CLASSE, Ithaca, New York
The development of high current, high brightness electron guns is critically important for FEL and ERL light source facilities. In this talk we will review the technical requirements of such projects and the status of on-going research throughout the community including results of emittance measurements and high current beam performance.
UTNL, Ibaraki
The University of Tokyo, Nuclear Professional School, Ibaraki-ken
University of Tokyo, Tokyo
Akita National College of Technology, Akita
We are developing an X-band linac system for monochromatic X-rays source. The monochromatic X-ray is obtained by Compton scattering. Our system has an X-band (11.424 GHz) 3.5-cell thermionic cathode RF gun, traversing wave accelerating tube and a Q-switch Nd:YAG laser with a wavelength of 532 nm. We adopt a laser pulse circulation system. The RF gun can generate multi-bunch electron beam. We aim to generate 1 μs maximum energy electron beam and collide it to circulated laser pulse. I will present a current status of beam measurement of this linac.
RISE, Tokyo
ISIR, Osaka
AIST, Tsukuba, Ibaraki
RIKEN, Saitama
We have been studying a pump-probe pulse radiolysis as an application of the S-band photo cathode RF-Gun. Pump-probe spectroscopy is well-known method of pulse radiolysis measurement. We had used 5MeV electron beam obtained from the photo cathode RF-Gun as a pump beam, and used the white light emitted from Xe flash lamp or generated by self-phase modulation in the water cell as a probe light. However, the white probe light with high intensity, good stability and broad spectrum is a key issue for pump-probe pulse radiolysis. Supercontinuum light with photonic crystal fiber (PCF) is a new technique of white light generation. Short pulse laser through PCF spreads its spectrum by nonlinear optical effect. Supercontinuum light has very continuous spectrum, and it is studied for various applications recently. For applying supercontinuum light as a probe of pulse radiolysis experiment, we have generated a supercontinuum radiation with 7 picoseconds pulse width IR (1064nm) laser and PCF, and measured its properties. The experimental results of supercontinuum generation and design of a supercontinuum based pulse radiolysis system will be presented.
TUB, Beijing
For the miniaturization of low energy linear accelerators, X-band pulsed magnetron with stable performance of 1.5 MW peak power is needed to be developed. This paper presents the 3D particle-in-cell (PIC) of an X-band coaxial magnetron. A time evolved electron flow exhibits N/2 spokes in the simulations, which confirms the generation of pi-mode. Computer modeling indicates the mode competition in the startup process according to the spectra. By changing the DC voltage, we got the voltage-current characteristics of this magnetron, and comparison with the experiment was also been presented.
KAERI, Daejon
We made an experiment apparatus for the investigation of nano particle synthesis by proton inducing. It is composed of water tank, thin sample case with large area, ultrasonic oscillator, beam entrance window, monitoring camera, etc. Pt nano particles were fabricated. Nano particle characteristics are influenced by the condition of the solution, such as concentrations of H2PtCl6, CP and IPA. The experiment apparatus was designed that Pt nano particles were fabricated fore conditions. For a proton induced synthesis, some parameters, such as beam energy, beam current, flux, total dose, dose rate, etc. are also known as important process variables. To identify the effects of these irradiation parameters, we investigated the properties of nano particles according to the changes of these parameters. The energy was changed in the range of 10 ~ 40 MeV, beam current 1 uA. It could be examined by using an experiment apparatus developed for this purpose.
UCLA, Los Angeles, California
High brightness ultrashort electron beams have been produced at the UCLA Pegasus photoinjector lab for use in time-resolved electron diffraction applications. Beams have been generated with high enough brightness to obtain single shot diffraction patterns of thin solid targets. These beams contain a few pC at 3.5 MeV in a 200 fs pulse. Pump-probe experiments on thin metal foils have already shown promising results on picosecond time scales*. Current research focuses on materials with processes that are observable on the sub-100 fs scale. To overcome rf jitter and synchronization problems, electro-optic sampling is used as a single shot time-of-arrival diagnostic** to help reconstruct the melting "movie."
*P. Musumeci, et al., Rev. Sci. Instrum. 80, 013302 (2009)
**C. Scoby, et al., PR-ST Beams and Accel. 13 (2010)
BNL, Upton, Long Island, New York
In polarized proton operation the luminosity of RHIC is limited by the head-on beam-beam effect, and methods that mitigate the effect will result in higher peak and average luminosities. Two electron lenses, one for each ring, are being constructed to partially compensate the head-on beam-beam effect in the two rings. An electron lens consists of a low energy electron beam that creates the same amplitude dependent transverse kick as the proton beam. We discuss design consideration, present the main parameters, and estimate the performance gains.
KACST, Riyadh
JINR, Dubna, Moscow Region
Cockcroft Institute, Warrington, Cheshire
At the National Centre for Mathematics and Physics (NCMP), at the King Abdulaziz City for Science and Technology (KACST), Saudi Arabia, a versatile low energy ion injector has been developed in collaboration with the QUASAR group. This project will allow for a broad experimental program with most different kinds of ions both in single pass setups, but also with ions stored in a fixed-energy electrostatic storage ring. In this contribution, the design of the injector is presented. It was designed for beams with energies of up to 30 kV/q and will allow for switching between different ion sources from e.g. duoplasmatron to electrospray ion sources and to thus provide the users with a wide range of different beams. The mechanical construction of the injector is summarized and the status of its assembly at KACST presented.
NIRS, Chiba-shi
For the beam profile diagnosis of heavy ion cancer therapy in HIMAC (Heavy Ion Medical Accelerator in Chiba), a MWPC (Multi-Wire Proportional Counter) detector is employed as a beam profile monitor. Due to the high rate beams (~ 108 pps), a gain reduction of output signals, which is caused by space charge effects, have been observed in the scanning beam experiments at HIMAC. In order to reduce the gain reduction by optimizing the parameters of MWPCs including anode radius, and distance between electrodes, a numerical calculation code was developed by employing two-dimensional fluid model. In order to understand the relations between the gain reduction and space charge distribution, the temporal evolution of the ion/electron distribution were calculated for several hundredμseconds, which is significantly longer than the time period required for ions to travel between the electrodes. The output signal was also evaluated by the current flux into the anode and compared with that obtained by the beam experiment at HIMAC. The dependence of the gain reduction on the MWPC parameters was analyzed from these calculation results.
Hiroshima University, Graduate School of Science, Higashi-Hiroshima
KEK, Ibaraki
Energy Recovery Linac (ERL) as synchrotron light source is planned to construct in KEK. Before the construction of full-set of ERL, compact ERL to study the accelerator technologies will be constructed. For the injector, a high voltage photoemission gun with DC operation and measurement systems for the low emittance beam will be developed. In order to observe bunch length and longitudinal beam profile, we have designed a single-cell deflecting cavity with 2.6 GHz dipole mode. We describe the optimization of the cavity, mechanical design and the measurements results with simulation.
CERN, Geneva
Gas Electron Multipliers (GEM) find their way to more and more applications in beam instrumentation. Gas Electron Multiplication uses a very similar physical phenomenon to that of Multi Wire Proportional Chambers (MWPC) but for small profile monitors they are much more cost efficient both to produce and to maintain. This paper presents the new GEM profile monitors intended to replace the MWPCs currently used at CERN's low energy Antiproton Decelerator (AD). It will be shown how GEMs overcome the documented problems of profile measurements with MWPCs for low energy beams, where the interaction of the beam with the detector has a large influence on the measured profile. Results will be presented from profile measurements performed at 5 MeV using four different GEM prototypes, with discussion on the possible use of GEMs at even lower energies needed at the AD in 2012.
