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| MOPC001 | The Status of TAC Infrared Free Electron Laser (IR-FEL) Facility | 61 |
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| Turkish Accelerator Complex (TAC) Infrared Free Electron Laser (IR-FEL) project was approved by State Planning Organization (DPT) as a first step of the national project. The facility will consist of 15 40 MeV superconducting electron linac and two different optical cavity systems with different undulator period length to obtain FEL in 2 185 microns wavelengths range. In this study, the results of optimization and current status of TAC IR FEL facility is presented. The facility will give opportunity to search applications in material science, biotechnology, nonlinear optics, semiconductors, medicine and chemistry using IR-FEL in Turkey and our region. | ||
| MOPC002 | Extension of the FERMI FEL1 to Shorter Wavelengths | 64 |
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We propose a modification of the first stage (FEL-1) of the FERMI@Elettra project in order to extend the wavelength from the original limit of 40 nm down to 20 nm. The modified setup takes advantage of a shorter radiator undulator period. We present the numerical studies that have been carried out to compare the expected performance of the new FEL-1 with that of the original FERMI setup*. Results show that the modified configuration represents a good alternative to the second stage of the project (FEL-2) in the wavelength range between 40 nm and 20 nm.
* C. J. Bocchetta et al. 'FERMI@Elettra Conceptual Design Report' ST/F-TN-07/12 (2007) |
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| MOPC003 | Estimation of Undulator Requirements for Coherent Harmonic Generation on FERMI@Elettra | 67 |
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The FERMI project is devoted to the realization of a FEL user facility based on the principle of coherent harmonic generation (CHG). The advantages of such a method (with respect, e.g., to self amplified spontaneous emission) is that the output properties of the light are strongly determined by the interaction of the seed laser with the electron beam within the modulator undulator. In CHG FELs therefore, in addition to the requirements for the radiator where FEL radiation is produced, it is important to understand and satisfy the requirements for the modulator. In this work, we present a study focused on the first stage (FEL-1) of the FERMI@Elettra setup. The study aims at providing an estimation of the undulator requirements in terms of magnetic field accuracy for both the modulator and the radiator. The work is based on numerical simulations of the FEL-1 using the numerical code GINGERH [1]. The required undulator tolerances have been obtained by means of a large number of simulation runs taking into account different sets of undulator parameters.
[1] W. Fawley, “A User Manual for GINGER-H and its Post-Processor XPLOTGINH” LCLS-TN-07-YY Technical note, Lawrence Berkeley National Laboratory (2007) |
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| MOPC004 | First Results from the Upgraded PITZ Facility | 70 |
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| During autumn and winter 2007 a general reconstruction of the PITZ facility was performed. A new spectrometer based on a dipole magnet with 180 degree deflection angle was inserted in the facility. The new spectrometer contains two screen stations for the measuring of the longitudinal phase space and the slice emittance. A new "Conditioning Test Stand" (CTS) was added to the facility. Using this CTS a new electron gun having an improved cooling system is under conditioning. A new photocathode laser system (developed by MBI) was installed and commissioned. The goal is to reach rise and fall times of the laser pulses of 2 ps. The system of laser diagnostic was upgraded. The results reached using this upgraded facility are reported. This concerns the conditioning results of the new gun. Furthermore, a gun will be characterised using the new diagnostics beamline and the new photocathode laser. Results of the commissioning and first measurements of the new diagnostics components will be reported. | ||
| MOPC005 | The ARC-EN-CIEL Radiation Sources | 73 |
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| The ARC-EN-CIEL project proposes a panoply of light sources for the scientific community on a 1 GeV superconducting LINAC (phase 2) on which two ERL loops (1 and 2 GeV) are added in phase 3. LEL1 (200-1.5 nm), LEL2 (10-0.5 nm) and LEL4 (2-0.2 nm) are three kHz High Gain Harmonic Generation Free Electron Laser sources seeded with the High order Harmonics generated in Gas, with 100-30 FWHM pulses. A collaboration, which has been set-up with the SCSS Prototype Accelerator in Japan for test this key concept of ARC-EN-CIEL, has led to the experimental demonstration of the seeding with HHG and the observation up the 7th non linear harmonic with a seed at 160 nm. Besides. LEL3 (40-8 nm) installed on the 1 GeV loop is a MHz FEL oscillator providing higher average power and brilliance. In addition, in vacuum undulator spontaneous emission source extend the spectral range above 10 keV and intense THz radiation is generated by edge radiation of bending magnets. Optimisations and light sources characteristics are described. | ||
| MOPC006 | Seeding of the Test FEL at MAX-lab | 76 |
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| The test FEL at MAX-lab has recently been completed. The system will be seeded at 263 nm by a tripled Ti:sapphire laser synchronized to the RF system and the gun laser. Issues important for the seeding will be presented, ranging from the laser system via the layout of photon and electron optics to timing/synchronization and the theoretical approach. Experimental results on the seeding operation will also be presented. | ||
| MOPC007 | Status and Upgrade Program of the FERMI@ELETTRA Linac | 79 |
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| FERMI@ELETTRA is a seeded FEL user facility under construction at Sincrotrone Trieste, Italy. It will use the existing normal conducting S-band linac and with the installation of seven accelerating sections received from CERN after the LIL decommissioning, will be operated at 1.2 GeV. After the successful commissioning of the new injector system of ELETTRA, the linac has been disconnected from the storage ring and now is being revised and upgraded with the installation of new important subsystems, i.e., a new photoinjector, bunch compressors, laser heater, additional accelerating structures, etc. Here a description of the upgrade program as well as the ongoing activities on the main parts of the machine are reported and discussed. | ||
| MOPC008 | The Impact of PSK Timing on Energy Stability of e-Beam at FERMI@ELETTRA | 82 |
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| The existing linac sections S1-S7 at ELETTRA will be upgraded for the FERMI@ELETTRA FEL project. These seven sections are 3/4 π-mode backward traveling wave (BTW) constant-impedance structures, powered by 45-MW klystrons (Thales TH 2132A) and with a SLED system to increase the RF peak power. Because of the strict requirement on the pulse-to-pulse beam energy stability (<0.1%) of the FERMI@ELETTRA project, the impact of phase shift keying (PSK), the timing of phase flipping, on beam energy needs to be revisited and evaluated. Here the results obtained with a simulation model built up by use of MATLAB simulink are present and discussed. | ||
| MOPC010 | Injector System for X-ray FEL at SPring-8 | 85 |
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The SPring-8 X-FEL based on the SASE process has been developed to generate X-rays of 0.1 nm by the combination of an 8 GeV high gradient linac (400 m) and a mini-gap undulator of in-vacuum type (90 m). The design goals of the slice beam emittance and peak current at the end of the linac are 1 π mm mrad and 3 kA, respectively. The injector of the linac generates an electron beam of 1 nC, accelerates it up to 30 MeV, and compresses its bunch length down to 20 ps step by step. The injector has been designed on the basis of the SCSS test accelerator. We adopted the following keys to toward the goals:
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| MOPC011 | Improvement and Recent Results of the DELTA Storage Ring FEL | 88 |
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| Several modifications to the storage ring FEL at DELTA have been conducted, in order to enhance speed and reproducability of mirror alignment as well as flexibility of electron beam settings. We present the new hardware design and experimental results at a laser wavelength of 470 nm. Lasing was achieved with different filling patterns, and the output power of the FEL was measured. By modulating the accelerating RF the laser macropulses can be forced into a Q-switch mode, varying between roughly 10 and 250 Hz without significant loss of outcoupled average power. A special input optics setup for a streak camera enables simultaneous measurement of electron beam and laser pulse dynamics, to study the correlations between them. Recent measurements will be presented. | ||
| MOPC012 | PSI XFEL Simulations with SIMPLEX and GENESIS | 91 |
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| The numerical simulation results of the SASE FEL process for PSI XFEL project are presented. The main purpose of the investigations using FEL simulation codes SIMPLEX and GENESIS is the reliable definition of the undulators design parameters (K value, period, segment length, number of segments) that provide desirable radiation characteristics such as wavelength, bandwidth, saturation length, peak power and the brightness. | ||
| MOPC013 | Effect of Jitter and Quadrupole Alignment Errors on SASE FEL Performance | 94 |
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| Numerical simulations of the radiation process at the European XFEL project are presented. The impact of quadrupole misalignments on the saturation length and saturation power is investigated using the simulation codes SIMPLEX and GENESIS. The influence of trajectory steering in the presence of BPM misalignments on the FEL performance is analyzed. The study is performed for the SASE 1 undulator designed for 0.1nm radiation wavelength. | ||
| MOPC014 | Optimization of the Focusing Lattice for European XFEL | 97 |
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| Detailed knowledge of the impact of the undulator section focusing lattice on the FEL performance is an important issue to ensure the stable operation of the facility with reliable tolerances. In this paper the results of numerical simulation studies for the European XFEL project are presented. The saturation length, saturation power and the spectral brightness of the SASE FEL are calculated for various focusing lattice arrangements. A focusing optics option with reduced number of FODO cells is discussed to reach the design goals with relaxed quadrupole magnet tolerances. The numerical simulations are performed using the SIMPLEX and GENESIS codes. | ||
| MOPC015 | Start-to-End Simulations of the PSI 250 MeV Injector Test Facility | 100 |
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| From 2003, PSI has been investigating the advanced Low Emittance Gun (LEG) based 6 GeV PSI XFEL facility to supply coherent, ultra-bright, and ultra-fast XFEL photon beams covering from 0.1 nm to 10 nm. To build whole facility within a 800 m space, required beam parameters in front of undulators are challenging. For the first two FEL beamlines (FEL 1 and FEL 2), the required normalized slice emittance, slice energy spread, and peak current are about 0.2 mm.mrd, 0.6 MeV, and 1.5 kA, respectively. However, the required beam parameters for the third FEL beamline (FEL 3) covering 1 nm to 10 nm are somewhat flexible. Therefore PSI has been developing two different gun technologies. The 1 MV high gradient pulsed diode and field emission based advanced LEG will be used for first two FEL beamlines, while the CTF3 gun type V based conventional RF photoinjector will be used for the third FEL beamline. To test those two injector technologies, a dedicated 250 MeV injector test facility will be constructed at PSI from 2008. In this paper, we describe beam dynamics in two accelerator optimizations of the CTF3 RF gun based 250 MeV injector test facility for the PSI XFEL project. | ||
| MOPC016 | Status of the CUTE-FEL Project | 103 |
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| We are building a Compact Ultrafast TErahertz Free-Electron Laser (CUTE-FEL), designed to lase around 80 microns, driven by a 10 MeV electron beam, and using a 5 cm period, 2.5 m long undulator. We present the latest status of the project, including acceleration and commissioning trials. | ||
| MOPC017 | Operation of the UVSOR-II CHG-FEL in Helical Configuration | 106 |
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| In the Coherent Harmonic Generation Free Electron Laser (CHG-FEL) configuration, an external laser source injected inside a first undulator modulates in energy, and consequently in phase, an electron bunch, allowing coherent radiation in a second undulator. The CHG-FEL implemented on UVSOR-II storage ring (Okazaki, Japan) consists of a 600 MeV electron beam, and of a 2.5 mJ Ti:Sa seeding laser at 800 nm wavelength, 1 kHz repetition rate, and 100 fs up to 2 ps pulse duration. Operation in planar configuration of the undulators is being characterized since 2005. Recent experiments enabled a step forward using helical configuration of the undulators. A description of the experimental setup is given, and the main results are presented: influence of seeding laser parameters (polarisation, average power, focusing) on the intensity and beam profile of the second and third coherent harmonics. Those investigations provide attractive insights for the future HGHG FEL sources, about to deliver sub-nm and sub-ps pulses. | ||
| MOPC018 | Seeding the FEL of the SCSS Test Accelerator with the 5th Harmonic of a Ti: Sa Laser Produced in Gases | 109 |
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| We present the strong amplification of the 5th harmonic of a Ti: Sa laser (10 Hz, 100 fs) generated in a Xe gas cell, i.e. 160 nm, and the generation of intense and coherent odd and even Non Linear Harmonics (NLH) from 80 nm to 23 nm. The experiment has been carried out on the SCSS (SPring-8 Compact SASE Source, Japan) Test Accelerator FEL. This facility is mainly based on a thermionic cathode electron gun, a C-band LINAC (5712 MHz, 35 MV/m) and an in-vacuum undulator (15 mm of period, 2 sections of 4.5 m length). The external source is properly focused in the first undulator section in order to efficiently interact with the electron beam (150 MeV, 10 Hz, 0.5-3 ps). In case of high peak current mode, the 160 nm seed light is amplified by a factor of 7000 in the first undulator section. Moreover, the amplification can be observed even for very low HHG seed level. This result opens new perspectives for seeding at short wavelengths in the XUV to soft X-Ray region. Association with NLH, HGHG (High Gain Harmonic Generation) and/or cascade schemes would allow the generation of fully coherent X-ray radiations from the “water window” spectral range to the Angstrom region. | ||
| MOPC019 | Velocity Bunching at FLASH | 112 |
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| The vacuum-ultra-violet free electron laser in Hamburg (FLASH) is a linac driven SASE-FEL. High peak currents are, in routine operation, produced using magnetic bunch compression chicanes. Longitudinal dispersion in these chicanes allow bunch length changes of relativistic electron beams. For low energy electron beams (~5 MeV), the velocity dependence on electron energy can be utilized for bunch compression. Since strong bunch compression at low beam energies gives rise to strong space charge interactions which has an impact on, for instance, beam emittance and is therefore not suitable for full compression to the kA peak currents needed for SASE operation. Moderate velocity bunching, however, might be used to optimize the total bunch compression system of FLASH or the European XFEL. Experiments on the velocity bunching process at FLASH are presented here. Results on bunch length and transverse emittance measurements are discussed and compared with numerical tracking calculations. | ||
| MOPC023 | ARC-EN-CIEL Beam Dynamics | 115 |
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| ARC-EN-CIEL project is based on a CW 1.3 GHz superconducting linac accelerator delivering high charge, subpicosecond and low emittance electron bunches at high repetition rate. According to the electron energy, it provides tunable light source of high brightness in the VUV to soft X-ray wavelength domain. The project will evolve into three phases: first and second phases are based on high brightness single pass SC linac configuration with a low average current (few μA), while third phase comports recirculation loops to increase the average current (up to 100 mA). This paper deals with electron beam dynamics issues for the single pass configuration in the two first phases from the RF gun to undulators including magnetic compression stages. In the ERL configuration of the third phase, the accelerator scheme and focusing are investigated in order to take into account collective effects as Beam Break Up instability. | ||
| MOPC024 | Calculation of Coherent Synchrotron Radiation in General Particle Tracer | 118 |
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General Particle Tracer (GPT) is a particle tracking code, which includes 3D space charge effect based on nonequidistant multigrid Poisson solver or point-to-point method. It is used to investigate beam dynamics in ERL and FEL injectors. We have developed a new routine to simulate coherent synchrotron radiation (CSR) in GPT based on the formalism of Sagan*. The routine can calculate 1D-wake functions for arbitrary beam trajectories as well as CSR shielding effect. In particular, the CSR routine does not assume ultrarelativistic electron beam and is therefore applicable at low beam energies in the injector. Energy loss and energy spread caused by CSR effect were checked for a simple circular orbit, and compared with analytic formulas. In addition, we enhanced the 3D space charge routine in GPT to obtain more accurate results in bending magnets.
