CEA, Gif-sur-Yvette
CERN, Geneva
Uppsala University, Uppsala
The probe beam LINAC, CALIFES, of the CLIC Test Facility (CTF3) has been developed by CEA Saclay, LAL Orsay and CERN to deliver trains of short bunches (0.75 ps) spaced by 0.666 ps at an energy around 170 MeV with a charge of 0.6 nC to the TBTS (Two-beam Test Stand) intended to test the high gradient CLIC accelerating structures. Based on 3 former LIL accelerating structures and on a newly developed RF photo-injector, the whole accelerator is powered with a single 3 GHz klystron delivering pulses of 45 MW through a RF pulse compression cavity and a network of waveguides, splitters, phase-shifters and an attenuator. We relate here results collected during the various commissioning and operation periods which led to nominal performances and stable beam characteristics delivered to the TBTS. Progress has been made in the laser system for beam charge and stability, in space charge compensation for emittance, in RF compression law for energy and energy spread. The installation of a specially developed RF power phase shifter for the first accelerating structure used in velocity bunching allows the control of the bunch length.
DESY, Hamburg
Uni HH, Hamburg
At present the Linac II at DESY consists of a 6A/150kV DC electron gun, a 400 MeV primary electron linac, a 800 MW positron converter, and a 450 MeV secondary electron/positron linac. To improve the maintainability of the system and to reduce operational risks the original 150kV diode gun will be replaced by a 100kV triode. Together with the gun the whole injection system will be upgraded and optimized for minimal load on the converter target and primary linac. The core of the new injector are a 5MeV standing wave/travelling wave hybrid structure and a magnetic energy filter. Simulations show that With 6A DC current up to 3.7A can be bunched into 20° of the 2.998 GHz RF. This phase range is narrow enough to fit after on-crest acceleration into the energy acceptance of the following accumulator ring PIA.
LLNL, Livermore, California
SLAC, Menlo Park, California
UCB, Berkeley, California
Continued progress in accelerator physics and laser technology have enabled the development of a new class of tunable x-ray and gamma-ray light sources based on Compton scattering between a high-brightness, relativistic electron beam and a high intensity laser pulse produced via chirped-pulse amplification (CPA). A precision, tunable, monochromatic (< 0.4% rms spectral width) source driven by a compact, high-gradient X-band linac designed in collaboration with SLAC is under construction at LLNL. High-brightness (250 pC, 3.5 ps, 0.4 mm.mrad), relativistic electron bunches will interact with a Joule-class, 10 ps, diode-pumped CPA laser pulse to generate tunable γ-rays in the 0.5-2.5 MeV photon energy range. This gamma-ray source will be used to excite nuclear resonance fluorescence in various isotopes. Fields of endeavor include homeland security, stockpile science and surveillance, nuclear fuel assay, and waste imaging and assay. The source design, key parameters, and current status will be discussed, along with important applications, including nuclear resonance fluorescence and high precision medical imaging.
KURRI, Osaka
Electron beam can be accelerated in two accelerator tubes up to 46 MeV at KURRI-LINAC. The development of irradiation field is planned to provide lower energy electron beam. For this purpose we had regulated several parameters, which results showed that low energy electron beam was obtained by acceleration in only the first accelerator tube, without the second one, which was filled with microwave from klystron operated at reduced voltage. Moreover, the timing between electron emission and microwave introduction into the first accelerator tube was varied to increase the electron energy loss in the second one, thereby reducing high-energy component of the beam. In this study we obtain lower energy electron beam by the following regulations: 1) the increase of the emission current from the electron gun relative to energy filled into the first accelerator tube results in the decrease of acceleration energy for each electron and 2) the total control of the timing and the buncher phase of microwave and the width of electron pulse eliminates a part of electron expected to be high-energy component. The regulations described above yield the low-energy electron beam with peak of 5.2 MeV.