RIKEN/SPring-8, Hyogo
SASE based X-ray free-electron laser is now under construction at the SPring-8 site. This project is aiming at realization of SASE FEL of 1 angstrom initially and approaches to seeded XFEL in the second stage. For this future extension, a very unique system was adopted, composed of a low emittance SHB-based injector with CeB6 cathode thermionic gun, normal conducting high gradient C-band acceleration system and high performance in-vacuum undulators. This presentation will provide a comprehensive project review and recent project progress.
USTC/NSRL, Hefei, Anhui
A Photo-Cathode RF Gun is under development at NSRL. In this paper, the drive laser system is introduced and performance parameters are presented. We adopt a BNL type gun with laser illuminating the cathode at oblique incidence. To orrect 'time slew' and 'elliptical spot' problems arisen on the cathode, an adjustable optical transport line is designed.
BNL, Upton, Long Island, New York
PVI, Oxnard
Institute of High Current Electronics, Tomsk
Electron clouds, which can limit machine performance, have been observed in many accelerators including RHIC at BNL. They can be suppressed by low secondary electron yield beam pipe surfaces. Additional concern for the RHIC machine, whose vacuum chamber is made from relatively high resistivity 316LN stainless steel, is high wall resistivity that can result in unacceptably high ohmic heating for superconducting magnets. The high resistivity can be addressed with a copper (Cu) coating; a reduction in the secondary electron yield can be achieved with a TiN or amorphous carbon (a-C) coating. Applying such coatings in an already constructed machine is rather challenging. We started developing a robotic plasma deposition technique for in-situ coating of long, small diameter tubes. The technique entails fabricating a device comprising of staged magnetrons mounted on a mobile mole for deposition of about 5 μm (a few skin depths) of Cu followed by about 0.1 μm of a-C. As a first step, a 15-cm Cu cathode magnetron is being designed and fabricated, after which, 30-cm long sample of the RHIC pipe are to be Cu coated. Deposition rates and affects on RF resistivity are to be measured.
BNL, Upton, Long Island, New York
The proposed electron ion collider, eRHIC, requires large average polarized electron current of 50mA, which is more than 20 times higher than the present experiment results of single polarization source, such as GaAs. To achieve the current requirement of eRHIC, we have designed the multi-cathode DC electron gun for injection. 24 GaAs cathodes will be prepared and emit electrons at the arranged pattern. Despite of ultra-high vacuum and precise timing, multi-cathode DC electron gun has high demand on the electric field symmetry, magnetic field shielding, and arcing prevention. In the paper, we present the 3D simulation results of the latest model for the multi-cathode DC electron gun. The results will give guidance to the actual design in the future.
Fermilab, Batavia
CERN, Geneva
UCSD, La Jolla, California
INFN-Ferrara, Ferrara
Magnetically confined hollow electron beams for controlled halo removal in high-energy colliders such as the Tevatron or the LHC may extend traditional collimation systems beyond the intensity limits imposed by tolerable material damage. They may also improve collimation performance by suppressing loss spikes due to beam jitter and by increasing capture efficiency. A hollow electron gun was designed and built. Its performance and stability were measured at the Fermilab test stand. The gun will be installed in one of the existing Tevatron electron lenses for preliminary tests of the hollow-beam collimator concept, addressing critical issues such as alignment and instabilities of the overlapping proton and electron beams.
INFN/LASA, Segrate (MI)
The production of Cs2Te photoemissive films used as laser driven electron sources in the high brightness photoinjectors at FLASH and PITZ, is a well established activity at INFN Milano since the '90s. Our total production is of more than 100 photocathodes, with an average QE of 8% (@ 254 nm) for fresh films and an operative lifetime that increased up to some months at FLASH. In the last two years, we have improved the standard diagnostic used during the cathode growth to better understand the material properties of the films. This activity is motivated by the need to improve the photocathode properties, mainly the energy distribution of the photoemitted electrons that influences the thermal emittance. The multiwavelengths diagnostic, i.e. the on-line measurements of the photocurrent and reflectivity from the film during its growth in the 239 nm ~ 436 nm range, has been deeply applied on several cathodes and the potentiality of this technique are discussed in this paper.
UVSOR, Okazaki
Kyoto IAE, Kyoto
Sokendai - Okazaki, Okazaki, Aichi
Thermionic RF guns are compact, economical and high brightness electron sources. However, when the guns are used for a driver linac of oscillator-type Free Electron Lasers (FELs), which requires moderate bunch charge (several tens pico-coulomb) and long macro-pulse duration (several micro-seconds), the guns have been suffered from the back-bombardment effect*. The effect induces beam current increment in a macro-pulse. And consequently the current increment leads to decrement of beam energy during a macro-pulse and significantly limits the beam macro-pulse duration after some bending magnets. Our group found a new energy compensation scheme called as cavity detuning** and the method was introduced to compensate the beam energy decrement in the thermionic RF gun used for KU-FEL***. In this presentation, we will introduce the principle of the method and experimental results. Detailed analysis of the method will be also presented.
* C.B. McKee et al., NIM, A296, pp. 716-719, 1990.
** H. Zen et al., IEEE Trans. of Nucl. Sci., vol. 56, No. 3, pp. 1487-1491
*** T. Yamazaki et al., Proc. of 23rd FEL Conf., pp. II-13-14, 2002.
ISIR, Osaka
KEK, Ibaraki
HU/AdSM, Higashi-Hiroshima
We conduct research on Free Electron Laser (FEL) in the infrared region and pulse radiolysis for radiation chemistry using the 40 MeV, 1.3 GHz L-band linac of Osaka University. At present, the L-band linac is equipped with a thermionic electron gun. It can accelerate a high-intensity single-bunch beam with charge up to 91 nC but the normalized emittance is large. In order to advance the research, we have begun development of a photocathode RF gun for the L-band electron linac in collaboration with KEK and Hiroshima University. We start the basic design of the RF gun cavity for the L-band linac at ISIR, Osaka University, based on the 1.5 cells, which is a normal conducting photocathode RF gun. A material of the cathode should be Cs2Te, which has the high quantum efficiency of a few percents, to produce a beam with high charge up to 30 nC/bunch. We improve the cooling system of the cavity for high duty operation to suppress the thermal deformation due to the heat load of input rf power. The simulation study has been also performed for the L-band linac at ISIR with a high charge electron beam. In this conference, we describe the details of the L-band photocathode RF gun development.
Tohoku University, School of Scinece, Sendai
Tohoku University, Research Center for Electron Photon Science, Sendai
A test accelerator for the coherent terahertz source (t-ACTS) has been under development at Laboratory of Nuclear Science, Tohoku University*. Intense coherent terahertz radiation will be generated by the very short electron bunch less than 100 fs using a thermionic RF gun (ITC RF-gun). ITC RF-gun is designed to have two cells uncoupled with each other, so that it can be operated at various combinations of different rf-power level and phase difference so as to optimize the longitudinal phase space distribution of the electron beam for bunch compression**. The gun employs single-crystal LaB6 cathode with small diameter of 1.8 mm to obtain a very small initial emittance with sufficiently high current density. The RF gun has been already manufactured and the measurement of RF characteristics is now in progress. We will present the results of low-power measurement and also discuss the effect of the cathode misalignment on the beam parameters such as transverse emittance and longitudinal phase space distribution.
* H. Hama et al., New J. Phys. 8 (2006) 292.