*D. Sagan, EPAC06, pp. 2829-2831. |
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| MOPC026 | Status of SPARX Project | 121 |
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| The SPARX project consists in an X-ray-FEL facility jointly supported by MIUR (Research Department of Italian Government), Regione Lazio, CNR, ENEA, INFN and Rome University Tor Vergata. It is the natural extension of the ongoing activities of the SPARC collaboration. The aim is the generation of electron beams characterized by ultra-high peak brightness at the energy of 1.2 and 2.4 GeV, for the first and the second phase respectively. The beam is expected to drive a single pass FEL experiment in the range of 13.5-6 nm and 6-1.5 nm, at 1.2 GeV and 2.4 GeV respectively, both in SASE and Seeded FEL configurations. | ||
| MOPC027 | A Fast Switching Mirror Chamber for FLASH | 124 |
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| Switching mirrors are used to provide several beamlines with FEL or synchrotron radiation from one source. Since most users do not need the nominal pulse density, this is a method to supply many experimental groups. So far, the switching process has a duration of several minutes. A study at DESY Zeuthen analyzes the possibility and accuracy of permanent switching, e.g. at half the FEL's pulse frequency of 1 to 10 Hz. A prototype satisfying highest demands on repetition accuracy of the position (below 1 μm) and yawing (about 1 arcsec) is being tested. In the course of the work many technical concepts from industry like PLC or Position-Velocity Streaming found their way into beamline technology, allowing fast proceedings in development. | ||
| MOPC028 | Experimental Layout of 30 nm High Harmonic Laser Seeding at FLASH | 127 |
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| Since 2004, the free-electron laser FLASH at DESY has operated in the Self-Amplified Stimulated Emission mode, delivering to users photon beams with wavelengths between 6.5 nm and 40 nm. In 2009, DESY plans to install a 3.9 GHz RF acceleration section for the production of electron bunches with high peak currents (~kA), but ten times larger pulse durations (~250 fs) compared to the present configuration. The relaxed timing requirements of the new configuration make it possible to externally seed FLASH with high harmonics of an optical laser (sFLASH). The aim of the project is to study the technical feasibility of seeding an FEL at 30 nm with a stability suited for user operation. sFLASH will use 10 m of gap-tunable undulators installed in front of the fixed gap SASE-undulator. A chicane behind the seeding undulators will allow to extract the output radiation for a careful characterisation and for first pump-probe experiments with a resolution in the 10 fs range by combining FEL and seed laser pulses. | ||
| MOPC029 | Longitudinal Structure of Electron Bunches at the Micrometer Scale from Spectroscopy of Coherent Transition Radiation | 130 |
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| At the free electron laser FLASH in Hamburg, a longitudinal bunch compression scheme is used resulting in a longitudinal current profile with a narrow leading spike. Part of this spike is responsible for producing high-intensity short FEL pulses via the SASE process. The width and the structure of the current spike, which are key parameters for the efficiency of the SASE process, are barely accessible to direct measurements in the time domain. Using an infrared multi-stage grating spectrometer, we have studied the spectral composition of coherent transition radiation from single electron bunches. The data show that the 'fundamental width' of the current spike is about 40 fs (fwhm) with prominent substructures down to the 10 fs scale. The intensity fluctuations of coherent radiation in the corresponding wavelength range are strongly correlated to the fluctuations of the FEL pulse energy. Extension of the method to the near infrared regime have revealed micro-structures with characteristic lengths from a few micrometers down to fractions of a micrometer. Their interrelation with the parameters of the electron beam and the compression system have been studied. | ||
| MOPC030 | Operation of FLASH at 6.5 nm Wavelength | 133 |
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| FLASH, the Free-Electron-Laser at DESY, Germany has been upgraded in 2007. A 6th accelerating module with eight 9-cell superconducting cavities of the TESLA type has been installed. In addition, another module has been replaced and the tuners of a third module have been repaired. In September 2007, a beam energy of 1 GeV has been achieved for the first time, followed by lasing at 6.5 nm shortly after. With this remarkable achievement, the initial design goals of the FEL in terms of beam energy and wavelength have been reached. | ||
| MOPC031 | Status of X-ray FEL/SPring-8 Machine Construction | 136 |
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| XFEL/SPring-8: the X-ray Free Electron Laser Project is under construction at SPring-8 site, which is aiming at generating 0.1 nm coherent radiation using 8 GeV electron beam. After the ground breaking in 2007, concrete piling has been completed. Construction of the accelerator tunnel will be completed in end of the FY2008, then machine installation will be started. The first electron beam acceleration is scheduled in FY2010. XFEL/SPring-8 based on SASE-FEL, and unique design, thermionic CeB6 gun, adiabatic bunching, C-band high gradient accelerator and in vacuum undulator. To reach 8 GeV within 400 m available tunnel length, we use 64 C-band klystron, which drives 128 accelerating tube at 37 MV/m. | ||
| MOPC032 | Progress of the Commissioning of the Test FEL at MAX-lab | 139 |
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| In a collaboration between MAX-lab and BESSY a seeded Harmonic Generation Free Electron Laser is being constructed at MAX-lab. The setup uses the existing MAX-lab facility together with a Ti:Sa 266 nm lasersytem used for both the gun and seeding and an optical klystron consisting of a modulator, a chicane and a radiator. The different parts of the system has been installed and commissioning with electrons of the full setup started during the fall of 2007. In this paper the progress of the commissioning of the Test FEL and our initial results are presented. | ||
| MOPC033 | Sapphire - A High Peak Brightness X-Ray Source as a Possible Option for a Next Generation UK Light Source | 142 |
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| In the UK there is increasing interest in a radiation source which would provide ultra-fast (from 100 fs down to a few fs and potentially below) multi-keV X-ray pulses with high peak brightness, in order to study rapid dynamical processes in electronic and molecular systems, complementary to the newly operational Diamond Light Source which has been designed principally for high time-averaged X-ray brightness. In this paper we present the results of our initial studies for one option for a cost-effective, staged, linac based source suitable as a national facility which can act additionally as a portal to larger X-ray free-electron laser facilities in Europe, the US and Japan. | ||
| MOPC034 | Collective Effects in a Short-Pulse FEL Driver | 145 |
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| There is much interest in the provision of coherent, tunable VUV and soft X-ray pulses of duration less than 10fs. A 1.3 GHz linac driver concept has been developed, and in this paper we address collective effects in the short electron bunches using start-to-end modelling. In particular, we examine the limitations from coherent radiation and induced microbunching, and their impact on the design of the accelerator system. | ||
| MOPC035 | PULSE - A High-Repetition-Rate Linac Driver for X-ray FELs | 148 |
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| We describe a staged concept for a linac-based free-electron laser providing coherent tunable VUV and soft X-ray output with pulse lengths less than 10 fs. Use of recent developments in high brightness injectors and 1.3 GHz cryomodules gives stable, reliable output with very good electron beam quality and flexible pulse pattern. Options for achieving repetition rates up to 1 MHz are examined. We also consider the development and demonstration of novel FEL concepts that access photon pulses in the attosecond regime. The combination of these parameters would open up new areas in femtosecond and attosecond science. | ||
| MOPC036 | Pancakes versus Beer-cans in Terms of 6D Phase-space Density | 151 |
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Uniformly filled ellipsoidal (waterbag) electron bunches can be created in practice by space charge blow out of transversely tailored ‘pancake’ bunches*. Ellipsoidal bunches have linear self fields in all dimensions, and will not deteriorate in quality under linear transport and acceleration. There is a discussion if such a bunch is better than a conventional beer-can shape. This paper compares the two approaches in terms of usable phase-space density. Detailed GPT simulations of a simplified setup show that although the pancakes approach requires less charge, it is the application that is decisive.
