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| MOPCH025 | Laser Comb: Simulations of Pre-modulated E- Beams at the Photocathode of a High Brightness RF Photoinjector | laser, gun, electron, simulation | 98 | ||
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A density modulated beam at the photocathode though the proper modulation of the laser beam pulse does not change substantially emittance and energy spread, properties directly related to FEL. It has been found that bunch density modulation is transformed into energy modulation along the propagation through the injector*. There are some physical arguments that suggest a possibility to use this modulation for the enhancement of the FEL process, or for the production of plasma wakes. Preliminary beam dynamics studies have been carried on to explore the use of electron beam pre-modulation at the cathode to adjust their longitudinal structure at the end of the beamline. Energy modulation at the end of the beamline could eventually be turned into current modulation through a magnetic compressor with R56<0. The feasibility of this experiment has to be investigated carefully, preliminary studies are discussed here. This paper focuses on simulations that explore the properties of the energy modulation at the end of the beamline correlated to the initial characteristics of the train of electron pulses.
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*M. Biagini et al. “Beam Dynamics Studies for the SPARC Project”, Proc. of PAC03. |
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| MOPCH027 | Metal Film Photocathodes for High Brightness Electron Injectors | laser, gun, vacuum, target | 104 | ||
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Advanced high brightness injectors require photocathodes with fast response,high quantum efficiency and good surface uniformity. Both Mg films deposited by laser ablation and Pb films deposited by vacuum arc could satisfy these requirements. Their emission and morphology are compared.
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| MOPCH036 | Photocathode Roughness Impact on Photogun Beam Characteristics | emittance, electron, gun, FEL | 121 | ||
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Photocathode surface roughness has an impact on photoelectron yield, bunch duration, beam emittance at the exit of femtosecond photogun with an accelerating field that is considered in assumption of quasi-stationary one in the paper. The main problem in investigating the impact is determination of the field near the surface, statistical properties of which are defined through rms values of deviation and slope in profile line of the surface roughness. Developed and created code allows determining the field with relative rms error not worse than 0.001%. The results of the investigation for rms values of roughness and its slope within respectively 500…0 nm and 20…0 degrees are presented and discussed.
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| MOPCH041 | Design of a New Preinjector for the MAX Recirculator to be Used in EUROFEL | gun, emittance, linac, simulation | 130 | ||
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The MAX-lab recirculator injector will be equipped with a new preinjector system. The aim is to reduce the emittance, increase the charge and achieve a proper timing between accelerator and laser systems. All is aimed at the MAX-lab test facility for HG built in collaboration with BESSY in the EUROFEL program. The preinjector system consists of a photo cathode RF-gun with an emittance compensating solenoid. Special issues regard the injection of the new beam into the beam path of the MAX recirculator and the conservation of beam parameters.
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| MOPCH042 | Progress in the Design of a Two-Frequency RF Cavity for an Ultra-Low Emittance Pre-Accelerated Beam | emittance, injection, electron, coupling | 133 | ||
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Today most of the X-rays Free-Electron Laser projects are based on state of the art RF guns, which aim at a normalized electron beam emittance close to 1 mm$·$mrad. In this paper we report on the progress made at PSI towards a hybrid DC + RF Low Emittance Gun (LEG) capable of producing a beam with an emittance below 0.1 mm.mrad. To reduce the intrinsic thermal emittance at the LEG cathode the electrons are extracted from nano-structured field-emitters. A gun test facility is under construction wherein after emission the beam is accelerated up to 500 keV in a diode before being injected and accelerated in a two-frequency 1.5-cell RF cavity. The fast acceleration in the diode configuration allows to minimize the emittance dilution due to the strong space charge forces. The two-frequency RF structure is optimized to limit the emittance blow-up due to the non-linearity of the RF field.
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| MOPCH048 | Linac Coherent Light Source Electron Beam Collimation | linac, undulator, collimation, LCLS | 148 | ||
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This paper describes the design and preliminary simulations of the electron beam collimation system in the Linac Coherent Light Source (LCLS) linac. Dark current is expected from the gun and some of the accelerating cavities. Particle tracking of the expected dark current through the entire LCLS linac, from L0-linac exit to FEL undulator entrance, is used to estimate final particle extent in the undulator as well as expected beam loss at each collimator or aperture restriction. A table of collimators and aperture restrictions is listed along with halo particle loss results, which includes an estimate of average continuous beam power lost on each individual collimator. In addition, the transverse wakefield alignment tolerances are calculated for each collimator.
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| MOPCH168 | Novel Development on Superconducting Niobium Film Deposition for RF Applications | plasma, vacuum, ion, laser | 457 | ||
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A new deposition technology has been developed, based on a cathodic arc system working under UHV conditions, to produce metallic thin films. The technique presents several advantages compared to standard sputtering, mainly: ionized state of the evaporated material, absence of gases to sustain the discharge, higher energy of atoms reaching the substrate surface, possibility to apply bias to the substrate and to guide the arc plasma using magnetic fields. Recent results on superconducting Niobium films deposited under several conditions and on sapphire substrate are reported. A cavity deposition system has been developed and the plasma transport to the cavity cell studied
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| MOPCH184 | Plasma Treatment of Bulk Niobium Surfaces for SRF Cavities | plasma, electron, ion, controls | 493 | ||
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Cavity surface preparation has been one of the major problems in superconducting radio-frequency (SRF) accelerator technology. Accelerator performance depends directly on the physical and chemical characteristics at the SRF cavity surface. The primary objective of our work is to explore the effects of various types of electric discharge plasmas to minimize surface roughness and eliminate or minimize deterioration of cavity properties by oxygen, hydrogen and other chemical contaminants. To optimize the plasma etching process, samples of bulk Nb are being exposed to three types of electrical discharge in various experimental set-ups. The surface quality obtained by the three methods was compared with samples treated with buffer chemical polishing techniques. Surface comparisons are made using digital imaging (optical) microscopy, scanning electron microscopy, and atomic force microscopy. In preliminary tests, samples compared with those treated conventionally have shown comparable or superior properties. Tests have also shown that surface quality varies with plasma conditions and their optimization to obtain the best SRF cavity surface is a major goal of the ongoing work.