Osaka Prefecture University, Sakai
Transient phenomena induced by pulsed electron beams have been investigated with a pulse-radiolysis system with a 18 MeV S-band electron linac at Osaka Prefecture University (OPU). In our recent work the coherent transition radiation from the electron bunches of linac beams, which is highly intense pulsed light in a submillimeter to millimeter wavelength range, has been applied to absorption spectroscopy with an L-band electron linac in the Research Reactor Institute, Kyoto University. In these experiments the effect of intensity of the radiation has been observed for several kinds of matters. In this work a new pump-probe system has been developed to investigate the transient phenomena induced by the pulsed coherent radiation by improving the OPU pulse-radiolysis system. The transition radiation is emitted from an Al foil. A part of the coherent radiation is also used as probe light. The pulse lengths of the radiation are from 5 ns to 4 μs. The characteristics of the system have been measured and the system has been optimized. The coherent synchrotron radiation source is under preparation in order to obtain half-cycle light.
Cockcroft Institute, Lancaster University, Lancaster
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
Compact X-ray sources are integral parts of systems used in medical, industrial and security applications. The X-ray dose rate for a particular application mainly depends on the energy and current of the beam used to hit the target, usually made of tungsten. In applications that need higher penetration (100s of mm in steel), the beam energy needed is in the range of 1-5 MeV which can only be obtained using an RF linear accelerator. In order to reduce the size of the linac, higher RF frequencies (X-band) should be used while in order to reduce the overall bulk, RF focusing is employed instead of solenoidal focusing. Thus the main attraction of an X-band linac compared to a lower frequency version is the amount of lead required for shielding the system, and hence its weight. For capturing and bunching the low energy dc beam, a bunching section is needed in front of the main linac. The bunching cavity can either be a part of the main linac cavity or an independently powered section which can be used for certain specific applications as a shorter 1 MeV linac. In this paper, the design and simulations of an X-band buncher to be suitable for compact X-ray sources is presented.
POSTECH, Pohang, Kyungbuk
KAPRA, Cheorwon
NFRI, Daejon
PAL, Pohang, Kyungbuk
An intense L-band electron linac is now being commissioned at ACEP (Advanced Center for Electron-beam Processing in Cheorwon, Korea) for irradiation applications. It is capable of producing 10-MeV electron beams with the 30-kW average beam power. The constant-impedance accelerating structure is operated under fully-beam-loaded condition with the RF power of peak 25 MW and the beam current of 1.45 A. The total attenuation coefficient of the structure is 0.17 and the RF filling time is 0.9 μs along the 2.3-m accelerating structure. To suppress the energy spread due to the transient beam loading effect, we consider three methods: modulating the beam current amplitude, modulating the RF amplitude, and adjusting the beam injection time. In this paper, we calculate the transient beam energy numerically for the above cases. We also propose the actual compensation method.
POSTECH, Pohang, Kyungbuk
KAPRA, Cheorwon
NFRI, Daejon
A C-band standing-wave electron linac for a compact X-ray source is now being commissioned at ACEP (Advanced Center for Electron-beam Processing in Cheorwon, Korea). It is designed to produce 4-MeV electron beam with pulsed 50-mA, using a 5-GHz RF power generated by a magnetron with pulsed 1.5 MW and average 1.2 kW. The accelerating structure is a bi-periodic and on-axis-coupled one operated with π/2-mode standing-waves. It is consisted of 3 bunching cells, 6 accelerating cells and a coupling cell. As a result of measurements, the beam energy is almost 4 MeV. In this paper, we present the design details and the commissioning status.
ANL, Argonne
Euclid TechLabs, LLC, Solon, Ohio
New technology needs to be developed for future compact linear colliders. The AWA Facility is dedicated to the study of advanced accelerator concepts towards this goal. The facility uses high charge short electron bunches to drive wakefields in dielectric loaded structures as well as in metallic structures (iris loaded, photonic band gap, etc). Accelerating gradients as high as 100 MV/m have been reached in dielectric loaded structures, and RF pulses of up to 44 MW have been generated at 7.8 GHz. In order to reach higher accelerating gradients, and also be able to generate higher RF power levels, several facility upgrades are underway: a new RF gun with a higher QE photocathode; a witness beam to probe the wakefields; additional klystrons and linac structures to bring the beam energy up to 75 MeV. The drive beam will consist of bunch trains of up to 32 bunches of 60 nC, corresponding to a beam power of 6 GW. The goal of future experiments is to reach accelerating gradients of several hundred MV/m and to extract RF pulses with GW power level. A key advantage of wakefield acceleration in structures is the ability to act on electrons and positrons in basically identical fashion.