*O. J. Luiten et al. Phys. Rev. Lett. Vol 93, 094802 (2004). |
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| MOPC037 | Single Spike Operation in SPARC SASE-FEL | 154 |
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| We describe in this paper a possible experiment with the existing SPARC photoinjector to test the generation of sub-picosecond high brightness electron bunches able to produce single spike radiation pulses at 500 nm in the SPARC self-amplified spontaneous emission free-electron laser (SASE-FEL). The main purpose of the experiment will be the production of short electron bunches as long as few SASE cooperation lengths and to validate scaling laws to foresee operation at shorter wavelength in the future operation with SPARX. The basic physics, the experimental parameters and 3-D simulations are discussed. Complete start-to-end simulations with realistic SPARC parameters are presented, in view of an experiment for tests on superradiant theory with the existing hardware. | ||
| MOPC038 | Ultra-high Brightness Electron Beams by All-optical Plasma-based Injectors | 157 |
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| We study the generation of low emittance high current mono-energetic beams from plasma waves driven by ultra-short laser pulses, in view of achieving beam brightness of interest for FEL applications. The aim is to show the feasibility of generating nC charged beams carrying peak currents much higher than those attainable with photoinjectors, together with comparable emittances and energy spread, compatibly with typical FEL requirements. We identified a particularly suitable regime which is based on a LWFA plasma driving scheme on a gas jet modulated in areas of different densities with sharp density gradients. Simulations show that in the first regime, using a properly density modulated gas jet, it is possible to generate beams at energies of about 30 MeV with peak currents of 20 kA, slice transverse emittances as low as 0.3 mm.mrad and energy spread around 0.4%. This beams break the barrier of 1018 A/(mm.mrad)2 in brightness, a value definitely above the ultimate performances of photo-injectors, therefore opening a new range of opportunities for FEL applications. A few examples of FELs driven by such kind of beams injected into laser undulators are finally shown. | ||
| MOPC040 | COBALD - an Inverse Compton Back-scattering Source at Daresbury | 160 |
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| An inverse Compton Back-scattering (CBS) ultra-short pulsed x-ray source driven by the multi-terawatt laser installed at Daresbury’s Energy Recovery Linac Prototype (ERLP) is being developed. Hard x-rays, ranging from 15 keV to 30 keV, depending on the backscattering geometry, will be generated through the interaction of the laser pulse and an electron bunch delivered by ERLP. The X-rays created contain 15 ·106 photons per pulse from head-on collisions, with a pulse duration comparable to that of the incoming electron bunch, and 5 ·106 photons per pulse from side-on collisions, where the laser pulse defines the pulse width. The peak spectral brightness of ≈1020 photons/s/mm2/mrad2/0.1% ΔE/E is close to that of 4th-generation synchrotron light sources. Called COBALD, it will initially be used as a short pulse diagnostic for the ERLP electron beam and will explore the extreme challenges of photon/electron beam synchronization, which is a fundamental requirement for all accelerator-based (whether FEL or spontaneous SR) dynamics programmes. Furthermore, a fast-melting experiment will be used as a diagnostic tool to provide further information on the stability of the source. | ||
| MOPC041 | Microfabrication of Relativistic Electron Beam by Laser and its Application to THz Coherent Synchrotron Radiation | 163 |
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| It is well known that broadband coherent synchrotron radiation (CSR) is emitted by an electron bunch whose length is shorter than radiation wavelength. However, even a long electron bunch can emit CSR when it has micro-density structure whose characteristic length is equal to the radiation wavelength. Recently, we have demonstrated that, by injecting amplitude modulated laser pulses into an electron storage ring, quasi-monochromatic and tunable terahertz (THz) CSR could be produced. In this method, periodic micro-density structure of THz scale was created on the electron bunch, as the result of the laser-electron interaction. The bunch emitted quasi-monochromatic THz radiation in a uniform dipole filed, not in an undulator. This new technology provides a way to imprint periodic wave patterns inside the electron bunch phase space. In adding to the light source applications, this would be a new tool to investigate electron beam dynamics. | ||
| MOPC043 | Design of LINAC Based Compact X-ray Source via Inverse Compton Scattering at Waseda University | 166 |
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| A table-top size soft X-ray source based on inverse Compton scattering has been developed at Waseda University. We have already succeeded in generating X-rays via inverse Compton scattering between 4.6 MeV electron beam generated from a photocathode RF-gun and 1047nm Nd:YLF laser. The energy of the X-ray is within the 'water window' region which can be applied for the soft X-ray microscope for biological observation. In 2007, new RF-gun cavity with Cs-Te photocathode in place of copper has been installed. The energy of electron beam became up to 5.5MeV due to the increase of Q-value of the gun cavity. According to this achievement, generated X-ray energies will cover overall the 'water window' region. We are planning a multi-pulse inverse Compton scattering X-ray generation system in order to enhance a luminous intensity of the X-rays. For this purpose, we are considering a multi-pulse UV laser system for generating a multi-bunch electron beam, the method for beam loading compensation, and the multi-pulse IR laser system for the Compton collisions. Experimental results of X-ray generation and multi-pulse X-ray plans will be presented at the conference. | ||
| MOPC045 | First Measurement Results of the PSI 500kV Low Emittance Electron Source | 169 |
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| The Paul Scherrer Insitute (PSI) is presently developing a low emittance electron source for the PSI-XFEL project. The target beam parameters at the source are I=5.5 A, Q=0.2 nC and a slice emittance below 0.2 mm.mrad. The gun concept consists of a high gradient "diode“ stage followed by a two-frequency two-cell cavity to allow fine tuning of the longitudinal phase space. This paper reports on the first experimental results obtained with the PSI 500 kV test stand. The facility consists of a 500 kV diode stage followed by a diagnostic beam line including an emittance monitor. An air-core transformer based high voltage pulser is capable of delivering a pulse of 250 ns FWHM with amplitude up to 500 kV. The diode gap between two mirror polished electrodes is adjustable to allow systematic gradient studies. The electrons are produced by a 266nm UV laser delivering 4μJoules on the Cu-cathode. | ||
| MOPC046 | Femtoslicing at BESSY - Detecting More Photons | 172 |
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The BESSY femtoslicing facility is now well established* and has proven its succesful operation for femtosecond laser-pump and x-ray-probe experiments**. However, many interesting physical phenomena cannot be addressed with the presently available comparably low number of photons detected at the sample. The most direct way to increase the photon flux is to increase the laser repetition rate. In order to preserve the excellent fs-signal to ps-background ratio special storage ring fill patterns and corresponding laser synchronisation schemes have been studied. We present calculations showing the influence of a dedicated new radiator promising better flux and polarisation properties. Recent results from a new beamline based on high transmission reflection zone plates will be presented. A new avalanche photo diode-array-based detection system has been successfully tested. This allows a parallel detection in the dispersion plane behind the monochomator. The status of these improvements will be presented.
*S. Khan et al. Phys. Rev. Lett, (97), 074801 (2006). |
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| MOPC047 | Status of Kharkov X-ray Generator NESTOR Based on Compton Back Scattering | 175 |
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| The purpose of the NESTOR (New Electron STOrage Ring) project is to create intense X-ray generator based on compact storage ring and Compton back scattering in the National Science Centre “Kharkov Institute of Physics and Technology”. It allows to carry out investigations in the wide range of fundamental and applied sciences such as physics, biology, medicine and so on. The facility consists of the compact 40-225 MeV storage ring, linear 35-90 MeV electron accelerator as an injector, transportation system and Nd:Yag laser and optical cavity. In addition to hard Compton radiation it is supposed to use 4 soft vacuum ultraviolet radiation channels of natural synchrotron radiation of dipole. The facility is going to be in operation in the middle of 2009 and the expected X-rays flux will be of about 1013 phot/s. In the paper the main facility parameters are presented. | ||
| MOPC048 | Coherent Synchrotron Radiation Burst from Electron Storage Ring under External RF Modulation | 178 |
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| It is known that a high-peak-current beam in an electron storage ring emits a burst of coherent synchrotron radiation (CSR) in the THz region. This CSR is powerful and easily obtained with no special expense, but is not used by synchrotron radiation users. This is because the burst arises from a fine time structure in the bunch due to longitudinal beam instabilities, and is unstable. We quantitatively investigated its time structure to find out how unstable it is. The measurements of CSR from one bunch showed that with an average period of 10ms (comparable with the damping time, 12 ms) the fluctuation of averaged power was about 10%. This would be reduced to 1% with 100 bunches. The fluctuation ratio had small dependence on beam charge, rf acceleration voltage and momentum compaction factor. The successive bursts had a correlation because the beam had a memory of former bursts. This worked to reduce the fluctuation in long period. When the rf phase was modulated with 2fs (twice of the synchrotron oscillation frequency), the burst structure was modulated with 2fs and the long term fluctuation was reduced. This modulation can be used to eliminate background noise in user experiments. | ||
| MOPC049 | Comparative Study of Vibration Stability at Operating Light Source Facilities and Lessons Learned in Achieving NSLS II Stability Goals | 181 |
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Understanding the correlation between storage ring vibration and electron beam oscillation is key in achieving the design beam parameters of a 3rd generation light source. Spectral properties of the vibration at the storage ring floor, in addition to amplitude, and its relation to the dynamic properties of the lattice govern the complex relation between lattice movement and beam jitter. Spectral characteristics are, in general, site-specific and motions exhibit spatial variability. To best describe the relationship between the ground motion field at the NSLS II site and the accelerator while quantifying the storage ring oscillations resulting from its interaction with the undisturbed site, field studies have been conducted at various light source facilities. By using the same metric data characterizing the achieved stability levels in operating light sources are generated and used in the assessment of the NSLS II stability which in turn linked to the specific site, subsurface and design characteristics. The paper summarizes the results of these comprehensive findings and presents an overall assessment of stability levels that can be achieved.
Work performed under the auspices of the US DOE. |
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| MOPC050 | Ground Motion Studies at NSLS II | 184 |
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In 3rd generation light sources such as the 3 GeV NSLS II under design at BNL, strict requirements associated with vibration on the storage ring floor are imposed in order to minimize the jitter in the electron beam. Spectral characteristics storage ring vibration and dynamic properties of the ring lattice are controlling parameters. Ground motion at the NSLS-II site is characterized by a complex spectrum consisting of fast and slow motions stemming from natural and cultural sources. Cultural noise with frequencies higher than a few Hz has the potential of dramatically affecting the accelerator performance. In this study, an array of vibration measurements at the undisturbed NSLS II site has been made in order to establish the “green-field” vibration environment and its spectral characteristics. Its interaction with the NSLS II accelerator structure and the quantification of the storage ring vibration, both in terms of amplitude and spectral content have been assessed through a state-of-the-art wave propagation and scattering analysis. This paper focuses primarily on the wave propagation and scattering aspect as well as on the filtering effects of accelerator structural parameters.
Work performed under the auspices of the US DOE. |
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| MOPC053 | BEAM DYNAMICS IN THE LASER-ELECTRON STORAGE RING FOR A COMPTON X-RAY SOURCE | 187 |
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| We present the lattice analysis and simulation study of the beam dynamics in the pulse mode of the laser-electron storage ring. Compton Scattering (CS), Intra-beam Scattering (IBS) with non-Gaussian beam and Synchro-tron Radiation (SR) are taken into consideration. Emittance growth, energy spread and phase space of the electron beam, as well as spatial and temporal distribution of the scattered photon are studied in this paper. | ||
| MOPC056 | Challenges for Beams in an ERL Extension to CESR | 190 |
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| Cornell University is planning to build an Energy-Recovery Linac (ERL) X-ray facility. In this ERL design, a 5 GeV superconducting linear accelerator extends the CESR ring. Currently CESR is used for the Cornell High Energy Synchrotron Source (CHESS). The very small electron-beam emittances would produce an x-ray source that is significantly better than any existing storage-ring light source. However, providing, preserving, and decelerating a beam with such small emittances has many issues. We describe our considerations for challenges such as optics, space charge, dark current, coupler kick, ion accumulation, electron cloud, intra beam scattering, gas scattering, radiation shielding, wake fields including the CSR wake, and beam stabilization. | ||
| MOPC057 | R&D Energy Recovery Linac at Brookhaven National Laboratory | 193 |
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| Collider Accelerator Department at BNL is in the final stages of developing the 20-MeV R&D energy recovery linac with super-conducting 2.5 MeV RF gun and single-mode super-conducting 5-cell RF linac. This unique facility aims to address many outstanding questions relevant for high current (up to 0.5 A of average current), high brightness energy-recovery linacs with novel Zigzag-type merger. We present the performance of the R&D ERL elements and detailed commissioning plan. | ||
| MOPC058 | ALICE (ERLP) Injector Design | 196 |
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| In this paper we look at how the ALICE (formerly ERLP) injector has been re-designed to meet more realistic criteria from the previous design. A key component of ALICE is the high brightness injector. The ALICE injector consists of a DC photocathode gun generating 80 pC electron bunches at 350 keV. These bunches are then matched into a booster cavity which accelerates them to an energy of 8.35 MeV. In order to do this, two solenoids and a single-cell buncher cavity are used, together with off-crest injection into the first booster cavity, where the beam is still far from being relativistic. The performance of the injector has been studied using the particle tracking code ASTRA. | ||
| MOPC059 | BBU Limitations for ERLs | 199 |
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| The BBU threshold in ERLs is a limitation on the maximum beam current due to the interaction of the electron bunches and the Higher Order Modes (HOMs) contained within the RF cavities. Several factors are involved in determining the threshold current; from the cavity the Q, R/Q and degeneracy of the modes all play an important part. From the beam transport the values of the lattice functions α, β and μ have an effect. We will discuss the limits on these variables to provide a BBU current threshold greater than 100 mA for a multiple cavity machine and what will be required to provide higher currents. Also three different cavity profiles were investigated with the aim of reducing the BBU threshold. The TESLA 9-cell cavity was used as a baseline for comparison against possible 7-cell cavity designs, using the TESLA cell shape for their inner cells. The ends of the 7-cell cavities join to different sized beampipes, with radii of 39 mm and 54 mm, to allow the most of the HOMs to propagate to a broadband HOM absorber. Two different beampipe to cavity to transitions were investigated. The optimised 7-cell cavity will be shown to provide an increase in the BBU threshold. | ||
| MOPC060 | Transverse Resistive-wall Wake of a Round Pipe with Finite Thickness and its Effect on the ERL Multi-bunch Beam | 202 |
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We already started to study the effect of resistive-wall wake on the multi-bunch beam in an ERL (energy recovery linac)-based light source*, because resistive-wall beam breakup(RWBBU) could be caused by the cumulative transverse wake generated by interaction between the resistive vacuum pipe and the intense multi-bunch beam. However the resistive-wall wake function of a round pipe used so far for studying the RWBBU was valid only in a limited time range and improper to the RWBBU simulation for a longer time period. Therefore we analytically derived an exact expression of resistive-wall impedance of a round pipe with finite thickness over all the frequency range and numerically calculated the resistive-wall wake functions of several different pipes from the exact impedance expression. The calculated wake functions enabled us to study and simulate the beam behavior in an ERL made of the pipes accurately. We will present the transverse resistive-wall wake of a round pipe with finite thickness and its effect on the ERL multi-bunch beam.
