CEA, Bruyeres-le-Chatel
A 15 MeV accelerator scheme based on a dc photo-injector and a rf superconducting linac as been proposed as a new facility for radiography applications. The overall beam dynamics simulation process based on SUPERFISH and PARMELA codes will be reviewed. We present the results for the following beam operating conditions; acceleration of limited number of bunches, up to twenty electron micro-pulses of 100 ps time duration and 200 nC bunch charge, at 352 MHz repetition rate.
KEK, Ibaraki
In the last couple of years, great achievements have been realized through world-wide developments of multi-beam klystrons (MBK) in the L-band and S-band. These MBKs are developed by industries such as Toshiba, Thales and CPI for the European X-FEL project or at the Naval Research Lab or by the Chinese Academy of Sciences for high-power, low-voltage radar systems. Some of them are already in operation at full specifications and are commercially available. The MBKs are superior to conventional single-beam klystrons through their ability to increase the output power dramatically while the operating voltage can be kept at a similar level. This talk will review the performances of these multi-beam klystrons, their design features, and future development plans.
ELSA, Bonn
DESY, Hamburg
Since 1966 a Varian factored injector is in use at the accelerator complex of the University of Bonn serving several experiments to investigate the subnuclear structure of matter. This injector will have to be replaced for several reasons. The new injector will operate in a single bunch mode of 2 A beam current and is currently under construction. Also a 2 μs long pulse mode of 500 mA beam current will be available for ordinary accelerator operation for hadron physics experiments. Produced by a pulsed thermionic 90 kV gun, compression of the pulses is achieved by a 500 MHz prebuncher as well as one β-matching travelling wave buncher running at the linac frequency of 3 GHz. The injector has been designed and optimised using the software package EGUN and numerical simulations based on the paraxial differential equations. The single bunch mode will allow to investigate single bunch instabilities within the Helmholtz alliance "Physics at the Terascale".
TU Darmstadt, Darmstadt
TEMF, TU Darmstadt, Darmstadt
IKP, Mainz
ANL, Argonne
Funding: Work supported by the DFG through SFB 634
At the superconducting Darmstadt linear accelerator S-DALINAC currently two upgrades of the injector are underway: The current upgrade for the injector mainly involves the superconducting rf part. In order to increase the maximum current from 60 uA to 150 or 250 uA the power coupler design had to be modified, resulting in major changes in the whole cryo-module. Second, an additional polarized electron source (SPIN) has been set-up at an offline test area. There, the polarized electrons are produced by photoemission at a strained GaAs cathode on a 100 kV platform. The test beam line includes a Wien filter for spin manipulation, a Mott polarimeter for polarization measurement and additional diagnostic elements. We will give an overview over the project, report on the status and present first measurement results including the proof of polarisation.
DESY Zeuthen, Zeuthen
INRNE, Sofia
DESY, Hamburg
YerPhI, Yerevan
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
INFN/LASA, Segrate (MI)
BESSY GmbH, Berlin
Uni HH, Hamburg
MEPhI, Moscow
Funding: This work was partly supported by the European Community, contracts RII3-CT-2004-506008 and 011935, and by the 'Impuls- und Vernetzungsfonds' of the Helmholtz Association, contract number VH-FZ-005.
The Photo Injector Test facility at DESY, Zeuthen site, (PITZ) was built to develop and optimize high brightness electron sources for Free Electron Lasers (FELs) like FLASH and the European XFEL. In the last shutdown a new RF gun cavity with improved water cooling was installed and conditioned. It is the first rf gun where the surface cleaning was done with dry ice technique instead of high pressure water rinsing and it showed a 10 times lower dark current emission than its precursor gun, even at cathode gradients as high as 60M V/m. In addition, a new photo cathode laser system was installed and will be available for operation in spring 2008. It will allow flat-top temporal laser shapes with 2ps rise/fall time. According to beam dynamics simulations this will further improve the beam quality reported at earlier conferences* and will lead to unprecedented low transverse projected emittance beams at a charge level of 1nC. This contribution will summarize the experimental results from the summer 2008 running period covering transverse projected emittance optimization, thermal emittance from the photocathode, longitudinal phase space and first transverse slice emittance measurements.
* L. Staykov et al., "Measurements of the Projected Normalized Transverse Emittance at PITZ", Proceedings of the FEL 2007, Novosibirsk, Russia, August 2007.
NPS, Monterey, California
Niowave, Inc., Lansing, Michigan
MIT, Middleton, Massachusetts
Stanford University, Stanford, Califormia
Funding: This research is supported by the Office of Naval Research and the Joint Technology Office.
