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| TUPMN093 | A Kilohertz Picosecond X-Ray Pulse Generation Scheme | 1133 |
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| The duration of the x-ray pulse generated at a synchrotron light source is typically tens of picoseconds. Shorter pulses are highly desired by the users. In electron storage rings, the vertical beam size is usually orders of magnitude less than the bunch length due to radiation damping; therefore, a shorter pulse can be obtained by slitting the vertically tilted bunch. Zholents proposed tilting the bunch using rf deflection. We found that tilted bunches can also be generated by a dipole magnet kick. A vertical tilt is developed after the kick in the presence of non-zero chromaticity. The tilt was successfully observed and a 4.2-ps pulse was obtained fom a 27-ps electron bunch at the Advanced Photon Source. Based on this principle we propose a short-pulse generation scheme that produces picosecond x-ray pulses at a repetition rate of 1~2 kHz, which can be used for pump-probe experiments. The tilt phenomenon can also be utilized for machine parameter measurement. | ||
| TUPMN104 | A Design Study for Photon Diagnostics for the APS Storage Ring Short-Pulse X-ray Source | 1156 |
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Funding: Work supported by U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
A short x-ray pulse source based on the crab cavity scheme proposed by Zholents* is being developed at the Advanced Photon Source (APS). Photon diagnostics that visualizes the electron bunches with transverse momentum chirp and verifies the performance of the short x-ray pulse is required. We present a design study for the imaging diagnostics inside and outside of the crab cavity zone, utilizing both x-ray and visible synchrotron radiation. Several design options of monochromatic and polychromatic x-ray optics will be explored for their compatibility with the short-pulse source. The diagnostics outside of the crab cavity zone will be used to map out stable operation parameters of the storage ring with crab cavities, and to perform single-bunch single-pass imaging of the chirped bunch, which facilitates the tuning of the crab cavity rf phase and amplitude so the performance of the short pulse source can be optimized while other users around the ring will not be disturbed.
* A. Zholents et al., NIM A 425, 385 (1999). |
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| TUPMN091 | Planned Use of Pulsed Crab Cavities for Short X-ray Pulse Generation at the Advanced Photon Source | 1127 |
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Funding: Work supported by the U. S. Department of Energy, Office of Science, Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
In recent years, we have explored application to the Advanced Photon Source (APS) of Zholents'* crab-cavity-based scheme for production of short x-ray pulses. Work concentrated on using superconducting (SC) cavities in order to have a continuous stream of crabbed bunches and flexibility of operating modes. The challenges of the SC approach are related to the size, cost, and development time of the cavities and associated systems. A good case can be made for a pulsed system** using room-temperature cavities. APS has elected to pursue such a system in the near term, with the SC-based system planned for a later date. This paper describes the motivation for the pulsed system and gives an overview of the planned implementation and issues. Among these are overall configuration options and constraints, cavity design options, frequency choice, cavity design challenges, tolerances, instability issues, and diagnostics plans.
*A. Zholents et al., NIM A 425, 385 (1999).**P. Anfinrud, private communication. |
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| FRPMN110 | Transverse Multibunch Bursting Instability in the APS Storage Ring | 4360 |
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Funding: Work supported by U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. The horizontal bursting instability was first observed in a single bunch in the APS in 1998, soon after operation began. Above the instability threshold, the bursting is characterized by exponentially growing bunch centroid oscillations that saturate, then decay, repeating quasi-periodically. More recently, bursting was also observed with multiple bunches in both the horizontal and vertical planes, showing that this is not purely a single-bunch phenomenon. On the other hand, the multibunch instability threshold is strongly dependent on bunch spacing, and the dependence is markedly different for the two transverse planes. Depending on the bunch spacing, the bunch-to-bunch oscillations are sometimes coupled, sometimes not. In this paper, we discuss the threshold in terms of the chromaticity required to stabilize the beam. We present instability imaging data using a streak camera that shows the bunch-to-bunch oscillation phase, and turn-by-turn beam position histories that give the bursting time dependence for different bunch spacings. Finally, we discuss the machine impedance and measured tune shift with current. |
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| FRPMN112 | Far-Field OTR and ODR Images Produced by 7-GeV Electron Beams at APS | 4372 |
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Funding: Work supported by U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357 We have investigated the angular distribution patterns (far-field focus) of optical transition radiation (OTR) and optical diffraction radiation (ODR) generated by 7-GeV electron beams passing through and near an Al metal plane, respectively. The 70-μrad opening angles of the OTR patterns provide calibration factors for the system. Effects of the upstream quadrupole focusing strength on the patterns as well as polarization effects were observed. The OTR data are compared to an existing OTR single-foil model, while ODR profile results are compared to expressions for single-edge diffraction. ODR was studied with impact parameters of about 1.25 mm, close to the gamma λ?bar value of 1.4 mm for 628-nm radiation. We expect angle-pointing information along the x axis parallel to the mirror edge is available from the single-lobe ODR data as well as divergence information at the sub-100-μrad level. Experimental and model results will be presented. |
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| FRPMN115 | A Novel FPGA-Based Bunch Purity Monitor System at the APS Storage Ring | 4384 |
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Funding: Work supported by U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357 Bunch purity is an important source quality factor for the magnetic resonance experiments at the Advanced Photon Source. Conventional bunch-purity monitors utilizing time-to-amplitude converters are subject to dead time. We present a novel design based on a single field-programmable gate array (FPGA) that continuously processes pulses at the full speed of the detector and front-end electronics. The FPGA provides 7778 single-channel analyzers (six per RF bucket). The starting time and width of each single-channel analyzer window can be set to a resolution of 178 ps. A detector pulse arriving inside the window of a single-channel analyzer is recorded in an associated 32-bit counter. The analyzer makes no contribution to the system dead time. Two channels for each RF bucket count pulses originating from the electrons in the bucket. The other four channels on the early and late side of the bucket provide estimates of the background. A single-chip microcontroller attached to the FPGA acts as an EPICS IOC to make the information in the FPGA available to the EPICS clients. |
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| FRPMN118 | LCLS-S1 Optical Transition Radiation Monitor | 4396 |
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Funding: Work supported by the U. S. Department of Energy, under Contract Nos. DE-AC02-06CH11357 and DE-AC03-76SF00515. ANL has developed a high-resolution optical transition radiation (OTR) imaging monitor system for the LCLS injection linac at SLAC. The imaging station, OTR-S1, will be located at the S1 spectrometer with a beam energy of 135 MeV. The system will be used to acquire 2-D transverse beam distributions of the accelerated photocathode-gun-generated electron beam. We anticipate an average beam current of 0.2-1 nC and nominal beam spot size of σ-x 130 microns, σ-y 100 microns. The imaging system was designed for a field of view h/v: 10x7.5 mm. The spatial resolution of ~12 microns was verified over the central 5x4 mm region in the visible. A 12-bit digital camera acquires the image and a Mac-based digital frame capturing system was employed for the initial lab-based performance testing of the device. We are reporting on system development, image capture system, testing methodology, and test data analysis. Commissioning results will be reported as they become available. |