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**Name:** AAC 2002 10th

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**Date:** 2002-01-01

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**Created at:** Fri Jul 27 23:53:36 -0700 2007

**Updated at:** Fri Jul 27 23:53:36 -0700 2007

title: | Plasma Wakefield Experiments |

format: | conference proceeding |

conference: | AAC 2002 10th |

year: | 2002 |

6 authors: | | | | | | |

abstract: | We discuss the recent experiments in the field of Plasma Wakefield Acceleration (PWFA), with emphasis on the FNAL experiment. After completion of this work, the next round of experiments will need to push the envelope on accelerating gradient, interaction length, stability, and accelerated charge. We present theoretical results dealing with plasma accelerator performance in the limit of high driver charge, and short wavelengths. We comment on the impact of such results on both the afterburner (single module) and staged (multiple modules) approaches to plasma-based accelerators. |

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title: | Velocity bunching experiment at the Neptune Laboratory |

format: | conference proceeding |

conference: | AAC 2002 10th |

year: | 2002 |

5 authors: | | | | | |

abstract: | In this paper we describe the ballistic bunching compression experiment at the Neptune photoinjector at UCLA. We have compressed the beam by chirping the beam energy spectrum in a short S-band high gradient standing wave RF cavity and then letting the electrons undergo velocity compression in the subsequent rectilinear drift. Using a standard Martin Puplett interferometer for coherent transition radiation measurement, we have observed bunch length as short as 0.4 ps with compression ratio in excess of 10 for an electron beam of 7 MeV and charge up to 0.3 nC. We also measured slice transverse emittance via quad scan technique. The observed emittance growth agrees with the predictions and the simulations. Extension of this scheme to a future advanced accelerator injector system where solenoidal magnetic field can compensate the emittance growth is studied. |

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title: | Plasma Density Transition Trapping as a Possible High-Brightness Electron Beam Source |

format: | conference proceeding |

conference: | AAC 2002 10th |

year: | 2002 |

2 authors: | | |

abstract: | Plasma density transition trapping is a recently proposed self-injection scheme for plasma wakefield accelerators. This technique uses a sharp downward plasma density transition to trap and accelerate background plasma electrons in a plasma wakefield. This paper examines the quality of electron beams captured using this scheme in terms of emittance, energy spread, and brightness. Two-dimensional particle-in-cell simulations show that these parameters can be optimized by manipulating the plasma density profile.We also develop, and support with simulations, a set of scaling laws that predicts how the brightness of transition trapping beams scales with the plasma density of the system. These scaling laws indicate that transition trapping can produce beams with brightness 5 1014 A= mrad 2. A proof-ofprinciple transition trapping experiment is planned for the near future. The proposed experiment is described in detail. |

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title: | A Resonant, THz Slab-Symmetric Dielectric-Based Accelerator |

format: | conference proceeding |

conference: | AAC 2002 10th |

year: | 2002 |

2 authors: | | |

abstract: | Slab-symmetric dielectric-loaded structures, consisting of a vacuum gap between dielectric-lined conducting walls, have become a subject of interest for short-wavelength acceleration due to their simplicity, relatively low power density, and advantageous beam dynamics. Such a structure can be resonantly excited by an external power source and is known to strongly suppress transverse wakefields. Motivated by the prospect of a high-power FIR radiation source, currently under construction at UCLA, we investigate a high-gradient slab- symmetric accelerator powered by up to 100 MW of laser power at 340 um, with a predicted gradient near 100 MeV/m. Three-dimensional simulation studies of the structure fields and wakes are presented and compared with theory, and a future experiment is discussed. |

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title: | Electron Beam Production and Characterization for the PLEIADES Thomson X-Ray Source |

format: | conference proceeding |

conference: | AAC 2002 10th |

year: | 2002 |

13 authors: | | | | | | | | | | | | | |

abstract: | We report on the performance of an S-band RF photocathode electron gun and accelerator for operation with the PLEIADES Thomson x-ray source at LLNL. Simulations of beam production, transport, and focus are presented. It is shown that a 1 ps, 500 pC electron bunch with a normalized emittance of less than 5 Tcmm-mrad can be delivered to the interaction point. Initial electron measurements are presented. Calculations of expected x-ray flux are also performed, demonstrating an expected peak spectral brightness of 1020 photons/s/mm2/mrad2/0.1% bandwidth. Effects of RF phase jitter are also presented, and planned phase measurements and control methods are discussed. |