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| MOPLS095 | Investigations of DC Breakdown Fields | vacuum, CERN, CLIC, ion | 777 | ||
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The need for high accelerating gradients for the future 30 GHz multi-TeV e+e- Compact Linear Collider (CLIC) at CERN has triggered a comprehensive study of DC breakdown fields of metals in UHV. The experimental setup is based on a capacitor discharge across a gap junction. The simple design and fully automated computer control enable breakdown fields and dark current of numerous materials to be measured. The study shows that Mo, W and Ti reach high breakdown fields, and are thus good candidates for the iris material of CLIC structures. For untreated Mo the breakdown field is higher than Cu but the conditioning speed is slower. Ti, on the other hand, shows acceptable conditioning speeds, but material erosion makes this solution problematic. Feasible solutions to increase the spark conditioning speed for the case of Mo are presented together with attempts to prevent Ti erosion. For some of the materials studied a significant reduction in the saturated breakdown field was observed upon gas exposure during intensive spark conditioning. As an example, a 50% decrease of the breakdown field of Mo is recorded when spark conditioning is carried out in an environment of 10-5 mbar air.
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| TUPCH101 | Modeling of Ultrafast Streak Cameras | electron, simulation, acceleration, electromagnetic-fields | 1250 | ||
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We present progress on modeling of streak camera with application to measurement of ultrafast phenomena. Our approach is based on treating the streak camera as a photocathode gun and applying modeling tools for beam optics, space charge, and electromagnetic fields. We use these models to compare with experimental results from a streak camera developed at the Advanced Light Source. Furthermore, we explore several ideas for achieving sub-100 fsec resolution.
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| TUPCH113 | Construction of the ALPHA-X Photo-injector Cavity | gun, vacuum, electron, injection | 1277 | ||
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We will describe the construction and low power testing of an RF cavity to be used as a photo-injector for the ALPHA-X project within the Department of Physics at the University of Strathclyde (UK). The gun is a two and a half cell S-band cavity, employing a metallic photo-cathode. RF power is coupled to the gun via a co-axial power coupler. The specification of the gun and the low power measurements made to achieve the correct mode frequency and field flatness will be presented.
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| TUPCH154 | RF Amplifier for Next Generation Light Sources | controls, power-supply, monitoring, vacuum | 1385 | ||
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This paper describes the design concepts and development issues around generating a compact 16kW 1.3GHz RF amplifier for use in the next generation of light sources. These amplifiers need to be operated for extended periods to maximise use of the facility and so high reliability and availability are of key importance. Equally important are the capabilities to have extensive self-monitoring and fault prediction, autonomous operation, low heat dissipation to air, and easy maintenance. The design and development of such an RF amplifier based on the latest e2v technologies 1.3GHz inductive output tube (IOT) will be described. The RF amplifier equipment makes extensive use of commercially available products and industry collaborations to produce an amplifier that meets all the requirements yet can be manufactured and operated in a most cost effective manner. Prototype equipment will be shown at EPAC 06.
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| TUPCH156 | Design and Simulation of a Cusp Gun for Gyro-amplifier Application in High Frequency RF Accelerators | electron, gun, simulation, cyclotron | 1391 | ||
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Gyro-amplifiers have potential as the high frequency RF drivers for particle accelerators. They require relativistic electron beams with low velocity spread and with a high fraction of the electron energy associated with the cyclotron motion. For harmonic operation and mode control an axis-encircling beam is desirable. The passage of an electron beam through a non-adiabatic magnetic field reversal (cusp) converts part of the electron beam's axial velocity into axis-encircling transverse velocity. A cusp-based electron beam forming system, yielding a 10MW, 150kV, 70A axis-encircling beam will be presented. This cusp gun is being designed as the electron beam source for a microwave gyro-amplifier that is relevant for high frequency accelerator applications. The latest results from numerical simulations and experiments will be presented and compared.
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| TUPCH164 | Ka-band Test Facility for High-gradient Accelerator R&D | vacuum, SLAC, CLIC, DIAMOND | 1408 | ||
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Achievement of high acceleration gradients in room-temperature structures requires basic studies of electric and magnetic RF field limits at surfaces of conductors and dielectrics. Facilities for such studies at 11.4 GHz have been in use at KEK and SLAC; facilities for studies at 17.1 GHz are being developed at MIT and UMd; and studies at 30 GHz are being conducted at CERN using the CLIC drive beam to generate short intense RF pulses. Longer pulse studies at 34 GHz are to be carried out at a new test facility being established at the Yale Beam Physics Laboratory, built around the Yale/Omega-P 34-GHz magnicon. This high-power amplifier, together with an available ensemble of components, should enable tests to be carried at up to about 9 MW in 1 mcs wide pulses at up to four output stations or, using a power combiner, at up to about 35 MW in 1 mcs wide pulses at a single station. RF pulse compression is planned to be used to produce 100-200 MW, 100 ns pulses; or GW-level, 1 mcs wide pulses in a resonant ring. A number of experiments have been prepared to utilize multi-MW 34-GHz power for accelerator R&D, and users for future experiments are encouraged to express their interest.
