DESY, Hamburg
The European XFEL project is entering the construction phase, based on the very successful experience of the TESLA linac technology and the SASE FEL concept, now serving the FLASH user facility at DESY. The EU-XFEL will be realized by a widespread international collaboration and it is also relevant for the ILC planning. A description of the overall layout of the facility, of the technical developments and industrialization efforts for the accelerator components, and of the international collaboration will be given.
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.
One of the possible options for the Advanced Photon Source (APS) upgrade is an energy-recovery linac (ERL). In its main operating mode, the ERL bunch length would be two picoseconds. Even though this bunch length is already a factor of 20 shorter than the present APS bunch length, some experiments might require shorter X-ray pulses. For the APS storage ring, we plan to use an rf deflection technique* to generate one-picosecond X-ray pulses. In this approach, an rf cavity is used to deliver longitudinally dependent vertical kick to the electron beam and then a pair of slits is used to slice vertically streaked X-ray beam. We investigate the possibility and benefits of utilizing this technique to generate shorter X-ray pulses at the ERL.
*A. Zholents, et al., Nucl. Instr. and Meth. A 425 (1999) 385.
DESY, Hamburg
The XFEL injector building has a length of 74.3 metres and is divided by 2.5 m long concrete shielding wall. The section upstream the shielding wall will have a length of 42.3 m and give place for the gun, accelerating module, 3rd harmonic section, laser heater and the beam diagnostics section. At its end the possibility for the beam dump is foreseen so that the tuning of the beam in the injector would become possible without any impact on the subsequent parts of the XFEL. Each of these components sets certain requirements on beam optics which may compete with each other. Downstream the shielding the beam will be vertically displaced by 2.75 m over the distance of 20 m by means of the so called dogleg - a combination of two four cell arcs (8 cell system). Since the vertical displacement takes place there it is important to optimize cells in such an order that the chromatic effects don't impact the beam quality noticeably. In this paper we describe the solution for the beam optics at the XFEL injector.
Kyoto IAE, Kyoto
An MIR-FEL facility, Kyoto University FEL (KU-FEL), has been developed for applications in "sustainable energy science", such as fundamental studies on high-efficiency solar cells. The KU-FEL, consisting of an S-band thermionic rf gun, a 3 m accelerator tube and a planer undulator, aims to generate 4-13 μmeter tunable FEL. The first lasing was achieved on March, 2008 at 12.4 μmeters by using a beamloading compensation method both in the rf gun and in the accelerator tube. *Furthermore, we introduced detuning to the rf gun and succeeded to generate an electron beam with macropulse duration of 5.1 μseconds, average current of 100 mA and energy spread of 0.5% which led to power saturation in FEL. In the conference, the improvements of the electron beam properties and power saturation of the KU-FEL will be discussed.
*H. Ohgaki et al., 'First Lasing at 12 um Mid Infrared Free Electron Laser at Kyoto University', Japanese Journal of Applied Physics, accepted for publication. (2008).
ANL, Argonne
SLAC, Menlo Park, California
Funding: Work Argonne supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract number DE-AC02-06CH11357.
A Beam-Loss Monitor (BLM) system based on the detection of Cerenkov radiation is in development at the Advanced Photon Source (APS) for the Linac Coherent Light Source (LCLS) free-electron laser. The electron beam will vary in energy nominally from 4 to 14 GeV with a beam charge of 0.2 to 1.0 nC and a maximum repetition rate of 120 Hz. To limit radiation-induced demagnetization of the undulator permanent magnets, the BLM will provide beam-loss threshold detection as part of the Machine Protection System (MPS). The detector incorporates a large volume (30 cc) fused silica Cerenkov radiator coupled to a photomultiplier tube (PMT). The output of the PMT is conditioned locally by a charge amplifier circuit and then digitized at the front end of the MPS rack electronics. During commissioning, the device will be calibrated by inserting a 1-micron aluminum foil into the beam, upstream of the undulator magnets. The present design calls for five BLM detector units to be distributed throughout the 33 undulator magnets. Beam-based testing is to begin at the APS storage ring during the summer of 2008. Details and status of the detector hardware, electronics, and simulations will be discussed.