** H. Hama et al., Nucl. Instr. and Meth., A 528, (2004) 371.
USTC/NSRL, Hefei, Anhui
Recently, great attention has been paid to short electron pulses because of requirement for FEL project. Our aim is a 0.2nC, 5ps, 2MeV electron bunch with a normalized emittance less than 10 mm mrad without compensation coil. To create such beams, an External Cathode Independently Tunable Cells RF gun (EC-ITCRF Gun) was advanced, which consists of two independent cavities and a diode gun. The RF power and its phase fed to the two cavities can be independently adjustable. The paper described simulating results of the beam dynamic in the gun and a test facility. After RF power exercising a week, the electric field in the cavities surface was reached 100MV/m and dark current was disappearance. Main parameters measured are as following: energy is of 1.98MeV, pulse bean current of 20A, beam width of 5ps and energy spread of 0.5% so on. Keyword: EC-ITC RF Gun, emittance, energy spread, external cathode
PSI, Villigen
As part of the SwissFEL project at Paul Scherrer Institute, an electron gun test stand has been built and operated. The goal is to achieve an exceptionally low emittance beam with a charge of 200pC for XFEL application. The electron gun consists of a High Gradient (HG) pulsed diode followed by an RF acceleration structure. The diode has an adjustable gap and the cathode is pulsed at up to 500 kV. The electrons were extracted either from a near-flat cathode surface or a dedicated photo-source recessed in a hollow cathode surface. For the diode electrtodes, many metals, geometries and surface treatments were studied for their HG and photo emission suitability. Polished metal electrodes, single tips, field emitter arrays and electrodes coated with different Diamond Like Carbon (DLC) types were tested. In particular, we found that DLC coating had useful properties. Surface electric fields over 250MV/m (350 ~ 400kV, in pulsed mode) with negligible parasitic electron emission were achieved; when UV laser illumination was applied to DLC electrodes, it was possible to extract electron bunches of over 60pC at gradients up to 150MV/m.
UMAN, Manchester
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
Gallium Arsenide (GaAs) photocathodes have in recent year been widely used and have become the focus for use in modern accelerators and light sources such as the Accelerators and Lasers in Combined Experiments (ALICE) and the International Linear Collider (ILC). Once activated to a Negative Electron Affinity (NEA) state and illuminated by a laser, these materials can be used as a high-brightness source of both polarised and un-polarised electrons. This work presents an effective preparation procedure including heat cleaning, atomic hydrogen cleaning and the activation process for NEA GaAs photocathode. The stability of quantum efficiency (QE) and lifetime of NEA GaAs photocathode have been studied in the load-lock and photocathode preparation system for the ALICE photo- electron gun which has a base pressure in the order of 10-11 mbar. These studies are also supported with experimental evidence from surface science techniques such as Photoelectron Spectroscopy (XPS) and Low Energy Electron Diffraction (LEED) to demonstrate the processes at the atomic level.
Muons, Inc, Batavia
JLAB, Newport News, Virginia
Many user facilities such as synchrotron radiation light sources and free electron lasers require accelerating structures that support electric fields of 10-100 MV/m, especially at the start of the accelerator chain where ceramic insulators are used for very high gradient DC guns. These insulators are difficult to manufacture, require long commissioning times, and often exhibit poor reliability. Two technical approaches to solving this problem will be investigated. Firstly, inverted ceramics offer solutions for reduced gradients between the electrodes and ground. An inverted design will be presented for 350 kV, with maximum gradients in the range of 5-10 MV/m. Secondly, novel ceramic manufacturing processes will be studied, in order to protect triple junction locations from emission, by applying a coating with a bulk resistivity. The processes for creating this coating will be optimized to provide protection as well as be used to coat a ceramic with an appropriate gradient in bulk resistivity from the vacuum side to the air side of an HV standoff ceramic cylinder. Example insulator designs are being computer modelled, and insulator samples are being manufactured and tested
BNL, Upton, Long Island, New York
AES, Medford, NY
PKU/IHIP, Beijing
RF electron guns with strained super lattice GaAs cathodes can produce higher brightness and lower emittance polarized electron beams, due to the higher field gradient at the cathode surface compared with DC guns. The vacuum in the gun must be better than 10-11 torr to obtain a sufficient cathode life time with high quantum efficiency (QE). Such high vacuum cannot be obtained easily in a normal conducting RF gun. We report on an experiment with a superconducting RF (SRF) gun, which can maintain a vacuum of nearly 10-12 torr because of cryo-pumping at the temperature of 4.2K . The GaAs cathode was activated by Cs'O treatment with a QE of 3% and exhibits a long lifetime in a preparation chamber. This cathode will be used in a 1.3 GHz - cell SRF gun to measure the destruction of the QE by ion and electron back-bombardment.
BNL, Upton, Long Island, New York
AES, Medford, NY
PKU/IHIP, Beijing
Superconducting RF (SRF) electron guns deliver higher brightness beams than DC guns because the field gradient at the cathode is higher. SRF guns with metal cathodes have been successfully tested. For the production of polarized electrons a Gallium-Arsenide (GaAs) cathode must be used, and an experiment to test this type of cathode is under way at BNL. Since the cathode will be normal conducting, the primary concern is cathode-driven heat load. We present measurements of the electric resistance of GaAs at cryogenic temperatures, a prediction of the heat load, and verification by measuring the quality factor of the gun with and without the cathode.
Kyoto IAE, Kyoto
UVSOR, Okazaki
RF gun has been chosen as injector for Kyoto University free electron laser because it can potentially produce an electron beam with high energy, small emittance, moreover inexpensive and compact configuration in comparison with other injectors. As for the RF gun cathode, thermionic cathode is simpler, easier to treat and reliable than photocathode. On the other hand, backbombardment electrons make cathode surface temperature and current density increase within the macropulse, as a result, beam energy and macropulse duration decrease, which means, it is difficult to generate stable FEL. The heating property of cathode not only depends on physical properties of the cathode material such as work function, but also backbombardment electrons energy. We investigated the heating property of six hexaboride materials against the backbombarding electrons by numerical calculation of the range and stopping power. In this investigation, the emission property of the cathode was also taken into account, since high electron emission is required for generation of high brightness electron beam. The results will be discussed.
CEA, Bruyeres le Chatel
GETINGE - La Calhene, Villebon sur Yvette
The original linac consists of an electron gun (45 kV, 6 A peak, 4 μs pulses @ 210 Hz) and 8 accelerating cells coupled with coupling cells in π/2 mode @ 3 GHz to provide for a 1 mA and 5 MeV beam. A loss of control of electron emission was experimentally observed due to anomalous heating of the cathode. We simulate the linac operation with the 2D1/2 MAGIC® electromagnetic PIC code to understand and suppress these phenomena. We show that electrons are accelerated back from the accelerating structure to the cathode. Their power is responsible for the unwanted cathode heating and emission control loss. To overcome these phenomena, a new design is proposed. A buncher cavity and a solenoid are inserted to improve the coupling between the electron beam and the accelerating cells.
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock
Precise and fast 3D space-charge calculations for bunches of charged particles are still of growing importance in recent accelerator designs. Whereas an adaptive discretization of a bunch is often required for efficient space charge calculations in practice, such a technique is not implemented in many computer codes. For instance, the FFT Poisson solver that is often applied allows only an equidistant mesh. An adaptive discretization following the particle density distribution is implemented in the GPT tracking code (General Particle Tracer, Pulsar Physics) together with a multigrid Poisson solver. The disadvantage of this approach is that jumps in the distribution of particles are not taken into account and the hierarchical construction of meshes in multigrid can not be used. In this paper we present an approach to an adaptive discretization which is based on the multigrid technique. The goal is that the error estimator needed for the adaptive distribution of mesh lines can be calculated directly from the multigrid procedure. The algorithm will be investigated for several particle distributions and compared to that adaptive discretization method implemented in GPT.