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| TUPCH175 | The Vacuum System of FAIR Accelerator Facility | vacuum, cryogenics, ion, quadrupole | 1429 | ||
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The FAIR accelerator complex consists of two superconducting synchrotrons (SIS100 and SIS300) with a circumference of 1083.6m each, a high energy beam transport system (HEBT) with a total length of about 2.5km and four storage rings (CR, RESR, HESR and NESR). Their length varies between 200m and 550m. For each of the subsystems, different vacuum requirements have to be fulfilled. The vacuum system of SIS100 and SIS300 consists of cryogenic and bakeable room temperature sections, where a pressure in the lower 10-12 mbar range is needed. For HEBT, also a combination of cryogenic and room temperature sections, a vacuum pressure of 10-9 mbar is sufficient. The storage rings will be operated in a pressure range from 10-9 mbar to 10-12 mbar. In the poster a detailed layout of the vacuum systems and technical solutions will be presented.
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| TUPCH178 | Deposition of Non Evaporable Getter (NEG) Films on Vacuum Chambers for High Energy Machines and Synchrotron Radiation Sources | vacuum, synchrotron, electron, controls | 1435 | ||
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Non Evaporable Getter (NEG) films, sputter deposited onto the internal surfaces of vacuum chambers reduce thermal out-gassing and provide conductance-free distributed pumping ability, allowing the achievement of very low pressure inside narrow and conductance limited chambers, like Insertion Devices. NEG films do show additional interesting features, like low secondary electron yield and low gas de-sorption rates under ions, electrons and photons bombardment. They seem therefore ideal to reduce electron multi-pacting and dynamic gas de-sorption induced beam instabilities in high energy machines. This paper presents SAES getters experience in the NEG coating of chambers of different geometries and sizes for a variety of projects related to high energy machines and synchrotron radiation facilities. Examples of applications, as well as most common issues related to chambers preparation, film deposition, characterization and quality control, are given. Areas where further work is still necessary to fully take advantage of NEG film properties will be also discussed.
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| TUPLS064 | Design and Commissioning of a Compact Electron Cooler for the S-LSR | electron, gun, proton, ion | 1639 | ||
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The ion cooler ring S-LSR has been constructed and commissioned in October 2005. The ring successfully stored a 7 MeV proton beam. The S-LSR is equipped with a compact-electron cooler which has a cooling solenoid length of 0.8 m, a toroid bending radius of 0.25 m and maximum magnetic field in the cooling section of 0.5 kG. The commissioning of the electron cooler was carried out with successful observation of both longitudinal and horizontal cooling of the proton beam. By varying the electric potential on the Pierce electrode in the gun, we have investigated the possibility of generating a hollow shaped electron beam, and studied its effect on the electron cooling process. Also the effect of the electrostatic deflector, installed in the toroid section in order to compensate the drift motion of the secondary electrons, was investigated. The design and results of the commissioning of the compact electron cooler are presented.
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| TUPLS066 | Peculiarities of Electron Cooler Operation and Construction at Ultra Low Energy in an Electrostatic Ring | electron, target, ion, KEK | 1645 | ||
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Few projects of electrostatic rings with electron cooler are discussed now. Electron cooling at low electron energy of 10 eV was realized at the KEK electrostatic ring. The electron cooling permits to suppress the ion multi scattering on residual gas atoms and allows increasing the ion lifetime. Peculiarities of an electron cooler operation and construction at ultra low energy in an electrostatic ring are considered. The cooler gun operation regime is cardinally changed at a reduction of the electron energy to a value comparable with a cathode work function. A virtual cathode and ohmic resistance of cathode emitter give an input in beam formation at ultra low energy. Effective electron cooling of heavy atomic and bimolecular ions at mass of 100-1000 is reached at a small photocathode diameter of 1 mm and a high magnetic expansion factor of 10-1000. The electron cooler construction has traditional design in KEK electrostatic ring. The cooler construction can be simplified at a small circumference of electrostatic ring. Straight cooler schemes without toroidal magnets permit to reduce ring space required for electron cooler.
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| TUPLS069 | Performance of Fermilab's 4.3 MeV Electron Cooler | electron, antiproton, gun, focusing | 1654 | ||
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A 4.3 MeV DC electron beam is used to cool longitudinally an antiproton beam in the Fermilab's Recycler ring. The cooling rate is regulated either by variation of the electron beam current up to 0.5 A or by a vertical separation of beams in the cooling section. The paper will describe steps that provided a stable operation and present the status of the cooler.
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| TUPLS088 | Energy Distribution of H- Ions from the ISIS Ion Source | ion, controls, ion-source, focusing | 1708 | ||
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We have used a specially designed retarding field energy analyzer with a resolution (Δ E /E) of approximately 2 x 10 -4 in order to measure the energy distribution, under different operating conditions, of the H- beam of the ISIS ion source. The poster presents the details of the analyzer and the first results obtained on the Ion Source Test Facility at RAL.
