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Staples, J. W.

Paper Title Page
MOPAS028 Demonstration of Femtosecond-Phase Stabilization in 2 km Optical Fiber 494
  • J. W. Staples, J. M. Byrd, R. B. Wilcox
    LBNL, Berkeley, California
  Funding: *This work is supported by the Director, Office of Science, High Energy Physics, U. S. Dept. of Energy under Contract no. DE-AC02-05CH1121

Long-term phase drifts of less than a femtosecond per hour have been demonstrated in a 2 km length of single-mode optical fiber, stabilized interferometrically at 1530 nm. Recent improvements include a wide-band phase detector that reduces the possibility of fringe jumping due to fast external perturbations of the fiber and locking of the master CW laser wavelength to a molecular absorption line. Mode-locked lasers may be synchronized using two wavelengths of the comb, multiplexed over one fiber, each wavelength individually interferometrically stabilized.

WEPMN116 Plans for Precision RF Controls for FERMI@ELETTRA 2310
  • L. R. Doolittle, J. M. Byrd, A. Ratti, J. W. Staples, R. B. Wilcox
    LBNL, Berkeley, California
  • G. D'Auria, M. Ferianis, M. M. Milloch, A. Rohlev
    ELETTRA, Basovizza, Trieste
  • M. W. Stettler
    CERN, Geneva
  FERMI@ELETTRA is a 4th generation light source under construction at Sincrotrone Trieste. It will be operated as a seeded FEL driven by a warm S-band linac presently serving as the injector for the ELETTRA storage ring. Operation as an FEL driver places much more stringent specifications on control of the amplititude and phase of the RF stations than in its present operation. This paper describes a conceptual design of an upgrade to the RF controls to achieve these specifications. The system consists of a stabilized distribution of the master oscillator signal providing a reference to local digital RF controllers . The RF reference distribution system takes advantage of recent breakthroughs in optical techniques where stabilized fiber lasers are used to provide a very accurate control of RF phases over long distances. The RF controller is based on recent improvements on modern digital systems, using a 14-bit high speed digitizer in combination with an FPGA and high speed DAC. This paper also presents experimental results of early tests performed as a feasibility study of the system.  
WEPMN118 Mechanical Design and Analysis of a 200 MHz, Bolt-together RFQ for the Accelerator Driven Neutron Source 2313
  • S. P. Virostek, M. D. Hoff, D. Li, J. W. Staples, R. P. Wells
    LBNL, Berkeley, California
  Funding: This work was supported by the U. S. Dept. of Energy under Contract No. DE-AC02-05CH11231 and by the Dept. of Homeland Security's Domestic Nuclear Detection Office under Award No. HSHQPB-05-X-00033.

A high-yield neutron source to screen sea-land cargo containers for shielded Special Nuclear Materials (SNM) has been designed at LBNL. The Accelerator-Driven Neutron Source (ADNS) utilizes the D(d,n)3He reaction to produce a forward directed neutron beam. Key components are a high-current radio-frequency quadrupole (RFQ) accelerator and a high-power neutron production target capable of delivering a neutron flux of >107 n/(cm2 s) at a distance of 2.5 m. The mechanical design and analysis of the four-module, bolt-together RFQ will be presented here. Operating at 200 MHz, the 5.1 m long RFQ will accelerate a 40 mA deuteron beam to 6 MeV. At a 5% duty factor, the time-average d+ beam current on target is 1.5 mA. Each of the 1.27 m long RFQ modules will consist of four solid OFHC copper vanes. A specially designed 3-D O-ring will be used to provide vacuum sealing between both the vanes and the modules. RF connections are made by means of canted coil spring contacts. Quadrupole mode stabilization is obtained with a series of 60 water-cooled pi-mode rods. A set of 80 evenly spaced fixed slug tuners is used for final frequency adjustment and local field perturbation correction.