KEK, Ibaraki
A new type of rotating anticathode X-ray generator has been developed, in which the electron beam up to 120keV irradiates the inner surface of a U-shaped Cu anticathode. A high-flux electron beam is obtained by optimizing the geometry of the combined function bending magnet. In order to minimize the sizes of the X-ray source, the electron beam is focused in a short distance by the combined function bending magnet, of which geometrical shape was determined by simulation with the codes of Opera-3D, General Particle Tracer (GPT) and CST STUDIO. The result of simulation clearly shows that the role of combined function in the bending magnet and the steering magnet is important to focus the beam in small sizes. FWHM sizes of the beam were predicted by simulation to be 0.45mm (horizontal) and 0.05mm (vertical) for a beam of 120keV and 75mA of which effective brilliance is about 500kW/mm2 with the supposition of a two-dimensional Gaussian distribution. The beam focus sizes on the target will be verified in the experiments by using the high-voltage power supply for the X-ray generator improved from 60kV to 120kV and 75mA.
ELSA, Bonn
DESY, Hamburg
In order to enhance the operating capabilities of the Bonn University Accelerator Facility ELSA, a new injector is currently under commissioning. Its purpose is to allow a single pulse mode as well as to increase the current of the unpolarized beam provided to the external hadron physics experiments. The injector will produce an up to 2 μs long pulse of 500 mA beam current or a single electron bunch with 2 A pulse current. Design and optimization of the injector were performed with Egun, PARMELA and numerical simulations based on the paraxial equation. A 1.5 ns long pulse is produced by a thermionic electron gun with 90 kV anode-cathode voltage, then compressed and pre-accelerated by a 500 MHz RF cavity and a four-cell travelling wave buncher. After acceleration of the electrons up to 25 MeV in the main linac the natural broadening of the energy distribution in the particle ensemble due to the acceleration process will be reduced by an energy compression system. Studies have been conducted concerning the adaptation of the optical elements in the transfer beamline to the booster synchrotron with respect to the new requirements of the injection into the synchrotron and its acceptance.
PSI, Villigen
The X-ray FEL facilities in an advanced stage of planning worldwide can be grouped in two categories. Those with normal conducting driver linacs aiming to bring the XFEL technology, after the impressive feasibility prove at LCLS, to regional user communities at affordable cost, and those with superconducting driver linacs capable to serve several photon hungry users simultaneously. The talk will review the rationales, technical choices and status of the main proposals and discuss some key R&D issues.
JLAB, Newport News, Virginia
Energy Recovering Linacs have become an important approach to providing high brightness electron beams for photon production, nuclear physics research, and cooling ions. The technology takes advantage of the ability of superconducting rf cavities to accelerate high average current beams with low losses. After the desired interaction the electrons can be decelerated to low energy so as to minimize the required rf power and electrical draw. When this approach is coupled with advanced continuous wave injectors, very high power, ultra-short electron pulse trains of high brightness can be achieved. This talk will review the status of worldwide programs including the on-going BNL and Cornell efforts, the Novosibirsk Multipass ERL, ALICE at Daresbury, the KEK/JAEA ERL, and the Peking ERL among others. We will also touch on the prospects for proposed machines such as the JLAMP advanced ERL FEL efforts at Jefferson Lab designed to produce ultra-high brightness beams of photons in the 10-100 nanometer soft X-ray region.
