224 research outputs found
Numerical Calculation of Coherent Synchrotron Radiation Effects Using TraFiC4
Coherent synchrotron radiation (CSR) occurs when short bunches travel on
strongly bent trajectories. Its effects on high-quality beams can be severe and
are well understood qualitatively. For quantitative results, however, one has
to rely on numerical methods. There exist several simulation codes utilizing
different approaches. We describe in some detail the code TraFiC4 developed at
DESY for design and analysis purposes, which approaches the problem from first
principles and solves the equations of motion either perturbatively or
self-consistently. We present some calculational results and comparison with
experimental data. Also, we give examples of how the code can be used to design
beamlines with minimal emittance growth due to CSR
Periodic Poisson Solver for Particle Tracking
A method is described to solve the Poisson problem for a three dimensional
source distribution that is periodic into one direction. Perpendicular to the
direction of periodicity a free space (or open) boundary is realized. In beam
physics, this approach allows to calculate the space charge field of a
continualized charged particle distribution with periodic pattern.
The method is based on a particle mesh approach with equidistant grid and
fast convolution with a Green's function. The periodic approach uses only one
period of the source distribution, but a periodic extension of the Green's
function.
The approach is numerically efficient and allows the investigation of
periodic- and pseudo-periodic structures with period lengths that are small
compared to the source dimensions, for instance of laser modulated beams or of
the evolution of micro bunch structures. Applications for laser modulated beams
are given.Comment: 33 pages, 22 figure
Transverse self-fields within an electron bunch moving in an arc of a circle
As a consequence of motions driven by external forces, self-fields (which are
different from the static case) originate within an electron bunch. In the case
of magnetic external forces acting on an ultrarelativistic beam, the
longitudinal self-interactions are responsible for CSR (Coherent Synchrotron
Radiation)-related phenomena, which have been studied extensively. On the other
hand, transverse self-interactions are present too. At the time being, existing
theoretical analysis of transverse self-forces deal with the case of a bunch
moving along a circular orbit only, without considering the situation of a
bending magnet with a finite length. In this paper we propose an
electrodynamical analysis of transverse self-fields which originate, at the
position of a test particle, from an ultrarelativistic electron bunch moving in
an arc of a circle. The problem will be first addressed within a two-particle
system. We then extend our consideration to a line bunch with a stepped density
distribution, a situation which can be easily generalized to the case of an
arbitrary density distribution. Our approach turns out to be also useful in
order to get a better insight in the physics involved in the case of simple
circular motion and in order to address the well known issue of the partial
compensation of transverse self-force.Comment: 23 pages, 14 figure
Impact of Optics on CSR-Related Emittance Growth in Bunch Compressor Chicanes
Abstract The dependence of emittance growth due to Coherent Synchrotron Radiation (CSR) in bunch compressor chicanes on optics has been noticed and empirically studied in the past. We revisit the subject, suggesting a model to explain slice emittance growth dependence on chicane optics. A simplified model to calculate projected emittance growth when it is mainly caused by transverse slice centroid offsets is presented. It is then used to find optimal compensation of centroid kicks in the single chicanes of a two-stage compression system by adjusting the phase advance of the transport in between and the ration of the compression factors
Electromagnetic fields and beam dynamics simulation for the superstructure of TESLA linear collider considering field asymmetry caused by HOM and power couplers
Some features of accelerating section field computation presented by the development of power and HOM couplers for TESLA linear collider are considered. The devices mentioned produce electromagnetic field asymmetry in the beam area, thus causing transverse kick. For this kick and its influence on beam under acceleration parameters estimation the dynamics modelling calculations were done. 3D-simulation code MAFIA was used for field computation. These data were further used in beam dynamics calculations by means of TRMTrace code. Standing wave mode was simulated while considering HOM couplers, and travelling wave in case of power couplers. Transverse kicks and focussing forces are calculated for one HOM coupler design and two coaxial FM couplers
Algorithm for calculating spectral intensity due to charged particles in arbitrary motion
An algorithm for calculating the spectral intensity of radiation due to the
coherent addition of many particles with arbitrary trajectories is described.
Direct numerical integration of the Lienard-Wiechert potentials, in the
far-field, for extremely high photon energies and many particles is made
computationally feasible by a mixed analytic and numerical method. Exact
integrals of spectral intensity are made between discretely sampled
trajectories, by assuming the space-time four-vector is a quadratic function of
proper time. The integral Fourier transform of the trajectory with respect to
time, the modulus squared of which comprises the spectral intensity, can then
be formed by piecewise summation of exact integrals between discrete points.
Because of this, the calculation is not restricted by discrete sampling
bandwidth theory, and hence for smooth trajectories, time-steps many orders
larger than the inverse of the frequency of interest can be taken.Comment: 19 pages, 6 figures, submitted to J. Comp. Phys. Changes in new
version: axis labels of figure 3 correcte
RF thermal and new cold part design studies on TTF-III input coupler for Project-X
RF power coupler is one of the key components in superconducting (SC) linac.
It provides RF power to the SC cavity and interconnects different temperature
layers (1.8K, 4.2K, 70K and 300K). TTF-III coupler is one of the most promising
candidates for the High Energy (HE) linac of Project X, but it cannot meet the
average power requirements because of the relatively high temperature rise on
the warm inner conductor, some design modifications will be required. In this
paper, we describe our simulation studies on the copper coating thickness on
the warm inner conductor with RRR value of 10 and 100. Our purpose is to
rebalance the dynamic and static loads, and finally lower the temperature rise
along the warm inner conductor. In addition, to get stronger coupling, better
power handling and less multipacting probability, one new cold part design was
proposed using 60mm coaxial line; the corresponding multipacting simulation
studies have also been investigated.Comment: 5 pages, 12 figures. Submitted to Chinese Physics C (Formerly High
Energy Physics and Nuclear Physics
First Observation of Self-Amplified Spontaneous Emission in a Free-Electron Laser at 109 nm Wavelength
We present the first observation of Self-Amplified Spontaneous Emission
(SASE) in a free-electron laser (FEL) in the Vacuum Ultraviolet regime at 109
nm wavelength (11 eV). The observed free-electron laser gain (approx. 3000) and
the radiation characteristics, such as dependency on bunch charge, angular
distribution, spectral width and intensity fluctuations all corroborate the
existing models for SASE FELs.Comment: 6 pages including 6 figures; e-mail: [email protected]
Isolated terawatt attosecond hard X-ray pulse generated from single current spike
Isolated terawatt (TW) attosecond (as) hard X-ray pulse is greatly desired for four-dimensional investigations of natural phenomena with picometer spatial and attosecond temporal resolutions. Since the demand for such sources is continuously increasing, the possibility of generating such pulse by a single current spike without the use of optical or electron delay units in an undulator line is addressed. The conditions of a current spike (width and height) and a modulation laser pulse (wavelength and power) is also discussed. We demonstrate that an isolated TW-level as a hard X-ray can be produced by a properly chosen single current spike in an electron bunch with simulation results. By using realistic specifications of an electron bunch of the Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL), we show that an isolated, >1.0 TW and similar to 36 as X-ray pulse at 12.4 keV can be generated in an optimized-tapered undulator line. This result opens a new vista for current XFEL operation: the attosecond XFEL
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