THPMN117 Design of a VHF-band RF Photoinjector with MegaHertz Beam Repetition Rate 2990
  • J. W. Staples, K. M. Baptiste, J. N. Corlett, S. Kwiatkowski, S. M. Lidia, J. Qiang, F. Sannibale, K. G. Sonnad, S. P. Virostek, R. P. Wells
    LBNL, Berkeley, California
  Funding: This work is supported by the Director, Office of Science, High Energy Physics, U. S. Dept. of Energy under Contract no. DE-AC02-05CH1121

New generation accelerator-based X-ray light sources require high quality beams with high average brightness. Normal conducting L- and S-band photoinjectors are limited in repetition rate and D-C (photo)injectors are limited in field strength at the cathode. We propose a low frequency normal-conducting cavity, operating at 50 to 100 MHz CW, to provide beam bunches at a rate of one MegaHertz or more. The photoinjector uses a re-entrant cavity structure, requiring less than 100 kW CW, with a peak wall power density less than 10 W/cm2. The cavity will support a vacuum down to 10 picoTorr, with a load-lock mechanism for easy replacement of photocathodes. The photocathode can be embedded in a magnetic field to provide correlations useful for flat beam generation. Beam dynamics simulations indicate that normalized emittances on the order of 1 mm-mrad are possible with gap voltage of 750 kV, with fields up to 20 MV/m at the photocathode, for 1 nanocoulomb charge per bunch after acceleration and emittance compensation. Long-bunch operation (10's of picosecond) is made possible by the low cavity frequency, permitting low bunch current at the 750 kV gap voltage.

TUPMN109 A High Repetition Rate VUV-Soft X-Ray FEL Concept 1167
  • J. N. Corlett, J. M. Byrd, W. M. Fawley, M. Gullans, D. Li, S. M. Lidia, H. A. Padmore, G. Penn, I. V. Pogorelov, J. Qiang, D. Robin, F. Sannibale, J. W. Staples, C. Steier, M. Venturini, S. P. Virostek, W. Wan, R. P. Wells, R. B. Wilcox, J. S. Wurtele, A. Zholents
    LBNL, Berkeley, California
  Funding: This work was supported by the Director, Office of Science, High Energy Physics, U. S. Department of Energy under Contract No. DE-AC02-05CH11231.

The FEL process increases radiation flux by several orders of magnitude above existing incoherent sources, and offers the additional enhancements attainable by optical manipulations of the electron beam: control of the temporal duration and bandwidth of the coherent output, and wavelength; utilization of harmonics to attain shorter wavelengths; and precise synchronization of the x-ray pulse with laser systems. We describe an FEL facility concept based on a high repetition rate RF photocathode gun, that would allow simultaneous operation of multiple independent FELs, each producing high average brightness, tunable over the soft x-ray-VUV range, and each with individual performance characteristics determined by the configuration of the FEL SASE, enhanced-SASE (ESASE), seeded, self-seeded, harmonic generation, and other configurations making use of optical manipulations of the electron beam may be employed, providing a wide range of photon beam properties to meet varied user demands. FELs would be tailored to specific experimental needs, including production of ultrafast pulses even into the attosecond domain, and high temporal coherence (i.e. high resolving power) beams.

FROAC05 Systems Design Concepts for Optical Synchronization in Accelerators 3807
  • R. B. Wilcox, J. W. Staples
    LBNL, Berkeley, California
  Funding: This work is supported by the Director, Office of Science, High Energy Physics, U. S. Dept. of Energy under Contract no. DE-AC02-05CH1121

Development of accelerator-based light sources is expanding the size of femtosecond laser systems from tabletop devices up to kilometer-scale facilities. New optical techniques are needed to maintain temporal stability in these large systems. We present methods for distributing timing information over optical fiber using continuous optical waves, and how these can be employed in advanced accelerators requiring less than 100fs timing stability. Different techniques combine to form a tool set that can provide for synchronization down to a few femtoseconds. Practical examples are given for timing systems applicable to FELs now under construction, with experimental results to show these systems can be built with required performance. For example, have demonstrated 2km fiber links with 5fs timing stability over 24 hours, and synchronized femtosecond lasers separated by a fiber link with 20fs RMS relative jitter.