ELETTRA, Basovizza
FERMI@Elettra is a single-pass FEL user-facility covering the wavelength range from 100 nm (12 eV) to 4 nm (310 eV) and is located next to the third-generation synchrotron radiation facility Elettra in Trieste, Italy. The first electron beam from the photocathode electron rf gun and injector system was extracted in August 2009. Commissioning and installation of the remaining linac and linac systems are continuing and will alternate through this year . The linac is based on normal conducting S-band technology. It uses fifteen 3 GHz 45 MW peak RF power plants powering the gun, the accelerating structures, and the RF deflectors, and when completed will be able to deliver greater than 1.5 GeV electron beams to the FEL undulator system. This paper provides a summary of the installation activities and discusses the performances results of the main subassemblies both during the initial checkouts and through the commissioning of the accelerator.
KEK, Ibaraki
JAEA/ERL, Ibaraki
ISSP/SRL, Chiba
Future light sources based on the Energy Recovery Linac (ERL) are expected to bring innovation to the synchrotron radiation (SR) science. Our Japanese collaboration team plans to construct a 5-GeV ERL which can produce super-brilliant and ultra-short pulses of SR as well as can be a driver for a proposed X-ray free-electron laser oscillator (X-FELO). In order to establish the key technologies for the ERL, we are conducting aggressive R&D efforts. Concerning our high-brightness photocathode DC electron gun, we succeeded to apply a DC high voltage of 500 kV through a support rod. Both cryomodules for the injector and the main-linac are also under development. In order to demonstrate reliable operations of such key technologies, we plan to construct the Compact ERL (cERL) at KEK. During FY2009, we prepared the infrastructure for the cERL which includes renovation of the building (the East Counter Hall), renovation of cooling-water system and electrical substation, installation of liquid helium refrigerator, and installation of a part of the rf source. In this paper, we present up-to-date status of the ERL and the Compact ERL projects in Japan.
HZB, Berlin
Energy recovery linacs (ERLs) are proving to be a powerful option to provide very high current beams with exceptional beam parameters and the flexibility to tailor these for many applications, from next-generation light sources to electron coolers. Helmholtz Zentrum Berlin (HZB) is focusing on ERLs for future x-ray light sources. Although ERL facilities exist for the IR and THz range, their moderate parameters (current, emittance, energy) are insufficient for future x-ray sources. HZB is therefore proposing to develop the 100-MeV ERL facility BERLinPro for accelerator studies and technology development to demonstrate the feasibility of an x-ray user facility. This paper presents an overview of the project and the key components of the facility.
PSI, Villigen
The Paul Scherrer Institute is commissioning a 250 MeV injector test facility in preparation for the SwissFEL project. Its primary purpose is the demonstration of a high-brightness electron beam meeting the specifications of the SwissFEL main linac. At the same time it is advancing the development and validation of the accelerator components needed for the realization of the SwissFEL facility. We report the results of the first commissioning phase, which includes the gun section of the injector up to 7 MeV electron energy. Electrons are generated by a 2.6-cell laser-driven photocathode RF gun operating at 3 GHz followed by an emittance compensating focusing solenoid. The diagnostic system for this phase consists of a spectrometer dipole, a series of screens and beam position monitors and several charge measuring devices. Slit and pinhole masks can be inserted for phasespace scans and emittance measurements. The completion of the entire injector facility proceeds in three stages, culminating with the integration of the magnetic compression chicane expected for early 2011.
JASRI/SPring-8, Hyogo-ken
RIKEN/SPring-8, Hyogo
The injector of the 8 GeV linac generates an electron beam of 1 nC, accelerates it up to 30 MeV, and compresses its bunch length down to 20 ps. Even slight RF instability in its multi-stage bunching section fluctuates the bunch width and the peak current of an electron beam and it accordingly results in unstable laser oscillation in the undulator section. The acceptable instabilities of the RF fields in the cavities, which permit 10% rms variation of the peak beam current, are only about 0.01% rms in amplitude and 120 fs rms in phase according to beam simulation. The long-term RF variations can be compensated by feedback control of the RF amplitude and phase, the short-term or pulse-to-pulse variations, however, have to be reduced as much as possible by improving RF equipment such as amplifiers. Thus we have carefully designed and manufactured the RF cavities, amplifiers and control systems, giving the highest priority to the stabilization of the short-term variations. Components of the injector will be completed by the end of the May 2010, and the injector will be perfected in the summer 2010. We will present the performance of the completed devices in the conference.