The Naval Postgraduate School (NPS) has begun the design and assembly of the NPS Free-Electron Laser (NPS-FEL). As part of this effort, the original dc gun-based injector system is being refurbished and upgraded. As described in the accompanying paper 'Status of the NPS-FEL' (these Proceedings), the overall NPS-FEL design parameters are for 40 MeV beam energy, 1 nC bunch charge, and 1 mA average beam current, in an energy-recovery linac configuration. As we move towards this configuration, the injector system will be incrementally upgraded to add photocathode capability, have a higher final beam energy, and improve the beam brightness, to meet the demands of the overall experimental program. This paper describes the current status of the injector system, the initial set of experiments planned, and the projected upgrade path.
Northern Illinois University, DeKalb, Illinois
ANL, Argonne
Funding: Work supported by the Department of Education under contract P116Z010035 with Northern Illinois University.
A simple, inexpensive, and compact low-energy (~20 KeV) photoemission electron source was designed, built and recently commissioned. It uses a commercial ultraviolet photocathode drive laser producing 3 ns RMS pulse. The source will eventually be used to drive a table-top THz radiation source, based on the Smith-Purcell free-electron laser scheme, and could also have potential application to time-resolved electron microcopy. We present experimental measurements of the photoemitted electron beam and numerical simulations of the anticipated parameters. We also discuss the generation of flat beams required to efficiently drive the THz radiation source.
Fermilab, Batavia
ANL, Argonne
Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357
Strong enhancements of the optical transition radiation (OTR) signal sampled after bunch compression in the Advanced Photon Source (APS) linac chicane have been observed as has been reported in LCLS injector commissioning. A FIR CTR detector and interferometer were used to monitor the bunch compression process of the PC gun beam down to sub-0.5 ps (FWHM) and correlate the appearance of spatially localized spikes of OTR signal (5 to 10 times brighter than adjacent areas) within the beam image footprint. We also observed that a beam from a thermionic cathode gun with much lower charge per micropulse (but a similar total macropulse charge to the PC gun) showed no enhancement of the OTR signal after compression. Reconstructions of the temporal profiles from the autocorrelations of both beams were performed and will be presented. Spectral-dependence measurements of the enhanced OTR were done initially at the 375-MeV station using a series of bandpass filters inserted before the CCD camera. Tests with an Oriel spectrometer with ICCD readout are now being planned to extend those studies. Discussions of the possible mechanisms for the OTR enhancements will be presented.
ISIR, Osaka
KEK, Ibaraki
HU/AdSM, Higashi-Hiroshima
Funding: This research is partly supported by the accelerator support program to universities conducted by the High Energy Accelerator Research Organization in Japan.
We have begun a three-year project to develop a photocathode rf electron gun for the 40 MeV L-band linac at ISIR, Osaka University in collaboration with KEK. The L-band linac with an rf frequency of 1.3 GHz is equipped with a thermionic electron gun and it can accelerate a high-intensity single-bunch electron beam with charge up to 91 nC/bunch. Because the large emittance of ~100 pi mm x mrad is a limiting factor in the experiments, it is required to develop a new electron gun capable of providing an electron beam with much lower emittance. Since a group at the Accelerator Laboratory of KEK is developing a photocathode rf electron gun in the L-band for the International Linear Collider Project, we have joined the group to learn how to develop such an rf gun and also to obtain support from KEK. In this first year, characteristics of the rf gun will be measured at KEK for ILC fabricated by FNAL. We plan to optimize the structure of the rf gun for ISIR with computer simulation. We will report the plan and progress to develop a photocathode rf gun for the L-band linac.
RISE, Tokyo
KEK, Ibaraki
University of Tokyo, Tokyo
ISIR, Osaka
HU/AdSM, Higashi-Hiroshima
AIST, Tsukuba, Ibaraki
Funding: Work supported by MEXT High Tech Research Project HRC707, JSPS Grant-in-Aid for Scientific Research (B)(2) 16340079
At Waseda University, we have been developing a high quality electron source based on photo-cathode rf gun which has a Cs-Te cathode with high quantum efficiency. Until now, at the Waseda University we have succeeded the soft X-ray generation via inverse-Compton scattering and pulse radiolysis system for studying the early processes of radiation chemistry with electron beams generated by copper cathode rf gun. Cs-Te rf gun is expected to generate higher charge electron bunches with a low emittance than a copper cathode because of its high quantum efficiency and also the high-quality multi-bunch electron beams. That enables us to extend the range of electron beam parameters for our application experiments. However, a Cs-Te cathode has a short life compared with a copper, so it has to be exchanged occasionally, thus we have developed a new rf-gun cavity which can be attached the compact cathode load-lock system. Moreover, we improved the design of an existing rf-gun cavity for the reduction of the dark current and the higher electric field. In this conference, the performance of the improved cavity and the result of electron beam generation experiments will be reported.