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| TUPLS089 | Pseudospark-sourced Beams of Electrons and Ions | electron, acceleration, brightness, ion | 1711 | ||
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A pseudospark discharge has undergone intensive studies with regard to its unusual and interesting discharge properties during last fifteen years. The pseudospark attracts significant attention from diverse fields such as pulsed-power switching, electron beam generation, free electron masers, ion beam generation, extreme-ultraviolet radiation sources, microthrusters and pseudospark-triggered wakefield acceleration. This paper will present experiments and measurements of pseudospark-sourced electron and ion beams for accelerators. Pulsed electron beams with current intensity over 108 Am-2, high brightness up to 1012A m-2 rad-2 and emittance of tens of mm mrad were produced from a multi-gap pseudospark discharge. The transportation of the pseudospark electron beams is also investigated in order to produce high peak current, high quality, short (~100 picosecond) or long duration (2~100ns) high-brightness electron beam pulses. Recent results from a high current density pseudospark-produced ion beam experimentally investigated with hydrogen gas will be presented.
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| TUPLS105 | Sputter Probes and Vapor Sources for ECR Ion Sources | ion, plasma, electron, ion-source | 1744 | ||
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Sputter probes are a promising method for injecting controlled quantities of metallic elements inside ECRIS ion source, provided that sputter rate can be controlled, so that high charge states and low sample consumption rate will be attained. Moreover pressure at the probe and inside source should be different. With a simple differential pumping scheme and a sputter probe at 25 mm from ECRIS plasma, a 200 nA current of 120Sn18+ was easily obtained. Typical results (for Sn and Ti) of an inductively heated rf oven are discussed for comparison. Improvements of sputter probe concept and geometry are also described.
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| WEPCH022 | Study of the Effect of Multipolar Components in the SPARC Emittance Compensation Gun Solenoid | emittance, quadrupole, multipole, gun | 1969 | ||
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The SPARC photoinjector rf gun requires a solenoid immediately downstream for emittance compensation. The analysis of the measured solenoid magnetic maps shows the existence of multipolar components added to the pure solenoid field. The effect of these added fields on beam dynamics and possible correction schemes have been studied from the theoretical point of view and by numerical calculations based on PARMELA/TREDI codes. An accurate 3D numerical modelization by using CST EM Studio has been done, in order to investigate the source of these multipolar components and to suggest some design modifications aimed to reduce their magnitude. The results of this study are presented here.
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| WEPCH054 | Matrix Formalism for Current-independent Optics Design | focusing, emittance, optics, space-charge | 2044 | ||
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Matrix formalism has been a powerful tool for beam optics designs. It not only facilitates computations but also plays an important role in formulating various design concepts. Here we extend the standard matrix formalism for the purpose of designing an optics that transports space-charge-dominated intense beam. Furthermore, we explore the concept of current-independent optics, which can be useful for systems such as high-brightness injectors and space-charge-dominated rings. Our discussion here is preliminary and limited to axisymmetric systems.
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| WEPCH166 | Beam Test of Thermionic Cathode X-band RF-gun and Linac for Monochromatic Hard X-ray Source | laser, electron, photon, linac | 2319 | ||
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A compact hard X-ray source based on laser-electron collision is proposed. The X-band linac is introduced to realize a very compact system. 2MeV electron beam with average current 2μampere at 10 pps, 200 ns of RF pulse is generated by a thermionic cathode X-band RF-gun. Beam acceleration and X-ray generation experiment by the X-band beam line are under way.
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| WEPCH172 | Electron Beam Pulse Processing toward the Intensity Modified Radiation Therapy (IMRT) | electron, radiation, laser, gun | 2334 | ||
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Radiation therapy attracts attention as one of the cancer therapies nowadays. Toward the next generation of the intensity modified radiation therapy (IMRT), the processing of electron beam pulse is studied using a photo cathode RF gun linac. Accelerated electron pulses will be converted to x-ray pulses by a metal target bremsstrahlung method or by a laser inverse Compton scattering method. Recently, the radiation therapy of cancer is developing to un-uniform irradiation as IMRT. A photo cathode RF gun is able to generate a low emittance electron beam pulse using a laser light pulse. We thought that a photo cathode RF gun can generate intensity and shape modified electron beam by processing of incident laser light. Because of a low emittance, an electron pulse is able to accelerate keeping shape. Electron beam processing by photo masks in incident optical system and generated beams are reported here. Images on photo masks were transported to a cathode surface by optical relay imaging. Beams were monitored by Desmarquest (Cr:Al2O3) luminescence. Spatially separation of a spot to a spot is about 0.3mm. Modified electron beam has fine spatial resolution.
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| WEPCH184 | Mechanical Properties of WC-Co by Nitrogen Ion Implantation: Improvement of Industrial Tools | ion, ion-source, heavy-ion, vacuum | 2364 | ||
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Ion implantation of WC-Co has been widely investigated for the improvement of wear resistance, but rarely for friction behavior. Although friction is closely associated with wear, more factors influence friction than wear, and low wear does not generally lead to low friction w6x. Therefore, we focus our study on the effects of ion implantation on the mechanical properties in WC-Co cermets, with particular interest in tool industry applications.