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
KEK, Ibaraki
The J-PARC RFQ (length 3.1m, 4-vane type, 324 MHz) accelerates a negative hydrogen beam from 0.05MeV to 3MeV toward the following DTL. We started the preparation of a new RFQ as a backup machine. The new cavity is divided by three unit tanks in the longitudinal direction. The unit tank consists of two major vanes and two minor vanes. A numerical controlled machining with a conventional ball-end-mill has been chosen for the vane modulation cutting instead of the wheel shape cutter. In this presentation we will report the machining procedure, the results of the vane machining, RF properties, and some topics during the fabrication.
PSI, Villigen
Phase I of the SwissFEL Injector Test Facility consists of a 2.6-cell S-band RF gun, a spectrometer, and a series of transverse beam diagnostic systems such as YAG screens, slit and pepper-pot masks. Its primary purpose is the demonstration of a high-brightness electron beam meeting the specifications of the SwissFEL main linac. Phase space characterization at beam energies up to 7 MeV, where space charge still dominates, is performed with YAG screens in combination with slit- and pinhole (pepper-pot) masks. Advanced image analysis is used to mitigate artefacts due to background, pixel readout noise, or dark current. We present our data analysis procedure for the slit scan method, with particular emphasis on image processing and its effect on the reconstructed emittance. Pepper-pot measurements using an independent analysis framework are used to cross-check the slit scan results.
PAL, Pohang, Kyungbuk
Since its completion in 1993, the PLS (Pohang Light Source) linear accelerator has been operated as the full energy injector to the PLS storage ring - a 2.5-GeV 3rd generation light source in Korea. After successful services for more than 15 years to the Korean synchrotron radiation users' community, the PLS is now being upgraded to meet ever-increasing user demands for brighter lights. The PLS-II, the major upgrade program to the PLS, is to increase the beam energy to 3 GeV, changing the storage ring lattice to accommodate large number of insertion devices with lower emittance, and to have the top-up injection as the default operating mode. In order to achieve high injection efficiency (> 80%), beam qualities including the energy spread, pulse length, and jitters in bunch arrival times to the storage ring rf bucket have to be reduced. After successful upgrade of the PLS linac one could further exploit its potential by, for example, implementing high-brightness electron source, which would open up new possibilities with the facility
DAE/VECC, Calcutta
TRIUMF, Vancouver
UBC & TRIUMF, Vancouver, British Columbia
TRIUMF (Canada) and VECC (India) are both planning to use the photo-fission route for producing neutron-rich radioactive ion beams in their respective RIB programmes. With this common goal the two institutes have entered into a collaboration to jointly design and develop a superconducting 1.3GHz 50MeV, 10 mA, CW electron linac which will be used as the fission driver. The first phase of the e-Linac collaboration aims at the development, production and full technical and beam test of a 10MeV injector cryo module (ICM) which forms the front-end of the final linac. The design and technical development of the ICM will be presented.
FZD, Dresden
To fulfil the demand of future high power and high luminosity FEL and Storage Ring sources, an intensive electron beam with short bunch length, small emittance and large bunch charge is required. Laser driven superconducting radio frequency (SRF) photocathode guns in combination with SRF LINACs appear to be the best solution. First long term operation was demonstrated at the FZD*. In difference to the normal conducting guns, the application of static magnetic fields is not possible. Instead, the use of a transverse electric (TE) mode in parallel to the accelerating mode was proposed. Numerical simulations have shown that such RF focusing can be applied to compensate emittance growth**. This contribution will introduce a possibility to use the existing coaxial RF coupler of TESLA like cavities, as RF power input for TE modes in parallel. An additional coupler component outside the module satisfies the job of combining two frequencies from different sources to one load. Thus, it corresponds to the working principle of a high power RF diplexer. Based on the 3 1/2 cell FZD SRF gun, a concrete technical implementation and results of its operation at the cold cavity will be presented.