RAS/INR, Moscow
DESY, Hamburg
DESY Zeuthen, Zeuthen
During development and operation of DESY L-band rf gun cavities, desires for further improvements were formulated. The next step of development is based on the proven advantages of existing cavities, but includes significant changes. The L-band 1.6 cell rf gun cavity is intended for operation in pulse mode with electric fields at the cathode of up to 60 MV/m, rf pulse length of ~1 ms and average rf power higher than existing gun cavities. In the new design the cell shape is optimized to have the maximal surface electric field at the cathode and lower rf loss power. The cavity cells are equipped with rf probes. Cooling circuits are designed to combine cooling efficiency with operational flexibility. In the report, the main design ideas and simulation results are described.
PSI, Villigen
Paul Scherrer Institute (PSI) is presently developing a low emittance electron source for the PSI-XFEL project. The electron gun consists of an adjustable diode configuration subject to pulses of 250 ns (FWHM) with amplitude up to 500 kV from an air-core transformer- based high-voltage pulser. The facility allows high gradient tests with different cathode configurations and emission processes (field emission and photo emission). In the first stage, the beamline is only made up of focussing solenoids followed by an emittance monitor. Selected beam characterization measurements, from photo-cathode operation driven by a 266 nm UV laser system delivering 4 uJ energy during 6.5 ps (FWHM), are presented and compared to the results of 3D particle tracking simulations.
UMAN, Manchester
The Hashemite University, Zarka
Based on Lienard-Weichert method of retarded potentials and the potential due to the image of charges on the cathode, a rigorous relativistic description of the beam transport inside the rf-photoinjector is presented. The velocity dependent effects are explicitly taken into account in a complete analytical description. Simulations are presented for parameters of the ELSA photo-cathode.
LBNL, Berkeley, California
Università Cattolica-Brescia, Brescia
Funding: US Deparment of Energy
The photocathode R&D program at Lawrence Berkeley National Laboratory is presented, including the status of the lab and experimental results. We will also present experimental result obtained at Brescia Italy and theoretical work on predicting minimum thermal emittance from metal cathodes and emittance growth due to stochastic Coulomb interaction.
Northern Illinois University, DeKalb, Illinois
Funding: Work supported by the Department of Defense under contract N00014-06-1-0587 with Northern Illinois University
We discovered, by modeling the AES/JLab direct-current photoinjector with several beam-simulation codes, that nominal injector settings would create a large diffuse beam halo as a consequence of the internal space-charge force in the beam. The injector-induced halo is sensitive to the injector settings, but if the settings are judiciously chosen, it can be largely circumvented. We present an exploration of the parameter space for the AES/JLab photoinjector. Measurement of beam halo will be a crucial aspect of commissioning this machine.
Northern Illinois University, DeKalb, Illinois
Funding: Work supported by the Department of Defense under contract N00014-06-1-0587 with Northern Illinois University
From the prospect of the high average current electron injectors, the most important advantage of the field-emission cathodes is their capability to generate very large current densities. Simulation of field-emission cathodes is complicated by the large range of spatial dimensions: from sub-micron scale, for a single field-emission tip, to millimeter scale, for a field-emitter array. To overcome this simulation challenge our numerical model is split in two steps. In the first step, only electrons emitted by a single tip are considered. In the second step, the beams originating from many single emitting tips are merged together to mimic the field-emitter array configuration. We present simulation results of injector based on field array emitters cathodes.
LANL, Los Alamos, New Mexico
AES, Medford, NY
Funding: This work is supported by ONR and HEL-JTO.
The LANL/AES 2.5-cell, normal-conducting radio-frequency (NCRF) injector has been fabricated. This room-temperature injector can be used to generate cw electron beams with average current greater than 100 mA and beam energy up to 2.5 MeV prior to injection into an energy-recovery linac. PARMELA simulations show the effectiveness of emittance compensation in generating high-brightness electron beams at relatively low accelerating gradients. We present the initial measurement results of the rf, accelerator and vacuum properties of the NCRF injector and the associated ridge-loaded waveguides. The impact of these rf measurement results on the planned thermal and electron beam tests will also be discussed.