PSI, Villigen
IFH, Zurich
Laser induced field emission has become an enabling technology for building ultra-low emittance electron sources for particle accelerators, such as the x-ray free-electron laser (SwissFEL) under development at the Paul Scherrer Institut (PSI). One approach consists of a sharp pyramidal tip with lateral dimensions of a few nanometers, illuminated by a laser to increase the extracted electron current. Another approaches uses conventional cathodes. In both cases, there are structural details on the nanometer scale, that determine the interaction between the laser and the cathode and thus directly the quantum efficiency of the emitter. We use a 3-d full-wave finite element time domain electromagnetic approach* to understand the nano-optical interaction between structure and laser pulse. For example, the lightning rod effect of sharp tips enhances the electric field in the vicinity. Also, optical antenna concepts have been proposed to enhance the electric field at the field emitter's tip so that higher currents can be extracted. We use dispersive material models for the metals in the optical region of the electromagnetic spectrum.
*Benedikt Oswald and Patrick Leidenberger, Journal of Computational and Theoretical Nanoscience, Vol 6(3), 2009, pp. 784-794. doi 10.1166/jctn.2009.1109
SUT, Noda-shi, Chiba
KEK, Ibaraki
New terahertz(THz) generator using the non-relativistic electron beam was developed based on the beam optics and the RF deflector. The conventional THz generators using the electron beam are almost based on the relativistic beam to utilize the lorentz factor as FELs or the strong magnet to make high electron density like gyrotrons or BWOs. Thus it causes that the total equipment becomes large. New THz generator uses the non-relativistic electron beam. And it consists of the beam optics which makes the sliced beam by using a anode slit to focus at second slit as the THz radiation plane. In this configuration, the RF deflector works to move for the transverse direction matched with the phase velocity of the radiated electromagnetic field. The moving sliced beam separates into a number of bunches through the second slit and the bunches makes the THz coherent radiation in zero time interval. In this new THz generator, no strong magnet is required and the large diameter beam can be utilized to generate the high power THz electromagnetic wave. In this paper, the design of new THz generator and its experimental results are reported.
BNL, Upton, Long Island, New York
Case Western Reserve University, Center for Synchrotron Biosciences, Upton, New York
Stony Brook University, Stony Brook
The diamond amplified photocathode has the potential to dramatically increase the average current available from photoinjectors, perhaps to the amphere-class performance necessary for flux-competitive fourth-generation light sources. Electron emission from a diamond amplifier has been observed from hydrogen-terminated diamond, using both photons and electrons to generate carriers. The diamond electron amplifier has been demonstrated, with an emission gain of 40. Very high average current densities (>10 A/cm2) have been transported through the diamond using x-ray generated carriers. The device relies on high-purity intrinsic diamond with low crystalline defect density, as well as a negative electron affinity achieved by hydrogen termination. The effects of diamond purity and crystalline defects on charge transport in the material, and emission from the diamond surface have been studied using a number of techniques and the process is now well understood. The electron affinity of diamond has been measured to be -1.1 eV; the fraction of the electrons produced in the material which are emitted from the surface has also been measured.
DESY, Hamburg
INFN/LASA, Segrate (MI)
Caesium telluride photocathodes are used as laser driven electron sources at the Free-Electron-Laser Hamburg, FLASH, and will be used at the European XFEL. One concern of the operation of photocathodes in these user facilities is the degradation of the quantum efficiency during operation. After improving vacuum conditions and removing contaminants, the cathode life time increased from a couple of weeks to several months. In this contribution we report on long time operation of Cs2Te cathodes in terms of QE measurements and investigations on the homogeneity of the electron emission. Another concern of electron guns operated with long RF-pulses (0.8 ms at FLASH) is the generation of dark current either from the cathode or from the gun body. During the last years a constant high amount of dark current, emitted from the gun body itself, was observed at FLASH. Caused by that during the shut-down 2009/2010 the RF-gun at FLASH, operated more than five years, was replaced. The improved dark current situation with the new RF-gun is presented in terms of dark current measurements under different operational conditions.
INFN/LNF, Frascati (Roma)
Istituto Nazionale di Fisica Nucleare, Milano
UCLA, Los Angeles
JASRI/SPring-8, Hyogo-ken
Shining a photocathode at the same time with an UV laser able to extract electrons and an IR laser properly tuned could influence the way the electron beam is generated. Such a process is under investigation at SPARC, through direct measurements, as much as through computer codes assessment studies.
TUB, Beijing
Smith-Purcell radiation (SPR) is emitted when an electron passes near the surface of a periodic metallic grating. The radiation wavelength λ observed at the angle θ measured from a direction of surface grating is determined by λ=D/|n|(1/β cosθ), Where D is the grating period, βc is the electron velocity, c is the speed of light, and the integer n is the spectral order. This radiation mechanism is widely applicated to THz radiation source, for which can be developed into tunable and compact one. In this paper, the radiation characteristics of terahertz (THz) SPR generated from the ultrashort electron beam are analyzed with the three-dimensional particle-in-cell simulation. For obtaining the intense THz radiation, the grating parameters and that of ultrashort electron beam are optimum. The radiation power and energy are obtained by the PIC simulation. The band width of train bunches is compared with that of single bunch. The formation factors including the longitudinal and transverse are calculated. Through this study, we observe that the radiation power is enhanced and the band width can be adjusted.
PSI, Villigen
In the framework of the SwissFEL project, an alternative electron source to an RF photo-gun was investigated. It consists of a high voltage (up to 500 kV), high gradient pulsed diode system followed by single stage RF acceleration at 1.5 GHz. The electrons are produced from photo-cathodes or from field emitter arrays. The final goal of this accelerator is to produce a 200 pC electron beam with a projected normalized emittance below 0.4 mm.mrad and a bunch length of less than 10 ps. We present comparisons between beam dynamic simulations and measurements, as well as thermal emittance and quantum efficiency (QE) measurements obtained by producing photo-electrons from various metal cathodes.
SLAC, Menlo Park, California
Simulations of ion migration in the LCLS RF gun and injector A. Brachmann On behalf of the LCLS commissioning team The motivation for this work was the observed surface contamination of the first LCLS RF gun copper cathode. We will present the results of simulations in regards to ion migration in the LCLS gun. Ions of residual gases will be created by interaction of molecular gas species with the UV drive laser beam and by the electron beam itself. The larger part of those ionized molecules remain in the vicinity of creation, are transported towards beam line walls or away from the cathode. However a significant fraction gains enough kinetic energy to be focused by RF and magnetic fields, reaching the cathode and producing an undesirable increase of the cathode's surface work function. Although this fraction is small, during long term operation, this effect becomes a significant factor limiting the source performance.
SLAC, Menlo Park, California
Surface characterization of the LCLS RF gun cathode A. Brachmann On behalf of the LCLS commissioning team The first copper cathode installed in the LCLS RF gun was used during LCLS commissioning for more than a year. However, after high charge operation (~ 500 pC), the cathode showed a decline of quantum efficiency due to surface contamination caused by residual ionized gas species present in the vacuum system. We report results of SEM, XPS and XAS studies that were carried out on this cathode after it was removed from the gun. X-ray absorption and X-ray photoelectron spectroscopy reveal surface contamination by various hydrocarbon compounds. In addition we report on the performance of the second installed cathode with emphasis on the spatial distribution of electron emission.
