SLAC, Menlo Park, California, USA
SLAC, Menlo Park, California, USA
Paul Scherrer Institut, Villigen, Switzerland
Coherent diffraction imaging of complex molecules, like proteins, requires a large number of hard X-ray photons, ~10+13/pulse, within a time ~10 fs or less. This is equivalent to a peak power of about one TW, much larger than that currently generated by LCLS or other proposed X-ray FELs. We study the feasibility of producing such pulses from LCLS and the proposed LCLS-II, employing a configuration beginning with a SASE amplifier, followed by a "self-seeding" crystal monochromator [1], and finishing with a long tapered undulator. Results suggest that TW-level output power at 8 keV is possible, with a total undulator length below 200 m. We use a 40 pC electron bunch charge, normalized transverse emittance of 0.2-mm-mrad, peak current of 4 kA, and electron energy about 14 GeV. We present a tapering strategy that extends the original "resonant particle" formalism by optimizing the transport lattice to maximize optical guiding and enhance net energy extraction. We also discuss the transverse and longitudinal coherence properties of the output radiation pulse. Fluctuation of such a tapered FEL is studied with realistic jitter measured at LCLS and with start-to-end simulation.
LBNL, Berkeley, California, USA
SLAC, Menlo Park, California, USA
An analysis is performed on various possible errors that may occur throughout a hybrid undulator. Of particular significance is the scaling of the various errors with variations in the gap of the device. Tuning strategies are considered for the mitigation of these errors for the entire range of usable gap. Sorting strategies for the reduction of the initial errors in the undulator are also considered. Specifically, the effectiveness of the sorting algorithm is evaluated with respect to the number of permanent magnet blocks used per pole as well as the size and distribution of the block population. The results of this analysis are applied to the LCLS-II undulators to determine the required machining and positioning tolerances and viable tuning strategies in order to meet the design requirements.
SLAC, Menlo Park, California, USA
LBNL, Berkeley, California, USA
The SLAC National Accelerator Laboratory is constructing the new FEL user facility LCLS-II, as a major upgrade to the Linear Coherent Light Source (LCLS). The upgrade will include two new Free Electron Lasers, to generate soft (SXR) and hard X-ray (HXR) SASE FEL radiation, based on planar, variable gap hybrid undulators with two different undulator periods (SXR 55 mm, HXR 32 mm). An systematic FEL tolerance analysis for the undulator lines, including tuning, alignment, yaw deformation, and phase correction tolerances has been performed. The methods and results are presented in this work.
SLAC, Menlo Park, California, USA
In the era of SASE FELs, the demand for position stability of undulator components scales down to the range of sub-micrometers per day. Simultaneously, the undulator length increases significantly, in order to reach X-ray wavelengths. To minimize the impact of the outside environment, the LCLS undulator is placed underground, but reliable data about ground motion inside such a tunnel were not available in the required stability range. Therefore, a new position monitor system has been developed and installed for the LCLS undulator. That system is capable to measure X-, Y- and Roll positions of each of the 33 undulator quadrupoles, with respect to stretched wires. Instrument resolution is about 20 nm and instrument drift is negligible small. Position data of individual quadrupoles can be correlated along the entire undulator, which has a length of 132 m. The system is under continuous operation since 2009. The report describes long term experience with the running system and the observed position stability of the undulator quadrupoles.
SLAC, Menlo Park, California, USA
Control and knowledge of the spectrum of FEL X-ray radiation at the LCLS is important to the quality and interpretation of experimental results. Narrow bandwidth is useful in experiments requiring high-brightness beams. Wide bandwidth is particularly useful for photon energy calibration using absorption spectra. Since LCLS was commissioned in 2009 measurements have been made of average and single shot spectra of X-ray FEL radiation at the LCLS over a range of 800 to 8000 eV, for fundamental and harmonic radiation. These include correlations with chirp, bunch current, undulator K-taper, electron beam energy, and charge as well as some specialized machine configurations. In this paper we present results and discuss the relationship of the electron beam energy distribution to the observed X-ray spectrum.
SLAC, Menlo Park, California, USA
The FEL of the Linac Coherent Light Source (LCLS) at SLAC is generated in a 132 m long undulator. By introducing a kink in the undulator setup and launching different electron pulses with a small kick, we achieved two FEL beams with a separation of about 10 σ. These beams were separated at down stream mirrors and brought to the entrances of the soft and hard X-ray hutches. This was done at low energy creating soft X-rays which require only a shorter length to get to saturation. At high energy the whole undulator has to be "re-pointed" pulse by pulse. This can be done using 33 undulator correctors creating two straight lines for the photons with small angle to point the FEL to different mirrors pulse by pulse even at high energy. Experiments will be presented and further ideas discussed to get different energy photons created and sent to the soft and hard X-ray mirrors and experiments.
SLAC, Menlo Park, California, USA
Understanding and controlling the transverse size and distribution of FEL X-ray radiation of the LCLS at the SLAC National Accelerator Laboratory is discussed. Understanding divergence, source size, and distributions under various conditions is a convolution of many effects such as the electron distribution, the undulator alignment, micro-bunching suppression, and beta-match. Measurements of transverse size along the X-ray pulse and other studies designed to sort out the dominant effects are presented and discussed.