*N. Nakamura et al., Proceedings of PAC07, Albuquerque, June 2007, pp. 1010-1012. |
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| MOPC061 | Progress in R&D Efforts on the Energy Recovery Linac in Japan | 205 |
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| The future synchrotron light sources, based on the energy recovery linacs (ERL), are expected to be capable of producing super-brilliant and/or ultra-short pulses of synchrotron radiation. The ERL-based light sources are under development at such institutes as the Cornell University, the Daresbury Laboratory, the Advanced Photon Source, and KEK/JAEA. The Japanese collaboration team, including KEK, JAEA, ISSP, and UVSOR, is working to realize the key technologies for the ERLs. Our R&D program includes the developments of ultra-low-emittance photocathode DC guns and of superconducting cavities, as well as proofs of accelerator-physics issues at a small test ERL (the Compact ERL). A 250-kV, 50-mA photo-cathode DC gun is under construction at JAEA. Two single-cell niobium cavities have been tested under high electric fields at KEK. The conceptual design of the Compact ERL has been carried out. We report recent progress in our R&D efforts. | ||
| MOPC062 | Results from ALICE (ERLP) DC Photoinjector Gun Commissioning | 208 |
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| The Energy Recovery Linac Prototype (ERLP) DC photoinjector gun has been commissioned and the beam characteristics measured. The gun has demonstrated the nominal ERLP parameters of 350 keV electron energy, 80pC bunch charge and ~140 ps bunch length (at 10% level). The bunch parameters were measured at different bunch charges from 1 pC up to 80 pC. Special attention was given to measurements of the beam transverse emittance (using a movable slit), correlated and uncorrelated energy spread (using an energy spectrometer) and bunch length (using a transverse RF kicker) at each bunch charge. The effect of the 1.3 GHz RF buncher on the bunch length was also investigated. The experimental results are then compared with ASTRA simulations. Experimental results obtained from the investigation of several other issues including the beam characteristics in the presence of field emission from the cathode and in the presence of strong beam halo are also presented and discussed. | ||
| MOPC063 | Characterisation of Electron Bunches from ALICE (ERLP) DC Photoinjector Gun at Two Different Laser Pulse Lengths | 211 |
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| In high-voltage DC photoinjector guns, the laser pulse duration affects the electron bunch characteristics and therefore is an important subject for experimental investigation and in the optimisation of the operation of the gun. Initial experimental study of this effect has been conducted using the Energy Recovery Linac Prototype (ERLP) photoinjector. During the commissioning of its DC photoinjector gun, the electron bunch parameters were measured at two laser pulse durations, ~7ps and ~28ps FWHM. The shorter laser pulse is the intrinsic output of the laser, while the longer pulse was produced with the use of a pulse stacker. The electron bunch parameters that were measured included transverse emittance, correlated and uncorrelated energy spread and bunch length. The experimental results and their comparison with computer simulations are presented and discussed. | ||
| MOPC064 | Beam Losses Due to Intra-Beam and Residual Gas Scattering for Cornell's Energy Recovery Linac | 214 |
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| In this paper we analyze particle loss rates in Cornell's x-ray Energy Recovery Linac. Because of the small beam emittances and high beam intensity, intra-beam scattering (IBS) can be a source of significant particles loss in the horizontal plane. It will result in radiation doses which should be carefully examined for adequate radiation protection. Additionally, scattering on the residual gas (RGS) causes particle losses in the vertical plane. With Mote-Carlo type simulations of the scattering processes and transport matrixes for particle-trajectory propagation we found the beam loss distribution along ERL. It indicated that 99% of the total beam loss will be due to IBS. However, the RGS contribution can not be ignored because it dominates scattering in the vertical plane causing IDs irradiation and damage. For both (IBS and RGS) processes the highest beam losses will occur at the end of deacceleration due to adiabatic anti-damping causing traverse betatron amplitudes to increase. These beamlosses can be consentrated in collimation sections. Knowing RGS beam loss rates at the ID locations, we estimate the ID’s life time and suggest a radiation protection scheme. | ||
| MOPC065 | Wake Field Simulations for Structures of the PITZ RF Photoinjector: Emittance growth estimations | 217 |
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| One of the main concerns in the design of electron guns is the generation of low-emittance beams. One source of emittance growth is the beam-surrounding effect, which can be estimated from the wake potentials along the beam path. For the calculation of these potentials an accurate knowledge of the short range wake fields induced in the different parts of the gun with geometrical discontinuities is necessary. The computation of these wake fields is a challenging problem, as an accurate resolution for both the small bunch and the large model geometry is needed. Here with the help of numerical wake-potential calculations we analytically estimate the emittance growth for the RF electron gun of the Photoninjector Test Facility at DESY Zeuthen (PITZ). | ||
| MOPC066 | Optimisation of a SRF High Average Current SRF Gun | 220 |
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| An approximately 100 mA and 10 MeV continuous wave electron injector is required to deliver high brightness electron bunches for the spontaneous and VUV radiation sources. One of possible solutions might be a Superconductive RF (SRF) gun. Optimisation of the first half cell of the gun has been carried out to maximise the acceleration whilst providing additional focussing through shaping of the cathode region to meet the design specification. In this paper, the cavity design and specification are presented together with some initial optimisations. | ||
| MOPC067 | Normal Conducting CW RF Gun Design for High Performance Electron Beams | 223 |
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| High repetition rate (>1 MHz), high charge (1 nC), low emittance (1 micron) electron beams are an important enabling technology for next generation light sources. Advanced Energy Systems has begun the development of an advanced, continuous-wave, normal-conducting radio frequency electron gun. This gun is designed to minimize thermal stress, allowing fabrication in copper, while providing low emittance electron beams. Beam dynamics performance will be presented along with thermal and stress analysis of the gun cavity design. | ||
| MOPC068 | Preliminary Characterization of the Beam Properties of the SPARC Photoinjector | 226 |
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| The SPARC photoinjector is the test prototype of the recently approved SPARX project. It is used as R&D facility to perform accurate beam dynamics studies, comparing measurements and simulations. Emittance measurements at the gun exit and at the full energy has been performed and benchmarked with the simulations. | ||
| MOPC071 | Development of a High Brightness Photo-Injector for Light Source Research at NSRRC | 229 |
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| A laser driven photo-cathode rf gun system is being installed at NSRRC gun testsite for high brightness electron beam and light source research. The photo-cathode rf gun cavity geometry has been modified from the BNL 1.6-cell structure for 2998 MHz operation. A 798 nm Ti:Saphire laser seeded 3 mJ regenerative amplifier is employed to produce 300 microjoules UV pulses at 266 nm wavelength from a third harmonic generator crystal for emission of photo-electrons from the Cu-cathode in the rf gun. First operation of this system with gaussian laser pulses is scheduled in summer 2008. Future plan for flattop laser pulse operation will be discussed. | ||
| MOPC072 | Photocathode Studies at FLASH | 232 |
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| Since several years, the DESY photoinjectors at FLASH and PITZ use cesium telluride photocathodes. One concern of operating an electron source with these cathodes is the degradation of the quantum efficiency (QE), starting from about 10 % to below 0.5 % during operation. To further understand this behavior the QE is monitored routinely. In this paper recent results from photocathode studies at FLASH are presented. | ||
| MOPC073 | Design of an Upgrade to the ALICE Photocathode Electron Gun | 235 |
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| The design of an upgrade to the GaAs photocathode electron gun of the Energy Recovery Linac Prototype (ERLP) at Daresbury Laboratory is presented. This proposed upgrade includes a reduction of the photocathode diameter from 32 to 10 mm and the installation of a dedicated photocathode preparation system with side loading of the photocathodes. The preparation system forms a united vacuum system with the gun but is separated by a gate valve. This allows for significant improvements to the vacuum conditions in the gun and a reduction of pollution from caesium vapour which improves gun stability under high voltage. This preparation facility will reduce the time taken for photocathode changeover from weeks to hours. The facility should provide photocathodes with higher quantum efficiency due to a more controllable preparation procedure and allows experiments to be performed with photocathodes activated to different levels of electron affinity. | ||
| MOPC074 | 3D Simulations of a Non-axisymmetric High Average Current DC Photocathode Electron Gun | 238 |
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| At high average currents, GaAs photocathode based electron guns are limited by the short operational lifetime of the photocathodes. One method to improve the cathode lifetime is to situate the photocathode off-axis to reduce the flow of ions back-bombarding the emitting surface. The results of 3D electrostatic and beam dynamic simulations are presented to demonstrate the feasibility of this scheme and the resultant beam quality achievable. | ||
| MOPC075 | Cs2Te Photocathode Robustness Studies | 241 |
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| Cs2Te photocathodes are used as laser driven electron sources at FLASH and PITZ. Besides many aspects of their performances, their robustness to gas exposition and the effect of pollutants on photocathode properties, and indirectly on the photoemitted electrons, are a field still rather unexplored. In this article we present the results of controlled exposition of Cs2Te photocathodes to gases typical present in the UHV environment of an RF Gun with respect to spectral response (QE vs. wavelength), and QE uniformity. Moreover, a comparison between polluted cathodes and fresh ones during operation in an RF Gun is presented. | ||
| MOPC078 | Tuning and Conditioning of a New High Gradient Gun Cavity at PITZ | 244 |
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| A new 1.3 GHz photo cathode electron gun (prototype 4.2) for the Photo Injector Test facility in Zeuthen (PITZ) was tuned in February 2007. The main difference in the mechanical design compared to earlier guns is a significantly improved cooling system. This gun is also the first copper gun cavity where a particle free cleaning using dry ice technique was applied while in the previous guns the high pressure ultra pure water rinsing technique was used. The cavity has been installed in a new Conditioning Test Stand (CTS) at PITZ in autumn 2007. It has been conditioned to an accelerating gradient of 60 MV/m and more. Dark current measurements have been performed to monitor the improvement of conditioning and to compare with the results from the previous guns. In this paper, RF measurement and tuning results as well as results of the conditioning and dark current measurements will be presented and discussed. | ||
| MOPC080 | Status of the FERMI@Elettra Photoinjector | 247 |
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| The new FERMI@Elettra photoinjector is presently undergoing high-power testing and characterization at MAX-Lab in Lund Sweden. This effort is a collaboration between Sincrotrone Trieste, MAX-Lab and UCLA. The 1.6-cell RF gun cavity and the focusing solenoid were successfully designed and built by the Particle Beam Physics Laboratory at UCLA, delivered to Sincrotrone Trieste at the beginning of 2008, and installed in the linac tunnel at MAX-Lab. Use of the MAX-Lab facility will allow the FERMI project to progress significantly with the photoinjector while waiting for the completion of the new linac building extension at Sincrotrone Trieste. We report here on the high-power conditioning of the RF cavity and the first beam tests. Furthermore, a preliminary characterization of the 5 MeV beam will also be presented. | ||
| MOPC083 | Flat Long Pulse Train Formation Using Multi-pass Structure | 250 |
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| Flat long pulse train is part of the requirements for International Linear collider. Here in Fermilab the construction of ILCTA at New Meon Lab will present the similar requirements (3MHz, 2810 Pulses, 5Hz) for the laser systems. In this paper we will report the effort to develop a new multi pass (MP) cavity based on Nd:YLF crystal end-pumped by diode laser. It takes a seed (1054 nm, 4-5ps) from a commercial laser and has a gain of 1000 or more. So far we already tested up to 1000 pulses with 1μs spacing and the pulse train amplitude fluctuation is less than 5% throughout the whole duration. We attribute this to the high optical to optical conversion efficiency achieved using Nd:YLF crystal inside the multi-pass structure. Test with 3MHz spacing train is also discussed and the integration of the new MP cavity into the current laser system is planned. | ||
| MOPC084 | A Laser-driven Acceleration Method | 253 |
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| A laser ion source (LIS) has been obtained with a repetitive pulsed laser at power density of the order of 1010 W/cm2 or higher, with pulse duration of the order of ns and repetition rate of the order of tens Hz. Any solid target can be ablated producing plasma with equivalent temperatures higher than 100 eV, densities higher than 1017/cm3 and charge states higher than 10+. Extracted current densities can be higher than 10 mA/cm2. The study of the electric fields generated inside the non equilibrium plasmas is a by-product of the research in ion generation. Ions are emitted from the plasma in the direction of the electric field with energies of the order of 50 eV/nucleon or higher, depending on the laser intensity. Emitted ions have a Boltzmann ion energy distribution depending on the ion charge state. Previous papers show that the electric field is as high as 10 MV/cm in our case. Magnetic trapping of electrons has been used to increase the ion acceleration, focusing and current. This new ion acceleration method based on LIS seems to be very interesting because it may permit to build accelerators with small dimensions and relatively low cost. | ||
| MOPC085 | High Power Neutron Converter for Low Energy Proton/Deuteron Beams: Liquid Metal Driving System | 256 |
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| Nowadays in BINP, Russia, the high-power high-temperature rotated graphite-made neutron converter is proposed in order to use neutron source for SPES (INFN-LNL, Italy) and SPIRAL-II (GANIL, France). The target is designed to produce up to 1014 neutron per second within the energy range of several MeV under irradiation by proton/deuteron beam of power up to 200 kW. One of main problem on the converter development is to provide the reliable and effective driving gear and cooling systems. The main elements of the system must be liquid metal pumps and motors, cooling channels and heat exchanger. This paper describes proposed scheme, its basic technical parameters, estimations of the system whole as well as of separate elements. The lead-tin alloy is used as the transmission agent. At present the prototype of liquid metal motor/pump is successfully manufactured and operates for more than 16000 h in continuous regime. | ||
| MOPC086 | IFMIF-EVEDA Accelerator: Beam Dump Design | 259 |
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| The IFMIF-EVEDA accelerator will be a 9 MeV, 125 mA cw deuteron accelerator prototype for verifying the validity of the accelerator design for IFMIF. A beam stop will be used for the RFQ and DTL commissioning as well as for the EVEDA accelerator tests. Therefore, this component must be designed to stop 5 MeV and 9 MeV deuteron beams with a maximum power of 1.12 MW. The first step of the design is the beam-facing material selection. The criteria used for this selection are low neutron production, low activation and good thermomechanical behavior. A thermomechanical analysis with ANSYS has been performed for a few materials which show good behavior from the radiological point of view. The input data are the expected beam shape and divergence at the beam dump entrance produced by the high energy beam line quadrupoles, a conical beam stop shape and the preliminary design of the cooling system. As a conclusion of the previous studies a conceptual design of the beam stop will be presented. | ||
| MOPC087 | The MERIT (nTOF-11) High Intensity Liquid Mercury Target Experiment at the CERN PS | 262 |
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The MERIT (nTOF-11) experiment is a proof-of-principle test of a target system for high power proton beams to be used as a front-end for a neutrino factory complex or a muon collider. The experiment took data in autumn 2007 using the fast extracted beam from the CERN Proton Synchrotron (PS) with a maximum intensity of about 30TP per pulse. The target system, based on a free mercury jet, is capable of intercepting a 4-MW proton beam inside a 15-T magnetic field Such a field is required to capture the low-energy secondary pions which will provide the source of the required intense muon beams. Particle detectors have been installed around the target setup in order to measure the secondary particle flux out of the target and probe cavitation effects in the mercury jet when hit with variable intensity beams. The data analysis is ongoing: the results presented at this conference will demonstrate the validity of the liquid mercury target concept.
