18266887
A model of the light curves of Gamma-Ray Bursts
Aims. An extreme Kerr black hole (BH) surrounded by a precessing disk is invoked to explain the light curves of gamma-ray bursts (GRBs) based on the coexistence of the Blandford-Znajek (BZ) and the magnetic coupling (MC) processes. Methods. The overall shape of the light curves and the duration of GRBs are interpreted by the evolution of the halfopening angle of the magnetic flux on the BH horizon, and the complex temporal structures are modulated by the precession and nutation of the jet powered by the BZ process. Results. The time profile of the emission exhibits a fast rise and a slow decay due to the effect of the evolution of the half-opening angle. The light curves of several GRBs are well fitted by this model with only six free parameters.
39487088
Restoration of rectangular pulse shape after edge erosion for a space-charge dominated electron bunch.
We present in this Letter a novel experimental method that demonstrates the time reversibility of the 1D cold-fluid equations for a space-charge dominated beam. A bunch of charged particles with an initially rectangular line-charge and velocity profile experiences edge erosion during transport through a focusing system due to the nonlinear, longitudinal space-charge forces at the edges. By imposing on the eroded beam pulse a linear velocity gradient at a proper location one can restore the rectangular line-charge profile downstream. [An experiment has been performed to demonstrate this principle.] This technique could be used to offset edge erosion and assure a rectangular pulse shape for efficient acceleration and uniform power flow in the interaction region for applications of intense, high-power beams.
17295428
Influences of the magnetic coupling process on the spectrum of a disk covered by the corona
Context. Recently, much attention has been paid to the magnetic coupling (MC) process, which is supported by the very high emissivity indexes observed in Seyfert 1 galaxy MCG-6-30-15 and GBHC XTE J1650-500. But the rotational energy transferred from a black hole is simply assumed to be radiated away from the surrounding accretion disk in the black-body spectrum, which is obviously not consistent with the observed hard power-law X-ray spectra. Aims. We introduce a corona into the MC model to make it more compatible with observations. Methods. We describe the model and the procedure of a simplified Monte Carlo simulation, compare the output spectra in the cases with and without the MC effects, and discuss the influences of the three parameters involved in the MC process on the output spectra. Results. It is shown that the MC process augments radiation fluxes in the UV or X-ray band. The emergent spectrum is affected by the BH spin and magnetic field strength at the BH horizon, while it is almost unaffected by the radial profile of the magnetic field at the disk. Conclusions. Introducing corona into the MC model will improve the fitting of the output spectra from AGNs and GBHCs.
55579613
Computer simulation of the Maryland Transport Experiment
The longitudinal dynamics of the high-perveance long-pulse electron beam in the Maryland Transport Experiment is examined for the special case of an initially parabolic bunch. Because the longitudinal dynamics can depend on details of time-dependent transverse beam parameters which are difficult to measure, sensitivity studies using r-z simulations have been used to demonstrate that the details of longitudinal beam evolution are insensitive to transverse mismatch, and the bunch length evolution can be accurately described by the one-dimensional envelope equation with the "geometry factor" appropriately chosen. Comparison of experimental data to r,z simulation and to the envelope solution is presented.<<ETX>>
27409140
Generation of space-charge waves due to localized perturbations in a space-charge dominated beam.
It has been found for the first time in experiments with an electron beam that space-charge waves can be generated not only in pairs. A single slow wave, a single fast wave, or combinations of the two waves with different amplitude and polarity relations have been produced experimentally in a space-charge dominated beam. Analytical solutions derived from one-dimensional fluid equations show the amplitude and polarity of each space-charge wave as a function of the initial perturbation parameters. The theory provides the correct interpretation of the experimental observations.
117533820
Longitudinal kinetic energy spread from focusing in charged particle beams
A charged particle beam can be given a longitudinal kinetic energy spread through focusing by magnetic solenoid lenses. Measurements of energy spread are reported and are compared with the results of computer simulations, which include several known sources of energy spread. These sources are discussed. The results of the measurements and the simulations agree, giving energy spreads which are two orders of magnitude larger than the initial thermal energy spread.<<ETX>>
29813748
Intrabeam scattering and touscheck lifetime for the optical stochastic cooling experiment at the MIT-Bates South Hall ring
A proof-of-principle experiment of optical stochastic cooling (OSC) at the MIT-Bates South Hall electron storage ring (SHR) has been proposed. To produce convincing cooling results, the ring will be run near 300 MeV. Beam emittance growth caused by Intrabeam scattering (IBS) is a major concern for the design of experiment. Touschek scattering imposes a dominant limit on beam lifetime. Evaluation of these effects is part of the design optimization process. Simulation analyses of cooling for a viable OSC experiment are presented.
22229601
Linac upgrading program for the FERMI project: Status and perspectives
FERMI@ELETTRA is a soft X-ray fourth generation light source under development at the ELETTRA laboratory. It will be based on the existing 1.0-GeV linac, revised and upgraded to fulfill the stringent requirements expected from the machine. The overall time schedule of the project is very tight and ambitious, expecting 10 nm photons for users by 2010. Here the machine upgrade program and the ongoing activities are presented and discussed.
53997503
A PERMANENT MAGNET PHASE SHIFTER FOR THE EUROPEAN X-RAY FREE ELECTRON LASER
In undulator systems with adjustable gaps phase shifters are needed to exactly control the phase retardation between electrons and the radiation field over the entire length of an undulator system. A phase shifter based on Permanent Magnet technology for the use in the European XFEL has been developed and tested. Specifications are given. This paper will explain its magnetic principle and design. Magnetic test results are presented and thoroughly discussed. Special attention is given to the operation in the XFEL.
92990894
COMMISSIONING OF THE SSRF STORAGE RING
The Shanghai Synchrotron Radiation Facility (SSRF) is a third generation light source with 3.5GeV beam energy. Its accelerator complex consists of a 150MeV linac, a full energy booster and a 3.5GeV storage ring. Commissioning of the storage ring on 3.0GeV beam energy began on Dec. 21st evening 2007 prior to the schedule. The first turn was observed after three hours with RF off. The beam was stored after twelve hours, and then cumulated up to 5 mA current. On Jan. 3, 2008, a beam with 100mA current is successfully obtained in the machine for the first time. Since then, the storage ring has been brought close to the designed specifications, and frequently operated with 100mA beam current for cleaning the vacuum chamber. In this paper, commissioning results of the storage ring is presented in details.
117072673
The longitudinal polarization scheme on the Beijing Tau-charm Factory