RIKEN/SPring-8, Hyogo
JASRI/SPring-8, Hyogo-ken
We present the design and performance of the beam diagnostic system of XFEL/SPring-8. The XFEL accelerator requires sub-um resolution beam position monitors (BPM), few-um resolution screen monitors, high-speed beam current monitors and a ten femtosecond resolution temporal structure measurement system. We designed an rf cavity BPM which has a resonant frequency of 4760 MHz and a position resolution of less than 1 um. For the screen monitor, thin stainless-steel foil (0.1 mm thick) is used to reduce beam divergence. In addition, a custom-made lens system having few-micron resolution was designed. For the beam measurement, we developed a differential current transformer (CT) with four ports, two are positive and the others are negative, to reduce common-mode noise. The rise time of the CT output pulse is 0.1 ns. To measure the temporal structure of a beam, we developed a C-band (5712 MHz) transverse deflecting cavity that has a disk-loaded backward traveling wave structure. The iris shape of the cavity is a race-track to separate x- and y-mode. This cavity can resolve a beam into femtosecond fragments. Thus, the beam diagnostic system satisfies the demands of the XFEL machine.
RIKEN/SPring-8, Hyogo
JASRI/SPring-8, Hyogo-ken
In the XFEL project at SPring-8, the resolution of a beam position monitor (BPM) is required to be less than 1 um. Therefore, we developed an rf cavity BPM (RF-BPM) to achieve a precise position resolution. The RF-BPM has two cavities: one is a TM110 cavity for position detection and the other is a TM010 cavity for phase reference and charge normalization. The resonant frequency is 4760 MHz and the loaded Q factor is approximately 50 for both cavities. The designed performance of the RF-BPM cavity was confirmed by low-level rf measurement. The rf signal is detected by an IQ demodulator to obtain the intensity and the phase. Although the BPM signal is a mixture of a position signal and a slope signal, the IQ demodulator can easily distinguish them because the phases of these signals are 90 degrees different from each other. We developed a new circuit that has small errors: the intensity error is 1 % and the phase error is 0.5 degree. The RF-BPM system has been tested by using a 250 MeV electron beam at the SCSS test accelerator. We report results of confirmed RF-BPM performances; position resolution, xy coupling, linearity, dynamic range, beam arrival timing measurements etc.
INFN/LNF, Frascati (Roma)
INFN-Roma II, Roma
Rome University La Sapienza, Roma
ENEA C.R. Frascati, Frascati (Roma)
One of the key diagnostics techniques for the full characterization of beam parameters for LINAC-based FELs foresees the use of RF deflectors. With these devices it is possible to completely characterize both the longitudinal and the transverse phase space. In the talk I will present the main design considerations for time resolved (sliced) beam parameter measurements using RF deflectors. Measurement setups for longitudinal pulse shape as well as phase space and transverse beam slice emittance characterizations are described. The main sources of errors are discussed and the design criteria of these devices are presented. In particular the SPARC RF deflector and the related diagnostic lines as well as recent measurement results from the SPARC facility are shown. RF deflectors in use or planned to be used in other FEL labs are then illustrated with an overview of these activities.
Uni HH, Hamburg
PSI, Villigen
DESY, Hamburg
A seeded free-electron laser operating in the soft X-ray (XUV) spectral range will be added to the SASE FEL facility FLASH. The seed beam will be generated by higher harmonics of a near infrared laser system. A dedicated transport system will guide the radiation into the electron accelerator environment. Within the seed undulator section compact diagnostic units have to be designed to control the transverse overlap of the photon and the electron beam. These units contain a BPM a wire scanner and an OTR screen for the electron diagnostic. A Ce:YAG screen and a MCP readout for the wire scanner are foreseen to measure the photon beam position.
PSI, Villigen
IAP Univ. Bern, Bern
The knowledge and control of electron bunch lengths is one of the key diagnostics in XFEL accelerators to reach the desired peak current in the electron beam. A compact electro-optical monitor was designed and build for bunch length measurements at the Swiss FEL. It is based on a mode locked ytterbium fiber laser probing the field-induced birefringence in an electro-optically active crystal (GaP) with a chirped laser pulse. The setup allows the direct time resolved single-shot measurement of the Coulomb field (THz-radiation) of the electron beam -and therefore the bunch length- with an accuracy as good as 200fs. Simulations of the signals expected at the SwissFEL and the results of first test at the SLS linac will be presented.
