SLAC, Menlo Park, California
UCLA, Los Angeles, California
Duke University, Durham, North Carolina
USC, Los Angeles, California
Funding: Work supported in part by the U.S. Department of Energy under contract number DE-AC02-76SF00515.
Recent progress in generating gradients in the 10's of GV/m range with beam driven plasmas has renewed interest in developing a linear collider based on this technology. This talk will explore possible configurations of such a machine, discuss the key demonstrations and the facilities needed to advance this effort and highlight possible alternative uses of this technology.
UCLA, Los Angeles, California
Instituto Superior Tecnico, Lisbon
Funding: Fundacao Calouste Gulbenkian and Fundacao para a Ciencia e Tecnologia under grants SFRH/BD/35749/2007.
The possibility of using a CO2 laser (10 micron wavelength) to drive a plasma density compression and achieve effective ion acceleration in gaseous targets (density>~ 1019cm-3) is explored. A parameter scan is performed with a set of particle in cell simulations in OSIRIS*, both in 2D and 3D, for various laser intensities, linear/circular polarization pulses, and plasma densities. Results show that, to generate the shock compression, plasma density must be increased above the critical value to account for the relativistic motion of the electrons. Under these conditions, 2-5MeV ions are observed with moderate intensity (a0=3) laser pulses. Finally, configurations to generate a shock structure are suggested, that will more efficiently accelerate the particles. This scenario is also of particular relevance to fast-ignition, inertial confinement fusion, and implications to those regimes can be obtained from numerical simulations by using the appropriate density normalization.
*R. A. Fonseca et al, LNCS 2329, III-342, Springer-Verlag, (2002)
SLAC, Menlo Park, California
UCLA, Los Angeles, California
Duke University, Durham, North Carolina
USC, Los Angeles, California
Funding: Work supported by the DOE under contract DE-AC02-76SF00515.
Plasma Wake-Field Acceleration (PWFA) has demonstrated acceleration gradients above 50 GeV/m. Simulations have shown drive/witness bunch configurations that yield small energy spreads in the accelerated witness bunch and high energy transfer efficiency from the drive bunch to the witness bunch, ranging from 30% for a Gaussian drive bunch to 95% for shaped longitudinal profile. These results open the opportunity for a linear collider that could be compact, efficient and more cost effective that the present microwave technologies. A concept of a PWFA-based Linear Collider (PWFA-LC) has been developed and is described in this paper. The scheme of the drive beam generation and distribution, requirements on the plasma cells, and optimization of the interaction region parameters are described in detail. The research and development steps, necessary for further development of the concept, are also outlined.
Instituto Superior Tecnico, Lisbon
UCLA, Los Angeles, California
Funding: F.C.Gulbenkian, F.C.T. [SFRH/BD/35749/2007, SFRH/BD/39523/2007, PTDC/FIS/66823/2006 (Portugal)], and European Community (project EuroLeap, contract #028514)
It is now accepted that self-trapped electrons in a laser wakefield accelerator operating in the "bubble" regime undergo strong periodic oscillations about the wakefield axis because of the focusing force provided by the ions. This betatron motion of the off-axis electrons results in the emission of x-ray radiation strongly peaked in the forward direction. Even though the x-rays are broadband with a synchrotron-like spectrum, their brightness can be quite high because of their short pulse duration and strong collimation. We employ particle tracking in particle in cell simulations with OSIRIS*, combined with a post-processing radiation diagnostic, to evaluate the features of the radiation mechanisms of accelerated electrons in LWFA experiments. We show and discuss results for a 1.5 GeV laser wakefield accelerator stage. A study of the angular dependence of the radiated power is also presented and compared with theoretical models. This analysis also allows for the direct calculation of the radiation losses of the self-injected bunch.
*R. A. Fonseca et al, LNCS 2329, III-342, Springer-Verlag, (2002)
SLAC, Menlo Park, California
UCLA, Los Angeles, California
Duke University, Durham, North Carolina
USC, Los Angeles, California
Funding: Work supported in part by the U.S. Department of Energy under contract number DE-AC02-76SF00515.
