| Paper |
Title |
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| MOPKF072 |
Towards Attosecond X-ray Pulses from the FEL
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482 |
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- A. Zholents, J.M. Byrd, W. Fawley, Z. Hao, M.C. Martin, D. Robin, F. Sannibale, R.W. Schoenlein, M. Venturini, M.S. Zolotorev
LBNL, Berkeley, California
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The ability to study ultrafast phenomena has been recently advanced by the demonstrated production and measurement of a single, 650-attosecond, soft x-ray pulses precisely synchronized to the pump laser pulse consisted of just few optical cycles. The next frontier is a production of attosecond x-ray pulses at even shorter wavelengths. Here we propose the method of ?seeded attosecond x-ray radiation? where an isolated, attosecond duration, short-wavelength x-ray pulse is radiated by electrons selected by their previous interaction with a few-cycle, intense laser pulse. In principle this method allows excellent synchronization between the attosecond x-ray probe pulse and a pump source that can be the same few-cycle laser pulse or another signal derived from it.
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| MOPKF073 |
Design Study of the Bending Sections between Harmonic Cascade FEL Stages
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485 |
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- W. Wan, J.N. Corlett, W. Fawley, A. Zholents
LBNL, Berkeley, California
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The present design of LUX (linac based ultra-fast X-ray facility) includes a harmonic cascade FEL chain to generate coherent EUV and soft X-ray radiation. Four cascade stages, each consisting of two undulators acting as a modulator and a radiator, respectively, are envisioned to produce photons of approximate wavelengths 48 nm, 12 nm, 4 nm and 1 nm. Bending sections may be placed between the modulator and the radiator of each stage to adjust and maintain bunching of the electrons, to separate, in space, photons of different wavelengths and to optimize the use of real estate. In this note, the conceptual design of such a bending section, which may be used at all four stages, is presented. Preliminary tracking results show that it is possible to maintain bunch structure of nm length scale in the presence of errors, provided that there is adequate orbit correction and there are 2 families of trim quads and trim skew quads, respectively, in each bending section.
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| MOPKF074 |
Harmonic Cascade FEL Designs for LUX
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488 |
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- G. Penn, J.N. Corlett, W. Fawley, M. Reinsch, W. Wan, J.S. Wurtele, A. Zholents
LBNL, Berkeley, California
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LUX is a proposed facility for ultrafast X-ray science, based on an electron beam accelerated to GeV energies in a recirculating linac. Included in the design are short duration (200 fs or shorter FWHM) light sources using multiple stages of higher harmonic generation, seeded by a 190–250 nm laser of similar duration. This laser modulates the energy of a group of electrons within the electron bunch; this section of the electron bunch then produces radiation at a higher harmonic after entering a second, differently tuned undulator. Repeated stages in a cascade yield increasing photon energies up to 1 keV. Most of the undulators in the cascade operate in the low-gain FEL regime. Harmonic cascades have been designed for each pass of the recirculating linac up to a final electron beam energy of 3.1 GeV. For a given cascade, the photon energy can be selected over a wide range by varying the seed laser frequency and the field strength in the undulators. We present simulation results using the codes GENESIS and GINGER, as well as the results of analytical models which predict FEL performance. We discuss lattice considerations pertinent for harmonic cascade FELs, as well as sensitivity studies and requirements on the electron beam.
