Consideration on the BPM alignment tolerance in X-ray FELs

Tanaka, Takashi; Kitamura, Hideo; Shintake, T.

doi:10.1016/j.nima.2004.04.040

Cited by 30 publications

(54 citation statements)

References 5 publications

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“…If the electron moves along a trajectory deviated from a straight line, the FEL gain is significantly reduced because of the mechanisms explained in [3,4].…”

Section: A Trajectory Errormentioning

confidence: 99%

“…The latter is in principle corrected by steering the electron beam so that it goes through the origins of beam position monitors (BPMs) that are aligned in line. It should be noted, however, that the alignment accuracy of BPMs with a conventional survey method is usually insufficient to achieve lasing, especially in the angstrom-wavelength region because the tolerance of the trajectory straightness becomes more stringent for shorter wavelengths [4].…”

Section: A Trajectory Errormentioning

confidence: 99%

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Undulator commissioning by characterization of radiation in x-ray free electron lasers

Tanaka

Goto

Hara

et al. 2012

Phys. Rev. ST Accel. Beams

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In x-ray free electron lasers (XFELs) where a long undulator composed of many segments is installed, there exist a number of error sources to reduce the FEL gain such as the trajectory error, K value discrepancy, and phase mismatch, which are related to the segmented-undulator structure. Undulator commissioning, which refers to the tuning and alignment processes to eliminate the possible error sources, is thus an important step toward realization of lasing. In the SPring-8 angstrom compact free electron laser (SACLA) facility, the undulator commissioning has been carried out by means of characterization of x-ray radiation, i.e., measurements of the spatial and spectral profiles of monochromatized spontaneous undulator radiation as well as by probing the FEL intensity. The achieved tuning and alignment accuracies estimated from the statistics of actual measurements in SACLA show the effectiveness of this commissioning scheme.

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“…If the electron moves along a trajectory deviated from a straight line, the FEL gain is significantly reduced because of the mechanisms explained in [3,4].…”

Section: A Trajectory Errormentioning

confidence: 99%

Section: A Trajectory Errormentioning

confidence: 99%

Undulator commissioning by characterization of radiation in x-ray free electron lasers

Tanaka

Goto

Hara

et al. 2012

Phys. Rev. ST Accel. Beams

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“…Because the overlap between them determines the strength of nonlinear interaction in order to form electron microbunches. Single-kick errors [6] due to position misalignments of the accelerator components decrease OF. For example, these misalignments are caused by position differences among the magnetic centers of quadrupole magnets and the error dipole field of the undulators.…”

Section: Introductionmentioning

confidence: 99%

Beam monitor system for an x-ray free electron laser and compact laser

Otake

Maesaka

Matsubara

et al. 2013

Phys. Rev. ST Accel. Beams

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A beam-monitor system for XFEL/SPring 8, ''SACLA,'' has been constructed. In order to maintain a stable self-amplified spontaneous emission (SASE) interaction, the straightness and overlap of the axes to within 3 m between the electron beams and the radiated x rays for an undulator section of about 100 m length is necessary. This straightness means relative alignment to an experimental target sample. Furthermore, a temporal stability of 30 fs in order to maintain a constant peak beam current is also necessary to conduct stable SASE lasing. The monitor system was developed to satisfy these spatial and temporal stability and resolution criteria. The system comprises spatial monitors, such as cavity-type beam-position monitors and screen monitors, as well as temporal measurement instruments, such as current monitors, waveguide spectrometers, coherent synchrotron-radiation detectors, a streak camera, and an rf deflector. Commissioning of SACLA started from March 2011, and the monitors performed sufficient roles to tune the beams for lasing. The achieved overall performances of the system, including data acquisition, are: the beam position monitor has a spatial resolution of 600 nm in rms; the bunchlength monitors show ability to observe bunch lengths from 1 ns in an injector with velocity bunching to less than 30 fs after three-stage bunch compressors. The less than 3 m spatial resolution of the screen monitor was also confirmed during practical beam operation. Owing to these fulfilled performances, such as the high spatial and temporal resolutions, stable lasing of SACLA has been achieved.

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“…Ref. [1] states that the gain degradation mainly comes from single kick errors (SKE) caused by mis-aligned quadrupole magnets, and error dipole fields of the undulators. To reduce the gain degradation, the angle of SKE should be well below a critical angle, y c , which is defined…”

Section: Introductionmentioning

confidence: 99%

“…In the case of the x-ray free-electron laser (XFEL) facility SACLA (SPring-8 Angstrom Compact free-electron LAser) [2], for example, consisting of a 8-GeV linear accelerator and a 100 mlong undulator beamline, y c at a wavelength of 0.1 nm is approximately 5 mrad [1]. Since the interval of BPMs is approximately 6 m in the undulator section, the beam position should be controlled within much less than 30 mm from a straight line.…”

Section: Introductionmentioning

confidence: 99%