UW-Madison/SRC, Madison, Wisconsin
Funding: This work is supported by the University of Wisconsin-Madison and MIT, and by the US NSF under award No. DMR-0537588
The Wisconsin FEL project is a 2.2 GeV, HHG seeded, FEL designed to provide six individual beamlines with photons from 5 to 900 eV. The FEL requires electron bunches with 1 kA peak bunch current and less than 1 mm*mrad transverse slice emittance. To meet those requirements a low frequency, SRF electron gun is proposed which uses "blow-out" mode bunches*. Blow-out mode produces ellipsoidal bunches which are easily emittance compensated**. They also have a very smooth density and energy distribution. Results of the modeling of the injector and a diagnostic beamline will be presented.
* O.J. Luiten, et al., Phys. Rev. Lett., 93, 094802-1 (2004)
** C. Limborg-Deprey, P. Bolton, NIM-A, 557 (2006) 106-116
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
The energy recovery linac prototype at Daresbury is now called ALICE (Accelerators and Lasers In Combined Experiments). This paper presents the results obtained in the past year, including the second (fourth) period of gun commissioning. Following the completion of gun commissioning in November 2007, the dedicated gun diagnostic line was removed and the electron gun attached to the booster cavity and hence the rest of the machine. The paper outlines some of the challenges experienced during the commissioning of both the photoinjector system and the superconducting cavities and presents the current status of the project as well as the very latest results from commissioning during the summer of 2008.
CLASSE, Ithaca, New York
Funding: Work supported by the National Science Foundation under contract PHY 0131508
Cornell University is planning to build an Energy-Recovery Linac (ERL) X-ray facility. The very small electron-beam emittance would produce an X-ray source that is significantly better than any existing storage-ring based light source. One major difference between an ERL and a typical light source is that the final electron beam emittance, and thus the X-ray beam brightness, is determined by the electron injector rather than the storage ring. We are currently constructing and commissioning an injector for an ERL with the goal of demonstrating the low emittances and high beam power required. The injector is designed to accelerate up to 100 mA cw electron bunches of 77 pC/bunch with an energy of 5 MeV (33 mA at 15 MeV) using 1.3 GHz superconducting cavities. A full suite of diagnostics will allow a complete phase space characterization for comparison with simulations and with the requirements. We will describe the current status of the injector along with results, difficulties and challenges to date.
DESY, Hamburg
Funding: We acknowledge the support of the European Community Research Infrastructure Activity under FP6 'Structuring the European Research Area' program (CARE, contract number RII-CT-2003-506395
Dry-Ice cleaning offers a dry and waterless cleaning option removing hydrocarbons and particles without residues. Complex excavations like Cu rf gun cavities and Nb multicell cavities in horizontal installation position can be cleaned in an effective way. In the recent past rf gun cathodes and cathode transportboxes could be cleaned satisfactory. A status report will be given.
ANL, Argonne
Fermilab, Batavia
New SRF cavity processing systems at ANL, including those for electropolishing (EP), high-pressure water rinsing (HPR), and single-cavity clean room assembly have been developed and operated at ANL for use with cavities for a range of electron and ion linac applications. Jointly with FNAL, systems for 1.3 GHz single- and multi-cell elliptical cavities for the linear collider effort have been developed. New systems for use with low-beta TEM-class cavities have also been built and used to process a set of new quarter-wave resonators as part of an upgrade to the ATLAS heavy-ion accelerator at ANL. All of the new hardware is located in a 200 m2 joint ANL/FNAL Superconducting Cavity Surface Process Facility (SCSPF) consisting of two separate chemical processing rooms, a clean anteroom, and a pair of class 10 and 100 clean rooms for HPR and clean assembly. Results of first cold tests for elliptical and TEM-class cavities processed in these facilities are presented.
JLAB, Newport News, Virginia
Fermilab, Batavia
KEK, Ibaraki
Funding: Supported by DOE
Jefferson Lab plays an active role in the ILC high-gradient SRF R&D. Eight 9-cell cavities have been processed and tested so far by using the state-of-the-art recipes. Five reached a maximum gradient of over 32 MV/m. However, not surprisingly, the high-gradient performance is not necessarily reached during the first test. Re-processing by progressively more material removal can improve performance ultimately, but the number of re-processing cycles needed is un-predictable. Some cavities are quench limited repeatedly at around 20 MV/m. The quench locations are near the equator weld of specific cells. Based on the non-trivial high-gradient experiences in the past two years, we come to the conclusion that new capabilities beyond the state-of-the-art must be added to the existing SRF infrastructures in order to reliably achieve high gradients at a low cost. Targeted R&D is required to identify and characterize gradient limiting defects and field emitters. An enhanced high-gradient R&D program is emerging at JLab for continued contribution to realize the ambitious ILC gradient yield goal.
