test stand setup has been prepared at DESY, Zeuthen Site, in order to test and to operate these protoypes under similar conditions as at the XFEL. The presentation describes the Modulator Test Facility at DESY (Zeuthen Site) and presents and discusses test results of the modulator prototype from Thomson Multimedia. |
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| THP087 | Simulation of Cathode Back-bombardment in a 100 MHz Thermionic RF Gun | gun, electron, wiggler, simulation | 944 |
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A 100 MHz thermionic rf gun is under consideration as the electron source for the X-ray Free Electron Laser Oscillator*. Because the source must operate continuously, back-bombardment of the cathode is a serious concern. We present results of simulations of back-bombardment, as well as strategies for reducing the back-bombardment power on the cathode. *K. J. Kim et al., Phys. Rev. Lett. 100, 244802 (2008) |
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| THP097 | Development of a Thermionic Electron Gun of the L-band Linac for FEL Operation | electron, gun, FEL, linac | 965 |
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We are conducting FEL experiments with the L band electron linac at Osaka University. The linac is equipped with a thermionic electron gun and the three-stage sub-harmonic buncher(SHB) system. In FEL experiments an 8μs long electron pulse is injected from the gun and the SHB system is turned on for generating a multi-bunch electron beam of an 8μs duration with 2nC charge per bunch and 9.2 ns intervals between bunches. It repeatedly amplifies light pulses stored in the optical resonator of the FEL. The roundtrip time of the light pulses is 37 ns, so that four light pulses are stored in the resonator. The FEL gain becomes higher at least in proportion to the peak current in the bunch or charge per bunch. The present charge value is limited by the high beam loading in the acceleration tube of the linac, exceeding a half of the input RF power. If the bunch intervals can be extended to 37 ns, the charge per punch can be made four times higher for the same beam loading, resulting in significant increase of the FEL gain. To generate such an electron beam, we are developing the electron gun system with a high-repetition-rate grid-pulser. We will report the outline of the study. |
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| THP104 | S-Band Photocathode Gun with a 1 kHz Repetition Rate | gun, vacuum, simulation, coupling | 974 |
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Photocathode RF guns are widely used as injectors for accelerators requiring very high quality beams such as free electron lasers and linear colliders and recently used as ultrafast electron diffraction sources. Even with the limited repetition rate, normal conducting photocathode RF guns generate very low emittance and short pulse electron beams thanks to their high accelerating field and the efficient positioning of focusing solenoids. We report our activity of the design and production of an S-band normal conducting photocathode gun. The RF characteristics, thermal heating and vacuum analyses are discussed. |
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| THP105 | Design of a 1 kHz Repetition Rate S-Band Photoinjector | gun, emittance, solenoid, cavity | 977 |
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At many laboratories S-band photoinjectors operate to provide high quality beams; however the repetition rates are limited to about 100 Hz. This limitation mainly occurs due to the guns where a high RF amplitude of about 100 MV/m is required to keep the beam quality from the space charge force. In this paper we design an injector consisting of an S-band gun with improved cooling and S-band acceleration modules for a repetition rate up to 1 kHz. The technical feasibility and beam dynamics optimization are discussed. |
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| THP106 | Design of a 10 fs Electron Beam with a Photocathode RF Gun and an RF Buncher | gun, solenoid, electron, target | 980 |
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Ultrashort electron beams can be used for investigating ultrafast dynamics of physical, chemical or biological systems. With an S-band photocathode gun, simulations have been done in order to generate ultrashort electron beams. Optimizations to generate ultrashort electron beams with a small beam divergence and to minimize the system sensitivity against RF jitter are reported. |
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| THP107 | Experimental Investigation of Pulsed Laser Heating of Thermionic Cathodes of RF Guns | laser, gun, diagnostics, dipole | 983 |
