SLAC, Menlo Park, California
BINP SB RAS, Novosibirsk
Funding: Work supported by the U.S. Department of Energy under contract number DE-AC02-76SF00515.
For proper operation of the LCLS x-ray free-electron laser, measurement and control of the electron bunch longitudinal phase space is critical. The LCLS accelerator includes two bunch compressor chicanes to magnify the peak current. These magnetic chicanes can generate significant coherent synchrotron radiation (CSR), which can distort the phase space distribution. We propose a diagnostic scheme by exciting a weak skew quadrupole at an energy-chirped, high dispersion point in the first bunch compressor (BC1) to reconstruct longitudinal phase space on an OTR screen after BC1, allowing a detailed characterization of the CSR effects.
SLAC, Menlo Park, California
Funding: Work supported by Department of Energy contract DE-AC03-76SF00515.
The beam stability for the Linac Coherent Light Source (LCLS) at SLAC is important for good X-Ray operation. Although most of the jitter tolerances are met, there is always room for improvement. Besides the short term pulse-to-pulse jitter, we will also discuss oscillation sources of longer time cycles from seconds (feedbacks), to minutes (cooling systems), and up to the 24 hours caused by the day-night temperature variations.
SLAC, Menlo Park, California
Funding: Work supported by Department of Energy contract DE-AC03-76SF00515.
The electron beam for the Linac Coherent Light Source (LCLS) at SLAC is accelerated by disk-loaded RF structures over a length of 1 km. The mainly longitudinal field can sometimes exhibit transverse components, which kick the beam in x and/or y. This is normally a stable situation, but when a klystron, which powers some of these structures, has to be switched off and another one switched on, different kicks can lead to quite a different orbit. Some klystrons, configured in an energy and bunch length feedback, caused orbit changes of up to 1 mm, which is about 20 times the σ beam size. The origins and measurements of these kicks and some efforts (orbit bumps) to reduce them will be discussed.
SLAC, Menlo Park, California
UCLA, Los Angeles, California
The Linac Coherent Light Source (LCLS) is an x-ray Free-electron Laser (FEL) being commissioned at SLAC. Recent beam measurements have shown that, using the LCLS injector-linac-compressors, the beam emittance is very small at 20 pC*. A similar low charge operation mode was also suggested and studied**. In this paper we perform start-to-end simulations of the entire accelerator including the FEL undulator and study the FEL performance versus the bunch charge. At 20 pC charge, these calculations associated with the measured beam parameters suggest the possibility of generating a longitudinally coherent single x-ray spike with 2-femtosecond duration at a wavelength of 1.5 nm. At ~100 pC charge level, our simulations show an x-ray pulse with 20 femtosecond duration and up to 1012 photons at a wavelength of 1.5 Å. These results open exciting possibilities for ultrafast science and single shot molecular imaging.
*A. Brachmann et. al., to be published.
**J. Rosenzweig et al., Nuclear Instr. and Meth. A 593, 39-44 (2008); S. Reiche et al., Nucl. Instr. And Meth. A 593, 45-48 (2008).
SLAC, Menlo Park, California
ELETTRA, Basovizza
Funding: Work supported by the U.S. Dept. of Energy contract #DE-AC02-76SF00515.
The Linac Coherent Light Source (LCLS) is an x-ray Free-Electron Laser (FEL) project presently in a commissioning phase at SLAC. The very bright electron beam required for the FEL is also susceptible to a micro-bunching instability* in the magnetic bunch compressors, prior to the FEL undulator. The uncorrelated electron energy spread can be increased by an order of magnitude to provide strong Landau damping against the instability without degrading the free-electron laser performance. To this end, a ‘laser-heater’ system has been installed in the LCLS injector, which modulates the energy of a 135-MeV electron bunch with an IR laser beam in a short undulator, enclosed within a four-dipole chicane. The last half of the chicane time-smears the energy modulation leaving an effective thermal energy spread increase. We present the first commissioning results of this system, its operational issues, and its impact on the micro-bunching instability.
*Z. Huang et. al., Phys. Rev. ST Accel. Beams 7, 074401 (2004).
SLAC, Menlo Park, California
Funding: This work is supported by the Department of Energy contract DE-AC02-76SF00515.
LCLS capabilities can be significantly extended with a second undulator aiming at the soft x-ray spectrum (1- 5 nm). To allow for simultaneous hard and soft x-ray operations, 14 GeV beams at the end of the LCLS accelerator can be intermittently switched into the SLAC A-line (the beam transport line to End Station A) where the second undulator may be located. In this paper, we discuss the A-line optics design for transporting the high-brightness LCLS beams using the existing tunnel. To preserve the high brightness of the LCLS beams, special attentions are paid to effects of incoherent and coherent synchrotron radiation. Start-to-end simulations using realistic LCLS beam distributions are carried out.
SLAC, Menlo Park, California
ASCo, Clayton, Victoria
Funding: Work supported by Department of Energy contract DE-AC02-76SF00515. This work was performed in support of the LCLS project at SLAC
The Linac Coherent Light Source is an x-ray Free-Electron Laser (FEL) project being commissioned at SLAC. The very bright electron beam required for the FEL is subjected to various sources of jitter along the accelerator. The peak current, centroid energy, and trajectory of the electron bunch are controlled precisely at the highest repetition rate possible with feedback systems. We report commissioning experience for these systems. In particular, there is high frequency content in the electron bunch current spectrum, and we report its impact on the systems. Due to the coupling of the betatron motion and the dispersion component of the electron trajectory, a fast in-line model* is incorporated. For the longitudinal feedback, we report the performance of two different configurations: one with RF system as direct actuators, which are nonlinear, and the other with artificially formed linear energy and energy-chirp actuators. Since the electron bunch is compressed to a final peak current of 2 to 3 kA, coherent synchrotron radiation and other wakefields are included for precise control of the electron bunch parameters. Machine performance is compared to start-to-end simulations.
*P. Chu et al., these PAC09 proceedings
SLAC, Menlo Park, California
Funding: Work supported by the U.S. Dept. of Energy contract #DE-AC02-76SF00515.
The Linac Coherent Light Source (LCLS) is a SASE 1.5-15 Å x-ray Free-Electron Laser (FEL) facility under construction at SLAC, and presently in an advanced phase of commissioning. The injector, linac, and new bunch compressors were commissioned in 2007 and 2008, establishing the necessary electron beam brightness at 14 GeV. The final phase of commissioning, including the FEL undulator and the long transport line from the linac, began in November 2008, with first 1.5-Å FEL light and saturation observed in mid-April 2009. We report on the accelerator, undulator, and FEL operations, although prior to the availability of the full x-ray diagnostics suite, which will not be ready until June 2009.
