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| WEXKI02 |
Demonstration of Optical Microbunching and Net Acceleration at 0.8 microns
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1894 |
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- C. M.S. Sears, E. R. Colby, R. Ischebeck, C. Mcguinness, R. Siemann, J. E. Spencer, D. R. Walz
SLAC, Menlo Park, California
- R. L. Byer, T. Plettner
Stanford University, Stanford, Califormia
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Formation, diagnosis, and acceleration of electron microbunches from an rf linac generated beam is presented. A PM-EM hybrid IFEL/chicane buncher was designed and commissioned to produce optical bunch trains suitable for injection into solid-state laser accelerators. Microbunching is independently diagnosed via coherent optical tranisition radiation (COTR). Net acceleration is obtained by splitting the laser power between the IFEL and an inverse transition radiation (ITR) accelerator.
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Slides
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| THPMS050 |
Designing Photonic Bandgap Fibers for Particle Acceleration
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3103 |
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- R. J. Noble, E. R. Colby, B. M. Cowan, C. M.S. Sears, R. Siemann, J. E. Spencer
SLAC, Menlo Park, California
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Funding: Supported by U. S. Dept. of Energy contract DE-AC02-76SF00515
Photonic bandgap (PBG) fibers with hollow core defects have been suggested for use as laser driven accelerator structures. The modes of a periodic PBG fiber lie in a set of allowed bands. A fiber with a central vacuum defect can support so-called defect modes with frequencies in the bandgap and electromagnetic fields confined spatially near the central defect. A defect mode suitable for relativistic particle acceleration must have a longitudinal electric field in the central defect and a phase velocity near the speed of light (SOL). We explore the design of the defect geometry to support well-confined accelerating modes in such PBG fibers. The details of the surface boundary separating the defect from the surrounding matrix are found to be the critical ingredients for optimizing the accelerating mode properties. We give examples of improved accelerating modes in fiber geometries with modified defect surfaces.
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| THPMS052 |
Optical Wakefield from a Photonic Bandgap Fiber Accelerator
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3106 |
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- C. M.S. Sears, E. R. Colby, B. M. Cowan, R. Ischebeck, C. Mcguinness, R. J. Noble, R. Siemann, J. E. Spencer, D. R. Walz
SLAC, Menlo Park, California
- R. L. Byer, T. Plettner
Stanford University, Stanford, Califormia
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Photonic Bandgap (PBG) structures have recently been proposed as optical accelerators for there high coupling impedance and high damage threshold (>2 GV/m). As a first step in preparing a PBG accelerator, we propose to first observe the optical wakefield induced incoherently by an electron beam traversing the structure in the absence of a coupled laser pulse. The electrons are coupled into the fiber via a permanent magnet quadrupole triplet. The electrons excite fiber modes with speed-of-light phase velocities. By observing the wakefield using a spectrometer, the accelerating mode frequencies are determined.
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| THPMS055 |
Beam Dynamics Measurements for the SLAC Laser Acceleration Experiment
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3115 |
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- J. E. Spencer, E. R. Colby, R. Ischebeck, D. J. McCormick, C. Mcguinness, J. Nelson, R. J. Noble, C. M.S. Sears, R. Siemann
SLAC, Menlo Park, California
- T. Plettner
Stanford University, Stanford, Califormia
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Funding: Work supported by U. S. Dept. of Energy contract DE-AC02-76SF00515.
The NLC Test Accelerator (NLCTA) at SLAC was built to address various beam dynamics issues for the Next Linear Collider. An S-Band RF gun has been installed with diagnostics and a low energy spectrometer (LES) at 6 MeV together with a large-angle extraction line at 60 MeV. This is followed by a matching section, buncher and final focus for the laser acceleration experiment, E163. The laser-electron interaction area is followed by a broad range (2\%), high resolving power (104) spectrometer (HES) for electron bunch analysis. Emittance compensating solenoids and the LES are used to 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 use of sextupoles for a large, 6D phase space volume and range of input conditions. Spot sizes of a few microns at the IP (or HES object) allow tests of microscale structures as well as high resolving power at the image of the HES. Tolerances, tuning sensitivities and diagnostics are discussed together with the latest commissioning results and their comparison to design expectations.
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| THPMS080 |
Inverse-Transition Radiation Laser Acceleration Experiments at SLAC
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3172 |
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- T. Plettner, R. L. Byer
Stanford University, Stanford, Califormia
- E. R. Colby, R. Ischebeck, C. Mcguinness, R. J. Noble, C. M.S. Sears, R. Siemann, J. E. Spencer, D. R. Walz
SLAC, Menlo Park, California
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We present a series of laser-driven particle acceleration experiments that are aimed at studying laser-particle acceleration as an inverse-radiation process. To this end we employ a semi-open vacuum setup with a thin planar boundary that interacts with the laser and the electromagnetic field of the electron beam. Particle acceleration from different types of boundaries will be studied and compared to the theoretical expectations from the Inverse-radiation picture and the field path integral method. We plan to measure the particle acceleration effect from transparent, reflective, black, and rough surface boundaries. While the agreement between the two acceleration pictures is straightforward to prove analytically for the transparent and reflective boundaries the equivalence is not clear-cut for the absorbing and rough-surface boundaries. Therefore, experimental observation may be the most reliable method for establishing the appropriate model for the interaction of the laser field with the particle beam in the presence of a loaded vacuum structure.
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| FRPMS072 |
Timing Stability and Control at the E163 Laser Acceleration Experiment
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4195 |
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- C. Mcguinness, E. R. Colby, R. Ischebeck, R. J. Noble, C. M.S. Sears, R. Siemann, J. E. Spencer, D. R. Walz
SLAC, Menlo Park, California
- R. L. Byer, T. Plettner
Stanford University, Stanford, Califormia
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Funding: DOE: DE-AC02-76SF00515 and DE-FG06-97ER41276
The laser acceleration experiments conducted for the E163 project at the NLC Test Accelerator facility at SLAC have stringent requirements on the temporal properties of the electron and laser beams. A system has been implemented to measure the relative phase stability between the RF sent to the gun, the RF sent to the accelerator, and the laser used to generate the electrons. This system shows rms timing stability better than 1 psec. Temporal synchronicity between the 0.5 psec electron bunch, and the 0.5 psec laser pulse is also of great importance. Cherenkov radiation is used to measure the arrival time of the electron bunch with respect to the laser pulse, and the path length of the laser transport is adjusted to optimize temporal overlap. A linear stage mounted onto a voice coil is used to make shot-by-shot fine timing adjustments to the laser path. The final verification of the desired time stability and control is demonstrated by observing the peak of the laser-electron interaction signal over the course of several minutes.
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