SLAC, Menlo Park, California
UW-Madison/SRC, Madison, Wisconsin
Funding: The work of AWC and JW was supported by the US Department of Energy under contract DE-AC02-76SF00515. The work of JB was supported by National Science Foundation Award No. DMR-0537588.
A single-pass high-gain X-ray free electron laser (FEL) calls for a high quality electron bunch. In particular, for a seeded FEL, and for a cascaded harmonic generation (HG) FEL, the electron bunch initial energy profile uniformity is crucial to preserve an FEL narrow bandwidth. After the acceleration, compression, and transport, the electron bunch energy profile entering the undulator can acquire temporal non-uniformity. During the cascading stages, the electron bunch energy profile is also not uniform temporally entering the next stage. We study the effects of the electron bunch initial energy profile on the FEL performance, cascaded HG FEL or single stage FEL amplifier. Concrete examples are discussed for seeded FEL projects being studied.
SLAC, Menlo Park, California
Static magnetic field undulators are capable of producing quasi-monochromatic synchrotron radiation of very high brightness. However, it is not possible to quickly change the properties such as polarization of the radiation in a static undulator. It is possible to construct an undulator using microwaves instead of static magnets where the electron beam is undulated by both electric and magnetic fields of an rf wave. A major advantage with a microwave undulator is that the radiation properties can be changed very quickly. The biggest challenge in developing a microwave undulator is in keeping the rf losses low. We are designing a microwave undulator with the aim of achieving at least a tenth of the flux obtained by the BL13 static magnetic field Elliptical Polarized Undulator in the SPEAR ring. We have considered circular waveguide modes and hybrid HE11 mode in a corrugated waveguide as possible candidates for the microwave undulator. It is found that a corrugated waveguide has the lowest rf losses with a very desirable field profile. It is also possible to use this device for a linac driven FEL. Our analysis of the corrugated waveguide cavity for the rf undulator will be presented.
NPS, Monterey, California
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). The basic 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. The NPS-FEL will make use of portions of the Stanford Superconducting Accelerator (decommissioned in 2007), in particular the injector system, Stanford/Rossendorf-style cryomodules and rf system. The injector will be gradually upgraded to improve beam properties and increase the injection voltage. Each cryomodule contains two, 9-cell TESLA-type 1.3 GHz cavities, each cavity powered by an individual 10 kW cw klystron. NPS has committed to refurbishing a building for the FEL, with approximate interior vault dimensions of 7 m x 20 m x 2.5 m. The building has overall dimensions of 12 m x 49 m and will house the vault, control room, and support equipment. This paper describes the overall goals of the program, initial experimental plans, and progress to date.
JASRI/SPring-8, Hyogo-ken
RIKEN/SPring-8, Hyogo
At SPring-8, the 8 GeV linac for an X-ray free electron laser (XFEL) is now under construction. In order to realize the XFEL, highly qualified electron beams are required. A measurement of spatial structure of such beam is very important for the beam tuning of XFEL. The spatial structure is measured with a screen monitor, which we now develop. The resolution of the measurement is required within 10 um. The screen monitor comprises a vacuum chamber with a thin metal (100 um, SUS) foil to emit OTR, lenses for focusing and a CCD camera system. The main feature of the monitor is a bright and high-resolution optical system. In order to realize this system, the lenses are placed close to the foil, the distance between the lenses and the foil is 100 mm, and the lenses have a large diameter (2 in.). This optical-geometrical structure also contributes much to reduce the airy radius of a near field image. Although the range of an observation wavelength is wide as which is form 400 to 800 nm, the resolution of the measurement on the foil is calculated as 2.5 um. The experimental data of the developed screen monitor also suggested the same resolution.
ANL, Argonne
Funding: Work at Argonne was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No DE-AC02-06CH11357.
The LCLS, now under construction at the Stanford Linear Accelerator Center (SLAC) in California, will be the world's first X-ray free-electron laser when it comes online next year. Design and production of the undulator system is the responsibility of a team from the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). Forty 3.4-m-long high-precision undulators, 37 laminated quadrupole magnets, plus 38 support and motion systems with micron-level adjustability and stability were constructed and delivered to SLAC, where final tuning, fiducialization, and installation are underway. An overview of the undulators and support systems, including achieved results, is presented.