Search

We investigate the motion of electrons in a plasma bubble (or an ion channel) under combined action of an oscillating laser field, quasistatic transverse wakefield, and longitudinal electric field. The longitudinal field E|| significantly influences the broadband resonance between betatron oscillations of electrons and oscillations of the laser wave, which results in the profoundly different electron dynamics at different signs and magnitudes of the longitudinal force -eE||. Specifically, we make a contrast between three representative cases: when this force is absent (-eE|| = 0), when it accelerates electrons (-eE|| > 0), and when it decelerates them (-eE|| < 0). We estimate the electron energy gain at given laser-plasma parameters. [ABSTRACT FROM AUTHOR]

We present a spatial and spectral characterization of a laser-plasma based betatron source which allows us to determine the betatron oscillation amplitude of the electrons which decreases with increasing electron energies. Due to the observed oscillation amplitude and the independently measured x-ray source size of (1.8±0.3)μm we are able to estimate the electron bunch diameter to be (1.6±0.3)μm. [ABSTRACT FROM AUTHOR]

High amplitude coherent electron-trajectories have been seen in 3D particle-in-cell simulations of the colliding pulse injection scheme of laser-wakefield accelerators in the bubble regime, and explained as a consequence of laser-driven coherent betatron oscillation in our recent paper [K. Németh et al., Phys. Rev. Lett. 100, 095002 (2008)]. In the present paper we provide more details on the shape of the trajectories, their relationship to the phase velocity of the laser and indicate the dependence of the phenomenon on the accuracy of the numerical representation and choice of laser/plasma parameters. [ABSTRACT FROM AUTHOR]

A new method for generating positrons has been proposed that uses betatron X-rays emitted by an electron beam in a high-K plasma wiggler. The plasma wiggler is an ion column produced by the head of the beam when the peak beam density exceeds the plasma density. The radial electric field of the beam blows out the plasma electrons transversely, creating an ion column. The focusing electric field of the ion column causes the beam electrons to execute betatron oscillations about the ion column axis. If the beam energy and the plasma density are high enough, these oscillations lead to synchrotron radiation in the 1–50 MeV range. A significant amount of electron energy can be lost to these radiated X-ray photons. These photons strike a thin (.5Xo), high-Z target and create e+/e- pairs. The experiment was performed at the Stanford Linear Accelerator Center (SLAC) where a 28.5 GeV electron beam with σr ≈ 10μm and σz ≈ 25μm was propagated through a neutral Lithium vapor (Li). The radial electric field of the dense beam was large enough to field ionize the Li vapor to form a plasma. The positron yield was measured as a function of plasma density, ion column length and electron beam pulse length. A computational model was written to match the experimental data with theory. The measured positron spectra are in excellent agreement with those expected from the calculated X-ray spectral yield from the plasma wiggler. After matching the model with the experimental results, it was used to design a more efficient positron source, giving positron yields of 0.44 e+/e-, a number that is close to the target goal of 1–2 e+/e- for future positron sources. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The effects of radiation reaction on electron beam dynamics are studied in the context of plasma-based accelerators. Electrons accelerated in a plasma channel undergo transverse betatron oscillations due to strong focusing forces. These oscillations lead to emission by the electrons of synchrotron radiation, with a corresponding energy loss that affects the beam properties. An analytical model for the single particle orbits and beam moments including the classical radiation reaction force is derived and compared to the results of a particle transport code. It is shown that the radiation could significantly affect the beam properties (e.g., increased relative energy spread) in plasma wakefield accelerators. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The Cornell Electron Storage Ring (CESR) undergoes significant changes in running conditions as operation for CLEO-c high energy physics is interleaved with synchrotron light operation for CHESS (Cornell High Energy Synchrotron Source). Two examples of CESR beam instrumentation applications that are being used to understand storage ring conditions are described: 1) measurement of coupling at the interaction point using the single bunch, multiple turn, type I CESR Beam Position Monitor (CBPM) electronics with continuous beam excitation and 2) measurement of individual bunch tunes to explore possible electron cloud effects using the multiple bunch, multiple turn, type II CBPM electronics with a shock-excited beam. Both applications use the same acquired data for a given bunch, which is turn-by-turn beam position data, and both applications extract the relevant information using the discrete Fourier transform of the time sequences. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Non-paraxial propagation of ultrashort, high power laser pulses in plasma channels is examined. In the adiabatic limit, pulse energy conservation, nonlinear group velocity, damped betatron oscillations, self-steepening, self-phase modulation, and shock formation are analyzed. In the non-adiabatic limit, the coupling of forward Raman scattering (FRS) and the self-modulation instability (SMI) is analyzed and growth rates are derived, including regimes of reduced growth. The SMI is found to dominate FRS in most regimes of interest. [ABSTRACT FROM AUTHOR]

The super-conducting Relativistic Heavy Ion Collider (RHIC) with two separate rings and six combined interaction regions will provide collisions between equal and unequal heavy ion species up to Au ions in typically 60 bunches. The betatron tunes of the two beams are among the most important parameters to be measured. The tunes have to be acquired at any moment during accelerator operation and in particular during the acceleration process. At RHIC the tune measurement device (ARTUS) consists of a fast horizontal and vertical kicker magnet and a dedicated beam position monitor in each ring. The system layout is descried and first experiences from operation is reported. [ABSTRACT FROM AUTHOR]