* J. Teichert et al., AIP Conf. Proc. 1149, 1119 - 1124 (2009).
** K. Flöttmann, D. Janssen, V. Volkov, Phys. Rev. ST Accel. Beams 7, 090702 (2004).
ANL, Argonne
A solid state Marx-based pulsed voltage supply is being developed at Argonne National Laboratory (ANL) with the capability of providing 300-kV pulses with 0.5-μs rise time, 1-μs fall time, 2-μs pulse flat top, and up to 10-Hz repetition rate. The supply is designed to operate a direct current (DC) thermionic prototype gun producing ≈ 0.1-μm beam emittance, a part of the ANL x-ray free-electron laser oscillator (XFELO) injector feasibility studies. The pulsed supply utilizes isolated gate bipolar transistor (IGBT) devices. Stage switching allows this supply to quickly charge the 200-pF gun capacitance and maintain 300-mA gun current during the pulse flat top. A second string of IGBT switches charges the stage capacitors and acts as a 'crowbar' to quickly remove high voltage from the gun at the pulse's fall time or during load arcing. We present an overview of the design and development of the XFELO injector DC gun pulsed power supply.
* Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH1137.
DESY, Hamburg
The FLASH RF system consists of several RF stations, which provide RF power up to 10MW at 1.3GHz, 1.3ms and 10Hz repetition rate, each, for the superconducting cavities and the RF gun of the FLASH linear accelerator. During the last upgrade of the FLASH facility several modifications have been made also to the RF system. The oldest RF stations were constructed and manufactured by FNAL more than 15 years ago and have been replaced. Since one additional superconducting accelerator module has been added and one superconducting module and the RF gun have been replaced, modification and rearrangement of the RF waveguide distributions were required. An XFEL type waveguide distribution for the new accelerator module ACC7 and a distribution without individual phase shifters for the exchanged module ACC1 have been installed. A new waveguide distribution for the RF gun allows phase tuning by changing the gas pressure in the waveguides. It will also allow supply the RF gun by a 10MW multi beam klystron instead of the still used 5MW single beam klystron at a later point of time.
ANL, Argonne
A 100 MHz thermionic rf gun is under consideration as the electron source for the X-ray Free Electron Laser Oscillator*. Because the source must operate continuously, back-bombardment of the cathode is a serious concern. We present results of simulations of back-bombardment, as well as strategies for reducing the back-bombardment power on the cathode.
*K. J. Kim et al., Phys. Rev. Lett. 100, 244802 (2008)
ISIR, Osaka
Tohoku University, Research Center for Electron Photon Science, Sendai
We are conducting FEL experiments with the L band electron linac at Osaka University. The linac is equipped with a thermionic electron gun and the three-stage sub-harmonic buncher(SHB) system. In FEL experiments an 8μs long electron pulse is injected from the gun and the SHB system is turned on for generating a multi-bunch electron beam of an 8μs duration with 2nC charge per bunch and 9.2 ns intervals between bunches. It repeatedly amplifies light pulses stored in the optical resonator of the FEL. The roundtrip time of the light pulses is 37 ns, so that four light pulses are stored in the resonator. The FEL gain becomes higher at least in proportion to the peak current in the bunch or charge per bunch. The present charge value is limited by the high beam loading in the acceleration tube of the linac, exceeding a half of the input RF power. If the bunch intervals can be extended to 37 ns, the charge per punch can be made four times higher for the same beam loading, resulting in significant increase of the FEL gain. To generate such an electron beam, we are developing the electron gun system with a high-repetition-rate grid-pulser. We will report the outline of the study.
ISIR, Osaka
Femtosecond electron beam, which is essential for pump-probe measurement, was generated with a 1.6-cell S-band photocathode rf gun. The rf gun was driven by femtosecond UV laser pulse (266 nm), which was generated with third-harmonic-generation (THG) of Ti:Sapphire femtosecond laser (800 nm). The longitudinal and transverse dynamics of the electron bunch generated by the UV laser was investigated. The bunch length was measured with the dependence of energy spread on acceleration phase in a linac, which was set at the downstream of the rf gun. Transverse emittance at the linac exit was also measured with Q-scan method.