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One proposed injector for the X-ray Free Electron Laser Oscillator* uses a 100 MHz thermionic rf gun to deliver very small emittances at a 1 MHz rate**. Since the required beam rate is only 1 MHz, 99\% of the beam must be dumped. In addition, back-bombardment of the cathode is a significant concern. To address these issues, we propose*** using a laser to quickly heat the surface of a cathode in order to achieve gated thermionic emission in an rf gun. We have investigated this concept experimentally using an existing S-band rf gun with a thermionic cathode. Our experiments confirm that thermal gating is possible and that it shows some agreement with predictions. Operational issues and possible cathode damage are discussed. *K. J. Kim et al., Phys. Rev. Lett. 100, 244802 (2008) |
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| THP108 | Pulsed Laser Heating of Thermionic Cathodes in RF Guns | laser, gun, electron, simulation | 986 |
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The proposed injector design for the X-ray Free Electron Laser Oscillator* uses a 100 MHz thermionic rf gun in order to obtain beams with very small emittances at high repetition rates**. The required beam rate is only 1 to 10 MHz, so 90 to 99\% of the beam must be dumped. In addition, back-bombardment of the cathode is a significant concern. To address these issues, we propose using a laser to quickly heat the surface of a cathode in order to achieve gated thermionic emission in an rf gun. This may be preferrable to a photocathode in some cases owing to the robustness of thermionic cathodes and the ability to use a relatively simple laser system. We present calculations of this process using analysis and simulation. We also discuss potential pitfalls such as cathode damage. *K. J. Kim et al., Phys. Rev. Lett. 100, 244802 (2008). |
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| THP109 | Potential for an Ultra-low Emittance Thermionic Triode Gun | gun, emittance, electron, space-charge | 989 |
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The proposed X-ray Free Electron Laser Oscillator* requires an ultra-low emittance gun that generates continuous electron bunches at 1 to 10 MHz. Recently, T. Shintake raised the possibility of using a pulsed triode gun with a thermionic cathode. In this paper, we investigate the feasibility for such a gun as part of an injector producing normalized emittances in the 0.1 μm range with 2 ps rms duration for 50 pC/bunch. We also explore some implementation concepts. *K. J. Kim et al., Phys. Rev. Lett. 100, 244802 (2008) |
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| THP111 | Development of a 500-kV Photo-Cathode DC Gun for ERL Light Sources | gun, high-voltage, radiation, electron | 995 |
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An electron gun capable of delivering high current and high brightness electron beam is indispensable for next generation energy recovery linac light sources. A high voltage photocathode DC gun is a promising gun for such new light sources. It is however difficult to apply DC high voltage on a ceramic insulator with a rod supporting cathode electrode because of field emission from the rod. In order to mitigate the problem, we have employed a segmented insulator with rings which guard the ceramics from the field emission and recently succeeded in applying 500-kV on the ceramics for eight hours without any discharge. This high voltage testing was performed with a simple configuration without NEG pumps and electrodes. The next step is to repeat the same high voltage testing with a full configuration necessary for beam generation. We have designed electrodes for the maximum surface electric field not to exceed 11 MV/m at 500 kV while keeping the distance between the electrodes 100 mm. NEG pumps with a pumping speed of 7200 L/s have been installed in the gun chamber. A photocathode preparation system was connected to the gun chamber and beam generation is planned this summer. |
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| THP112 | CW Superconducting RF Photoinjector Development for Energy Recovery Linacs | cavity, SRF, niobium, plasma | 998 |
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ERLs have the powerful potential to provide very high current beams with exceptional and tailored parameters for many applications, from next-generation light sources to electron coolers. However, the demands placed on the electron source are severe. It must operate CW, generating a current of 100 mA or more with a normalized emittance of order 1 μm rad. Beyond these requirements, issues such as dark current and long-term reliability are critical to the success of ERL facilities. As part of the BERLinPro project, Helmholtz Zentrum Berlin (HZB) is developing a CW SRF photoinjector in three stages, the first of which is currently being installed at HZB's HoBiCaT facility. It consists of an SRF-cavity with a Pb cathode and a superconducting solenoid. Subsequent development stages include the integration of a high-quantum-efficiency cathode and RF components for high-current operation. This paper discusses the HZB roadmap towards an ERL-suitable SRF photoinjector, the present status of the facility and first cavity tests. |