348 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
Axial representation of external electromagnetic fields for particle tracking in accelerators
We derive a power series representation of an arbitrary electromagnetic field
near some axis through the coaxial field components on the axis. The obtained
equations are compared with Fourier-Bessel series approach and verified by
several examples. It is shown that for each azimuthal mode we need only two
real functions on the axis in order to describe the field in a source free
region near to it. The representation of dipole mode in a superconducting
radio-frequency gun is analyzed.Comment: 23 pages, 5 figure
Detuning related coupler kick variation of a superconducting nine-cell 1.3 GHz cavity
Superconducting TESLA-type cavities are widely used to accelerate electrons
in long bunch trains, such as in high repetition rate free electron lasers. The
TESLA cavity is equipped with two higher order mode couplers and a fundamental
power coupler (FPC), which break the axial symmetry of the cavity. The passing
electrons therefore experience axially asymmetrical coupler kicks, which depend
on the transverse beam position at the couplers and the rf phase. The resulting
emittance dilution has been studied in detail in the literature. However, the
kick induced by the FPC depends explicitly on the ratio of the forward to the
backward traveling waves at the coupler, which has received little attention.
The intention of this paper is to present the concept of discrete coupler kicks
with a novel approach of separating the field disturbances related to the
standing wave and a reflection dependent part. Particular attention is directed
to the role of the penetration depth of the FPC antenna, which determines the
loaded quality factor of the cavity. The developed beam transport model is
compared to dedicated experiments at FLASH and European XFEL. Both the observed
transverse coupling and detuning related coupler kick variations are in good
agreement with the model. Finally, the expected trajectory variations due to
coupler kick variations at European XFEL are investigated and results of
numerical studies are presented
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
Superradiant Cherenkov-Wakefield radiation as THz source for FEL facilities
An electron beam passing through a tube which is lined on the inside with a
dielectric layer will radiate energy in the THz range due to the interaction
with the boundary. The resonant enhancement of certain frequencies is
conditioned by structure parameters as tube radius and permittivity of the
dielectric layer. In low loss structures narrow-band radiation is generated
which can be coupled out by suitable antennas. For higher frequencies the
coupling to the resistive outer metal layer becomes increasingly important. The
losses in the outer layer prohibit to reach high frequencies with narrow-band
conditions. Instead short broad-band pulses can be generated with still
attractive power levels. In the first section of the paper a general theory of
the impedance of a two-layer structure is presented and the coupling to the
outer resistive layer is discussed. Approximate relations for the radiated
energy, power and pulse length for a set of structure parameters are derived
and compared to numerical results in the following section. Finally first
numerical result of the out-coupling of the radiation by means of a Vlasov
antenna and estimates of the achieved beam quality are presented.Comment: submitted for publicatio
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
OPTIMIZATION ISSUES IN FINITE ELEMENT CODES FOR SOLVING OPEN DOMAIN 3D ELECTROMAGNETIC SCATTERING AND CONFORMAL ANTENNA PROBLEMS
The first part of the paper presents the implementation and performance of a new absorbing boundary condition (ABC) for truncating finite element meshes. This ABC can be applied conformally to the surface of the structure for scattering and antenna radiation calculations. Consequently, the computational domain is reduced dramatically, thus allowing the simulation of much larger structures, and results are presented for three-dimensional bodies. The latter part of the paper discusses optimization issues relating to the solver's CPU speed on parallel and vector processors. It is shown that a jagged diagonal storage scheme leads to a four-fold increase in the FLOP rate of the code, and a standard matrix profile reduction algorithm substantially reduces the inter-processor communication.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50414/1/241_ftp.pd
- …