For the MERIT collaboration. |
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| MOPC088 | High Power Neutron Converter for Low Energy Proton/Deuteron Beams: Test Facility | 265 |
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| This paper presents conceptual design of test facility, that is now under creation in the framework of development of high power neutron targets for SPES (INFN-LNL, Italy) and SPIRAL-II (GANIL, France). General destination of facility is to test different target systems and elements (hot converter unit, liquid metal driving gear and cooling systems) as well as experimental checking of supply, protection and control methods etc. Also, this facility must be used as a base for input quality control of targets as a whole in future. The structure, general features and experimental possibilities of facility are described. | ||
| MOPC089 | About Carbides-made Nanoceramics Fission Target for RIB Production | 268 |
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| Intensities of RIBs can be increased with improvement of release efficiency of fission targets. One of factor, which limits release efficiency of targets, is efficiency of release of isotopes from target material. This paper presents investigation of dependence of release efficiency from ceramics target on its grain size and inter-grains pores, as well shows some efficiency limits and ways to improve it. Simulations were performed for uniform target material made from powder of uranium carbide. Inter-grain spaces are taken relative to grain sizes, as another parameter to optimize is high density of target material. Results show that optimal grain size is in the range of hundreds - thousands nanometers, while recent target materials utilize one order more sizes of grains. In addition, key points of production of such ceramics are discussed. The beam technologies allow producing the nanopowders from carbides of different metals with controlled grain size. Exact methods also give to us possibilities to obtain ceramics with optimal ratio between grain and pores sizes. Possible problems and preliminary program of experiments and tests are discussed. | ||
| MOPC090 | Driver Beam-led EURISOL Target Design Constraints | 271 |
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The EURISOL (European Isotope Separation Online) Design Study is addressing new high power target design challenges. A three-step method* was proposed to split the high power linac proton driver beam into one H- branch for the 4 MW mercury target that produces radioactive ion beams (RIB) via spallation neutron-induced fission in a secondary actinide target and three 100 kW H+ branches for the direct targets producing RIBs via fragmentation and spallation reactions. This scheme minimises transient thermo-mechanical stresses on targets and preserves the cw nature of the driver beam in the four branches. The heat load for oxides, carbides, refractory metal foils and liquid metals is driven by the incident proton driver beam while for actinides, exothermic fission reactions are an additional contribution. This paper discusses the constraints that are specific to each class of material and the target design strategies. An emphasis is placed on the modern engineering numerical tools and experimental methods used to validate the target designs.
*A. Facco, R. Paparella, D. Berkovits, Isao Yamane, "Splitting of high power, cw proton beams", Physical Review Special Topics - Accelerators and Beams (2007). |
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| MOPC091 | Benchmarking of Collimation Tracking Using RHIC Beam Loss Data | 274 |
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| State-of-the-art tracking tools were recently developed at CERN to study the cleaning efficiency of the Large Hadron Collider (LHC) collimation system. These tools can be benchmarked using data taken from operations of the Relativistic Heavy Ion Collider (RHIC) multi-stage collimation system. This article reviews preliminary simulation results on both the location and the intensity of proton losses around the RHIC lattice. Comparison with live measurements from the beam loss monitors are also shown in order to assess the accuracy of the predictions in the LHC case. | ||
| MOPC092 | Single Particle Multi-turn Dynamics During Crystal Collimation | 277 |
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| As the increase in luminosity remains a high-profile issue for current and future accelerator projects, protecting superconducting magnets from beam induced quenches implies using state-of-the-art halo cleaning devices given the required beam intensities. In CERN's LHC case, a multi-stage collimation system is being set up so as to provide a halo cleaning efficiency up to 99.995%. In order to improve this system even further, US-LARP funded studies have started to appreciate the use of a silicon-based crystal as a primary target for the halo particles. Dedicated experiments have recently been performed in an SPS extraction line for a bent silicon crystal in case of single-pass particles. This article compares the published results of this experiment with simulations using established tracking codes. The goal is to better describe the main physics mechanisms involved in the beam-crystal interaction. A simple algorithm is then introduced to allow for fast tracking of the effect of a crystal on a high energy proton beam over many turns. The general feasibility of single particle, multi-turn crystal experiments at the SPS (CERN) and Tevatron (Fermilab) and their outline are discussed. | ||
| MOPC093 | Experimental Study of Radiation Damage in Carbon Composites and Graphite Considered as Targets in the Neutrino Super Beam | 280 |
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Carbon composites have been of primary interest as materials of choice for a multi-MW neutrino superbeam which desires low-Z pion production target. Beam on target experiments conducted at BNL made the case stronger in their favor, as compared to graphite, by demonstrating their excellent shock resistance which is directly linked with their extremely low thermal expansion. Since target survivability also depends on resistance to prolonged radiation, a series of irradiation damage studies on carbon composites and graphite were launched. While carbon composites at moderate doses exhibited interesting behavior of damage reversal through thermal annealing, at higher dose levels of peak proton fluences >5x1020 protons/cm2 they exhibited serious structural degradation. The experimental study also showed that graphite suffered similar damage when subjected to same fluence level. The paper discusses the findings of the experimental studies focusing on these materials and attempts to explain their structural degradation observed under high proton fluences given the excellent survivability record, especially of graphite, under high neutron fluences in nuclear reactor settings.
Work performed under the auspices of the US DOE. |
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| MOPC094 | Irradiation Effects on the Physio-mechanical Properties of Super-alloys Characterized by Low Thermal Expansion | 283 |
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In an effort to address the limitations on high power accelerator target performance prompted by the elevated dose levels and the associated irradiation damage, an experimental study has been undertaken to evaluate the potential applicability of super alloys characterized by low thermal expansion over certain thermal regimes. The intriguing properties associated with materials such as super-Invar and the “gum” metal (Ti-12Ta-9Nb-3V-6Zr-O) are observed in their un-irradiated state. Irradiations were performed using the 200 MeV protons of the BNL Linac and/or a neutron flux generated by the stopping of the primary 112 MeV protons upstream of the exposed super-alloys. The paper presents the post-irradiation analysis results which reveal interesting damage reversal by the super-invar and unexpected low threshold of radiation resistance by the “gum” metal.
