118275882
Longitudinal Beam Dynamics with Space Charge in an FEL Driver Accelerator
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>>
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.
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.
1122949
Considerations on Beam Quality Control in MIT X-Ray FEL
The x-ray FEL at MIT[1] is one example of a design for a new generation linac-based light source. Such a new machine requires very high quality electron beams. Besides the usual requirements on beam parameters such as emittance, energy spread, peak current, there are new challenges emerging in the design studies, e.g., the arrival timing of electron beam must reach precision below tens of femtoseconds level to ensure the laser seed overlaps the desired sections of electron bunch in the multiple-stage HGHG process. In this paper we report the progress on design optimization towards high quality and low sensitivity beams.
12960221
Study of the Electron Beam Dynamics in the FERMI @ ELETTRA Linac
A study of the electron beam dynamics in the linac is conducted for the FERMI free electron laser (FEL) founded for construction at the Sincrotrone Trieste
123258592
The LEP impedance model
The bunch current in LEP is limited by collective effects slightly below its design value. To understand this limitation, a set of experiments has been carried out to obtain a model of the impedance seen by the circulating beam. From measurements of the current dependance of the synchrotron and betatron frequencies information about the longitudinal and transverse reactive impedance has been obtained. The growth rate of the m=1 head-tail instability has been observed to gain some knowledge of the resistive transverse impedance. The dependence of the transverse mode-coupling threshold on bunch length has been measured. The energy loss per turn of a stable bunch is given by the longitudinal resistive impedance and has been measured by recording the change of the synchronous phase angle with current. All these quantities represent integrals over products of bunch mode spectra and impedances. By measuring them for different bunch lengths the frequency dependence of the impedances can be estimated. From these results a model of the LEP impedance has been obtained which can be used to estimate the current limitation under different operating conditions.<<ETX>>
117072673
The longitudinal polarization scheme on the Beijing Tau-charm Factory
67837860
Design of a superconducting linac cavity for high-current energy recovery linac operation
The RHIC electron cooler as well as other applications (such as a linac-ring version of eRHIC) requires a very high average current CW electron linac in an energy recovery mode. In this paper we present the design of a 5-cell superconducting linac cavity for velocity of light particles. This cavity will operate at 703.75 MHz with a large beam pipe aperture of 19 cm diameter and ferrite HOM absorbers in the beam pipe, in addition to the conventional HOM couplers for low frequency HOMs. We will report the design of the cavity geometry using the BuildCavity and Superfish codes, loss factor simulations with ABCI, detailed HOM simulations with MAFIA (with and without the ferrite absorbers) and beam breakup simulations using the code TDBBU.