SLAC, Menlo Park, California
UW-Madison/SRC, Madison, Wisconsin
FEL/Duke University, Durham, North Carolina
DEEI, Trieste
A single-pass high-gain x-ray free electron laser (FEL) calls for a high quality electron bunch. In particular, for a seeded FEL amplifier and for a harmonic generation FEL, the electron bunch initial energy profile uniformity and peak current uniformity are crucial for generating an FEL with a narrow bandwidth. After the acceleration, compression, and transportation, the electron bunch energy profile entering the undulator can acquire temporal non-uniformity both in energy and local density. We study the effects of the electron bunch initial energy profile non-uniformity and local density variation on the FEL performance. Intrinsically, for a harmonic generation FEL, the harmonic generation starts with an electron bunch having energy modulation as well as density bunching at the previous stage FEL wavelength and its harmonics. Its effect on the harmonic generation FEL in the radiator is then studied.
SLAC, Menlo Park, California
LLNL, Livermore, California
The Linac Coherent Light Source (LCLS) is a Free Electron Laser (FEL) operating with a fundamental wavelength ranging from 1.5-0.15 nm. Characterization of the higher harmonics present in the beam is important to users, for whom harder X-rays can either extend the useful operating wavelength range or represent a background to measurements. We present here measurements of the power in both the second and third harmonics.
SLAC, Menlo Park, California
The Linac Coherent Light Source at SLAC is a hard X-ray FEL which was designed for single electron bunch operation. Although most user experiments are not interested in multiple bunches from an S-band linac due to their short (ns) separation, there are some advantages with multi-bunch operation. Starting with two bunches where the delayed light of one bunch is used to seed the light of a second bunch, to many more bunches to increase the likelihood of rare target collisions, multi-bunch operation would open more options for the LCLS. In the past the SLAC Linac has operated with a few dedicated bunches for the SLC (Stanford Linear Collider), and up to 1400 bunches for some fixed target experiments, so a few bunches for the LCLS seems possible even with the original single bunch design. This paper will describe how the current RF implementation supports multi-bunch operation. Initial experimental tests with two bunches are presented.
SLAC, Menlo Park, California
This talk is about the experience gained in commissioning the X-Ray diagnostics at the LCLS over the past year. Though the designs of the diagnostics are based largely on technology from synchrotron light sources, the high intensity and high brightness of LCLS X-Ray beam are well outside of the range of parameters for synchrotron light sources, so the diagnostics must perform in essentially new territory. It turned out that some capabilities of the diagnostics were not utilized because the FEL beam was so strong right from the beginning. On the other hand, in some cases the diagnostics were used to perform novel measurements that were not envisioned in the original design. The talk will cover each of the diagnostics systems, how it performed, and what it told us about the FEL beam.
SLAC, Menlo Park, California
During undulator commissioning of the Linac Coherent Light Source (LCLS) x-ray Free Electron Laser (FEL) at the SLAC National Accelerator Laboratory it was shown that saturation lengths much shorter than the installed length of the undulator line can routinely be achieved. This frees undulator segments that can be used to provide enhanced spectral properties and at the same time, test the concept of FEL Afterburners. In December 2009 a project was initiated to convert undulator segments at the down-beam end of the undulator line into Second Harmonic Afterburners (SHAB) to enhance LCLS radiation levels in the 10 20 keV energy range. This is being accomplished by replacement of gap-shims increasing the fixed gaps from 6.8 mm to 9.9 mm, which reduces their K values from 3.50 to 2.25 and makes the segments resonant at the second harmonic of the upstream unmodified undulators. The paper reports experimental results of the commissioning of the SHAB extension to LCLS.