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| WEPLS028 | Improvement of Electron Generation from a Laser Plasma Cathode through Modified Preplasma Conditions Using an Artificial Prepulse | laser, electron, plasma, acceleration | 2448 | ||
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We have been studying the effects of laser prepulses, plasma cavity formation, wave breaking processes in the laser plasma acceleration. It is important to control the preplasma conditions, so as to stabilize the laser plasma acceleration. The modification of the conditions of the laser plasma interaction through an artificial prepulse, magnetic fields, and/or gas density modulation will affect on the characteristics of accelerated electron beams. As the first step, we carry out experiments with an artificial prepulse. If a shockwave driven by the artificial prepulse matches the main pulse foccal position, localized wave breaking may occur effectively, and consequent electron generation will be enhanced. We use a pulse with 10% energy of the main pulse and 300 ps duration to be focused on the interaction point of the gas jet, to change the plasma distribution there. Using the single-shot diagnosis, we investigate the mechanism and technique to improve the properties of electron beams. We observed a strong correlation between the generation of monoenergetic electrons and optical guiding of the main pulse, during the interaction of 11 TW 37 fs laser pulse and He gas jet.
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| WEPLS029 | Monoenergetic 200fs (FWHM) Electron Bunch Measurement from the Laser Plasma Cathode | electron, radiation, laser, plasma | 2451 | ||
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A laser plasma accelerator is the most promising approach to compact accelerators that can generate femtosecond electron bunches. It is expected that the electron bunch duration less than 100fs can be achieved owing to the high frequency of plasma waves. Since the time-resolution of the fastest streak camera is only 200fs, we have to use the coherent transition radiation (CTR) measurement or E/O (electro-optical) method. We plan to perform a single-shot measurement by getting the whole CTR spectrum by a IR polychromator in near future. As the first step forward it, we used a IR bolometer with different filters and obtained the average spectrum. We can generate monoenergetic electron bunches in the condition of laser intensity 3x1019W/cm2 and electron density 6x1019cm-3. The charge is estimated to be about 10pC using ICT (Integrated Current Transformer). The electron bunch accelerated by plasma waves penetrates 300um Ti-foil, and transition radiation is emitted. We measure CTR spectrum using a bolometer. Spectrum distribution of CTR depends on the electron bunch distribution, therefore we can evaluate the bunch duration from it. In the experiment, bunch duration can be estimated.
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| WEPLS043 | Progress of the Rossendorf SRF Gun Project | gun, ELBE, TESLA, vacuum | 2469 | ||
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In this paper we report the status and the progress of the superconducting RF gun project in Rossendorf. The gun is designed for cw operation mode with 1 mA current and 10 MeV electron energy. The cavity consists of three cells with TESLA geometry, a special designed half-cell in which the photo cathode will be inserted and a choke filter, which prevents the leakage of RF power by the coaxial line between the cathode and the cavity cell. A double tuner allows the tuning of the half-cell and the TESLA cells separately. In 2005 the fabrication of two cavities with RRR300 and RRR40 was finished. We present the results of the field measurement and the warm tuning of the cavity cells as well as the tuning and performance measurement of the choke filter. The fabrication of the double tuner has been also finished. In a test bench we measured the properties of the tuner (tuning range, resolution) at LN2 temperature. Further activities concern the diagnostic beam line of the gun, the new cathode preparation and cathode transfer system, the driver laser and the LHe transfer line.
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| WEPLS044 | Design of a Superconducting Cavity for a SRF Injector | emittance, gun, laser, electron | 2472 | ||
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In a collaboration between BESSY, DESY, FZR, MBI and BINP a 3-1/2 cell superconducting RF electron gun is under development at the FZ - Rossendorf. The status of the project and the progress obtained in the last year is reported on this conference. The motivation for the design of a new gun cavity, presented in this paper, is the new FEL project at BESSY. This FEL is designed for a bunch charge of 2.5 nC and the transverse emittance should be comparable with that of the current SRF gun project. In order to compensate the high bunch charge a high electric field on the cavity axis is necessary. In the present paper we will present the design of a 1-1/2 cell cavity for a superconducting RF gun. The active length of the cavity (without beam tube) is 14.4 cm. For the magnetic peak field the conservative value of 130 mT is assumed. The obtained particle energy is 6.6 MeV, corresponding to an accelerating field strength of 45.6 MV/m . In the TESLA cavity the same magnetic peak field is connected with an accelerating field strength of approximately 31 MV/m. Tracking calculation of electron bunches are in progress and will be also reported.
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| WEPLS047 | 3-1/2 Cell Superconducting RF Gun Simulations | gun, emittance, simulation, focusing | 2481 | ||
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A 3-1/2 cell superconducting RF photocathode gun is being developed at Forschungszentrum Rossendorf to produce a high peak current, low emittance electron beam. This technology is essential to the realisation of many large scale facilities. The gun is designed for CW operation mode with 1 mA current and 9.5 MeV electron energy, and it will be installed at the ELBE superconducting electron linear accelerator. The gun will have a 3-1/2 cell niobium cavity operating at 1.3 GHz. The cavity consists of three cells with TESLA geometry and a specially designed half-cell in which the photocathode will be placed. Typical ERL-based projects require ~100 mA average current, and therefore suitable upgrade paths are required. Simulations have been carried out to evaluate the design and to determine suitable upgrades for higher current operation. Simulations of alternative cathode surface shapes are presented. Several couplers have been identified that can provide higher power to the cavity, whose integration and suitability has been verified. All the investigations that have identified possible solutions to higher current operation are discussed in this report.