An electron beam driven Plasma Wake-Field Accelerator (PWFA) has recently sustained accelerating gradients above 50GeV/m for almost a meter. Future experiments will transition from using a single bunch to both drive and sample the wakefield, to a two bunch configuration that will accelerate a discrete bunch of particles with a narrow energy spread and preserved emittance. The plasma works as an energy transformer to transform high-current, low-energy bunches into relatively lower-current higher-energy bunches. This method is expected to provide high energy transfer efficiency (from 30% up to 95%) from the drive bunch to the accelerated witness bunch. The PWFA has a wide variety of applications and also has the potential to greatly lower the cost of future accelerators. We discuss various possible uses of this technique such as: linac based light sources, injector systems for ring based synchrotron light sources, and for generation of electron beams for high energy electron-hadron colliders.
UCLA, Los Angeles, California
Duke University, Durham, North Carolina
Plasma Wake Field Accelerator (PWFA) has a very attractive accelerating gradient which can be three orders of magnitude higher than that of the traditional accelerator. In this paper the positron acceleration in a particle beam driven PWFA is studied both in the linear and weakly nonlinear region by using Particle In Cell (PIC) simulation. A preliminary parameters design is obtained for such acceleration scheme.
UCLA, Los Angeles, California
SLAC, Menlo Park, California
Duke University, Durham, North Carolina
USC, Los Angeles, California
Funding: Work supported by DOE under contracts DE-FG03-92ER40727, DE-FG52-06NA26195, DE-FC02-07ER41500, DE-FG02-03ER54721.
Recent Plasma Wake-Field Acceleration (PWFA) experiments at Stanford Linear Accelerator Center has demonstrated electron acceleration from 42GeV to 84GeV in less than one meter long plasma section. The accelerating gradient is above 50GeV/m, which is three orders of magnitude higher than those in current state-of-art RF linac. Further experiments are also planned with the goal of achieving acceleration of a witness bunch with high efficiency and good quality. Such PWFA sections with 25 GeV energy gain will be the building blocks for a staged TeV electron-positron linear collider concept based on PWFA (PWFA-LC). We conduct Particle-In-Cell simulations of these PWFA sections at both the initial and final witness beam energies. Different design options, such as Gaussian and shaped bunch profiles, self-ionized and pre-ionized plasmas, optimal bunch separation and plasma density are explored. Theoretical analysis of the beam-loading* in the blow-out regime of PWFA and simulation results show that highly efficient PWFA stages are possible. The simulation needs, code developments and preliminary simulation results for future collider parameters will be discussed.
*M. Tzoufras et al, Phys. Rev. Lett. {10}1, 145002 (2008).
UCLA, Los Angeles, California
SLAC, Menlo Park, California
Funding: Work supported by DOE grant numbers: DE-FG03-92ER40727, DE-FG52-06NA26195, DE-FC02-07ER41500, DE-FG02-03ER54721
The fourth generation of light sources (such as LCLS and the XFEL) require high energy electron drivers (16-20GeV) of very high quality. We are exploring the possibility of using a high transformer ratio PWFA to meet these challenging requirements. This may have the potential to reduce the size of the electron drivers by a factor of 5 or more, therefore making these light source much smaller and more affordable. In our design, a high charge (5-10nC) low energy driver (1-3GeV) with an elongated current profile is used to drive a plasma wake in the blowout regime with a high transformer ratio (5 or more). A second ultra-short beam that has high quality and low charge beam (1nC) can be loaded into the wake at a proper phase and be accelerated to high energy (5-15GeV) in very short distances (10s of cms). The parameters can be optimized, such that high quality (0.1% energy spread and 1mm mrad normalized emittance) and high efficiency (60-80%) can be simultaneously achieved. The major obstacle for achieving the above goals is the electron hosing instabilities in the blowout regime. In this poster, we will use both theoretical analysis and PIC simulations to study this concept.
UCLA, Los Angeles, California
Instituto Superior Tecnico, Lisbon
Funding: Work Supported by DOE Grant DEFG02-92ER40727
Controlling the trapping of electrons into accelerating wakefields is an important step to obtaining a stable reproducible electron beam from a laser wakefield accelerator (LWFA). Recent experiments at UCLA have focused on using the different ionization potentials of gases as a mechanism for controlling the trapping of electrons into an LWFA. The accelerating wakefield was produced using an ultra-intense (Io ~ 1019 W / cm2 ), ultra-short (τFWHM ~ 40 fs) laser pulses. The laser pulse was focused onto the edge of column of gas created by a gas jet. The gas was a mixture of helium and nitrogen. The rising edge of the laser pulse fully ionizes the helium and the first five bound electrons of the nitrogen. Only at the peak of the laser pulse is it intense enough to ionize the most tightly bound electrons of the nitrogen. Electrons which are ionized at the peak of laser pulse are born into a favorable phase space within the accelerating wakefield and are subsequently trapped and accelerated. The accelerated electrons were dispersed using a dipole magnet with a ~ 1 Tesla magnetic field onto a phosphor screen. Electron beam energy spectrum charge and divergence were measured.