ISIR, Osaka
KEK, Ibaraki
Photocathode rf electron linac facilities have been developed in Osaka University to reveal the hidden dynamics of intricate molecular and atomic processes in materials. One of the linacs was developed using a booster linear accelerator and a magnetic bunch compressor. This linac was successfully produced a 100-fs high-brightness electron single bunch and initiated the first experimental study of radiation chemistry in the femtosecond time region. Another was constructed with a photocathode rf gun to generate a near-relativistic 100-fs electron beam with a beam energy of 1~4 MeV. A time-resolved MeV electron diffraction was successfully developed with this gun to study the ultrafast dynamics of structure change in materials.
Diamond, Oxfordshire
Photocathode RF guns are widely used as injectors for accelerators requiring very high quality beams such as free electron lasers and linear colliders and recently used as ultrafast electron diffraction sources. Even with the limited repetition rate, normal conducting photocathode RF guns generate very low emittance and short pulse electron beams thanks to their high accelerating field and the efficient positioning of focusing solenoids. We report our activity of the design and production of an S-band normal conducting photocathode gun. The RF characteristics, thermal heating and vacuum analyses are discussed.
Diamond, Oxfordshire
At many laboratories S-band photoinjectors operate to provide high quality beams; however the repetition rates are limited to about 100 Hz. This limitation mainly occurs due to the guns where a high RF amplitude of about 100 MV/m is required to keep the beam quality from the space charge force. In this paper we design an injector consisting of an S-band gun with improved cooling and S-band acceleration modules for a repetition rate up to 1 kHz. The technical feasibility and beam dynamics optimization are discussed.
Diamond, Oxfordshire
Ultrashort electron beams can be used for investigating ultrafast dynamics of physical, chemical or biological systems. With an S-band photocathode gun, simulations have been done in order to generate ultrashort electron beams. Optimizations to generate ultrashort electron beams with a small beam divergence and to minimize the system sensitivity against RF jitter are reported.
ANL, Argonne
One proposed injector for the X-ray Free Electron Laser Oscillator* uses a 100 MHz thermionic rf gun to deliver very small emittances at a 1 MHz rate**. Since the required beam rate is only 1 MHz, 99\% of the beam must be dumped. In addition, back-bombardment of the cathode is a significant concern. To address these issues, we propose*** using a laser to quickly heat the surface of a cathode in order to achieve gated thermionic emission in an rf gun. We have investigated this concept experimentally using an existing S-band rf gun with a thermionic cathode. Our experiments confirm that thermal gating is possible and that it shows some agreement with predictions. Operational issues and possible cathode damage are discussed.
*K. J. Kim et al., Phys. Rev. Lett. 100, 244802 (2008)
**P. N. Ostroumov et al., Proc. Linac08, 676-678.
***M. Borland et al., these proceedings.
ANL, Argonne
The proposed injector design for the X-ray Free Electron Laser Oscillator* uses a 100 MHz thermionic rf gun in order to obtain beams with very small emittances at high repetition rates**. The required beam rate is only 1 to 10 MHz, so 90 to 99\% of the beam must be dumped. In addition, back-bombardment of the cathode is a significant concern. To address these issues, we propose using a laser to quickly heat the surface of a cathode in order to achieve gated thermionic emission in an rf gun. This may be preferrable to a photocathode in some cases owing to the robustness of thermionic cathodes and the ability to use a relatively simple laser system. We present calculations of this process using analysis and simulation. We also discuss potential pitfalls such as cathode damage.
*K. J. Kim et al., Phys. Rev. Lett. 100, 244802 (2008).