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| WEPLS051 | Dark Current Investigation of TTF and PITZ RF Guns | gun, PITZ, DESY, LEFT | 2493 | ||
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The dark current is one of the limiting factor in the operation of RF guns at high gradient. The continuous request of higher brilliance sources and further emittance minimization, leads to apply higher gradients in the RF gun cavity, with the consequence of a significant dark current production. In this context we set up a collaborative effort to identify the dark current sources in the gun, in order to discriminate between the gun and cathode contribution. A critical analysis and organization of dark current measurements, taken during the operation of TTF and PITZ guns, with several cathodes operated at different accelerating fields and solenoids focusing, is presented. Potential areas of improvement are also discussed, together with a possible associated program.
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| WEPLS052 | High QE Photocathode at FLASH | gun, laser, vacuum, electron | 2496 | ||
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The RF gun-based photoinjector of the VUV-FEL/TTF at DESY continues to use high quantum efficiency (QE) photocathodes produced at LASA, Milano. To study the photocathode behavior during beam operation, an online QE monitoring tool has been installed. In this paper, we present the hardware and software setup for the online QE measurement and the results so far obtained. The measured QEs are usually higher than at TTF phase 1. We compare the QE values taken in the RF gun with data measured just after production with a continuous UV light source.
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| WEPLS053 | RF Design of a Cartridge-type Photocathode RF Gun in S-band Linac | linac, gun, vacuum, simulation | 2499 | ||
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A cartridge-type photocathode RF gun is under development in collaboration with SPring-8 and Hamamatsu Photonics. Each type of cathode (Cs2Te, Mg, diamond, Ag-Cs-O) is sealed in a cartridge-type vacuum tube. Several tubes can be installed in a vacuum chamber. The cathode in the tube is inserted into a center hole in the back plate of the RF gun by a vacuum manipulator. These cartridge-type photocathodes with high QE or sensitivity for visible lights, which are prepared in a factory, can be used for a long time without vacuum breaking. Since a load-lock system for forming a new high QE film is not needed, the cartridge-type RF gun becomes compact. We are going to introduce this cartridge-type system to our linac with the BNL-GUN-IV RF gun this summer. Now, we are calculating the gun parameters of the transmission cavity which has a back plate with a center hole 8mm in diameter with SUPERFISH and simulating the beam dynamics after modifying the beam line to install the system with PARMELA. We aim to use reliable Mg and high-QE Cs2Te and try diamond and Ag-Cs-O for radiation chemistry applications. The detailed numerical design and construction will be presented.
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| THOPA02 | Status of the SCSS Test Accelerator and XFEL Project in Japan | emittance, electron, undulator, radiation | 2741 | ||
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Construction of the SCSS* 250 MeV test accelerator was completed in October 2005, and the beam commissioning was started in November 2005. The first light at visible wavelength, which is the spontaneous radiation from undulator, was observed right after machine commissioning. We expect the first SASE beam around 60 nm in 2006. The purpose of the test accelerator is to assemble all hardware components in a real machine, and check their performance, reliability and stability. It is also very important to build all control software and link to the main frame to see system performance. All experience will provide feedback to 8 GeV XFEL design, whose construction will start in April 2006.
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*http://www-xfel.spring8.or.jp |
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| THPCH010 | Electron Beam-laser Interaction near the Cathode in a High Brightness Photoinjector | laser, electron, emittance, space-charge | 2805 | ||
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The production of high charge short bunches in a high brightness photoinjector requires laser pulses driving the cathode with GW range peak power on a mm spot size. The resulting transverse electric field experienced by the electron beam near the cathode is of the order of 200-500 MV/m, well in excess of a typical RF accelerating field of 50-100 MV/m. We present here an analytical and computational study of the resultant beam dynamics. Simulations including the electron beam-laser interaction have been performed with the code HOMDYN taking into account the superposition of incident and reflected laser pulses as well as space charge fields. Under this conditions the emittance degradation is negligible, as predicted by analytical methods, but a longitudinal charge modulation occurs on the scale of the laser wavelength, in case of oblique incidence, driven by the longitudinal component of the laser field. Preliminary simulations up to the photoinjector exit show that charge modulation is transformed into energy modulation via the space charge field, which may produce enhanced microbunching effects when the beam is further compressed in a magnetic chicane.
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| THPCH151 | Commissioning of the Laser System for SPARC Photoinjector | laser, simulation, gun, emittance | 3146 | ||
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In this paper we report the commissioning of the SPARC photoinjector laser system. In the high brightness photoinjector the quality of the electron beam is directly related to the features of the laser pulse. In fact the temporal pulse shape, the temporization and the transverse distribution of the electron beam is determined by the incoming laser pulse. The SPARC laser system is based on an amplified Ti:Sapphire active medium and the pulse shape is imposed by a programmable acousto-optics dispersive filter. The transfer-line has been designed to reduce the angular jitter and to preserve to the cathode the temporal and spatial features of the laser pulse. The laser system has been integrated with the accelerator apparatus. The diagnostics and the control system has been completed. We present the measured performances and the simulations we carried out.
