A Tapered Dielectric Structure for Laser Acceleration at Low Energy
This paper extends the physics of the Micro-Accelerator Platform (MAP), which is in development as an optical structure for laser acceleration of relativistic electrons. The MAP is a resonant, optical-scale, slab-symmetric device that is fabricated from dielectric materials using layer-deposition techniques. For stand-alone applications, low-energy electrons ( ~ 0.3) must be synchronously accelerated to relativistic speeds for injection into the MAP. Even lower energies are desired for other particle species (e.g. protons or muons). In this paper, we present design and simulation studies on a tapered geometry and associated coupling scheme that can produce synchronous acceleration at < 1 within a MAP-like structure.

title: On Computing Upper Limits to Source Intensities
abstract: A common problem in astrophysics is determining how bright a source could be and still not be detected in an observation. Despite the simplicity with which the problem can be stated, the solution involves complicated statistical issues that require careful analysis. In contrast to the more familiar confidence bound, this concept has never been formally analyzed, leading to a great variety of often ad hoc solutions. Here we formulate and describe the problem in a self-consistent manner. Detection significance is usually defined by the acceptable proportion of false positives (background fluctuations that are claimed as detections, or Type I error), and we invoke the complementary concept of false negatives (real sources that go undetected, or Type II error), based on the statistical power of a test, to compute an upper limit to the detectable source intensity. To determine the minimum intensity that a source must have for it to be detected, we first define a detection threshold and then compute the probabilities of detecting sources of various intensities at the given threshold. The intensity that corresponds to the specified Type II error probability defines that minimum intensity and is identified as the upper limit. Thus, an upper limit is a characteristic of the detection procedure rather than the strength of any particular source. It should not be confused with confidence intervals or other estimates of source intensity. This is particularly important given the large number of catalogs that are being generated from increasingly sensitive surveys. We discuss, with examples, the differences between these upper limits and confidence bounds. Both measures are useful quantities that should be reported in order to extract the most science from catalogs, though they answer different statistical questions: an upper bound describes an inference range on the source intensity, while an upper limit calibrates the detection process. We provide a recipe for computing upper limits that applies to all detection algorithms.

title: 3D Simulations for a Micron‐Scale, Dielectric‐Based Acceleration Experiment
abstract: An experimental program to demonstrate a dielectric, slab‐symmetric accelerator structure has been underway for the past two years. These resonant devices are driven by a side‐coupled 800‐nm laser and can be configured to maintain the field profile necessary for synchronous acceleration and focusing of relativistic or nonrelativistic particles. We present 3D simulations of various versions of the structure geometry, including a metal‐walled structure relevant to ongoing cold tests on resonant properties, and an all‐dielectric structure to be constructed for a proof‐of‐principle acceleration experiment.

title: DEVELOPING PETA-SCALABLE ALGORITHMS FOR BEAM DYNAMIC SIMULATIONS
abstract: Peta-scalable software packages for beam dynamic simulations are being developed and used at Argonne national laboratory. The standard Particle-In-Cell (PIC) method and direct Vlasov solvers in up to 4 dimensions have been developed and benchmarked with respect to each other. Both of them have successfully run on 32 thousands processors on BG/P at Argonne Leadership Computing Facility. Peta-scale computing facility at ANL provides suitable environment for simulating beams in large scale. We have simulated charged beams through traditional PIC method as well as direct solving of the Vlasov equation in higher dimensions. Several scalable Poisson solvers have been developed and incorporated with these methods. High-order numerical methods have been adopted for solving the Poisson and Vlasov equations. Preliminary results on direct Vlasov solvers have been obtained in up to 4 dimensions. Domain decomposition method has been used for the parallelization in these software packages, and good scaling has been achieved. These packages have been successfully applied in end-to-end simulation of linear accelerators and large scale accelerator design optimizations. There are still lots of places can be improved for the PIC method and lots of challenges exist in the direct Vlasov solvers, therefore, more efforts are needed in both algorithms and applications.  Plasma and charged beams are of great importance in modern science and technology. Their researches become more and more rely on the simulations. Simulating plasma and charged beams has three different methods: microscopic model, kinetic model and fluid model. In the microscopic model, each charged particle is described by 6 variables (x, y, z, z y x v v v , , ). Therefore, for N particles, there are 6N variables in total. This requires solving the Vlasov equation in 6N dimensions, which exceeds the capability of current supercomputers for large N. On the other end is the fluid model which is the simplest model, because it treats the plasma as a conducting fluid with electromagnetic forces exerted on it. This leads to solving the Magneto-hydrodynamics (MHD) equations in 3D (x, y and z). MHD solves for the average quantities, such as density and charge, which makes it difficult to describe the fine structure in the plasma. Between these two models is the kinetic model, which solves for the charge density function by solving the Boltzmann or Vlasov equations in 6 dimensions (x, y, z, z y x v v v , , ). The Vlasov equation describes the evolution of a system of particles under the effects of self-consistent electromagnetic fields. The model been used in current beam dynamics simulations is the kinetic model. There are two different ways to solve it. The dominant one is the so called Particle-In-Cell (PIC) method, which utilizes the motion of the particles along the characteristics of the Vlasov equation using a Lagrange-Euler approach [1, 2]. The PIC method has the advantages of fast speed and easy implementation, but similar to MHD, it is hard to capture the fine structures in the plasma. Furthermore, there is noise associated with the finite number of particles in the simulations. With petascale computing, one-to-one simulation can be realized for 9 10 particles. But for more intense beams, PIC method still uses macro particles. The other way to solve the kinetic model is to solve the Vlasov equation directly. But the challenge is the high dimensions. For example, in order to simulate beam in 3D, Vlasov equation has to be solved in 6D. This clearly needs peta-scale computing, and the peta-scalable algorithms are critical to the success. During the past 5 years, we have developed several software packages to meet these demands. This paper presents our efforts on developing peta-scalable algorithms to simulate charged beams in linear accelerators. PARALLEL POISSON SOLVERS In both approaches, Poisson’s equation has to be solved in 2D or 3D to account for the space charge effect. In designing peta-scalable algorithms, it is usually the most challenging part. Therefore, we present our work on this first. Several different methods have been adopted and are given in following: Fourier Method This is the most standard method for solving the Poisson’s equation in box region with Cartesian coordinate system. The potential has been expanded in Fourier series in all three directions. Periodic and Dirichlet zero boundary conditions have been applied in all three directions. ___________________________________________ * This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357. jin_xu@anl.gov ∑ ∑ ∑ −