JLAB, Newport News, Virginia
Jefferson Laboratory (JLab) is currently developing a new 500kV DC electron gun for future use with the FEL. The design consists of two inverted ceramics which support a central cathode electrode. This layout allows for a load-lock system to be located behind the gun chamber. The electrostatic geometry of the gun has been designed to minimize surface electric field gradients and also to provide some transverse focusing to the electron beam during transit between the cathode and anode. This paper discusses the electrode design philosophy and presents the results of electrostatic simulations. The electric field information obtained through modeling was used with particle tracking codes to predict the effects on the electron beam.
HU/AdSM, Higashi-Hiroshima
We report that a lifetime of GaAs photocathode activated the surface to negative electron affinity (NEA) at various temperatures. An electron source with the NEA-GaAs photocathode is an important device for high-average-current electron accelerators, such as a next-generation light source based on an energy recovery linac, in which a high power laser is illuminated to the photocathode for generation of the electron beam of 100mA. For example, the laser power of 15W should be needed for the quantum efficiency of 1% and the wavelength of 800nm. Consequently the high power laser causes to rise the GaAs temperature. The degradation of photo emission from the cathode is enhanced by a thermal desorption of Cs due to the temperature rise, even if the beam is not extracted. We have measured the cathode lifetime at various temperatures between room temperature and 100 C.
HU/AdSM, Higashi-Hiroshima
JAEA/ERL, Ibaraki
KEK, Ibaraki
A NEA-GaAs photocathode is an important component for the next generation light source based on the ERL. Although the NEA-GaAs cathode has high quantum efficiency, deterioration of the NEA surface becomes serious with a high current operation. Therefore improvement of a vacuum in the cathode chamber is essential to get a long lifetime of the NEA-GaAs cathode. We are developing a photocathode test bench consisting of titanium (TP340) chamber, whose outgas rate is 1/1000 smaller than one of a SUS chamber, a cryo-pump (4000l/s) and a NEG pump (1900l/s). We report mainly the vacuum performance of the system.
KEK, Ibaraki
Hiroshima University, Graduate School of Science, Higashi-Hiroshima
Tohoku University, School of Scinece, Sendai
Compact ERL (cERL) is a test accelerator to establish accelerator technologies for GeV-class synchrotron light source based on ERL (Energy Recovery Linac), and will be constructed in KEK. It consists of an injector with photo cathode 500 kV DC gun, a merger section, super conducting RF cavities for acceleration and energy recovery, return loops, and a beam dump. To operate and test the photo cathode gun before installing it in the cERL injector, Gun Test Facility is constructing in KEK, AR south experimental hall. The Gun Test Facility has two photo cathode guns, 200 kV gun developed by Nagoya University and new 500 kV gun which is being developed, laser system to be emitted electrons from photo cathode surface, beam transport lines, and a beam diagnostics system. The diagnostics system consists of a double slit emittance measurement system, beam position monitors, transverse profile monitors, and a deflecting cavity to measure the bunch length and the longitudinal profile. In this presentation, the progress in the construction of the Gun Test Facility and the beam dynamics simulation will be presented.
JAEA/ERL, Ibaraki
KEK, Ibaraki
HU/AdSM, Higashi-Hiroshima
Nagoya University, Nagoya
A 500-kV, 10-mA photocathode DC gun has been designed and is now under fabrication by the collaboration efforts of JAEA, KEK, Hiroshima Univ. and Nagoya Univ. The Cockcroft-Walton generator and the ceramic insulator are installed upright in the SF6 tank. We have adopted a multiple-stacked cylindrical ceramic insulator, because this type of ceramic insulator has shown good stability and robustness at the 200-kV Nagoya polarized gun and the 250-kV JAEA FEL gun. The vacuum chamber, the guard-rings and the support-rod electrode are made of titanium alloy with very low out-gassing and robustness to high voltage performances. The Cockcroft-Walton generator, the ceramic insulator, the vacuum chamber and the guard-rings have been assembled and a high-voltage test has been successfully done with up to 550kV. The high-voltage test and up-to-date status of the gun development will be presented in detail.
CERN, Geneva
Electron-cloud is one of the main limitations for particle accelerators with positively charged beams of high intensity and short bunch spacing, as SPS at CERN. The Secondary Electron Yield (SEY) of the inner surface of the vacuum chamber is the main parameter governing the phenomenon. The effect could be eliminated by coating the magnets vacuum chambers with a material of low SEY, which does not require bake-out and is robust against air exposure. For such a purpose amorphous carbon coatings were produced by magnetron sputtering of graphite targets. They exhibit maximum SEY between 0.9 and 1.1 after air transfer to the measuring instrument. After 1 month air exposure the SEY rises to values between 1.1 and 1.4. Storage under nitrogen or by packaging in Al foil makes this increase negligible. The coatings have a similar XPS C1s spectrum for a large set of deposition parameters and exhibit an enlarged line-width compared to pure graphite. The static outgassing without bake-out depends on deposition parameters and is in a range from 1 to 10 times higher than that of stainless steel. Instead, electron stimulated outgassing is lower than for stainless steel and is dominated by CO.
KEK, Ibaraki
Ultra Finish Technology Co., Ltd., Yokosuka
Sokendai, Ibaraki
Niobium electropolishing for SRF cavities are generally considered to be the best technology today. However, hydrofluoric and sulphuric acid mixture usually used in the EP process is harmful and requires us carefully controlled handling of it and the many additional facilities. In this article, we propose a new application of electrochemical buffing onto niobium SRF cavity. In the method of electrochemical buffing, a rotating disk with abrasive fine particles where electrolyte is supplied is pressed against the workpiece. The disk and the work function as a cathode and an anode, respectively and an aqueous solution of sodium nitrate is used for the electrolyte. This technique brings us a couple of advantages like high etching rate, ultra small surface roughness, cost-effective and environment-compatible polishing.
PSI, Villigen
In the framework of the SwissFEL activities at PSI we developed a powerful UV laser system delivering wavelength-tunable pulses at a central wavelength varying from 260 to 283 nm. The laser system based on a ultra-stable frequency-trippled Ti:sapphire amplifier delivers mJ pulse energy within a duration of 1-10 ps with 1.5 nm spectral width. Temporal flattop pulses are achieved by direct UV shaping with a UV Dazzler and a prism-based stretcher. The system is used to explore thermal emittance and quantum efficiency dependence on photon energy from metallic photo-cathode (Cu and Mo). With pepperpot techniques we have measured the predicted theoretical limit for thermal emittance (0.4 mm.mrad / mm rms laser spot size at 283 nm and 0.6 mm.mrad / mm at 263 nm) for metallic photocathodes.
JASRI/SPring-8, Hyogo-ken
RIKEN/SPring-8, Hyogo
Low electro-magnetic noise interference (EMI) is required to the klystron modulator power supply for XFEL/SPring-8 project in order to realize the highly stable beam operation with aid of various feedback loops using high-performance beam monitors. The dominant noise source is the thyratron switching noise, associated with its rapid voltage swing of 50 kV maximum. To suppress the noise leakage, special care was taken to the enclosure design of klystron modulator, i.e., using thick steel plates a monocoque enclosure was fabricated, in which all of the high power circuits was installed. The rapid image current flows on the inner surface, thus EMI was minimized. A special co-axial feed-though was developed for filtering the conducted noise on power line for thyratron and klystron heaters. In this presentation, we will report the details of the devices and the results of the noise suppression.