JASRI/SPring-8, Hyogo-ken
The acceleration gradient is limited by breakdown in an accelerating rf structure, including its surface condition of the inner wall. The surface treatment is an important technique to achieve the maximal acceleration gradient of an accelerating structure. We chose chemical etching as a method of surface treatment for accelerating rf structures made of copper. To study rf breakdown and effect of surface treatments, we used a pillbox-type single cell rf gun cavity. The highest cathode surface field (190 MV/m) of rf gun cavity was accomplished with this surface treatment under rf-conditioning elapsed time (21 days) in 2004. SPring-8 rf gun has been operating with the highest gradient in the world. This indicates that our treatment is considerably effective to improve the inner cavity surface made of copper. Further, we developed the high-pressure chemical etching for more complicated inner structures in 2006. Using a cartridge-type photocathode rf gun, high-field experiments were performed with cathode plugs chemical etching treated under deferent pressure condition. We report these results on highest gradient, using test copper samples treated with high-pressure chemical etching.
RIKEN Spring-8 Harima, Hyogo
RIKEN/SPring-8, Hyogo
A klystron modulator power supply for XFEL project at SPring-8 has been developed, which concepts are a compact body, a low noise, and a good stability. The cooling system of the power supply is one of the most important key for the stable modulator. For example, temperature change of insulation oil in the tank caused drift of the klystron voltage, and higher oil temperature deteriorates insulation oil and electric components. We adopted simple and compact cooling systems utilizing natural conviction cooling, because of low costs, limited space, and maintenance free. In order to estimate the requisite cooling ability, we designed four types of cooling panels and measured the natural conviction heat transfer coefficient between the oil and each cooling panels. Using the results, we designed cooling systems composed of water cooling panels placed on the side walls and a water pipe hanged from the ceiling panel. The temperature of the inner oil of the power supply in the rated operation was suppressed below 43 degree C, which is agreed with our expectation. In this paper we present the design and ability of the power supply, and the key point of oil cooling.
KEK, Ibaraki
SUT, Noda-shi, Chiba
University of Tokyo, Tokyo
The multi beam electron tube with a lot of beam pipes is required for the low applied voltage and the high frequency because the efficiency has a limit according to the perveance. However, the total heater power becomes too high if many thermal cathodes are used. Thus the cold cathode such as the carbon nano tube (CNT) is suitable for such a multi beam electron tube. Further the cold cathode has the advantage to work as a switching device since the metal grid close to the cathode can be used. The design and the fundamental test of the partial model will be presented.
ORNL, Oak Ridge, Tennessee
Funding: Oak Ridge National Laboratory, P.O. Box 2008 Oak Ridge, Tennessee 37831-6285 managed by UT-BATTELLE, LLC for the U.S. Department of Energy Under Contract DE-AC05-00OR22725
Observations of several of the 81 klytron output waveforms into their respective superconducting cavities do not correspond with their rectangular klystron inputs in open loop mode. This can't be completely explained by a drooping high voltage power supply especially when the waveform is parabolic. Some possible causes and effects of these anomalies are presented.
JASRI/SPring-8, Hyogo-ken
I developed a 3-D pulse shaping system in UV as an ideal laser for yearlong stable photoinjector. At SPring-8, the laser's pulse-energy stability has been improved to 0.7~1.4% at the UV (263 nm) under the laser environmental control included humidity. In addition, the ideal spatial and temporal profiles of an UV-laser pulse are essential to suppress emittance growth in an rf gun. I apply a deformable mirror that automatically shapes the spatial profile with a feedback routine, based on a genetic algorithm, and a pulse stacking system consisting of three birefringence Alpha-BBO crystal rods for temporal shaping at the same time. The 3D shape of the laser pulse is spatially top-hat (flattop) and temporally a square stacked chirped pulse. Using a 3D-shaped laser pulse with diameter of 0.8 mm on the cathode and pulse duration of 10 ps (FWHM), we obtain a normalized emittance of 1.4 pi mm mrad with a beam energy of 26 MeV. To keep the mirror away from beam axis, I developed a new hollow laser incidence with an axicon final focusing. Furthermore, I am developing a laser-induced Schottky-effect-gated photocathode gun using Z-polarization of the laser source with the hollow incidence.