13419104
Evolution characteristics of the central black hole of a magnetized accretion disc
Evolution characteristics of a Kerr black hole (BH) are investigated by considering the coexistence of disc accretion with the Blandford-Znajek process (the BZ process) and magnetic coupling of the BH with the surrounding disc (MC process). (i) The rate of extracting energy from the rotating BH in the BZ process and that in MC process are expressed by a unified formula, which is derived by using an improved equivalent circuit. (ii) The mapping relation between the angular coordinate on the BH horizon and the radial coordinate on the disc is given in the context of general relativity and conservation of magnetic flux. (iii) The power and torque in the BZ process are compared with those in MC process in detail. (iv) Evolution characteristics of the BH and energy extracting efficiency are discussed by using the characteristic functions of BH evolution in the corresponding parameter space. (v) Power dissipation on the BH horizon and BH entropy increase are discussed by considering the coexistence of the above energy mechanisms.
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.
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>>
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.
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.
119090605
Choice of heavy baryon currents in QCD sum rules
In this paper we investigate the effects due to the mixing of two interpolating currents for ground state baryons within the framework of Heavy Quark Effective Theory using the QCD sum rule approach. Both two-point and three-point sum rules, thus the mass, coupling constant and Isgur-Wise function sum rules are considered. It is interesting to contrast those results with each other. Based on the Isgur-Wise functions obtained in this paper, we also analyze the effects of current mixing to Lambda-type and and Sigma-type semi-leptonic decays Lambda_b-->Lambda_c\ell\bar\nu, \Sigma_b-->\Sigma_c\ell\bar\nu and \Sigma_b-->\Sigma^*_c\ell\bar\nu. Decay widths corresponding to various mixing parameters are obtained and can be compared to the experimental data.
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.
119534509
Measurement of the average local energy spread of electron beam via coherent harmonic generation
The local energy spread of electron beam is a very important parameter for high-gain free-electron lasers (FELs), especially the seeded FELs. Highly accurate measurement of the extremely small local energy spread is rather challenging. In this paper, a simple method to accurately measure the average local energy spread based on the coherent harmonic generation is proposed. A one-dimensional analytical estimation is given to show the principle of this method, and three-dimensional simulation codes have been used to verify the theory. This method has been demonstrated on the Shanghai deep ultraviolet FEL, and the results show that the average local energy spread is about only 1.2 keV at the exit of the 136 MeV linac, which agrees well with the numerical simulations.
111146977
Coherent synchrotron radiation detector for a non-invasive subpicosecond bunch length monitor
A Coherent Synchrotron Radiation (CSR) detector has been developed in a collaboration involving CEBAF and the University of Virginia (UVA) to monitor non-destructively the length of a sub-picosecond bunch with high sensitivity. The monitor employs a state of the art GaAs Schottky whisker diode developed at UVA, which is operated at room temperature at a wavelength of a few hundred microns. The detector is capable of detecting radiation power as low as ten nanowatts, depending on the operating wavelength. In this paper we describe the details of design specifications, parameter ranges, and features of the monitor and also report its performance and comparison between the measurement results and calculation. The measurement results are cross-compared with an independent bunch length measurement using a phase modulation and detection technique. Following a brief discussion of the need for such a monitor, the following topics are discussed: brief discussion on the theory of the device and the experimental arrangement, the properties of the Schottky diode detectors which are particularly convenient for our application, a summary of the measurement results, a summary of future plans and improvements to the monitor, and finally, a set of conclusions.
125862664
Dynamical Breaking of Supersymmetry and Its Restoration at High Temperatures
The dynamical breaking of the supersymmetric Higgs model is discussed without adding the Fayet—Iliopoulos term to the Lagrangian. It is shown, in terms of the Nambu—Jona-Lasinio mechanism, that the supersymmetry breaking can be realized dynamically in the supersymmetric Higgs model. The supersymmetry behavior at finite temperatures is also investigated and it is shown that the supersymmetry broken dynamically at zero temperature can be restored at finite temperatures.