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
3 GeV rapid cycling synchrotron (RCS) of J-PARC accelerates proton beams from the 181 MeV up to 3 GeV. The RCS injects the beam to the Main Ring and transports it to the muon production target and neutron production target in the Materials and Life Science Experimental Hall. Proton beams in the RCS are fast extracted by kicker magnets at the repetition rate of 25 Hz. The rise time of the magnetic field is approximately 260 ns due to the propagation time through the coaxial cable and the kicker magnet itself. The flat-top length of it is required to 840 ns in order to extract two beam bunches. Pulse forming lines (PFL) and thyratrons are used to make the rise time and the flat-top, at the maximum charging voltage of 80 kV. Two thyratrons, which is a CX1193C made by e2V Ltd., are used for a power supply. 16 thyratrons are used in the eight power supplies of the kicker system. Since thyratrons are gaseous discharge switching devices, they often make misfire or self-breakdown in several hours. In this paper, present status of operation and voltage adjustment method of the reservoir and cathode heater power supply of the thyratrons in the kicker system are described.
Diversified Technologies, Inc., Bedford, Massachusetts
Diversified Technologies, Inc. (DTI) recently delivered a 500 kW CW, 33 kV solid-state test stand for the evaluation and conditioning of high power tetrodes employed in accelerator and radar systems. The test system consists of DTI-manufactured and commercially-sourced power supplies, a DTI high voltage opening switch, and DTI controls. Combining an opening switch and fast responding power supplies allows the hi-potting and high power burn-in to be consolidated in one test stand. Faulty tubes, which would not operate in a crowbar-equipped modulator, and could not be processed to health on a high potter, can be revived to health with this fast opening switch circuitry. By limiting peak fault current and follow-on-current, the total energy in an arc event is greatly minimized, reducing damage inside the tube. If greater energy (or action) is required for initial tube processing, additional load capacitance downstream of the switch can be added into the circuit for 'spot knocking' purposes. This test stand is capable of operation in pulsed mode as well as CW. This paper will address the design and construction of the test stand and discuss results since its installation.
Diversified Technologies, Inc., Bedford, Massachusetts
Diversified Technologies, Inc.(DTI) has delivered a fully solid state Klystron Power Supply for the ISIS Front End Test Stand to Rutherford Appleton Laboratory in the UK. The new pulsed power supply drives a Toshiba E3740A klystron in preparation for construction of a system to demonstrate high quality intense chopped beams. DTI's system represents a significant advance in solid-state high power accelerator technology based upon a hard switch developed for the US Department of Energy (DOE) to meet similar requirements for the International Linear Collider(ILC). The system includes two 220 kW switching power supplies, a 110 kV solid state hard switch pulse modulator, mod anode and filament power supplies, klystron fault protection, and interfaces to the ISIS controls. This paper will address the design and construction of the KPS system, as well as test results from the installation at RAL in May 2009.
KEK, Ibaraki
We have continued high gradient R&D of ICHIRO 9-cell cavities at KEK. The maximum gradient of ICHIRO 9-cell cavity #5 that has no end groups on beam tube was still limited around 36MV/m so far. The 9-cell performances were sometimes limited by triggered field emission (FE) by multipactings. We suspected the residual gas in the cavity might be one of the sources of triggered FE. The cavity was closed during vertical test in our system. Other labs evacuated cavity during vertical test. In order to improve the vacuum of cavity during vertical test, we made evacuation system in our cavity test stand. The comparison of results for vertical test with and without evacuation will be reported.
KEK, Ibaraki
A waveguide vacuum valve for WR90 waveguide was designed, fabricated and tested. The valve consists of a modified commercial gate valve sandwitched with smooth tapers. The TE10 traveling wave in WR90 waveguide is "transmoded" into TE11+TM11 mode in the taper, going through the gate valve and is tapered back to the normal mode in WR90. The test has been successfully done. The valve stably trasmitted 40MW peak power with 500ns pulse width and this is limited by available RF power source.
RadiaBeam, Marina del Rey
JLAB, Newport News, Virginia
NCSU, Raleigh, North Carolina
University of Texas El Paso, W.M. Keck Center for 3D Innovation, El Paso, Texas
University of Texas at El Paso, El Paso, Texas
A key issue for high average power, normal conducting radio frequency (NCRF), photoinjectors is efficient structure cooling. To that end, RadiaBeam has been developing the use of Solid Freeform Fabrication (SFF) for the production of NCRF photoinjectors. In this paper we describe the preliminary design of a high gradient, very high duty cycle, photoinjector combining the cooling efficiency only possible through the use of SFF, and the RF efficiency of a re-entrant gun design. Simulations of the RF and thermal-stress performance will be presented, as well as material testing of SFF components.
SLAC, Menlo Park, California
LLNL, Livermore, California
In support of the T-REX program at LLNL and the High Gradient research program at SLAC, a new X-band multi-cell RF gun is being developed. This gun, similar to an earlier gun developed at SLAC for Compton X-ray source program, will be a standing wave structure made of 5.5 cells operating in the pi mode with copper cathode. This gun was designed following criteria used to build SLAC X-band high gradient accelerating structures. It is anticipated that this gun will operate with surface electric fields on the cathode of 200MeV/m with low breakdown rate. RF will be coupled into the structure through a symmetric final cell with a shape optimized to eliminable both dipole and quadruple field components. In addition, geometry changes to the original gun, operated with Compton X-ray source, will include a wider RF mode separation, reduced surface electric and magnetic fields.
KEK, Ibaraki
University of Fukui, Faculty of Engineering, Fukui
Nippon Advanced Technology Co. Ltd., Ibaraki-prefecture
The two electrostatic septa are one of the most important device for the slow extraction in 50GeV proton synchrotron. We have developed the thin ribbon type septum in order to reduce the beam loss. If alignment of ribbons is poor, the effective thickness seen from the beam become large, and it would increase the beam-hitting rate. The alignment of ribbon over 1.5m long septa was measured by a laser-focus displacement meter. The achieved effective thickness of septa is estimated to be 0.075mm and 0.080mm respectively. We will report a high voltage conditioning and a performance under beam commissioning.
ORNL, Oak Ridge, Tennessee
ORNL RAD, Oak Ridge, Tennessee
LANL, Los Alamos, New Mexico
BNL, Upton, Long Island, New York
The diamond stripper foils in use at the Spallation Neutron Source worked successfully with no failures until May 3, 2009, when we started experiencing a rash of foil failures after increasing the beam power to ~840 kW. The main contributions to foil failure are thought to be 1) convoy electrons, stripped from the incoming H− beam, that strike the foil bracket and may also reflect back from the electron catcher, and 2) vacuum breakdown from the charge developed on the foil by secondary electron emission. In this paper we will detail these and other failure mechanisms, and describe the improvements we have made to mitigate them.
DESY, Hamburg
BINP SB RAS, Novosibirsk
For the European XFEL project horizontal multi-beam klystrons will be installed in the XFEL tunnel and will be connected to the double tank pulse transformers. Both, the klystron and pulse transformer need for the normal operation to be filled with oil. To avoid the possible oil leakage during connection of the klystron and transformer tank inside tunnel, the connection module (CM) was proposed. The CM will be mounted on the support platform of the klystron and through the tube socket connected to the guns electrodes outside of the tunnel and will transported to the tunnel together with klystron. The connection to the pulse transformer tank will be done only with HV cable, because the CM has inside it the filament transformer. To reduce the weight and volume of the oil the design of filament transformer was done as high frequency coaxial one with coupling factor of 0.58 and working frequency about 1 kHz. The CM has the built-in current and voltage monitors. In this paper we give an overview about design and test result of the CM together with klystron.
