LBNL, Berkeley, California
LLNL, Livermore, California
Funding: Supported by the US DOE at LBNL and LLNL under contracts DE-AC02-05CH11231 and DE-AC52-07NA27344, LARP, SciDAC, and ComPASS. Computuational resources of the NERSC were employed.
It has been shown* that the ratio of longest to shortest space and time scales of a system of two or more components crossing at relativistic velocities is not invariant under Lorentz transformation. This implies the existence of a frame of reference minimizing an aggregate measure of the ratio of space and time scales. It was demonstrated that this translated into a reduction by orders of magnitude in computer simulation run times, using methods based on first principles (e.g., Particle-In-Cell), for particle acceleration devices and for problems such as: free electron laser, laser-plasma accelerator, and particle beams interacting with electron clouds. Since then, speed-ups ranging from 75 to more than four orders of magnitude have been reported for the simulation of either scaled or reduced models of the above-cited problems. In ** it was shown that to achieve full benefits of the calculation in a boosted frame, some of the standard numerical techniques needed to be revised. The theory behind the speed-up of numerical simulation in a boosted frame, latest developments of numerical methods, and example applications with new opportunities that they offer are all presented.
* J.-L. Vay, Phys. Rev. Lett. 98, 130405 (2007).
**J.-L. Vay, Phys. of Plasmas 14, 1 (2008).
LBNL, Berkeley, California
LLNL, Livermore, California
SLAC, Menlo Park, California
Funding: This work was supported by the Office of Science, U. S. Department of Energy, under Contract No. DE-AC02-05CH11231.
A new set of resonances for electron cloud dynamics in the presence of a magnetic field has been found. For short beam bunch lengths and low magnetic fields where lb << 2*π/ωc, (lb = bunch duration, ωc = non-relativistic cyclotron frequency) resonances between the bunch frequency and harmonics of the cyclotron frequency cause an increase in the electron cloud density in narrow ranges of magnetic field near the resonances. For ILC parameters the increase in the density is up to a factor of approximately 3, and the spatial distribution of the electrons is broader near resonances, lacking the well-defined density "stripes" of multipactoring found for non-resonant cases. Simulations with the 2D computer code POSINST, as well as a single-particle tracking code, were used to elucidate the physics of the dynamics. The resonances are expected to affect the electron cloud dynamics in the fringe fields of conventional lattice magnets and in wigglers, where the magnetic fields are low. Results of the simulations, the reason for the bunch-length dependence, and details of the dynamics will be discussed.
C.M. Celata is presently also a visitor in Physics, Mathematics, and Astronomy at California Institute of Technology.
LBNL, Berkeley, California
LLNL, Livermore, California
PPPL, Princeton, New Jersey
Voss Scientific, Albuquerque, New Mexico
The Heavy-Ion Fusion Sciences Virtual National Laboratory is pursuing an approach to target heating experiments in the warm dense matter regime, using space-charge-dominated ion beams that are simultaneously longitudinally bunched and transversely focused. Longitudinal beam compression by large factors has been demonstrated in the Neutralized Drift Compression Experiment (NDCX) with controlled ramps and forced neutralization. Using an injected 30 mA K+ ion beam with initial kinetic energy 0.3 MeV, axial compression leading to ~100X current amplification and simultaneous radial focusing to a few mm have led to encouraging energy deposition approaching the intensities required for eV-range target heating experiments. We discuss the status of several improvements to NDCX to reach the necessary higher beam intensities, including:
- greater axial compression via a longer velocity ramp;
- beam steering dipoles to mitigate aberrations in the bunching module;
- time-dependent focusing elements to correct considerable chromatic aberrations; and
- plasma injection improvements to establish a plasma density always greater than the beam density, expected to be >1013 cm-3.
LBNL, Berkeley, California
LLNL, Livermore, California
Funding: Supported by the US-DOE under Contracts DE-AC02-05CH11231 and DE-AC52-07NA27344, and a DOD SBIR Phase II. Used resources of NERSC, supported by the US-DOE under Contract DE-AC02-05CH11231.
