SLAC, Menlo Park, California, USA
The SLAC National Accelerator Laboratory has been running the Linac Coherent Light Source (LCLS), the first x-ray Free Electron Laser since 2009. Undulator magnet damage from radiation, produced by the electron beam traveling through the 133-m long straight vacuum tube, has been and is a concern. A damage measurement experiment has been performed in 2007 in order to obtain dose versus damage calibrations. Radiation reduction and detection devices have been integrated into the LCLS undulator system. The accumulated radiation dose rate was continuously monitored and recorded. In addition, undulator segments have been routinely removed from the beamline to be checked for magnetic (50 ppm, rms) and mechanic (about 0.25 μm, rms) changes. A reduction in strength of the undulator segments is being observed, at a level, which is now clearly above the noise. Recently, potential sources for the observed integrated radiation levels have been investigated. The paper discusses the results of these investigation as well as comparison between observed damage and measured dose accumulations and discusses, briefly, strategies for the new LCLS-II upgrade, which will be operating at more than 300 times larger beam rate.
MOP050
SLAC, Menlo Park, California, USA
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Minimizing beam loss is particularly important for LCLS-II because of very high average power beams, radiation sensitive undulators, and the high cost of adding shielding to existing accelerator enclosures. For example, for acceptable undulator magnet lifetime, dark current originating at the cathode must be attenuated by approximately a factor of 10-7 in a single pass before it reaches the undulator. Multi-stage, high-efficiency collimation is necessary. The system is described in this paper. A model of beam halo and dark current is developed that includes sources due to Touschek, intra-beam, and beam-gas scattering, as well as field emission from superconducting cavities, photo-emission from stray light on the cathode, and cathode field emission. The location and gap of the collimators is optimized using tracking analysis and other tools developed and validated at Cornell. Collimator efficiency is estimated by tracking secondaries using a modified version of Lucretia which call GEANT4. Finally collimator jaw design is optimized to produce a minimum leakage using FLUKA. These topics are discussed in this paper.
SLAC, Menlo Park, California, USA
Overcompression of the Linac Coherent Light Source (LCLS) x-ray Free Electron Laser (FEL) at the SLAC National Accelerator Center is studied. The studies and operational implications are summarized in this talk.
TUC02
SLAC, Menlo Park, California, USA
LBNL, Berkeley, California, USA
PSI, Villigen PSI, Switzerland
DESY, Hamburg, Germany
SLAC, Menlo Park, California, USA
LBNL, Berkeley, California, USA
Fermilab, Batavia, Illinois, USA
The LCLS-II is an FEL facility proposed in response to the July 2013 BESAC advisory committee, which recommended the construction of a new FEL light source with a high-repetition rate and a broad photon energy range from 0.2 keV to at least 5 keV. A new CW 4-GeV electron linac is being designed to meet this need, using a superconducting (SC) L-band (1.3 GHz) linear accelerator capable of operating with a continuous bunch repetition rate up to 1 MHz at ~16 MV/m. This new 700-m linac is to be built at SLAC in the existing tunnel, making use of existing facilities and providing two separate FELs, preserving the operation of the existing FEL, which can be fed from either the existing copper or the new SC linac. We briefly describe the acceleration, bunch compression, beam transport, beam switching, and electron beam diagnostics. The high-power and low-level RF, and cryogenic systems are described elsewhere.
