A recirculating linac-based facility for ultrafast X-ray science Page: 3 of 3
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following undulator, tuned to a higher harmonic of the
seed laser. The electron pulse is then delayed in a short
chicane, and the process repeated by modulating a fresh
portion of the beam this time with the harmonic radiation
produced in the previous undulator. Using a tunable
optical parametric amplifier as the seed, and variable
undulators, allows significant tunability in four stages of
harmonic generation, variable flux up to 1013 photons per
pulse, and variable pulse duration depending on the seed
laser parameters . Two chains of cascaded harmonic
generation are proposed, providing exceptional flexibility
in producing EUV and soft x-ray pulses. Circular
polarization is attainable by use of elliptical undulators,
and flux stability of 0.1% or better is obtained in seconds
from random pulse-pulse flux variations of 10-20% at 10
kHz repetition-rate. The use of tapered undulators allows
tailoring of flux to individual experiments, to avoid space-
charge effects in, for example, photoemission processes.
Sophisticated laser systems will be an integral part of
the LUX facility, providing experimental excitation
pulses, stable timing signals, as well as the electron
source through the photocathode laser. Each endstation
will have it's own dedicated laser system and optical
manipulation and diagnostics, and optical tables and
equipment will be contained within a stable and controlled
environment. Multiple tuneable lasers covering a range of
267-3000 nm and pulse durations of 50 fs are required
for experiment initiation, together with temporal and
spatial filtering to optimize performance for specific
experimental applications. Distribution systems using
fibre-optic transmission lines will provide optical seed
pulses to each beamline, with feedback based on
interferometric measurements to stabilize the path lengths
. Developments in laser technology are expected to
result in significant improvements in the coming years,
which will be incorporated into our design with minimal
impact on accelerator systems.
Synchronization and timing of the ultra-short x-ray
pulses to the experimental excitation pulse is critical to
studies of ultra-fast dynamics. For LUX we propose to
generate inherently stable pulses by using seeded lasers
systems and bunch manipulation. In the case of EUV and
soft x-ray production, the cascaded harmonic generation
seed laser oscillator also drives the sample excitation laser,
resulting in timing stability of approximately 20 fs. For
our scheme of hard x-ray production by bunch
manipulation followed by x-ray pulse compression, we
find that the phase jitter of the deflecting cavities with
respect to the experimental laser pulse dominates timing
issues. Phase and amplitude feedback of the deflecting
cavities is expected to provide x-ray pulse to laser pulse
timing stability of 50 fs or better. To stabilize all timing
and rf signals in the facility, we propose to use a phase-
locked laser oscillator as the facility master oscillator. The
RF gun, linacs, and deflecting cavities may thus be phase-
locked to the experimental excitation lasers, and timing
jitter between the optical laser and the x-ray pulse emitted
by the beam minimized .
A recirculating linac user facility is proposed to addmss
the growing national and international need for ultrafast x-
ray scientific research. The LUX facility is based on
existing accelerator technology, coupled with an array of
advanced tunable femtosecond lasers, and is capable of
performing an enormous variety of pump-probe type
experiments with soft and hard x-rays. The facility has
been specifically designed with a view toward solving
problems in ultrafast science, and it's impact will be
across all fields of science, from biology, chemistry, and
physics, to novel areas such as quantum computing,
spintronics, and highly nonlinear phenomena.
 J. N. Corlett et al, "Feasibility study for a
recirculating linac-based facility for femtosecond
dynamics", LBNL formal report LBNL-51766, December
 J. N. Corlett, et al, " A Recirculating Linac Based
Synchrotron Light Source for Ultrafast X-ray Science",
Proc. EPAC'02, Paris, France, June 2002.
 L.-H. Yu et al, "High-Gain Harmonic-Generation Free-
Electron Laser", Science 289 932-934 (2000).
 A. Zholents et al "Generation of subpicosecond x-ray
pulses using RF orbit deflection", NIM A 425 (1999)
 J. Corlett et al, "Techniques for Synchronization of X-
ray Pulses to the Pump Laser in an Ultrafast X-ray
Facility", this conference.
 J. Staples et al, "The LBNL Femtosource 10 kHz
Photoinjector", this conference.
 S. Lidia et al, "An Injector for the Proposed Berkeley
Ultrafast X-Ray Light Source", this conference.
 D. Edwards et al, "The Flat Beam Experiment at the
FNAL Photoinjector", Proc. XXth International Linac
Conference, Monterey, 2000.
 A. Zholents et al, "Longitudinal phase-space control in
the Berkeley Femtosecond X-ray light source", this
 TESLA Technical Design Report, DESY 2001-011,
 L. Harwood, C. Reece, "CEBAF at 12 and 25 GeV",
Proc. SRF2001, Tsukuba, Japan, Sept. 2001.
 S. De Santis et al "Collective effects analysis for the
Berkeley femtosource", this conference
 R. Wells et al, "Recirculating linac vacuum system",
 D. Li et al, "Deflecting rf cavity design for a
recirculating linac-based facility for ultrafast x-ray
science", this conference.
 W. Fawley et al, "Simulation studies of an XUV/soft
x-ray harmonic-cascade FEL for the proposed LBNL
recirculating linac", this conference.
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Corlett, J.N; Barletta, W.A.; DeSantis, S.; Doolittle, L.; Fawley, W.M.; Green, M.A. et al. A recirculating linac-based facility for ultrafast X-ray science, article, May 6, 2003; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc737871/m1/3/: accessed September 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.