UCLA, Los Angeles, California
Funding: This work was supported by The Department of Energy Grant No.DEFG02-92ER40727.
The self-guiding of relativistically intense but ultra-short laser pulses has been experimentally investigated as a function of laser power, plasma density and plasma length in the so-called "blowout" regime. Although etching of the short laser pulse due to diffraction and local pump depletion erodes the the head of the laser pulse, an intense portion of the pulse is guided over tens of Rayleigh lengths, as observed by imaging the exit of the plasma. Spectrally-resolved images of the laser pulse at the exit of the plasma show evidence for photon acceleration as well as deceleration (pump depletion)in a well defined narrow guided region. This is indicative of the self-guided pulse residing in the wake excited in the plasma. Energy outside the guided region was found to be minimized when the initial conditions at the plasma entrance were closest to the theoretical matching conditions for guiding in the blowout regime. The maximum extent of the guided length is shown to be consistent with the nonlinear pump depletion length predicted by theory.
Instituto Superior Tecnico, Lisbon
UCLA, Los Angeles, California
Funding: F.C.Gulbenkian, F.C.T. [SFRH/BD/35749/2007, PTDC/FIS/66823/2006 (Portugal)], and European Community - New and Emerging Science and Technology Activity, FP6 program (project EuroLeap, contract #028514)
We address full particle-in-cell simulations of the next generation of Laser Wakefield Accelerators with energy gains > 10 GeV. The distances involved in these numerical experiments are very demanding in terms of computational resources and are not yet possible to (easily) accomplish. Following the work on simulations of particle beam-plasma interaction scenarios in optimized Lorentz frames by J.-L. Vay*, the Lorentz transformation for a boosted frame was implemented in OSIRIS**, leading to a dramatic change in the computational resources required to model LWFA. The critical implementation details will be presented, and the main difficulties discussed. Quantitative comparisons between lab/boost frame results with OSIRIS, QuickPIC***, and experiment will be given. Finally, the results of a three-dimensional PIC simulation of a > 10 GeV accelerator stage will be presented, including a discussion on radiation emission.
* J.-L. Vay, PRL 98, 130405 (2007)
** R.A. Fonseca et al., LNCS 2329, III-342 (Springer-Verlag, 2002)
*** C. Huang, et al., JCP 217, Issue 2, 20 (2006)
USC, Los Angeles, California
UCLA, Los Angeles, California
Duke University, Durham, North Carolina
Funding: Work supported by US Department of Energy.
Plasma Wakefield Accelerator has been proven to be a promising technique to lower the cost of the future high energy colliders by offering orders of magnitude higher gradients than the conventional accelerators. However, it has been shown that ion motion is an important issue to account for in the extreme regime of ultra high intensities and ultra low emittances, characteristics of future high energy colliders. In this regime, the transverse electric field of the beam is so high that the plasma ions cannot be considered immobile at the time scale of electron plasma oscillations, thereby leading to a nonlinear focusing force. Therefore, the transverse emittance of a beam matched to the initial linear focusing will not be preserved under these circumstances. However, Vlasov equation predicts a matching profile even in the nonlinear regime. Furthermore, we extend the idea and introduce a plasma section that can match the entire beam to the mobile-ion regime of plasma. We also find the analytic solution for the optimal matching section. Simulation results will be presented.
SLAC, Menlo Park, California
UCLA, Los Angeles, California
USC, Los Angeles, California
High gradient acceleration of electrons has recently been achieved in meter scale plasmas at SLAC. Results from these experiments show that the wakefield is sensitive to parameters in the electron beam which drives it. In the experiment the bunch lengths were varied systematically at constant charge. Here we investigate the correlation of peak beam current to the wake amplitude. The effect of beam head erosion will be discussed and an experimental limit on the transformer ratio set. The results are compared to simulation.