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Spencer, J.E.

Paper Title Page
TPAE015 Laser and Particle Guiding Micro-Elements for Particle Accelerators 1434
 
  • T. Plettner, R.M. Gaume, J. Wisdom
    Stanford University, Stanford, Califormia
  • J.E. Spencer
    SLAC, Menlo Park, California
 
  Funding: Department of Energy contract DE-AC02-76SF00515, DARPA contract DAAD19-02-1-0184.

Laser driven particle accelerators based on the current generation of lasers will require sub-micron control of the laser field as well as precise beam guiding. Hence the fabrication techniques that allow integrating both elements into an accelerator-on-chip format become critical for the success of such particle accelerators. Micromachining technology for silicon has been shown to be one such feasible technology in PAC2003 but with a variety of complications on the laser side. Fortunately, in recent years the fabrication of transparent ceramics has become an interesting technology that could be applied for laser-particle accelerators in several ways. We discuss this area, its advantages such as the range of materials it provides and various ways to implement it followed by some different test examples that have been considered. One important goal of this approach is an integrated system that could avoid the necessity of having to inject either laser or particle pulses into these structures.

 
TPAE027 Calculations for Tera-Hertz (THz) Radiation Sources 1994
 
  • J.E. Spencer, Y.A. Hussein
    SLAC, Menlo Park, California
 
  Funding: This work was supported by the U.S. Department of Energy under contract DE-2-76SF00515.

We explore possibilities for THz sources from 0.3 - 30 THz. While still inaccessible, this broad gap is even wider for advanced acceleration schemes extending from X or, at most, W band RF at the low end up to CO2 lasers. While the physical implementations of these two approaches are quite different, both are proving difficult to develop so that even lower frequency, superconducting RF seems to be the currently preferred means. Similarly, the validity of modelling techniques varies greatly over this range of frequencies but generally mandates coupling Maxwell’s equations to the appropriate device transport physics for which there are many options. Here we calculate radiation from shaped transmission lines using finite-difference, time-domain (FDTD) simulations of Maxwell’s equations coupled to Monte-Carlo techniques for both the production and transport physics of short electron pulses. Examples of THz sources that demonstrate coherent interference effects will be discussed with the goal of optimizing on-chip THz radiators for different applications - ultimately including improved electron sources and accelerators.

 
TPAE028 Beam Dynamics Studies for a Laser Acceleration Experiment 2024
 
  • J.E. Spencer, E.R. Colby, R.J. Noble, D.T. Palmer, R. Siemann
    SLAC, Menlo Park, California
 
  Funding: Support of this work was under U.S. Dept. of Energy contract DE-AC02-76SF00515.

The NLC Test Accelerator at SLAC was built to address various beam dynamics issues for the Next Linear Collider. An S-Band RF gun, originally proposed for the NLCTA, is being installed together with a large-angle extraction line at 60 MeV. This is followed by a matching section, final focus and buncher for the laser acceleration experiment, E163. The laser-electron interaction area is followed by a broad range, high resolution spectrometer (HES) for electron bunch analysis. The RF gun is discussed in another paper. We discuss only the beam dynamics and high resolution analysis system at 6 MeV based on using Parmela and high-order Transport for bunch charges from 50 pC to 1 nC. Beyond the diagnostics, this system uses the emittance compensating solenoids and a low energy, high resolution spectrometer (LES) to help tune for best operating point and match to the linac. Optical symmetries in the design of the 25.5° extraction line provide 1:1 phase space transfer without linear dispersion or use of sextupoles for a large, 6D phase space volume and range of input conditions. Tolerances and tuning sensitivities (knobs) for certain parts of the system are discussed.

 
TPAE029 High-Harmonic Inverse Free-Electron-Laser Interaction at 800 nm 2113
 
  • C.M.S. Sears, E.R. Colby, B.M. Cowan, R. Siemann, J.E. Spencer
    SLAC, Menlo Park, California
  • R.L. Byer, T. Plettner
    Stanford University, Stanford, Califormia
 
  Funding: This work supported by Department of Energy contracts DE-AC03-76SF00515 (SLAC) and DE-FG03-97ER41043-II (Stanford).

The inverse Free Electron Laser (IFEL) interaction has recently been proposed and used as a short wavelength modulator forμbunching of beams for laser acceleration experiments*,**. These experiments utilized the fundamental of the interaction between the laser field and electron bunch. In the current experiment, we explore the higher order resonances of the IFEL interaction from a 3 period, 1.8 centimeter wavelength undulator with a picosecond, 0.25 mJ/pulse laser at 800 nm. The resonances are observed by adjusting the gap of the undulator while keeping the beam energy constant. We will also discuss diagnostics for obtaining beam overlap and statistical techniques used to account for machine drifts and analyze the data.

*W. D. Kimura, et. al., Phys. Rev. S.T. Acc. & Beams 4 101301 (2001). ** P. Musumeci, et. al., AAC 2004 Proceedings. Pg 170.

 
TOPA008 First Observation of Laser-Driven Acceleration of Relativistic Electrons in a Semi-Infinite Vacuum Space 650
 
  • T. Plettner, R.L. Byer, T.I. Smith
    Stanford University, Stanford, Califormia
  • E.R. Colby, B.M. Cowan, C.M.S. Sears, R. Siemann, J.E. Spencer
    SLAC, Menlo Park, California
 
  Funding: Department of Energy DE-FG03-97ER41043.

We have observed acceleration of relativistic electrons in vacuum driven by a linearly polarized laser beam incident on a thin gold-coated reflective boundary. The observed energy modulation effect follows all the characteristics expected for linear acceleration caused by a longitudinal electric field. As predicted by the Lawson-Woodward theorem the laser driven modulation only appears in the presence of the boundary. It shows a linear dependence with the strength of the electric field of the laser beam and also it is critically dependent on the laser polarization. Finally, it appears to follow the expected angular dependence of the inverse transition radiation process.

 
WPAE034 Fast Neutron Damage Studies on NdFeB Materials 2351
 
  • J.E. Spencer, S.D. Anderson, R. Wolf
    SLAC, Menlo Park, California
  • A. Baldwin, D.E. Pellet
    UCD, Davis, California
  • M. Boussoufi
    UCD/MNRC, McClellan, California
  • J.T. Volk
    Fermilab, Batavia, Illinois
 
  Funding: Support of this work was under U.S. Dept. of Energy contracts DE-AC02-76SF00515, DE-AC02-76CH03000 and LCRD contract DE-FG02-03ER41280.

Many materials and electronics need to be tested for the radiation environment expected at linear colliders (LC) where the accelerator and detectors will be subjected to large fluences of hadrons, leptons and gammas over the life of the facility. Although the linacs will be superconducting, there are still many potential uses for NdFeB in the damping rings, injection and extraction lines and final focus. Our understanding of the radiation damage situation for rare earth permanent magnet materials was presented at PAC2003 and our first measurements of fast neutron, stepped doses at the UC Davis McClellan Nuclear Reactor Center (UCD MNRC) were presented at EPAC2004 where the damage appeared proportional to the distances between the effective operating points and Hc. Here we have extended those doses and included more commercial samples together with the induced radioactivities associated with their respective dopants. Hall probe data for the external induction distributions are compared with vector magnetization measurements for the different materials.