13276418
Generating monoenergetic heavy-ion bunches with laser-induced electrostatic shocks.
A method for efficient laser acceleration of heavy ions by electrostatic shock is investigated using particle-in-cell (PIC) simulation and analytical modeling. When a small number of heavy ions are mixed with light ions, the heavy ions can be accelerated to the same velocity as the light ions so that they gain much higher energy because of their large mass. Accordingly, a sandwich target design with a thin compound ion layer between two light-ion layers and a micro-structured target design are proposed for obtaining monoenergetic heavy-ion beams.
36422466
Comment on "generating high-current monoenergetic proton beams by a circularly polarized laser pulse in the phase-stable acceleration regime".
In a recent Letter X.Q. Yan et al. [1] propose a method named phase-stable acceleration to accelerate protons or ions via a circularly polarized laser pulse interacting with an ultrathin target. The key point of this method is that the target should be as thin as possible so that the foil can be more easily accelerated due to the small mass. Based on this, an expression is obtained as follows [1,2]:
44994799
Internal shock model for the X-ray flares of Swift J1644+57
Swift J1644+57 is an unusual transient event, likely powered by the tidal disruption of a star by a massive black hole. Multiple short time-scale X-ray flares were seen over a span of several days. We propose that these flares could be produced by internal shocks. In the internal shock model, the forward and reverse shocks are produced by collisions between relativistic shells ejected from a central engine. The synchrotron emission from the forward and reverse shocks could dominate in two quite different energy bands; under some conditions, the relativistic reverse shock dominates the X-ray emission and the Newtonian forward shock dominates the infrared and optical emission. We show that the spectral energy distribution of Swift J1644+57 could be explained by an internal shock model.
14538301
Measuring dark energy with gamma-ray bursts and other cosmological probes
It has been widely shown that cosmological parameters and dark energy can be constrained by using data from Type Ia supernovae (SNe Ia), the cosmic microwave background (CMB) anisotropy, the baryon acoustic oscillation (BAO) peak from Sloan Digital Sky Survey (SDSS), the X-ray gas mass fraction in clusters, and the linear growth rate of perturbations at z = 0.15 as obtained from the 2dF Galaxy Redshift Survey. Recently, gamma-ray bursts (GRBs) have also been argued to be promising standard candles for cosmography. In this paper, we present constraints on the cosmological parameters and dark energy by combining a recent GRB sample including 69 events with the other cosmological probes. First, we find that for the ΛCDM cosmology this combination makes the constraints stringent, and the best fit is close to the flat universe. Second, we fit the flat Cardassian expansion model and find that this model is consistent with the ΛCDM cosmology. Third, we present constraints on several two-parameter dark energy models and find that these models are also consistent with the ΛCDM cosmology. Finally, we reconstruct the dark energy equation of state parameter w(z) and the deceleration parameter q(z). We see that the acceleration could have started at a redshift from zt = 0.40 to 0.65. This difference in the transition redshift is due to different dark energy models that we adopt. The most stringent constraint on w(z) lies in the redshift range z ~ 0.3-0.6.
109204818
Performance Limiting Effects in X‐Band Accelerators
Acceleration gradient is a critical parameter for the design of future TeV‐scale linear colliders. The major obstacle to higher gradient in room‐temperature accelerators is rf breakdown, which is still a very mysterious phenomenon that depends on the geometry and material of the accelerator as well as the input power and operating frequency. Pulsed heating has been associated with breakdown for many years however there have been no experiments that clearly separate field and heating effects on the breakdown rate. Recently, such experiments have been performed at SLAC with both standing‐wave and travelling‐wave structures. These experiments have demonstrated that pulsed heating is limiting the gradient. Also, a dual‐moded cavity has been designed to better distinguish the electric field, magnetic field and pulsed heating effects on breakdown.
73619195
Probing the cosmographic parameters to distinguish between dark energy and modified gravity models
Aims. In this paper we investigate the deceleration, jerk and snap parameters to distinguish between the dark energy and modified gravity models using high redshift gamma-ray bursts (GRBs) and supernovae (SNe). Methods. We first derive the expressions of deceleration, jerk and snap parameters in dark energy and modified gravity models. In order to constrain the cosmographic parameters, we calibrate the GRB luminosity relations without assuming any cosmological models using SNe Ia. Then we constrain the model parameters (including dark energy and modified gravity models) using type Ia supernovae and gamma-ray bursts. Finally we calculate the cosmographic parameters. GRBs can extend the redshift-distance relation up to high redshifts, because they can be detected to high redshifts. Results. We find that the statefinder pair (r, s) could not be used to distinguish between some dark energy and modified gravity models, but these models could be differentiated by the snap parameter. Using the model-independent constraints on cosmographic parameters, we conclude that the ΛCDM model is consistent with current data.
124213992
High performance computation on beam dynamics problems in high intensity compact cyclotrons
This paper presents the research progress in the beam dynamics problems for future high intensity compact cyclotrons by utilizing the state-of-the-art high performance computation technology. A “Start-to-Stop” model, which includes both the interaction of the internal particles of a single bunch and the mutual interaction of neighboring multiple bunches in the radial direction, is established for compact cyclotrons with multi-turn extraction. This model is then implemented in OPAL-CYCL, which is a 3D object-oriented parallel code for large scale particle simulations in cyclotrons. In addition, to meet the running requirement of parallel computation, we have constructed a small scale HPC cluster system and tested its performance. Finally, the high intensity beam dynamics problems in the 100 MeV compact cyclotron, which is being constructed at CIAE, are studied using this code and some conclusions are drawn.