The development of advanced accelerators often involves the modeling of systems that involve a wide range of scales in space and/or time, which can render such modeling extremely challenging. The Adaptive Mesh Refinement technique can be used to significantly reduce the requirements for computer memory and the number of operations. Its application to the fully self-consistent modeling of beams and plasmas is especially challenging, due to properties of the Vlasov-Maxwell system of equations. Most recently, we have begun to explore the application of AMR to the modeling of laser plasma wakefield accelerators (LWFA). For the simulation of a 10GeV LWFA stage, the wake wavelength is O[100μm] while the electron bunch and laser wavelength are typically submicron in size. As a result, the resolution required for different parts of the problem may vary by more than two orders of magnitude in each direction, corresponding to up to 6 orders of magnitude of possible (theoretical) savings by use of mesh refinement. We present a summary of the main issues and their mitigations, as well as examples of application in the context of LWFA and similar beam-plasma interaction setup.
LLNL, Livermore, California
LBNL, Berkeley, California
Funding: Work performed under the auspices of US Department of Energy by LLNL under Contract DE- AC52-07NA27344 and by LBNL under Contract DE-AC03-76SF00098.
The Virtual National Laboratory for Heavy-Ion Fusion is developing a physics design for NDCX-II, an experiment to study warm dense matter heated by ions near the Bragg-peak energy. Present plans call for using about thirty induction cells to accelerate 30 nC of Li+ ions to more than 3 MeV, followed by neutralized drift-compression. To heat targets to useful temperatures, the beam must be compressed to a sub-millimeter radius and a duration of about 1 ns. An interactive 1-D particle-in-cell simulation with an electrostatic field solver, acceleation-gap fringe fields, and a library of realizable analytic waveforms has been used for developing NDCX-II acceleration schedules. Multidimensional source-to-final-focus simulations with the particle-in-cell code Warp have validated this 1-D model and have been used both to design transverse focusing and to compensate for injection non-uniformities and 3-D effects. Results from this work are presented, and ongoing work to replace the analytic waveforms with output from circuit models is discussed.
LBNL, Berkeley, California
TU Darmstadt, Darmstadt
GSI, Darmstadt
LLNL, Livermore, California
Ion acceleration from high-intensity, short-pulse laser irradiated thin foils has attracted much attention during the past decade. The emitted ion and, in particular, proton pulses contain large particle numbers (exceeding a trillion particles) with energies in the multi-MeV range and are tightly confined in time (< ps) and space (source radius a few micrometers). The generation of these high-current beams is a promising new area of research and has motivated pursuit of applications such as tabletop proton sources or pre-accelerators. Requirements for an injector are controllability, reproducibility and a narrow (quasi-monoenergetic) energy. However, the source provides a divergent beam with an exponential energy spectrum that exhibits a sharp cutoff at its maximum energy. The laser and plasma physics group of the TU Darmstadt, in collaboration with GSI and LBNL, is studying possibilities for transport and RF capture in conventional accelerator structures. First results on controlling laser-accelerated proton beams are presented, supported by WARP simulations.
LBNL, Berkeley, California
LLNL, Livermore, California
FZK, Karlsruhe
Funding: Supported by the US-DOE under Contract DE-AC02-05CH11231, the US-LHC LARP, and the US-DOE SciDAC program ComPASS. Used resources of NERSC, supported by the US-DOE under Contract DE-AC02-05CH11231.
At PAC05, we presented the package WARP-POSINST for the modeling of the effect of electron clouds on high-energy beams. We present here the latest developments in the package. Three new modes of operations were implemented: 1) “build-up mode” where, similarly to Posinst (LBNL) or Ecloud (CERN), the build-up of electron clouds is modeled in one region of an accelerator driven by a legislated bunch train; 2) “quasi-static mode” where, similarly to Headtail (CERN) or Quickpic (USC/UCLA), the “frozen beam” approximation is used to split the modeling of the beam and the electrons into two components evolving on their respective time scales; and 3) “Lorentz boosted mode” where the simulation is performed into a moving frame where the space and time scales related to the beam and electron dynamics fall in the same range. The implementation of modes (1) and (2) was primary motivated by the need for benchmarking with other codes, while the implementation of mode (3) fulfills the drive toward fully self-consistent simulations of e-cloud effect on the beam including the build-up phase. We also present benchmarking with other codes and selected results from its application to e-cloud effects.