50 research outputs found
Use of Coherent Transition Radiation to Set Up the APS RF Thermionic Gun to Produce High-Brightness Beams for SASE FEL Experiments
We describe use of the Advanced Photon Source (APS) rf thermionic gun, alpha
magnet beamline, and linac to produce a stable high-brightness beam in excess
of 100 amperes peak current with normalized emittance of 10 pi mm-mrad. To
obtain peak currents greater than 100 amperes, the rf gun system must be tuned
to produce a FWHM bunch length on the order of 350 fs. Bunch lengths this short
are measured using coherent transition radiation (CTR) produced when the rf gun
beam, accelerated to 40 MeV, strikes a metal foil. The CTR is detected using a
Golay detector attached to one arm of a Michelson interferometer. The alpha
magnet current and gun rf phase are adjusted so as to maximize the CTR signal
at the Golay detector, which corresponds to the minimum bunch length. The
interferometer is used to measure the autocorrelation of the CTR radiation. The
minimum phase approximation is used to derive the bunch profile from the
autocorrelation. The high-brightness beam is accelerated to 217 MeV and used to
produce SASE in five APS undulators installed in the Low- Energy Undulator Test
Line (LEUTL) experiment hall. Initial optical measurements showed a gain length
of 1.3 m at 530 nm. * Work supported by U. S. Department of Energy, Office of
Basic Energy Sciences, under Contract No. W-31-109-ENG-38.Comment: LINAC2000 MOB17 3 pages 8 figure
Imaging Techniques for Relativistic Beams: Issues and Limitations
Characterizations of transverse profiles for low-power beams in the
accelerators of the proposed linear colliders (ILC and CLIC) using imaging
techniques are being evaluated. Assessments of the issues and limitations for
imaging relativistic beams with intercepting scintillator or optical transition
radiation screens are presented based on low-energy tests at the Fermilab A0
photoinjector and are planned for the Advanced Superconducting Test Accelerator
at Fermilab.Comment: 8 pages, 11 Figures, LCWS1
Synchronization and Characterization of an Ultra-Short Laser for Photoemission and Electron-Beam Diagnostics Studies at a Radio Frequency Photoinjector
A commercially-available titanium-sapphire laser system has recently been
installed at the Fermilab A0 photoinjector laboratory in support of
photoemission and electron beam diagnostics studies. The laser system is
synchronized to both the 1.3-GHz master oscillator and a 1-Hz signal use to
trigger the radiofrequency system and instrumentation acquisition. The
synchronization scheme and performance are detailed. Long-term temporal and
intensity drifts are identified and actively suppressed to within 1 ps and
1.5%, respectively. Measurement and optimization of the laser's temporal
profile are accomplished using frequency-resolved optical gating.Comment: 16 pages, 17 figures, Preprint submitted to Elsevie
High-Brightness Beams from a Light Source Injector: The Advanced Photon Source Low-Energy Undulator Test Line Linac
The use of existing linacs, and in particular light source injectors, for free-electron laser (FEL) experiments is becoming more common due to the desire to test FELs at ever shorter wavelengths. The high-brightness, high-current beams required by high-gain FELs impose technical specifications that most existing linacs were not designed to meet. Moreover, the need for specialized diagnostics, especially shot-to-shot data acquisition, demands substantial modification and upgrade of conventional linacs. Improvements have been made to the Advanced Photon Source (APS) injector linac in order to produce and characterize high-brightness beams. Specifically, effort has been directed at generating beams suitable for use in the low-energy undulator test line (LEUTL) FEL in support of fourth-generation light source research. The enhancements to the linac technical and diagnostic capabilities that allowed for self-amplified spontaneous emission (SASE) operation of the FEL at 530 nm are described. Recent results, including details on technical systems improvements and electron beam measurement techniques, will be discussed. The linac is capable of accelerating beams to over 650 MeV. The nominal FEL beam parameters used are as follows: 217 MeV energy; 0.1-0.2% rms energy spread; 4-8 um normalized rms emittance; 80-120 A peak current from a 0.2-0.7 nC charge at a 2-7 ps FWHM bunch
Characterizing Transverse Beam Dynamics at the APS Storage Ring Using a Dual-Sweep Streak Camera
Abstract. We present a novel techniquefor characterizingtransverse beam dynamics using a dual-sweep streak camera. The camera is used to record the front view of successive beam bunches and/or successive turns of the bunches. This extension of the dual-sweep technique makesit possible to display non-repeatablebeam transverse motion in two fast and slow time scales of choice, and in a single shot. We present a study of a transverse multi-bunch instability in the AM storage ring. The positions, sizes, and shapes of 20 bunches (2.84 ns apart) in the train, in 3 to 14 successive turns (3.68 w apart) are recorded in a single image, providing rich information about the unstable beam. These include the amplitude of the oscillation(-0.0 at the head of the train and -2 mm towards the end of the train), the bunch-tobunch phase difference, and the significant transverse size growth withh the train. In the second example, the technique is used to characterize the injection-kicker induced beam motion, in support of the planned storagering top-up operation. By adjustingthe time scale of the dual sweep, it clearly shows the amplitude (d.8mm) and direction of tie kick, and the subsequent decoherence (-500 turns) and damping (-20 ms) of the stored beam. Since the storagering has an insertion device chamber with full vertical aperture of 5 mm, it is of special interestto track the vertical motion of the beam. An intensified gated camera was used for this purpose. The turn-by-turn x-y motion of a single-bunch beam was recorded and used as a diagnosticfor coupling correction. Images taken with uncorrectedcoupling will be presented. .