Work performed under the auspices of the US DOE. |
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| MOPC095 | Mechanical and Thermal Prototype Testing for a Rotatable Collimator for the LHC Phase II Collimation Upgrade | 286 |
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| The Phase II upgrade to the LHC collimation systems calls for complementing the 30 high robust Phase I graphite collimators with 30 high Z, low impedance Phase II collimators. The design for the collimation upgrade has not been finalized. One option is to use metallic rotatable collimators and this design will be discussed here. The Phase II collimators must be robust in various operating conditions and accident scenarios. A series of prototype collimator jaws have been tested for both mechanical and thermal compliance with the design goals. Collimator jaw shape after thermal expansion benchtop tests were compared to ANSYS simulation results. Mechanical tests were also performed to demonstrate fabrication precision and collimator movement operation as designed. | ||
| MOPC096 | Design of a Rotatable Copper Collimator for the LHC Phase II Collimation Upgrade | 289 |
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The Phase II upgrade to the LHC collimation systems calls for complementing the 30 high robust Phase I graphite collimators with 30 high Z, low impedance Phase II collimators. The design for the collimation upgrade has not been finalized. One option is to use metallic rotatable collimators and this design will be discussed here. The Phase II collimators must be robust in various operating conditions and accident scenarios. Design issues include:
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| MOPC098 | LHC Particle Collimation by Hollow Electron Beams | 292 |
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| Electron Lenses built and installed in Tevatron have proven themselves as safe and very reliable instruments which can be effectively used in hadron collider operation for a number of applications, including compensation of beam- beam effects, DC beam removal from abort gaps, as a diagnostic tool. In this presentation we consider a possibility of using electron lenses with hollow electron beam for ion and proton collimation in LHC. | ||
| MOPC099 | Ion Catcher System for the Stabilisation of the Dynamic Pressure in SIS18 | 295 |
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| In synchrotrons operated with intermediate charge state heavy ion beams, intensity dependent beam losses have been observed. The origin of these losses is the change of charge state of the beam ions at collisions with residual gas atoms. The resulting m/q deviation from the reference beam ion leads to modified trajectories in dispersive elements, which finally results in beam loss. At the impact on the beam pipe, gas molecules are released by ion stimulated desorption which increase the vacuum pressure locally. In turn, this pressure rise will enhance the charge change- and particle loss process and finally cause significant beam loss within a very short time. In order to suppress and control the gas desorption process, a dedicated ion catcher system incorporating NEG coated surfaces and low-desorption rate materials has been developed and two prototypes were installed in SIS18. The design of the scraper and measured effect on the dynamic residual gas pressure are presented. | ||
| MOPC100 | Design Status of the FAIR Synchrotrons SIS100 and SIS300 and the High Energy Beam Transport System | 298 |
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| The present status of system- and technical design and R&D for the new heavy ion synchrotrons SIS100 and SIS300 and the HEBT system is summarized. The overall machine planning and the general layout has been completed and the detailed technical machine design has been started. Device and component specifications, technical parameter lists and technical design reports are in preparation with the goal to enable international partners or industry to finalize the component design to achieve production readiness. In the frame of international working groups the distribution and sharing of the work packages, especially of the cryomagnetic system is under discussion. | ||
| MOPC101 | Design Considerations of Fast-cycling Synchrotrons Based on Superconducting Transmission Line Magnets | 301 |
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| Fast cycling synchrotrons have become necessary components of contemporary accelerator systems for advanced nuclear and high-energy physics programs. We explore a possibility of using super-ferric dipole magnets of up to 2 Tesla B-field powered by a superconducting transmission line conductor. We present both the LTS and the HTS conductor design options for these magnets and their impact on both static and dynamic power losses with operation cycles from o.5 Hz to 5 Hz, depending on the beam energy and the size of the accelerator ring. We also discuss expected B-field quality and the corrector magnets options. We outline magnet string inter-connections and creation of space for the corrector magnets and discuss option for a superconducting dump switch of the quench protection system. | ||
| MOPC103 | Short Circuit Tests: First Step of LHC Hardware Commissioning Completion | 304 |
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| The Large Hadron Collider operation relies on 1232 superconducting dipoles with a field of 8.33T and 400 superconducting quadrupoles with a strength of 220 T/m powered at 12kA, operating in superfluid He at 1.9K. For dipoles and quadrupoles as well as for many other magnets more than 1700 power converters are necessary to feed the superconducting circuits. Between October 2005 and September 2007 the so-called short circuit tests were carried-out in the 15 underground areas where the power converters of the superconducting circuits are located. The tests were aimed at the qualification of the normal conducting components of the circuits: the power converters, the normal conducting DC cables between the power converters and the LHC cryostat, the interlocks and energy extraction systems. In addition, the correct functioning of the infrastructure systems (AC distribution, water and air cooling, control system) were validated. The final validation test for each underground area was the powering of all converters at ultimate current during 24h. This approach highlighted a few problems that were solved long before the beginning of magnet commissioning and beam operation. | ||
| MOPC104 | A New Method of Beam Stacking in Storage Rings | 307 |
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| Use of barrier buckets at synchrotron storage rings has paved way for development of new techniques for beam stacking in storage rings. The Fermilab Recycler, anit-proton storage ring, has been augmented with multipurpose broad-band barrier rf systems. Recently we have developed a new beam accumulation scheme called "longitudinal phase-space coating" that can be used for stacking beam over already e-cooled high intensity low emittance antiproton beam and demonstrated with beam experiments. Multi-particle beam dynamics simulations convincingly validate the concepts and practicality of the method. Starting with a proof-of-principle beam experiment both protons and anti-protons have been stacked a number of times using this technique in the Recycler. We present the results from both simulations and experiments. The method presented here is the first of its kind. | ||
| MOPC105 | Activities of Hitachi Relating to Construction of J-PARC Accelerator | 310 |
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| The Japan Proton Accelerator Research Complex (J-PARC) consists of a 330-m-long linac, a 3-GeV rapid cycle synchrotron with a circumference of 350 m, and a 50-GeV synchrotron with a circumference of 1,570 m. Owing to a collaboration between the Japan Atomic Energy Agency (JAEA) and the High Energy Accelerator Research Organization (KEK), the accelerators will be commencing operations at the site of JAEA Tokai Research and Development Center. The beam commissioning of the entire accelerator system is planned to take place before the end of 2008. Along with the JAEA and KEK, Hitachi has contributed to the construction of the system by manufacturing some major equipment with specifications that are of the highest level in the world. | ||
| MOPC106 | Injection and Acceleration of Au31+ in the BNL AGS | 313 |
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| Injection and acceleration of ions in a lower charge state reduces space charge effects, and, if further electron stripping is needed, may allow elimination of a stripping stage and the associated beam losses. The former is of interest to the accelerators of the GSI FAIR complex, the latter for BNL RHIC collider operation at energies lower than the current injection energy. Lower charge state ions, however, have a higher likelihood of electron stripping which can lead to dynamic pressures rises and subsequent beam losses. We report on experiments in the AGS where Au31+ ions were injected and accelerated instead of the normally used Au77+ ions. Beam intensities and the average pressure in the AGS ring are recorded, and compared with calculations for dynamic pressures and beam losses. The experimental results will be used to benchmark the STRAHLSIM dynamic vacuum code and will be incorporated in the GSI FAIR SIS100 design. | ||
| MOPC108 | AGS Polarized Proton Operation in Run 8 | 316 |
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| A dual partial snake scheme has been used for AGS polarized proton operation for several years. It has provided polarized proton beams with 1.5*1011 protons per bunch and 65% polarization for the RHIC spin program. There is still residual polarization loss due to both snake resonances and horizontal resonances. Several schemes were tested in the AGS to mitigate the loss. This paper presents the experiment results and analysis. | ||
| MOPC110 | Commissioning of the Heidelberg Cryogenic Trap for Fast Ion Beams (CTF) | 319 |
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| At the MPI für Kernphysik, a cryogenic electrostatic heavy-ion storage ring (CSR) is being developed. As a cryogenic test facility (CTF), an electrostatic ion beam trap is nearing completion. It will store ions between two electrostatic mirrors, confining them radially by two einzel lenses set apart by 30 cm. This linear, open design leaves room for testing beam diagnostic devices developed for the CSR, e.g. split ring electrodes and a residual gas monitor. As for the CSR, parts of the vacuum system will be brought in direct contact with superfluid helium, to achieve an operating temperature of 2-10 K. Under these conditions, we expect residual gas pressures in the 10-15 mbar range, and storage times on the order of minutes for light molecular ions. We will present first results from the commissioning of the CTF, especially the temperatures and residual gas pressures reached in the trap, as well as experiences with the position stability of the mechanical suspension of the trap electrodes in cryogenic operation. | ||
| MOPC111 | Lattice Studies for Spin-filtering Experiments at COSY and AD | 322 |
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| In the framework of the FAIR project, the PAX collaboration has proposed a research program based on polarized antiprotons. Polarized antiprotons are to be produced by spin-dependent attenuation on a polarized hydrogen target. For a better understanding of this mechanism it is planned to perform Spin-Filtering studies with protons at COSY (Jülich). In a second phase, it is envisioned to study Spin-Filtering with antiprotons at the AD (CERN). Which will allow for the determination of the total spin-dependent transverse and longitudinal cross sections. In order to achieve the required long storage times, a storage ring section has to be developed which minimizes the spin-independent losses due to Coulomb scattering. The Coulomb-loss cross section for single scattering losses at fixed energy is proportional to the acceptance angle. Therefore, at the target point the beta functions should be as small as possible. Fot the 'low-beta' section, superconducting quadrupole magnets are utilized. It is composed of two (COSY) and three (AD) SC quadrupoles on each side of the target. Results of the lattice studies and requirements for the superconducting quadrupole magnets will be discussed | ||
| MOPC112 | HESR Linear Lattice Design | 325 |
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| The High Energy Storage Ring (HESR) is a part of the future Facility for Antiproton and Ion Research (FAIR) at GSI in Darmstadt. The ring is used for hadron physics experiments with a pellet target and the PANDA detector, and will supply antiprotons of momenta from 1.5 GeV/c to 15 GeV/c. The ring will consist of two 180 degree bending sections (arcs) of 157 m length, each, and two 132 m long straight sections. In one of the straight sections the PANDA experiment will be installed, the other straight section will be equipped with a High Energy Electron Cooler. A longitudinal and transverse stochastic cooling system will be used in the momentum range from 3.8 GeV/c to 15 GeV/c. Adjustment of beta functions at target and electron cooler, to achieve highest beam lifetimes, most efficient cooling and highest luminosities are the main design requirements. The basic design consists of FODO cell structures in the arcs. The arc quadrupole magnets are grouped into four families, to allow a flexible adjustment of transition energy, horizontal and vertical tune, and dispersion. The details of the linear lattice and operation modes will be discussed in this presentation. | ||
| MOPC113 | Head-on Beam-beam Compensation with Electron Lenses in the Relativistic Heavy Ion Collider | 328 |
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| The working points for polarized proton operation in the Relativistic Heavy Ion Collider (RHIC) are currently constrained between 2/3 and 7/10, and the beam and luminosity lifetimes are limited by head-on beam-beam effects. To further increase the bunch intensity, we propose a low energy Gaussian electron beam, or electron lens, to collide head-on with the proton beam in order to compensate the large tune shift and tune spread generated by the proton-proton collisions in 2 interaction points. In this article, outline of the RHIC head-on beam-beam compensation with e-lenses and parameters for both proton and electron beams are presented. | ||
| MOPC114 | Status of the Electrostatic and Cryogenic Double Ring DESIREE | 331 |
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| DESIREE is a double electrostatic storage ring being built at the Manne Siegbahn Laboratory and Stockholm University. The two rings in DESIREE have the same circumference, 8.7m, and a common straight section along which stored ions can interact. The ion optics for both rings will be housed in a single double walled vacuum chamber built like a cryostat with a radiation screen and several layers of super insulation in between the two chambers. The inner chamber, which holds all the optical elements, will be cooled by four cryogenerators attached to the bottom of this chamber. It is constructed in pure aluminum to ensure good thermal conductivity over the whole structure. The whole accelerator structure will be cooled below 20K. This low temperature in combination with the unique double ring structure will result in a powerful machine for studying interactions between cold molecular ions close to zero relative energy. The outer vacuum chamber is constructed in steel with a high magnetic permeability to provide an efficient screening of the earth magnetic field. DESIREE will be provided with two injectors which will be able to supply both positive and negative ions to both rings. | ||
| MOPC116 | On the Possibility of Realizing Shortest Bunches in Low-energy Storage Rings | 334 |
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| For some very interesting experiments in future low-energy storage rings it is highly desirable to realize ultra-short bunches in the nanosecond regime. These bunches could then be used for collision studies with atomic or molecular gas jet targets where the time structure of the bunches would be used as a trigger for the experiment. Thus, the control of the longitudinal time structure of the stored beam is of central importance since it directly determines the resolution of the envisaged experiments. Since many years, it has been a significant challenge for the storage ring accelerator-physics community to develop techniques to reduce the duration of bunches. Up to now, all methods that have been developed go along with various difficulties, which can include reduced stored-beam lifetimes. Thus, novel and innovative concepts for the manipulation and control of the longitudinal beam structure have to be developed. In this paper, novel approaches to realize shortest bunches in storage rings are presented. | ||
| MOPC117 | Hybrid Snake Spin Resonance in RHIC | 337 |
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| Simulations reveal a potential polarization loss during low beta squeeze. This depolarization appears to be driven by a spin tune modulation caused by spin precession through the strong low beta quads due to the vertical fields. The modulation of the spin tune introduces an additional snake resonance condition at νs0 ± n νx - νz l = integer which while the same numerology as the well known sextupole resonance, can operate in the absence of sextupole elements. | ||
| MOPC118 | Coordination of the Commissioning of the LHC Technical Systems | 340 |
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| The Large Hadron Collider operation relies on 1232 superconducting dipoles with a field of 8.33T and 400 superconducting quadrupoles with a strength of 220 T/m powered at 12kA, operating in superfluid He at 1.9K. For dipoles and quadrupoles as well as for many other magnets more than 1700 power converters are necessary to feed the superconducting circuits. A sophisticated magnet protection system is crucial to detect a quench and safely extract the energy stored in the circuits (about 1GJ only in one of the dipole circuits) after a resistive transition. Besides, in such complex architecture, many technical services (e.g. cooling and ventilation, technical network, electrical distribution, GSM network, controls system, etc.) have to be reliably available during commissioning. Consequently, the commissioning of the technical systems and the associated infrastructures has been carefully studied. Procedures, automatic control and analysis tools, repositories for test data, management structures for carrying out and following up the tests have been put in place. This paper briefly describes the management structure and the tools created to ensure safe, smooth and rapid commissioning. | ||
| MOPC119 | Low-Output-Impedance RF System for the ISIS Second Harmonic Cavity | 343 |