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| THPCH152 | Temporal Quantum Efficiency of a Micro-structured Cathode | laser, electron, target, simulation | 3149 | ||
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In this work the experimental and simulation results of photoemission studies for photoelectrons are presented*. The cathode used was a Zn disc having the emitting surface morphologically modified. Two different excimer lasers were employed like energy source to apply the photoelectron process: XeCl (308nm, 10ns) and KrF (248nm, 20ns). Experimental parameters were the laser fluence (up to 70 mJ/cm2) and the anode-cathode voltage (up to 20 kV). The output current was detected by a resistive shunt with the same value of the characteristic impedance of the sistem, about 100 ?. In this way, our device was able to record fast current signals. The best values of global quantum efficiency were approximately 5x 10-6 for XeCl and 1x 10-4 for KrF laser, while the peaks of the temporal quantum efficiency were 8x 10-6 and 1.4x10-4, respectively. The higher efficiency for KrF is ascribed to higher photon energy and to Schottky effect. Several electron-beam simulations using OPERA 3-D were carried out to analyze the influence of the geometrical characteristics of the diode. Simulating the photoemission by cathodes with micro-structures the output current was dependent on cathode roughness.
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*L. Martina et al. Rev. Sci. Instrum., 73, 2552 (2002). |
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| THPCH161 | Status of the Polarized Electron Gun at the S-DALINAC | electron, laser, gun, quadrupole | 3173 | ||
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Aiming at an extension of the experimenting capabilities for nuclear structure physics at low momentum transfer at the superconducting Darmstadt electron linear accelerator S-DALINAC, a polarized electron gun is being constructed. The new injector will be able to supply the S-DALINAC with 100 keV polarized electrons and should complement the present, unpolarized thermionic source. The design requirements are a degree of polarization of at least 80%, a mean current intensity of 0.06 mA and a 3 GHz cw structure. The basic design of the gun was adapted from the source of polarized electrons at MAMI, Mainz*, and optimized in various simulations. The active material is a strained layer GaAs crystal which is exposed to an 830 nm pulsed laser beam. We report on the status of the polarized source, the preparation setup and a test beam line.
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*K. Aulenbacher et al., Nucl. Instrum. Meth. A 391, 498 (1997). |
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| THPCH165 | ERLP Quantum Efficiency Scanner | laser, ERLP, controls, linac | 3179 | ||
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The Energy Recovery Linac Prototype (ERLP) under construction at Daresbury Laboratory will utilise a photoinjector as its electron source. In order to characterise the performance of the photo-cathode wafer, a low power laser is scanned across its surface and the resultant current measured to build up a map of the quantum efficiency of the wafer.
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| THPCH174 | Multipactor Electron Gun with CVD Diamond Cathodes | electron, DIAMOND, gun, ion | 3203 | ||
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A Multipactor Electron Gun (MEG) is developed for the high power microwave generation in the Accelerator Lab of Tsinghua University. This paper presents the recent experimental results of the S-band MEG using hydrogen-terminated and CsI-terminated CVD diamond cathodes. The gun design, cathode preparation and high power experiment are described. An electron beam with 5 μs macro-pulse, 10 Hz repetition rate, greater than 900 mA beam current was obtained.calculation and computer simulation. The properties of the secondary electron emission cathodes are also discussed.
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| THPCH176 | Deposition of Lead Thin Films Used as Photo-cathodes by Means of Cathodic Arc under UHV Conditions | vacuum, plasma, gun, ion | 3209 | ||
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The cathodic arc technology has been used for various technical purposes for many years. Recently, it has been demonstrated that the cathodic arc can be operated under ultra-high vacuum (UHV) conditions and it might solve the problem of the oxygen contamination coming from water remnants. It opens a new road to many applications where very pure metallic and/or superconducting films are needed. The paper reports on recent experimental studies aimed on the deposition of superconducting films of pure lead (Pb) by means of the UHV cathodic arc. Such layers can be used as photo-cathodes needed for modern accelerator injectors. The system configuration, used for thin film deposition inside the RF Gun designed at DESY, is also described and the main results and characteristics of thin superconducting Pb-films are presented.
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| THPCH193 | Comparison between H-ion and Heat Cleaning of Cu-metal Cathodes | gun, DIAMOND, GTF, LCLS | 3245 | ||
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Understanding the quantum efficiency (qe) of a metal photocathode in an s-band RF gun is important to limit the drive laser energy requirement and provide the best quality electron beam. Systematic measurements of the qe vs. wavelength for varying surface contamination have been performed on copper samples using x-ray photoelectron spectroscopy (XPS). The sample is first cleaned to the theoretical limit of qe using a 1 keV hydrogen ion beam. The H-ion beam cleans an area approximately 1cm in diameter and has no effect on the surface roughness while removing essentially all contaminants and lowering the work function to 4.3eV. The sample is then exposed to atmospheric contaminants (nitrogen and oxygen) and measured again with XPS to determine the degree of contamination and the effect on the qe. The goal is to determine the best procedure for transferring and installing cathodes in an s-band gun. These results and comparison with a heat cleaned cathode are presented.
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| THPLS066 | Improvement on the Single Bunch Operation of the TLS Injector | electron, gun, booster, linac | 3439 | ||
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The improvement of the TLS (Taiwan Light Source) injector on single bunch operation is presented in this study. Limited by the existing design of the TLS injector, the single bunch operation was not optimized in terms of bunch purity for specific users of TLS. A high voltage pulser was implemented to improve the situation. This pulser has been integrated into the high-voltage-deck electronics of electron gun for single bunch generation. Both high-voltage pulses and the associated electron bunches are monitored with a wideband digital oscilloscope. The result shows that the bunch purity can be greatly improved by using the newly installed pulser. It also greatly eliminates the beam losses while injected into the booster ring.