KEK, Ibaraki
Mitsubishi Electric Corp., Communication Systems Center, Amagasaki City, Hyogo
The L-band inductive output tube (IOT) without trolly was developed to operate under higher applied voltage. The operation frequency of conventional IOTs is tuned using its trolly. This mechanism is based on the lower frequency IOT. However it causes less insulation voltage of the ceramics since the electric insulation oil is not available for its trolly and the length of the insulation ceramics is limited because it is a part of the resonant cavity. In case of IOTs, it is important to increase the applied voltage for higher output power since the grid gap is very narrow and its area cannot be increased to keep the gain. Thus we developed an IOT which has a longer insulating ceramic and the input cavity is filled with vacuum to use the electric insulation oil. Further the dielectric waveguide can solve to feed the input microwave to the cathode grid without trolly. These new features of the IOT is very effective for the fixed frequency application such as the accelerator, for example the energy recovery linac. The design and the experimental results will be presented in this report.
CPI, Beverley, Massachusetts
The VIL409 Heatwave IOT-based RF amplifier was designed to meet the requirements of the EMMA accelerator at the Daresbury Laboratory. The VIL409 was successfully commissioned in September 2009. The VIL409 provides up to 90 kW RF output power ver a 5.5 MHz bandwidth centered at 1.3 GHz. It operates at a fixed 1.6 millisecond pulse at up to 20 Hz. Within limits, the user has control of the IOT beam voltage and the IOT grid bias voltage. Normal operation is to achieve smooth control of the output via the LLRF input alone. The IOT grid may be pulsed or operated at a constant voltage; pulsing achieves greatly enhanced energy efficiency. The VIL409 has an embedded processor that controls all internal functions of the amplifier system and interfaces directly to the EPICS control system. The embedded controller provides real-time pulse data to EPICS and operates slow-moving interlocks. Safety and IOT-protective interlocks are hard-wire circuits which operate in the microsecond timeframe. The VIL409 can be operated locally or controlled remotely on the EPICS controls network. This paper describes the VIL409 high power RF amplifier system.
LANL, Los Alamos, New Mexico
Compa Industries, Inc., Los Alamos, New Mexico
An major upgrade is replacing much of the 40 year-old proton drift tube linac RF system with new components at Los Alamos Neutron Science Center (LANSCE). When installed for the LANSCE-R project, the new system will reduce the total number of electron power tubes from twenty-four to eight in the RF powerplant. A new 200 MHz high power cavity amplifier has been developed at LANSCE. This 3.2 MW final power amplifier (FPA) uses a Thales TH628 Diacrode, a state-of-the-art tetrode that eliminates the large anode modulator of the triode-based FPA that has been in use for four decades. Drive power for the FPA is provided by a new tetrode intermediate power amplifier and a solid-state driver stage. The new system has sufficient duty-factor capability to allow LANSCE to return to 1 MW beam operation. Prototype RF power amplifiers have been designed, fabricated, and assembled and are being tested. High voltage DC power became available through innovative re-engineering of an installed system. Details of the electrical and mechanical design of the FPA and ancillary systems are discussed. Power test results have validated the design and construction of this very high power amplifier system.
SLAC, Menlo Park, California
The SLAC National Accelerator Laboratory Klystron Department is developing a 10 MW, 5 Hz, 1.6 ms, 1.3 GHz plug-compatible Sheet-Beam Klystron as a less expensive and more compact alternative to the ILC baseline Multiple-Beam Klystron. Earlier this year a beam tester was constructed and began test. Device fabrication issues have complicated the analysis of the data collected from an intercepting cup for making beam quality measurements of the 130 A, 40-to-1 aspect ratio beam. Since the goal of the beam tester is to confirm 3d beam simulations it was necessary to rebuild the device in order to mitigate unwanted effects due to imperfect focusing construction. Measurements are underway to verify the results of this latest incarnation. Measurement will then be made of the beam after transporting through a drift tube and magnetic focusing system. In the klystron design, a TE oscillation was discovered during long simulation runs of the entire device which has since prompted two design changes to eliminate the beam disruption. The general theory of operation, the design choices made, and results of testing of these various devices will be discussed.
JLAB, Newport News, Virginia
Cockcroft Institute, Lancaster University, Lancaster
The use of an injection locked CW magnetron to drive a 2.45 GHz superconducting RF cavity has been successfully demonstrated. With a locking power less than -27 dB with respect to the output and with a phase control system acting on the locking signal, cavity phase was accurately controlled for hours at a time without loss of lock whilst suppressing microphonics. The phase control accuracy achieved was 0.8o r.m.s. The main contributing disturbance limiting ultimate phase control was power supply ripple from the low specification switch mode power supply used for the experiment.
DESY, Hamburg
JLAB, Newport News, Virginia
The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock
BNL, Upton, Long Island, New York
In this contribution, we report Quantum Efficiency (QE) test results with a hybrid lead/niobium superconducting RF (SRF) photoinjector at 2K and new Pb arc deposited cathodes at 300K. The ultimate goal of our effort is to build a Nb injector with the superconducting cathode made of lead, which, as reported in the past, demonstrated superior QE compared to other metallic superconducting elements. At first, we present the test results obtained with a 1.6-cell high purity Nb cavity with the emitting lead spot in the center of the back plate. The QE test results at room temperature and the SEM surface analysis of eight Pb cathodes, deposited recently under various conditions, are discussed in the second part of this contribution.
HU/AdSM, Higashi-Hiroshima
KEK, Ibaraki
ISIR, Osaka
IAP/RAS, Nizhny Novgorod
JINR, Dubna, Moscow Region
Aim of Super-conducting Test Facility (STF) at KEK is demonstrating technologies for International Linear Collider. In STF, one full RF unit will be developed and beam acceleration test will be made. In super-conducting accelerator, precise RF control in phase and power is essential because the input RF power should be balanced to beam accelerating power. To demonstrate the system feasibility, the beam accelerating test is an important step in R&D phase of STF and ILC. To provide ILC format beam for STF, we develop an electron source based on photo-cathode L-band RF gun. To generate ILC format beam, we developed a laser system based on Yb fiber oscillator in 40.6 MHz. The pulse repetition is decreased by picking pulses in 2.7 MHz, which meets ILC bunch spacing, 364 ns. The pulse is then amplified by YLF laser up to 8 uJ per pulse in 1 mm. The light is converted to 266 nm by SHG and FHG. Finally, 1.5 uJ per pulse is obtained and 3.2 nC bunch charge will be made. We report the basic performance of the laser system from the accelerator technology point of a view.
JASRI/SPring-8, Hyogo-ken
We have developed a laser-induced Schottky-effect-gated photocathode gun since 2006. This new type of gun utilizes a laser's coherency to realize a compact laser source using Z-polarization of the IR laser on the cathode. This Z-polarization scheme reduces the laser pulse energy by reducing the cathode work function due to Schottky effect. Before this epoch-making scheme, photocathode guns had never utilized laser's coherency. A hollow laser incidence is applied with a hollow convex lens that is focused after passing the beam through a radial polarizer. According to our calculations (convex lens: NA=0.15), a Z-field of 1 GV/m needs 1.26 MW at peak power for the fundamental wavelength (792 nm) and 0.316 MW for the SHG (396 nm). Therefore, we expect that this laser-induced Schottky emission requires just a compact femtosecond laser oscillator as a laser source. Besides, a dichromatic laser scheme (photo-exciting: 780 nm; gating: 30 um) should be applied to polarized electron sources for International Linear Collider (ILC). We report the first feasibility study of this laser-induced Schottky-effect on several metal photocathodes by comparing radial and azimuthal polarizations.