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| Low-output-impedance RF system for the second harmonic cavity in the ISIS synchrotron has been developed by the collaboration between Argonne National Laboratory, US, KEK, Japan and Rutherford Appleton Laboratory, UK. Low output impedance is realized by the feedback from plate output to grid input of the final triode amplifier, resulting in less than 30 Ω over the frequency range of interest. Precise control of the second harmonic voltage can then be realized without considering beam loading effects. Beam test scenario in the ISIS synchrotron is discussed. | ||
| MOPC120 | J-PARC RCS Non-linear Frequency Sweep Analysis | 346 |
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| A standard method to measure the S21-transfer function of a system of amplifier and cavity involves a network analyzer and a linear or logarithmic frequency sweep. However, to characterize the transfer function of the broadband (Q=2) RCS RF system, we measure and analyze several harmonics at the same time under high power ramping conditions. A pattern driven DDS system generates frequency and amplitude as in accelerator operation. During the 20ms acceleration part of the cycle, a large memory oscilloscope captures the RF-signals. The data are analyzed off-line with a down-conversion process like in a multi-harmonic LLRF-system, resulting in multi-harmonic amplitude and phase information. Using this setup in the cavity test phase we were able to find and cure resonances before installation into the tunnel. We show examples. RCS is in the commissioning phase and has reached the milestone of acceleration to final energy and beam extraction. 10 RF systems are in operation, and the low-level RF system controls the fundamental h(2) and the second harmonic h(4). Using a multi-harmonic analysis during beam operation allows checking the RF system behavior with and without beam-loading. | ||
| MOPC121 | Progress on Dual Harmonic Acceleration on the ISIS Synchrotron | 349 |
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| The ISIS synchrotron at the Rutherford Appleton Laboratory in the UK is currently undergoing an RF upgrade. Four, h=4 cavities have been installed in addition to the existing 6, h=2, cavities and should be capable of increasing the operating current from 200 to 300 μA. Two of the four cavities have been in operation for the last 2 user cycles improving trapping lossess and increasing operating currents beyond 200 μA. The remaining two cavities were commissioned in the spring of 2008. This paper reports on hardware commissioning, beam tests and beam simulation results. | ||
| MOPC122 | Experiments with Fe-ion Beam Generation Acceleration and Accumulation in ITEP-TWAC Facility | 352 |
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| The laser ion source (LIS) developed in collaboration ITEP-TRINITI-CERN with an upgraded version of powerful 100J CO2-laser has been used for Fe-ion beam generation at the input of the pre-injector U-3 delivering separated species of Fe16+ ions with energy of 1.1 MeV/u to booster synchrotron UK for acceleration up to the energy of 160 MeV/u and accumulation in the storage ring U-10 using multiple charge exchange injection technique. First results of Fe-ion beam treating from laser ion source to accumulator ring are presented. | ||
| MOPC123 | Lattice Study for the Carbon Ion Synchrotron forTherapy with Electron Cooling | 355 |
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| In this paper the preliminary design of magnet lattice of the Carbon Ion Therapy Facility with electron cooling is described. The influence of misalignments of magnetic elements on ring parameters and the layout of orbit correction are estimated. The different methods of ion extractions from the synchrotron are considered, i.e., the pellet extraction, recombination extraction and the extraction on the sextupole resonance. | ||
| MOPC124 | Ion Optical Design of SIS100 and SIS300 | 358 |
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| The ion optical layout of the two synchrotrons SIS100/300 of the FAIR project is presented. SIS100 will provide high intensity ion beams of all species from H to U up to a magnetic rigidity of 100 Tm. To minimize the space charge effects and to reach the necessary ion intensities for the FAIR project SIS100 will be operated with intermediate charge state heavy ions (U28+). The ion optical layout of SIS100 has been optimized for this purpose. The layout assures the separation of beam particles which are ionized by collisions with residual gas molecules from the circulating beam. Since SIS100 and SIS300 will be installed in the same tunnel, the lattice layout of SIS300 has to follow precisely the geometry of SIS100. SIS300 will provide beams of highly charged heavy ions with a maximum rigidity of 300 Tm. In addition, it will function as a stretcher ring for SIS100. The beam transfer system from SIS100 to SIS300 is designed to fit in a single straight section of the two machines. The effect of dynamic field errors in SIS300 has been considered and the maximum tolerable error levels for the operation of SIS100, such as tracking errors and power supply ripples have been investigated. | ||
| MOPC125 | The HESR RF-system and Tests in COSY | 361 |
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| Two RF cavities will be installed in the High-Energy Storage Ring (HESR) of the future International Facility for Antiproton and Ion Research (FAIR) at the GSI in Darmstadt, one “small” cavity for barrier-bucket operation and one “large” cavity to accelerate and decelerate the beam and for bunch rotation. Additionally a barrier bucket with h=1..5 will be formed by this cavity to separate the decelerated beam from the refilled beam in the high luminosity mode (HL). Both prototype cavities have been built and first RF measurements were carried out. The recent results will be presented. | ||
| MOPC126 | Beam Acceleration with Full-digital LLRF Control System in the J-PARC RCS | 364 |
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| In the J-PARC RCS (Rapid Cycling Synchrotron) we employ a full-digital LLRF control system to accelerate an ultra-high intensity proton beam. The key feature is the multi-harmonic RF signal generation by using direct digital synthesis (DDS) technology. By employing a full-digital system, highly accurate, stable and reproductive RF voltages are generated in the wide-band RF cavities loaded by magnetic alloy (MA) cores. The beam commissioning of the J-PARC RCS has been started in October 2007. The accelerators, the linac and the RCS, show good stability. The beam orbit and the longitudinal beam shape and phase are reproductive from cycle to cycle especially thanks to the stability of the linac energy, the RCS bending field and the frequency and voltage of the RCS RF. This reproductivity makes the beam commissioning efficient. We present the examples of the orbit signals and the longitudinal current signals. Also, we discuss the longitudinal beam control performance and future plans. | ||
| MOPC128 | J-PARC Accelerator Scheme for Muon to Electron Conversion Search | 367 |
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| The searching for coherent neutrino-less conversion of a muon to an electron (COMET) at sensitivity of 10?16 has been proposed as an experiment using the J-PARC Nuclear and Particle Experimental (NP) Hall. The experiment is planned to utilize a 56 kW, 8 GeV-bunched proton beam slowly extracted from the J-PARC main ring. The 1 MHz beam pulsing with an extremely low bunch to bunch gap background is needed to eliminate beam-related background events and keep an experimental sensitivity as high as possible. The 8 GeV extraction energy is rather lower than an ordinary energy. The beam size must be less than apertures of the extracted orbit in the ring and the transport line to the NP Hall. Accelerator scheme to satisfy above requirements will be reported in this paper. | ||
| MOPC129 | Lattice without Transition Energy for the Future PS2 | 370 |
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The Large Hadron Collider (LHC) will be commissioned very soon. Improvements of the LHC injection complex are considered in the upgrade possibilities. In the injection complex it is considered that the aging Proton Synchrotron (PS) would be replaced with a new fast cycling synchrotron PS2. The energy range would be from 5-50 GeV with a repetition rate of 0.3 Hz. This is a report on the PS2 lattice design using the Flexible Momentum Compaction (FMC) method*. The design is trying to fulfill many requirements: high compaction factor, racetrack shape with two long zero dispersion straight sections, circumference fixed to a value of 1346 meters (CPS2=15/77 CPS), using normal conducting magnets and avoiding the transition energy.
*D. Trbojevic et al. ”Design Method for High Energy Accelerator Without Transition Energy”, EPAC 90, Nice, June 12-16 (1990) pp. 1536-1538. |
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| MOPC130 | Space Charge Loss Mechanisms Associated with Half Integer Resonance on the ISIS Synchrotron | 373 |
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| ISIS is the spallation neutron source at the Rutherford Appleton Laboratory in the UK. Operation centres on a 50 Hz proton synchrotron, which accelerates ~3·1013 ppp from 70 to 800 MeV, corresponding to mean beam powers of 0.2 MW. Beam loss limits operational intensity, and a main contributing mechanism is the action of half integer resonance under high space charge. Progress on studies using particle in cell simulations to explore the evolution of envelope motion, associated 2:1 parametric halo, growth of particles from the outer core, and effects of dispersion and longitudinal motion is presented. Comparisons are made with relevant theoretical models and progress on experimental studies summarised, presently emphasising the simplified 2D coasting beam case. | ||
| MOPC131 | Ions for LHC: Towards Completion of the Injector Chain | 376 |
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| The CERN LHC experimental programme includes heavy ion physics with collisions between two counter-rotating Pb82+ ion beams at a momentum of 2.76 TeV/c/nucleon per beam and luminosities as high as 1·1027 cm-2 s-1. To achieve the beam parameters required for this operation the ion accelerator chain has undergone substantial modifications. Commissioning with beam of the various elements of this chain started in 2005 and in 2007 it was the turn of the final stage, the Super-Proton-Synchrotron (SPS) following extensive changes to the low-level RF hardware. The major limitations of this mode of operation of the SPS (space charge, intra-beam scattering) are presented, together with the performance reached so far. The status of the pre-injector performance will also be reviewed together with a description of the steps required to reach nominal performance. | ||
| MOPC132 | Acceleration Voltage Pattern for J-PARC RCS | 379 |
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| The beam commissioning has been started at the J-PARC RCS. Some acceleration voltage patterns are tested to prevent the beam losses. The calculation code for the acceleration voltage pattern is usually based on the differential equation of the longitudinal synchrotron motion. We have developed the code based on the forward-difference equation which satisfies the synchronization with the bending magnetic field ramping accurately. This is very useful especially at the rapid cycling synchrotron where the ramping rate is high. The results of the test are described. | ||
| MOPC133 | Radiation Level in the J-PARC Rapid Cycling Synchrotron after First Study | 382 |
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| The 3GeV RCS (Rapid-Cycling Synchrotron) in J-PARC has been commissioned in October of 2007. The most important issue in the beam study is to reduce unnecessary beam loss and to keep the beam line clean for the sake of maintenance and upgrade of the machines. In order to achieve this purpose, we observed the beam loss monitors located around the RCS beam line and observed them for beam commissioning. We also investigated the residual dose of accelerator components during an interval of beam study. From these results, we found that beam loss points were the injection junction point, the branch of H0 dump and extraction line, transverse collimators, and dispersion maximum points in the arcs. Especially, the entrance of the primary collimator chamber and the current transformer of the H0 dump line were the most radio-activated points in the RCS. To make the best use of these results for beam commissioning, we managed to minimize the beam losses and succeeded in suppressing the residual dose to a level low enough to allows us to work close to those components. | ||
| MOPC134 | The Status of the J-PARC RF Systems | 385 |
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| The first acceleration of a proton beam at the J-PARC Rapid Cycling Synchrotron started in October 2007. The R&D for magnetic alloy (MA) loaded rf-systems to realize a high field gradient accelerating system for a rapid cycling machine has been initiated in 1996 with the aim of surpassing standard ferrite loaded cavities. The RCS RF system is broad-band and designed to cover both the RCS accelerating frequency range and the second harmonic for bunch shape manipulation. The optimum Q value of the RCS cavities is approximately 2. This is realized by combining a high-Q parallel inductor with an un-cut core configuration. The beam commissioning of the 50GeV Main Ring synchrotron will start in May 2008. Acceleration and slow-beam extraction are planned for December 2008. In case of the MR RF system, the accelerating frequency swing is small. The Q-value in the order of 20 has been selected to reduce transient beam loading due to the multiple-batch injection scheme. The MR RF cavities realize the Q-value by a cut-core configuration. The details of the RF systems and the results of beam accelerations are summarized. | ||
| MOPC135 | Present Status and Future improvement of HIRFL-CSR | 388 |
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| The HIRFL-CSR project is a national mega project of China, which concentrates on heavy ion synchrotron and cooling storage ring. It is finished recently. The present commissioning results, testing experiments are introduced in this paper. The future improvement of the machine is also shown. | ||
| MOPC136 | Beam Bunch Leakage and Control in the SNS Ring | 391 |
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| In recent neutron production operations at SNS, beams contaminated the longitudinal extraction gap of the accumulator ring due to the limitation of the beam choppers. It caused significant beam loss and activation in the ring and in the extraction beam line. From simulations with computer models and in experimental measurements, properly utilizing the ring RF systems with additional storage turns after the beam accumulations in the ring effectively reduced beam loss in the SNS accelerator systems. Simulations and beam measurement results will be discussed | ||
| MOPC137 | The Cryogenic Storage Ring Project at Heidelberg | 394 |
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| At the Max-Planck-Institut für Kernphysik in Heidelberg a next generation electrostatic storage ring at cryogenic temperatures is under development. The main perspective of this unique cryogenic storage ring (CSR) is the research on ions, molecules and clusters up to bio molecules in the energy range of 20 keV -300 keV at low temperatures down to 2 Kelvin. The achievement of this low temperature for all material walls seen by the ions in the storage ring not only causes a strong reduction of black body radiation incident onto the stored particles, but also acts as a large cryopump, expected to achieve a vacuum of better than 1·10-15 mbar (corresponding to 1·10-13 mbar room temperature äquivalent). The low temperature and the extreme low vacuum will allow novel experiments to be performed, such as rotational and vibrational state control of molecular ions and their interaction with ultra-low energy electrons and laser radiation. A 20 W at 2 K refrigerator was designed and successfully commissioned. A connection with the fully assembled cryogenic prototype ion trap is under way. In this paper the concept and the status of the cryogenic storage ring will be presented. | ||
| MOPC139 | Refractory Ovens for ECR Ion Sources and Their Scaling | 397 |
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| The radiofrequency (rf) oven can be used as a metal vapour injector for Electron Cyclotron Resonance ion source; the application to high temperature boiling metals (like Cr, Ti and V) was recently demonstrated. Duration and reusability of oven parts were excellent, since crucible only need to be maintained at a temperature Ts larger than other parts; for vanadium case, achieved Ts was up to 2300 K with about 280 W of rf power, with the present design and size, tailored to our 14.4 GHz ECRIS. Optimization for different sources is discussed, and modern design tools are reviewed. Materials, more than rf power coupling, emerge as ultimate limits. Comparisons of results with resistive oven and sputter probes and with different metals are briefly reported. | ||
| MOPC140 | Status of the Multipurpose Fully Superconducting ECR Ion Source | 400 |
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| The MSECRIS source has been designed with the aim to exceed the highest currents of highly charged heavy ions available up to now. It is based on a minimum B trap made of a hexapole and three solenoids. The design magnetic field is 2.7 T for the hexapole and 4.5 T for the mirror field, in order to permit to operate not only at 28 GHz but also at higher frequency, thus increasing the plasma density and finally the beam current. Such high level of magnetic field is a challenge because of the forces arising on the superconducting coils and it largely exceeds the highest magnetic field available for existing ECRIS. A description of the source and of its preliminary results will be given. The source has been built in the frame of the European collaboration EURONS/JRA07-ISIBHI and it is now installed at the EIS testbench of GSI. | ||
| MOPC141 | Design of a Novel Tubular Electron String Ion Source (TESIS) | 403 |
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The project, started in 2007 is directed to creation of Tubular Electron String Ion Source (TESIS) and to basic studies of electron strings in tubular geometry. The collaboration consists of JINR (Dubna) and Russian Federal Nuclear Center (Sarov, Russia), Manne Siegbahn Laboratory (Stockholm, Sweden), TRIUMF and Atomic Energy of Canada Ltd. (Canada). Tubular concept of ion source has been proposed few years ago*. Preliminary theoretical estimations and numerical simulations have been done**,*** that allowed to start experimental realization of this project. New tubular source with a superconducting solenoid up to 5 Tesla should be constructed in 2009. It is expected that this new TESIS (“Krion-T1”) will meet all rigid conceptual and technological requirements and should provide ion output on a level, approaching to 10 mA of Ar16+ ions in the pulse mode and about 10 mA of Ar16+ ions in the average current mode. Having these output parameters, “Krion-T1” TESIS should be an operational prototype of further TESIS sources for all kinds of the possible applications. Simulation results and a basic scetch of the TESIS construction will be presented.