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| THPLS092 | Nb-Pb Superconducting RF-Gun | dipole, DESY, laser, emittance | 3493 | ||
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We report on the status of an electron RF-gun made of two superconductors: niobium and lead. The presented design combines the advantages of the RF performance of bulk niobium superconducting cavities and the reasonably high quantum efficiency of lead, as compared to other superconducting metals. The concept, mentioned in a previous paper, follows the attractive approach of all niobium superconducting RF-gun as it has been proposed by the BNL group. Measured values of quantum efficiency for lead at various photon energies, analysis of recombination time of photon-broken Cooper pairs for lead and niobium, and preliminary cold test results are discussed in this paper.
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| THPLS093 | Status of the Photocathode RF Gun System at Tsinghua University | gun, laser, scattering, BNL | 3496 | ||
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An S-band high gradient photocathode RF gun test stand is in construction process at Tsinghua University. The photocathode RF gun test stand is a primary step of a femtosecond hard x-ray source based on Thomson scattering. The photocathode RF gun system adopts Ti:Sap laser, BNL IV type 1.6 cell RF gun, compact compensation solenoid. We foresee to conduct investigations on the thermal emittance contribution of surface roughness, the emittance compensation technique under various laser shape and its application to Thomson scattering x-ray source. Except for the transportation of laser, correction of laser front for glazing incidence and laser pulse shaping system, other parts of the photocathode RF gun test stand have been constructed, and we can start very primary experiment on the RF gun test stand, such as measurements of dark current, QE and energy of the beam. The experimental results are reported.
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| THPLS094 | First Measurement Results at the LEG Project's 100 keV DC Gun Test Stand | emittance, gun, diagnostics, SNR | 3499 | ||
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The Low Emittance Gun Project (LEG) at PSI aims at developing a high-brightness, high-current electron source: a 20-fold improved brightness compared to present state-of-the-art electron guns. The source is intended to form the basis for a cost-efficient implementation of a high-power X-ray FEL light-source for scientific research at PSI. A field emitter array (FEA) cathode is being considered a source candidate. In order to study pulsed field emission from such a cathode and to investigate space charge compensation techniques as well as to develop diagnostic procedures to characterize the beam resulting from an FEA cathode, a 100 keV DC gun test stand has been built. The test stand gun and diagnostics have been modeled with the codes MAFIA and GPT. From extensive parameter studies an optimized design has been derived and construction of the gun and diagnostics have recently been completed. We report on the commissioning of the test stand and present first measurement results.
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| THPLS104 | Optimization Studies of the FERMI@ELETTRA Photoinjector | emittance, laser, electron, gun | 3520 | ||
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In the framework of the FERMI@ELETTRA project the electron beam characteristics strongly depend from the two operating modes: FEL1 (100nm-40nm) with a photon pulse around 100fs and FEL2 (40nm-10nm) with a long photon pulse (~1ps) having a high resolution spectral bandwidth. We present the multi-particles tracking code results concerning the photoinjector, which includes the RF gun and the first two accelerating sections, describing two possible electron bunch lengths, satisfying the two FEL operation modes. The injector optimization relative to the two options, aimed to produce a very low projected emittance (around 1 mm mrad) with a uniform behavior of the slice parameters (emittance and energy spread) along the bunch, is described in this paper. Moreover sensitivity studies, time and energy jitters estimations are presented for both cases.
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| THPLS105 | Characterization of the SPARC Photo-injector with the Movable Emittance Meter | emittance, laser, space-charge, diagnostics | 3523 | ||
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As a first stage of the commissioning of SPARC accelerator a complete characterization of the photo-injector is planned. The objective is the optimization of the RF-gun setting that best matches the design working point and, generally, a detailed study of the emittance compensation process providing the optimal value of emittance at the end of the linac. For this purpose a novel beam diagnostic, the emittance-meter, consisting of a movable emittance measurement system, was conceived and built. This paper presents the results of the first measurements with the emittance-meter showing the characteristics and the performance at the SPARC photo-injector.
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| THPLS108 | Performance Test of RF Photo-Cathode Gun at the PAL | gun, laser, emittance, electron | 3529 | ||
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A RF photo-cathode (RF PC) gun with 1.6 cell cavity is installed for the fs-FIR (Femto-second Far Infrared Radiation) facility being built at the Pohang Accelerator Laboratory (PAL). A short, intense, and low emittance electron beams are produced by the RF PC gun. Performance test of the gun is done include the measurement of RF chraterizations such as a resonant frequency, a mode separation, and etcs. The diagnostics of the beam according to the beam parameters such as phase, charge, and energy, and emittance are done. In this article, we present the measurement results of the RF charaterizations and the beam parameter diagnostics of the RF PC gun at the PAL.
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| THPLS115 | Simulation and Optimisation of a 100 mA DC Photo-Injector | electron, emittance, gun, ASTRA | 3550 | ||
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A prototype 100mA injector is presently being designed and manufactured jointly between Thomas Jefferson National Accelerator Facility (J-Lab) and Advanced Energy Systems (AES). This paper discusses the physics optimisation and performance of the injector, which has been studied using the space-charge tracking code ASTRA. The objective is to operate the 7MeV injector with 135pC electron bunches at 748.5MHz repetition rate. We show that the longitudinal and transverse electron bunch properties can be realised within the constraints of the design.
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