| Paper | Title | Page |
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| THBAU05 | Precision Measurement of the Undulator K Parameter using Spontaneous Radiation | 548 |
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| Obtaining a precise and uniform value of the undulator parameter, K, over the full undulator length is critical for producing high-gain FEL radiation, especially in a hard x-ray source such as the LCLS. At an FEL wavelength of 1.5-Å the relative variation of K over the full undulator must be (dK/K)rms < 0.015%. Transverse misalignments, construction errors, radiation damage, and temperature variations all contribute to a different K value in each few-meter-long undulator segment. It is therefore important to measure relative K precisely, after installation and alignment, using beam-based techniques, if possible. We propose a fairly simple method using the angle-integrated spontaneous radiation spectrum of two interfering undulators, and the natural shot-to-shot energy centroid jitter of the electron beam, to measure the relative K error between two segments using both ideal and measured undulator fields. By 'leap-frogging' to different pairs of undulators with extended separations we hope to confirm or correct the value of K, including proper tapering, over the entire 130-m long FEL undulator. | ||
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| THPPH056 | Initial Search for 9-keV XTR from a 28-GeV Beam at SPPS* | 714 |
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| The potential to use x-ray transition radiation (XTR) as a beam diagnostic and coherent XTR (CXTR) as a gain diagnostic in an x-ray FEL was proposed previously. At that time we noted that the unique configuration of the SLAC Sub-picosecond Photon Source (SPPS) with its known x-ray wiggler source, a special three-element x-ray monochromator, x-ray transport line, and experimental end station with x-ray detectors made it an ideal location for an XTR feasibility experiment. A test of XTR intensity with respect to the x-rays emitted by the SPPS wiggler was proposed. The three-element monochromator was first adjusted to transport 9-keV or 1.3-Angstrom x rays from the SPPS wiggler source to the camera. The expected source strength in the bandpass of the monochromator was about 2x107 photons per 3 nC electron pulse, and our calculated XTR intensity was about 103 photons. We first successfully imaged the SPPS x-ray beam with the ANDOR x-ray CCD by using an Al-foil attenuation of 4x103. The wiggler gap was then opened, and x-ray images recorded with the Ti foils out for background evaluation and with the Ti foils inserted to search for XTR. Initial images will be presented. | ||
| FRAAU05 | Quantitative Detection of Femtosecond X-Ray Pulses | 802 |
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A detection system for femtosecond X-ray pulses has been developed within close cooperation between the Deutsche Elektronen-Synchrotron in Hamburg and the Physikalisch-Technische Bundeanstalt in Berlin. It is based on photoionization of xenon gas and, hence, radiation hard. Photoions generated are extracted by an electric field and, in contrast to former devices developed for the vacuum-ultraviolet spectral range*, detected by an amplifying open electron multiplier. Operation is performed at low gas pressure in the range between 0.1 and 0.01 Pa. Thus, the detector is almost transparent and may be used as a fast online monitor for quantitative and pulse-resolved determination of photon numbers and pulse energies of X-ray free electron lasers. After design and construction, a prototype has been successfully characterized and calibrated for photon energies from 4 to 10 keV in the PTB laboratory at the electron storage ring BESSY II in Berlin. First application has recently been realized in collaboration with the Linear Coherent Light Source at the Sub-Picosecond Pulse Source in Stanford with up to 1·106 photons per pulse detected at a photon energy of 9.4 keV.
* M. Richter et al., Appl. Phys. Lett. 83, 2970-2972 (2003) |
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