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title: | Longitudinal Beam Shaping and Compression Scheme for the UCLA Neptune Laboratory |

format: | conference proceeding |

conference: | AAC 2002 10th |

year: | 2002 |

3 authors: | | | |

abstract: | We are developing a new beamline which will serve as a venue for future beam- plasma interaction experiments using the 14MeV electron beam produced by the UCLA Neptune 1.625-cell photoinjector and PWT linac. An examination of the first and second-order optics indicates that when certain nonlinear effects are minimized through the use of sextupole magnets, the longitudinal dispersion is dominated by a negative R 5 6- Simulations using the matrix transport code ELEGANT indicate that for an appropriately chirped initial beam, this beamline can be used to create a ramped picosecond to sub-picosecond beam that is ideal for driving large amplitude wake fields in a plasma and producing high transformer ratios. |

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title: | Bunched Beam Injection in a Plasma Accelerator |

format: | conference proceeding |

conference: | AAC 2002 10th |

year: | 2002 |

6 authors: | | | | | | |

abstract: | An experiment on phase-locked injection of ~ 100 fs electron bunches in a plasma beat wave accelerator is presented. We consider using an IFEL microbunching technique to produce ultrashort electron bunches prebunched at the exact wavelength of the plasma wave 340 Jim (~lTHz). It is proposed to generate 100 MW of 1 THz radiation by difference frequency generation in a nonlinear crystal, mixing the same two CC>2 lines as used to drive the plasma accelerator. |

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title: | Inverse Free Electron Laser Experiment at the Neptune Laboratory |

format: | conference proceeding |

conference: | AAC 2002 10th |

year: | 2002 |

6 authors: | | | | | | |

abstract: | We present an Inverse Free Electron Laser accelerator proposed for construction at the UCLA Neptune Laboratory. This experiment will use a 1 TW CO2 laser to accelerate through two strongly tapered undulators an electron beam from 16 MeV up to 5 MeV. The scheme proposed is the diffraction dominated IFEL interaction. The Raleigh range of the laser beam is about 2 cm, much shorter than the interaction length (the undulator length is 50 cm). In this regime adiabatic capture is possible in the first part of the undulator. In the focus region, we propose a solution to the problem of the dephasing between electrons and photons due to the |

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title: | Energy Loss of a High Charge Bunched Electron Beam in Plasma: Nonlinear plasma response and linear scaling |

format: | conference proceeding |

conference: | AAC 2002 10th |

year: | 2002 |

4 authors: | | | | |

abstract: | There has been much experimental and theoretical interest in blowout regime of plasma wakefield acceleration (PWFA), which features ultra-high accelerating fields, linear transverse focusing forces, and nonlinear plasma motion. Using an exact analysis, we examine here a fundamental limit of nonlinear PWFA excitation, by an infinitesimally short, relativistic electron beam. The beam energy loss in this case is shown to be linear in charge even for nonlinear plasma response, where a normalized, unitless charge exceeds unity, and relativistic plasma effects become important or dominant. The physical bases for this persistence of linear response are pointed out. As a byproduct of our analysis, we re-examine the issue of field divergence as the point-charge limit is approached, suggesting an important modification of commonly held views of evading unphysical energy loss. Deviations from linear behavior are investigated using simulations with finite length beams. The peak accelerating field in the plasma wave excited behind a finite-length beam is also examined, with the artifact of wave spiking adding to the apparent persistence of linear scaling of the peak field amplitude well into the nonlinear regime. On the other hand, at large enough normalized charge, linear scaling of fields collapses, with serious consequences for plasma wave excitation efficiency. The dramatic implications of these results for observing the collapse of linear scaling in planned experiments are discussed. |

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