title: Transition Density and Pressure at the Inner Edge of Neutron Star Crusts
abstract: Using the nuclear symmetry energy that has been recently constrained by the isospin diffusion data in intermediate-energy heavy ion collisions, we have studied the transition density and pressure at the inner edge of neutron star crusts, and they are found to be 0.040 fm$^{-3}$ $\leq \rho_{t}\leq 0.065$ fm$^{-3}$ and 0.01 MeV/fm$^{3}$ $\leq P_{t}\leq 0.26$ MeV/fm$^{3}$, respectively, in both the dynamical and thermodynamical approaches. We have also found that the widely used parabolic approximation to the equation of state of asymmetric nuclear matter gives significantly higher values of core-crust transition density and pressure, especially for stiff symmetry energies. With these newly determined transition density and pressure, we have obtained an improved relation between the mass and radius of neutron stars.

title: Effects of hadronic potentials on elliptic flows in relativistic heavy ion collisions
abstract: Within the framework of a multiphase transport (AMPT) model that includes both initial partonic and final hadronic interactions, we show that including mean-field potentials in the hadronic phase leads to a splitting of the elliptic flows of particles and their antiparticles, providing thus a plausible explanation of the different elliptic flows between $p$ and ${\bar p}$, $K^+$ and $K^-$, and $\pi^+$ and $\pi^-$ observed in recent Beam Energy Scan (BES) program at the Relativistic Heavy-Ion Collider (RHIC).

title: Triangular flow in heavy ion collisions in a multiphase transport model
abstract: We obtain a new set of parameters in a multiphase transport (AMPT) model that are able to describe both the charged particle multiplicity density and the elliptic flow measured in Au+Au collisions at center-of-mass energy {radical}(s{sub NN})=200 GeV at the Relativistic Heavy Ion Collider, although they still give somewhat softer transverse momentum spectra. We then use the model to predict the triangular flow due to fluctuations in the initial collision geometry and study its effect relative to those from other harmonic components of anisotropic flows on the dihadron azimuthal correlations in both central and midcentral collisions.

title: ISOSPIN AND MOMENTUM DEPENDENCE OF LIQUID-GAS PHASE TRANSITION IN HOT ASYMMETRIC NUCLEAR MATTER
abstract: The liquid-gas phase transition in hot neutron-rich nuclear matter is investigated within a self-consistent thermal model using different interactions with or without isospin and/or momentum dependence. The boundary of the phase-coexistence region is shown to be sensitive to the density dependence of the nuclear symmetry energy as well as the isospin and momentum dependence of the nuclear interaction.

title: Transition density and pressure in hot neutron stars
abstract: Using the momentum-dependent effective interaction (MDI) for nucleons, we have studied the transition density and pressure at the boundary between the inner crust and the liquid core of hot neutron stars. We find that their values are larger in neutrino-trapped neutron stars than in neutrino-free neutron stars. Furthermore, both are found to decrease with increasing temperature of a neutron star as well as increasing slope parameter of the nuclear symmetry energy, except that the transition pressure in neutrino-trapped neutron stars for the case of small symmetry energy slope parameter first increases and then decreases with increasing temperature. We have also studied the effect of the nuclear symmetry energy on the critical temperature above which the inner crust in a hot neutron star disappears and found that with increasing value of the symmetry energy slope parameter, the critical temperature decreases slightly in neutrino-trapped neutron stars but first decreases and then increases in neutrino-free neutron stars.