PSI, Villigen
The PSI 250 MeV Injector, a precursor to the SwissFEL with its extreme jitter and stability demands poses new challenges for the synchronization system. Our concept is double-tracked: low risk electrical and best potential performance and flexibility optical. The electrical distribution system, being established first, relies on reliable technology. Optimized to achieve a benchmark jitter performance of around 10fs and a long term drift stability of some 10fs in the most critical parts of the machine it will also backup the optical system. Sub 10fs jitter and drift figures are being aspired for the latter. In this contribution, both systems are presented, measurements of electrical and optical reference signal jitter and long term cable and coupler drifts will be shown. A cable temperature stabilization system and the influence of mechanical noise will be discussed, too. Finally, first jitter measurements of the optical system will be presented.
SLAC, Menlo Park, California
ANL, Argonne, Illinois
We present the performance of the cavity beam position monitor (BPM) system for the Linac Coherent Light Source (LCLS) undulator at SLAC. The construction and installation phase of 36 BPMs have been completed. Commissioning is underway. The X-band cavity BPM employs a TM010 monopole reference cavity and a TM110 dipole cavity designed to operate at nominal center frequency of 11.384 GHz. The signal processing electronics features a low-noise single-stage three-channel heterodyne receiver that has selectable gain and phase locking local oscillator. The approximately 40MHz intermediate frequency is digitized to 16 bits at a 119 MHz sampling rate then reduced to baseband digitally. Phase and charge are normalized with respect to the reference cavities. System requirements include sub-micron position resolution for a single-bunch beam charge of 200 pC. Early commissioning results indicate single-bunch resolutions better than 500 nm rms and stabilities better than 1 micron drift over 24 hours.
INFN/LNF, Frascati (Roma)
ELETTRA, Basovizza
The single pass functionality available in the recent release of the Libera Brilliance software, takes particular interest when compared with requirements of FEL machines, that need stable and precise control of the beam trajectory throughout Linacs and transfer lines in order to meet the stringent beam quality and transverse position constraints inside undulators. Results from tests performed on Libera with beam from ELETTRA, SPARC and DAΦNE, operating in Sincrotrone Trieste and LNF Frascati, are reported to characterize the resolution of single shot transverse beam position measurements.
INFN/LNF, Frascati (Roma)
The SPARC FEL facility is under commissioning at the Frascati National Laboratories of INFN. The synchronization system is working as expected and various devices are used to monitor its performances. In particular this paper is focused on a comparison between the results obtained using different methods and instruments to perform laser, RF and beam synchronization measurements. Both electro-optical and full electrical techniques are used to obtain information about the phase noise of the RF fields inside the accelerating structures, the phase noise of the IR laser oscillator, the time of arrival of the laser UV pulse on the cathode and the time of arrival of the accelerated electron bunch at a selected reference position along the linac.
SLAC, Menlo Park, California
By scanning the electron beam energy in LCLS, the sharp K-edge absorption energies in nickel and yttrium were exploited to measure spectral features of x rays from a single undulator section. We show measurements obtained using a Ni foil, with beam energy tuned to scan the first harmonic across the K-edge, and similar measurements obtained using the yttrium component of a YAG screen, with the beam tuned to match the third harmonic. These spectral features allow the precise determination of the position of central ray, and provide some measure of the undulator K parameter. A refinement of this method should allow precise matching of the K parameters of multiple undulator sections after their installation in March 2009.
Uppsala University, Uppsala
Uni HH, Hamburg
DELTA, Dortmund
FYSIKUM, AlbaNova, Stockholm University, Stockholm
DESY, Hamburg
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin
We present very promising recent results from the optical replica synthesizer experiment in FLASH where we manipulate ultrashort electron bunches in FLASH with a laser in order to stimulate them to emit a coherent light pulse with the temporal structure of the electron bunches and subsequently analyze the light pulses with laser diagnostic (FROG) methods.