*Donets E. D. et al. Rev. Sci. Instrum. 73, 696 (2002). |
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| MOPC142 | Study of the Post Extraction Acceleration Gap in the ISIS H- Penning Ion Source | 406 |
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| The RAL Front End Test Stand (FETS) is being constructed to demonstrate a chopped H- beam of up to 60 mA at 3 MeV with 50 pps and sufficiently high beam quality for future high-power proton accelerators (HPPA). The injection energy into the RFQ will be in the range of 50 to 70 keV whereas the standard ISIS H- Penning ion source operates at 35 keV, therefore the post extraction acceleration voltage must be increased. In order to finalise the design of the FETS post extraction system, a study is conducted on the Ion Source Development Rig (ISDR) at ISIS. This study shows how beam transport is affected by different post extraction acceleration voltages and gap lengths. Beam, current, profile and emittance measurements are presented along with theoretical calculations. | ||
| MOPC143 | Multi-beamlet Study of Beam Transport in the ISIS H- Ion Source Analysing Magnet | 409 |
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| The RAL Front End Test Stand (FETS) is being constructed to demonstrate a chopped H- beam of up to 60 mA at 3 MeV with 50 pps and sufficiently high beam quality for future high-power proton accelerators (HPPA). The existing 90° analysing magnet on the ISIS H- Penning ion source does not perfectly transport the beam after extraction. The present ion source has a 10 mm x 0.6 mm slit extraction aperture. To understand how the beam is transported in the analysing magnet, new ion source aperture plates are manufactured with 5 individual holes instead of a slit. These holes produce separate beamlets that are used to study transport in the sector magnet. This paper details the experiments with the modified aperture plates on the Ion Source Development Rig (ISDR) at ISIS. | ||
| MOPC144 | Installation of the Front End Test Stand High Performance H- Ion Source at RAL | 412 |
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| The RAL Front End Test Stand (FETS) is being constructed to demonstrate a chopped H- beam of up to 60 mA at 3 MeV with 50 pps and sufficiently high beam quality for future high-power proton accelerators (HPPA). This paper details the first stage of construction- the installation of the ion source. | ||
| MOPC145 | Commissioning of the ECR Ion Sources at CNAO Facility | 415 |
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| The Centro Nazionale di Adroterapia Oncologica (National Center for Oncological Hadrontherapy, CNAO) is the Italian center for deep hadrontherapy. It will deliver treatments with active scanning both with proton and carbon ion beams. At CNAO two ECR sources of the Supernanogan type (built by the Pantechnik company according to specifications set by INFN) are installed and run continuously and in parallel, to allow the fast change of the particle species. The two sources are identical and can provide both particle species after a simple switch from one gas to the other, which allows as well to run the facility, in emergency, with only one source. Each source is equipped with a dedicated beam line including a spectrometer and beam diagnostics. Optimisation of beam emittance and intensity is of primary importance to obtain the necessary current at the RFQ-LINAC and then at injection. The preliminary tests have shown the complete fulfillment of the specifications in terms of beam current and emittance and the final tests are ongoing. A description of the source design and performance will be presented. | ||
| MOPC146 | Development of Piezoelectric Pulse Gas Valve for Small ECR Ion Source | 418 |
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| In a conventional ion source, the source gas is continuously fed even in its pulse operation. This requires a high load to a vacuum pumping system. The situation is prominent when the gas load is relatively higher in such a high current ion source. In order to improve this situation, we try to supply gas only when it is needed by synchronizing the gas feed with the extraction of the ion beam. We have developed a small pulse-gas-valve using a commercially available disc-shape piezoelectric element. This valve is small enough to be mounted in our ECR ion source and is capable of very fast open-and-close operation of an order of kHz repetition. A small ECR ion source with this valve will be presented. | ||
| MOPC147 | Measurement of Ion Beam from Laser Ion Source for RHIC EBIS | 421 |
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| Laser ion source (LIS) is a candidate of the primary ion source for the RHIC EBIS. LIS will provide intense charge state 1+ ions to EBIS for further ionization. We measured plasma properties of a variety of atomic species such as Si, Fe and Au using the second harmonics of Nd:YAG laser (532 nm wave length, up to 0.82 J / 6 ns). Since a suitable laser power density for production of charge state 1+ ions is different from different species, laser power density was optimized to obtain a maximum beam intensity in each species. Also the results of emittance measurement using pepper pot after ion extraction with about 20 kV extraction voltage will be shown. Based on the obtained results, performance of the LIS as the primary ion source for EBIS will be discussed in this paper. | ||
| MOPC148 | Target Life Time of Laser Ion Source for Low Charge State Ion Production | 424 |
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| Laser ion source produces ions by irradiating pulsed laser shots onto the solid state target. For the low charge state ion production, laser spot diameter on the target can be over several millimeters using the high power laser such as Nd:YAG laser (532 nm wave length, 0.82 J / 6 ns). In this case, damages to the target surface is small while there is a visible crater in case of the best focused laser shot (laser spot diameter can be several tens of micrometers) for high charge state ion production. Because damage to the target surface is small, target is not required to be moved to use fresh surface after each laser shot to stabilize plasma. In this paper, the results of target life time measurements will be shown. | ||
| MOPC150 | Modifications to the Analysing Magnet in the ISIS Penning Ion Source | 427 |
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| A full 3D electromagnetic finite element analysis and particle tracking study is undertaken of the ISIS Penning surface plasma ion source using CST Particle Studio 2008. The existing 90° analysing magnet is found to have a magnetic field index of 1.3, causing beam divergence and contributing to beam loss. Different magnet pole piece geometries are modelled and the effect of space charge investigated. Based on this modelling, three new sets of poles are manufactured and tested on the Ion Source Development Rig. The results are presented herein. | ||
| MOPC151 | Status of the Versatile Ion Source VIS | 430 |
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| The characteristics of the ideal injector for high power proton accelerators has been studied in the past with the TRIPS ion source built at INFN-LNS, Catania and now in operation at INFN-LNL, Legnaro. The beam production must obey to the request of high brightness, stability and reliability. The new Versatile Ion Source (VIS) is a permanent magnet version of the TRIPS source with a simplified and robust extraction system. It operates up to 80 kV without a bulky high voltage platform, producing multi-mA beams of protons and H2+. The description of the source design and the preliminary performance will be presented. An outline of the forthcoming developments is given, with particular care to the use of a low loss dc break and to the use of a travelling wave tube amplifier to get an optimum matching between the microwave generator and the plasma. | ||
| MOPC153 | Construction and Test of the Superconducting Coils for RIKEN SC-ECR Ion Source | 433 |
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| A superconducting ECR ion source is under development to increase the intensity of the beams with high charge state such as U35+ provided to the RI-beam factory at RIKEN. The ion source consists of six superconducting solenoids and a set of superconducting sextupoles. The axial magnetic fields are 3.8 T at the injection peak and 2.2 T at the extraction peak. The sextupole magnetic field is 2.0 T on the inner surface of the plasma chamber with a diameter of 15 cm. The conductors use NbTi/copper wires with copper/SC ratio of 1.3 and size of 1.25 mm x 0.92 mm. The sextupole coils are difficult to design and fabricate because the maximum experience magnetic field is about 7.3 T and the magnetic force acting on the coils changes by the strength of the radial field of the solenoids along the axis. The design, construction and the results of the excitation test will be presented in this paper. | ||
| MOPC154 | Method for Efficiency and Time Response Measurement on Diverse Target Ion Sources with Stable Alkali | 436 |
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Developments of new setups for radioactive ion beam production by the isotope-separator-on-line (ISOL) method are underway at GANIL in the frame of the SPIRAL (Système de Production d’Ions Radioactifs Accélérés en Ligne) and SPIRAL-II projects. The measurement of total efficiency and time behaviour of these new target/ion-source systems (TISSs) is a crucial step for these devices which aims to produce short-lived isotopes with high intensity. The overall atom-to-ion transformation efficiency depends on several processes: diffusion of the atoms out of the production target, effusion towards the ion source and ionization. The efficiency can be extracted using the ratio between the emerging yield and implanted flux in the TISS. Several methods have already been developed to achieve these measurements: the use of stable or radioactive beams, gas injection, or the introduction of solid material into the TISS. This paper focuses primarily on a method that uses stable alkali. A pulsed/CW alkali ion gun has been built and will be used to optimise diverse TISSs.
[1] C. Eléon et al., Proceedings of the XVe International Conference EMIS, 24-29th June 2007, Deauville, France, to be published. |
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| MOPC155 | Transport System for Ion Implantation | 439 |
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| ITEP in collaboration with MEPHI and IHE (Tomsk) develops the high intensity ion beam generation and transport systems for low energy (1-50 keV) ion implantation. Such facilities are used for semiconductor technology. The Bernas type ion source is used for ribbon ion beam production. The periodical system of electrostatic lenses (electrostatical undulator) was proposed for ribbon beam transport line. The design of transport system and the results of beam dynamics investigation are presented. The influence of the electrodes construction errors on the beam dynamics is discussed. | ||
| MOPC156 | ECR Ion Source for the KEK All-ion Accelerator | 442 |
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R&D works to realize an all-ion accelerator (AIA)* -capable of accelerating all ions of any possible charge state, based on the induction synchrotron concept, which was demonstrated using the KEK 12 GeV-PS**, are going on. As an ion source for the KEK-AIA, an electron cyclotron resonance (ECR) ion source has been developed. Permanent magnets made of NdFeB to generate a cusp field and 9.4 GHz microwave to energize plasma electrons have been employed. The microwave power of 750 W generated in a traveling wave tube is focused into the interaction region with a horn antenna. Regarding the cut off density for 9.4 GHz, the vacuum and the gas feeding system has been designed. The base pressure of 1·10-5 Pa is reached with a single turbo molecular pump of 300 l/min, and the gas flow rate less than 1 cc/min is maintained with a mass flow controller. The plasma chamber is water-cooled against Joule heating. The geometry of the extraction electrodes and the downstream transport line have been optimized by IGUN simulations. The whole system will be embedded in the high voltage terminal box of 200 kV. Details of the design and the preliminary test will be described at this conference.
*K. Takayama, Y. Arakida, T. Iwashita, Y. Shimosaki, T. Dixit, and K. Torikai, J. of Appl. Phys. 101, 063304 (2007). |