University of Oslo, Oslo, Norway
UCLA, Los Angeles, California, USA
SLAC, Menlo Park, California, USA
TUB, Beijing, People's Republic of China
MPI, Muenchen, Germany
We present the first results from experimental studies of the electron hose instability in the plasma-wakefield acceleration experiments at FACET. Theory and PIC simulations of an electron beam as it travels through a plasma indicate that hosing may lead to a significant distortion of the transverse phase space. The FACET dump line is equipped with a Cherenkov light based spectrometer which can resolve transverse motion as a function of beam energy. We compare the predictions from simulations and theory to the experimental results obtained.
Duke ECE, Durham, North Carolina, USA
STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom
UCLA, Los Angeles, California, USA
We analyze the use of a relativistic laser pulse with a controlled frequency chirp incident on a rising plasma density gradient to drive an acceleration structure for proton and light ion acceleration. The Chirp Induced Transparency Acceleration (ChITA) scheme is described with an analytical model of the velocity of the snowplow at critical density on a pre-formed rising plasma density gradient that is driven by positive chirp in the frequency of a relativistic laser pulse. The velocity of the ChITA-snowplow is shown to depend upon rate of rise of the frequency of the relativistic laser pulse, the normalized magnetic vector potential of the laser pulse and the plasma density gradient scale-length. We observe using 1-D OSIRIS simulations the formation and forward propagation of ChITA-snowplow, being continuously pushed by the chirping laser at a velocity in accordance with the analytical results. The trace protons reflect off of this propagating snowplow structure and accelerate monoenergetically. The control over ChITA-snowplow velocity allows the tuning of accelerated proton energies.
USC, Los Angeles, California, USA
BNL, Upton, Long Island, New York, USA
UCLA, Los Angeles, California, USA
MPI, Muenchen, Germany
Instituto Superior Tecnico, Lisbon, Portugal
We demonstrate experimentally for the first time the self-modulation of a relativistic electron bunch in a plasma. This demonstration serves as a proof-of-principle test for the mechanisms of transverse self-modulation of particle bunches in plasmas. It indicates the possibility of using long electron or proton bunches as drivers for plasma based accelerators. The long (~5ps) bunch available at BNL-ATF is used in this experiment and in the particle-in-cell OSIRIS. We use the 2D version for cylindrically symmetric geometries. The energy of the beam particles is measured after the plasma exit in the experiment. The obvious energy gain and loss by electrons indicates the excitation of longitudinal wakefields, and hence of transverse focusing fields. Both simulations and experiments show that the electron beamlets are formed at the scale of the plasma wavelength, and the number of beamlets changes as the plasma density is varied. We also measured the variation in beam transverse size downstream from the plasma as well as the variations in coherent transition radiation energy to demonstrate the effect of transverse self–modulation.
MPI, Muenchen, Germany
USC, Los Angeles, California, USA
SLAC, Menlo Park, California, USA
UCLA, Los Angeles, California, USA
IPFN, Lisbon, Portugal
* N. Kumar et al., Phys. Rev. Lett. 104, 255003 (2010).
** J. Vieira et al., submitted (2011).
SLAC, Menlo Park, California, USA
UCLA, Los Angeles, California, USA
When a positron beam enters a plasma, plasma electrons are drawn in toward the beam axis, creating a region of extremely large charge density with complicated, nonlinear fields. Few analytic solutions exist to describe these fields, and this necessitates the use of simulations to model positron beam and plasma interactions. This presentation should cover recent work on positron PWFA simulations using the QuickPIC* particle-in-cell code. I will discuss the computational challenges associated with positron PWFA and specific applications of the simulations for future experimental tests at the FACET user facility at SLAC.
* C. Huang et al., "QuickPIC: A highly efficient particle-in-cell code for modeling wakefield acceleration in plasmas," J. Comp. Phys. 217, 658 (2006).
USC, Los Angeles, California, USA
BNL, Upton, Long Island, New York, USA
LANL, Los Alamos, New Mexico, USA
IPFN, Lisbon, Portugal
UCLA, Los Angeles, California, USA
Current Filamentation Instability, CFI, is of central importance for the propagation of relativistic electron beams in plasmas. CFI has potential relevance to astrophysics, magnetic field and radiation generation in the afterglow of gamma ray bursts, and inertial confinement fusion, energy transport in the fast-igniter concept. An experimental study of this instability is underway at the Accelerator Test Facility, ATF, at Brookhaven National Laboratory with the 60MeV electron beam and centimeter length capillary discharge plasma. The experimental program includes the systematic study and characterization of the instability as a function of beam (charge, transverse and longitudinal profile) and plasma (plasma density) parameters. Specifically, the transverse beam profile is measured directly at the plasma exit using optical transition radiation from a thin gold-coated silicon window. Experimental results show the reduction of the beam transverse size and the appearance of multiple (1-4) filaments and are a function of the plasma density. We will present simulation and experimental results, provide discussion of these results and outline next steps in the experiment.