Sokendai, Ibaraki
KEK, Ibaraki
RISE, Tokyo
At Laser Undulator Compact Source (LUCX) at KEK, we designed and made a new RF Gun with high mode separation of 8.6 MHz and high Q value as compared to earlier guns. This paper presents fabrication details, low power measurements and tuning procedures followed in making the gun cavity. We also discuss in detail, experimentation done using this gun and show the measurement results. Currently we produce 100 bunch per train but we plan to go for 300 or more bunch per train operation. This will make possible to have higher charge available for laser-beam collisions to generate high flux soft X-rays by Inverse Compton Scattering at our setup.
CERN, Geneva
The high charge PHIN photo injector is studied at CERN as an electron source for the CLIC Test Facility (CTF3) drive beam as an alternative to the present thermionic gun. The objective of PHIN is to demonstrate the feasibility of a laser-based electron source for CLIC. The photo injector operates with a 2.5 cell, 3 GHz RF gun using a Cs2Te photocathode illuminated by UV laser pulses generated by amplifying and frequency quadrupling the signal from a Nd:YLF oscillator running at 1.5GHz. The challenge is to generate a beam structure of 1908μbunches with 2.33nC perμbunch at 1.5GHz leading to a high integrated train charge of 4446nC and nominal beam energy of 5.5MeV with current stability below 1%. In the present test stand, a segmented beam dump has been implemented allowing a time resolved measurement of the energy and energy spread of the electron beam. In this paper we report and discuss the measured transverse and longitudinal beam parameters for both the full and time gated train of bunches, and the obtained photocathode quantum efficiency. Laser pointing and amplitude stability results are discussed taking into account correlation between laser and electron beam.
INFN-Bari, Bari
BINP SB RAS, Novosibirsk
The charge breeding technique is used for Radioactive Ion Beam (RIB) production in the Isotope Separation On Line (ISOL) method in order of optimizing the re-acceleration of the radioactive element ions produced by a primary beam in a thick target. That technique is realized by using a device capable of increase the radioactive ion charge state from +1 to a desired value +n. In some experiments a continuous RIB of a certain energy could be required. The EBIS based charge breeding device cannot reach a real CW operation because the high charge state ions produced are extracted by the same part where the 1+ ions are injected, that is, from the electron collector. In this way, the ions extraction system, placed in the electron beam collector, can be left only to extract the n+ ions, and then the CW operation, at least in principle, could be reached. In this paper, a charge breeding test experiment based on a EBIS which has an e-gun with hollow cathode will be described. Furthermore, the status report of the experiment that is under way at the INFN Laboratori Nazionali di Legnaro (LNL) will be presented.
STFC/RAL/ISIS, Chilton, Didcot, Oxon
The Front End Test Stand (FETS) under construction at the Rutherford Appleton Laboratory is the UK's contribution to research into the next generation of High Power Proton Accelerators (HPPAs). Running at duty cycles of up 50 Hz with pulse lengths of 2 ms are required. This paper presents initial Hminus beam currents and emittance measurements for long pulse lengths.
Muons, Inc, Batavia
ORNL, Oak Ridge, Tennessee
Development of novel modifications of H- source designs is proposed. The new source will be an advanced version of a Penning DT SPS (Dudnikov-Type Penning Surface Plasma Source) which will generate brighter beam in noiseless discharge, deliver up to 20 mA average current with better electrode cooling using new materials, and have longer lifetime, fast beam chopping capability, and reduced cesium loss.
Muons, Inc, Batavia
LBNL, Berkeley, California
Induction linear accelerators are featured in accelerator-based research currently supported by the Office of Fusion Energy Sciences. Over the next few years, the research will concentrate on developing intense ion sources and on studying the physics of spatial compression, neutralized transport, and focusing of the beam. The large diameter of lithium alumino-silicate ion emitters for large currents represents the current state of the art for emission densities of 1-1.5 mA/cm2. Also, operating temperatures of the surface are limited by the temperature of alumina-potted heater packages. We propose a novel system for increasing the emission of lithium ions from β-eucryptite through modification of the surface morphology by sputter etching with argon plus other gases. The resulting local field enhancement will increase the ion emission over that of a microscopically flat surface. In addition, a free-standing graphite heater assembly will be used to increase the temperature of the surface of the emission source.
The University of Tokyo, Nuclear Professional School, Ibaraki-ken
University of Tokyo, Tokyo
We are commissioning the cathode, Na2KSb at the wavelength of 266, 400 nm with thermo-mechanically modified structure and improved vacuum system (2·10-08 Pa). We could improve RF reflection waveform and obtain the maximum energy of 22 MeV. We estimate the electrical field of 50 MV at the cathode. So far, we have obtained the quantum efficiencies of 1.1, 0.01% and the maximal charges of 4.6, 1 nC for 266, 400 nm. We are observing and checking carefully individual difference of QE of the cathodes for 266, 400 nm, and we have obtained 22 MeV energy. This new RF photocathode RF gun system has been already used for subpicosecond time-resolved radiation chemistry.
NSRRC, Hsinchu
National Chiao Tung University, Hsinchu
NTHU, Hsinchu
A 25-30 MeV S-band linac system that equipped with thermionic cathode rf gun is being constructed at NSRRC for generation of ultrashort relativistitic electron beam. According to simulation studies, high quality GHz repetition rate electron pulses of about 50 pC as short as few tens fsec can be produced. This injector system will be used as the driver for experiments on fsec head-on inverse Compton scattering X-ray source and high power wake field microwave sources. The progress of our construction work will be presented.
UMAN, Manchester
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
EMMA (Electron Model with Many Applications) is the first proof-of-principle non-scaling FFAG accelerator and is presently under construction at Daresbury Laboratory in the UK. To probe different parts of the bunch phase space during the acceleration from 10 to 20 MeV (which requires rapid resonance crossing), electron bunches are needed with sufficiently small emittance. To understand the phase space painting into the 3000 mm-mrad EMMA acceptance, we have modelled ALICE (Accelerators and Lasers in Combined Experiments) - which acts as an injector for EMMA - using GPT and compared the estimated emittances with measurements made with a variety of screen-based methods. Although the emittances are not yet as small as desired, we obtain reasonable agreement between simulation and measurement.
LPI, Moscow
Short pulses of electrons of femtosecond and attosecond duration are necessary for numerous applications: studying fast processes in physics, chemistry, biology and medicine*. Previous calculations revealed that it is possible to obtain such short bunches by applying quasi-static electric voltage to a needle placed into a laser focus**,***. This paper presents results of computer simulation of the electron bunch evolution for various parameters of the problem (quasi-static and laser electric fields, radius of curvature of the needle, velocity of electron emission etc.). Simple model for analytical calculation of bunch evolution was elaborated to precisely assess its shortening in the case when one can neglect space-charge forces in the bunch. Influence of velocity dispersion in the bunch due to emission process is discussed and the way to optimize the bunching was proposed. Bunch dynamics accounting for space-charge forces was studied using analytical solution of equation of motion.
* P.Emma. Proc. EPAC04, p. 225, Lucerne, Suisse.
** V.A.Papadichev. Proc. EPAC08, p. 2812, Genoa, Italy.
*** V.A.Papadichev. Proc. EPAC08, p. 2815, Genoa, Italy.