**P. N. Ostroumov et al., Proc. Linac08, 676-678.
ANL, Argonne
The proposed X-ray Free Electron Laser Oscillator* requires an ultra-low emittance gun that generates continuous electron bunches at 1 to 10 MHz. Recently, T. Shintake raised the possibility of using a pulsed triode gun with a thermionic cathode. In this paper, we investigate the feasibility for such a gun as part of an injector producing normalized emittances in the 0.1 μm range with 2 ps rms duration for 50 pC/bunch. We also explore some implementation concepts.
*K. J. Kim et al., Phys. Rev. Lett. 100, 244802 (2008)
Sokendai, Ibaraki
KEK, Ibaraki
RISE, Tokyo
At Laser Undulator Compact X-ray Source (LUCX) facility at KEK, we have developed a RF gun with increased mode separation. Using this RF gun we have successfully generated a bunch train of 300 bunches per train with 160 nC total charge and with peak to peak energy difference less than 0.85% at 5.2 MeV. We plan to generate and accelerate 8000 bunches per train with 0.5 nC per bunch. These bunches will then collide in the collision chamber with laser pulses to produce soft x-ray. After successful results from above work, we take next step and are now designing and fabricating a new 3.5 cell RF gun and a high gradient standing wave linac to achieve 50 MeV beam with 8000-bunches per train. This compact source will be used for future research. This paper details achieved results with existing gun for generation of long bunch train and lists out proposed activity.
JAEA, Ibaraki-ken
JAEA/ERL, Ibaraki
KEK, Ibaraki
HU/AdSM, Higashi-Hiroshima
Nagoya University, Nagoya
Tohoku University, School of Scinece, Sendai
An electron gun capable of delivering high current and high brightness electron beam is indispensable for next generation energy recovery linac light sources. A high voltage photocathode DC gun is a promising gun for such new light sources. It is however difficult to apply DC high voltage on a ceramic insulator with a rod supporting cathode electrode because of field emission from the rod. In order to mitigate the problem, we have employed a segmented insulator with rings which guard the ceramics from the field emission and recently succeeded in applying 500-kV on the ceramics for eight hours without any discharge. This high voltage testing was performed with a simple configuration without NEG pumps and electrodes. The next step is to repeat the same high voltage testing with a full configuration necessary for beam generation. We have designed electrodes for the maximum surface electric field not to exceed 11 MV/m at 500 kV while keeping the distance between the electrodes 100 mm. NEG pumps with a pumping speed of 7200 L/s have been installed in the gun chamber. A photocathode preparation system was connected to the gun chamber and beam generation is planned this summer.
ISIR, Osaka
KEK, Ibaraki
Tohoku University, Research Center for Electron Photon Science, Sendai
HU/AdSM, Higashi-Hiroshima
We are developing an L-band photocathode RF gun in collaboration with KEK and Hiroshima University. The RF gun will be used not only at Osaka University but also at STF of KEK, so that it can be stably operated at the input RF power of 5 MW with 1 ms duration and a 5 Hz repetition rate, resulting in the average input power of 25 kW. The water-cooling system of the 1.5 cell cavity is designed, which can take the heat with the temperature rise of the cavity body by 5°C at the flow rate of cooling water of 358~723 liter/min. The several parts of the RF cavity are assembled with brazing and the most crucial process is brazing of three main components of the RF cavity into one. The brazing has to be tight and perfect not to allow vacuum leak, while the brazing filler metal must not go out on to the inner surface of the cavity to avoid discharge triggered by the scabrous filler metal on the cavity wall. Test experiments are conducted and a guideline is concluded for such brazing.
SLAC, Menlo Park, California
SLAC has developed a comprehensive suite of 3D parallel electromagnetic codes based on the finite-element method to solve large-scale computationally challenging problem with high accuracy. The ACE3P (Advanced Computational Electromagnetic 3P) code suite includes the Omega3P eigenmode and S3P S-parameter solvers in the frequency domain for cavity prototyping and optimization, T3P time-domain solver for wakefields and impedances, Track3P particle tracking solver for simulating multipacting and dark current, and Pic3P Particle-in-cell code for RF Gun design. These capabilities with recent advances and the latest applications addressing important RF related accelerator phenomena will be presented.