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| THPKF075 |
LUX - A Recirculating Linac-based Facility for Ultrafast X-ray Science
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2436 |
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- J.N. Corlett, W.A. Barletta, S. De Santis, L.R. Doolittle, W. Fawley, P.A. Heimann, S.R. Leone, D. Li, S.M. Lidia, G. Penn, A. Ratti, M. Reinsch, R.W. Schoenlein, J.W. Staples, G.D. Stover, S.P. Virostek, W. Wan, R. Wells, R.B. Wilcox, A. Wolski, J.S. Wurtele, A. Zholents
LBNL, Berkeley, California
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We present design concepts for LUX - a proposed source of ultra-fast synchrotron radiation pulses based on a recirculating superconducting linac. The source produces high-flux VUV-x-ray pulses with duration of 100 fs or less at a 10 kHz repetition rate, optimized for the study of ultra-fast dynamics across many fields of science. Cascaded harmonic generation in free-electron lasers (FEL's) produces coherent radiation in the VUV-soft x-ray regime, and a specialized technique is used to compress spontaneous emission for ultra-short-pulse photon production in the 1 - 10 keV range. High-brightness electron bunches of 2-3 mm-mrad emittance at 1 nC charge in 30 ps duration are produced in an rf photocathode gun and compressed to 3 ps duration following an injector linac, and recirculated three times through a 1 GeV main linac. In each return path, harmonic cascades are inserted to produce seeded FEL radiation in selected photon energy ranges from approximately 20 eV with a single stage of harmonic generation, to 1 keV with a four-stage cascade. The lattice is designed to minimize emittance growth from effects such as coherent synchrotron radiation (CSR), and to propagate electron beams carrying nm-scale density modulation in the final stages of cascaded harmonic generation. Synchronization of tens of femtoseconds is achieved by use of an optical master oscillator distributing timing signals over actively stabilized fiber, and generation of rf signals from the optical master oscillator. We describe technical developments in key areas including injection from a high repetition rate rf photocathode gun, lattice design, UV and soft x-ray production by high-gain harmonic generation, a kicker design for rapid transfer of the electron beam between radiator beamlines, lasers systems concepts, and synchronization between experimental pump lasers and the x-ray pulse.
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| TUPLT159 |
First Commissioning Experiments at DARHT-II
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1497 |
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- C. Ekdahl, E.O. Abeyta, L. Caudill, K.C.D. Chan, D. Dalmas, S. Eversole, R.J. Gallegos, J. Harrison, M. Holzscheiter, E. Jacquez, J. Johnson, B.T. McCuistian, N. Montoya, K. Nielsen, D. Oro, L. Rodriguez, P. Rodriguez, M. Sanchez, M. Schauer, D. Simmons, H.V. Smith, J. Studebaker, G. Sullivan, C. Swinney, R. Temple
LANL, Los Alamos, New Mexico
- H. Bender, W. Broste, C. Carlson, G. Durtschi, D. Frayer, D. Johnson, K. Jones, A. Meidinger, K. Moy, R. Sturgess, C.-Y. Tom
Bechtel Nevada, Los Alamos, New Mexico
- Y.-J. Chen, T. Houck
LLNL, Livermore, California
- S. Eylon, W. Fawley, E. Henestroza, S. Yu
LBNL, Berkeley, California
- T. Hughes, C. Mostrom
Mission Research Corporation, Albuquerque, New Mexico
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The second axis of the Dual Axis Radiographic Hydro-Test (DARHT) facility will provide up to four short(< 150 ns) radiation pulses for flash radiography of high-explosive driven implosion experiments[1]. The DARHT-II linear induction accelerator (LIA) will produce a 2-kA,18-MeV,2-micro-s electron beam. A fast kicker will cleave four short pulses out of the beam, which will focused onto a tantalum target for conversion to bremsstrahlung pulses for radiography. The first tests of the second axis accelerator were designed to demonstrate the technology, and to meet the modest performance requirements for closing out the DARHT-II construction project. These experiments demonstrated that we could indeed produce a 1.2 kA beam with pulse length 0.5-1.2 s and accelerate it to 12.5 MeV. These de-rated parameters were chosen to minimize risk of damage in these first experiments with this novel accelerator. The beam was stable to the BBU instability for these parameters. In fact, we had to reduce the magnetic guide field by a factor of 5 before any evidence of BBU was observed. We will discuss the results of these experiments and their implications, as well as our plans for continuing with DARHT-II commissioning.
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