165 research outputs found
Traveling wave method for simulating geometric beam coupling impedance of a beamscreen with pumping holes
In particle accelerators, pumping holes in a vacuum chamber can be a source
of unwanted broadband coupling impedance, leading to beam instabilities.
Analytical methods have been previously developed to estimate the impedance of
holes in circular-like chambers e.g. the beamscreen of the Large Hadron
Collider (LHC). More sophisticated chamber designs like that of the High Energy
LHC (HE-LHC) and the Future Circular Collider (FCC-hh) call for a different way
to calculate the impedance. We propose using decomposition of the wakefield
into synchronous traveling waves and employing a numerical solver to find the
impedance of each wave. This method is compared to the direct time domain
wakefield calculation method and its greater sensitivity to small impedances is
shown
Investigations into X-band dielectric disk accelerating structures for future linear accelerators
Dielectric disk accelerating (DDA) structures are being studied as an
alternative to conventional disk-loaded copper structures. This paper
investigates numerically an efficient X-band DDA structure operating at a
higher order mode of TM02-{\pi}. This accelerating structure consists of
dielectric disks with irises arranged periodically in a metallic enclosure.
Through optimizations, the RF power loss on the metallic wall can be
significantly reduced, resulting in an extremely high quality factor Q_0=111064
and a very high shunt impedance R_shunt=605 M{\Omega}/m. The RF-to-beam power
efficiency reaches 46.6% which is significantly higher than previously-reported
CLIC-G structures with an efficiency of only 28.5%. The optimum geometry of the
regular and the end cells is described in detail. Due to the wide bandwidth
from the dispersion relation of the accelerating mode, the DDA structure is
allowed to have a maximum number of 73 regular cells with a frequency
separation of 1.0 MHz, which is superior to that of conventional RF
accelerating structures. In addition, the DDA structure is found to have a
short-range transverse wakefield lower than that of the CLIC-G structure.Comment: 13 pages, 15 figures, submitted for a journa
Local power coupling as a predictor of high-gradient breakdown performance
A novel quantity for predicting the high-gradient performance of radio
frequency accelerating structures is presented. The quantity is motivated,
derived and compared with earlier high-gradient limits and experiments. This
new method models a nascent RF breakdown as a current-carrying antenna and
calculates the coupling of the antenna to an RF power source. With the help of
an electron emission model to describe a nascent breakdown, the antenna model
describes how a breakdown modifies the local surface electric field before it
fully develops in any given structure geometry. For the structure geometries
that this method was applied to, it was found that the calculated
breakdown-loaded electric field was well-correlated with observed spatial
breakdown distributions, and gave consistent values for the maximum
breakdown-limited accelerating gradient between different geometries.Comment: 16 pages, 22 figures. Submitted to Physical Review Accelerators and
Beam
Analysis of Long-range Wakefields in CLIC Main Linac Accelerating Structures with Damping Loads
The baseline design of the CLIC accelerating structure foresees a moderate detuning and heavy damping of high order modes (HOMs), which are the source of long-range transverse wakefields. Such unwanted fields produce bunch-to-bunch instabilities so the HOMs must be suppressed. In order to damp these modes, the CLIC RF structure is equipped with lossy material inserted into four rectangular waveguides coupled to each accelerating cell. The lossy material absorbs EM (electromagnetic) wave energy with little reflection back to the accelerating cells. In the past, computations of the long-range wake of CLIC accelerating modes have been done using perfectly absorbing boundaries to terminate the damping waveguides. In this paper, 3D EM simulations of CLIC baseline accelerating structure with HOMs damping loads will be presented. A comparison between different EM codes (GdfidL, CST PARTICLE STUDIO®) will be discussed as well as the analysis of different types of absorbing materials with respect to the wakefields damping
750 MHz radio frequency quadrupole with trapezoidal vanes for carbon ion therapy
High-frequency linear accelerators are very suitable for carbon ion therapy,
thanks to the reduced operational costs and the high beam quality with respect
to synchrotrons, which are presently the only available technology for this
application. In the framework of the development of a new linac for carbon ion
therapy, this article describes the design of a compact 750 MHz Radio Frequency
Quadrupole (RFQ) with trapezoidal vanes. A new semi-analytic approach to design
the trapezoidal-vane RFQ is introduced together with the relevant beam dynamics
properties. The RFQ is split into two decoupled rf cavities, both of which make
use of a novel dipole detuning technique by means of length adjustment. The
splitting is described both from the rf and the beam dynamics point of view.
The paper concludes with the rf design of the full structure, including maximum
surface field and thermal studies.Comment: Revised version published in Physical Review Accelerators and Beams
on 31 December 202
Longitudinal phase space reconstruction simulation studies using a novel X-band transverse deflecting structure at the SINBAD facility at DESY
A transverse deflecting structure (TDS) is a well-known device for
characterizing the longitudinal properties of an electron bunch in a linear
accelerator. The standard use of such a cavity involves streaking the bunch
along a transverse axis and analysing the image on a screen downstream to find
the bunch length and slice properties along the other transverse axis. A novel
X-band deflecting structure, which will allow the polarization of the
deflecting field to be adjusted, is currently being designed as part of a
collaboration between CERN, DESY and PSI. This new design will allow bunches to
be streaked at any transverse angle within the cavity, which will open up the
possibility of new measurement techniques, which could be combined to
characterize the 6D phase space distribution of bunches. In this paper, a
method is presented for reconstructing the longitudinal phase space
distribution of bunches by using the TDS in combination with a dipole.
Simulations of this technique for the SINBAD-ARES beamline are presented and
the key limitations related to temporal resolution and induced energy spread
are discussed.Comment: 6 page
Design, fabrication and low-power RF measurement of an X-band dielectric-loaded accelerating structure
Dielectric-loaded accelerating (DLA) structures are being studied as an
alternative to conventional disk-loaded copper structures to produce the high
accelerating gradient. This paper presents the design, fabrication and
low-power RF measurement of an externally-powered X-band DLA structure with a
dielectric constant epsilon_r=16.66 and a loss tangent tan_delta=0.0000343. A
dielectric matching section for coupling the RF power from a circular waveguide
to an X-band DLA structure consists of a very compact dielectric disk with a
width of 2.035 mm and a tilt angle of 60 degree, resulting in a broadband
coupling at a low RF field which has the potential to survive in the high-power
environment. Based on simulation studies, a prototype of the DLA structure was
fabricated. Results from bench measurements and their comparison with design
values are presented. The detailed analysis on the fabrication error which may
cause the discrepancy between the RF measurements and simulations is also
discussed.Comment: 16 pages, 28 figures. arXiv admin note: substantial text overlap with
arXiv:2008.0920
Broadband Electromagnetic Characterization of Materials for Accelerator Components
Electromagnetic (EM) characterization of materials up to high frequencies is a major requirement for the correct modeling of many accelerator components: collimators, kickers, high order modes damping devices for accelerating cavities. In this scenario, the coaxial line method has gained much importance compared to other methods because of its applicability in a wide range of frequencies. In this paper we describe a new coaxial line method that allows using only one measurement setup to characterize the material in a range of frequency from few MHz up to several GHz. A coaxial cable fed at one side is filled with the material under test and closed on a known load on the other side. The properties of the material are obtained from the measured reflection coefficient by using it as input for a transmission line (TL) model or for 3D EM simulations, which describe the measurements setup. We have applied this method to characterize samples of SiC (Silicon Carbide) which could be used for LHC collimators and for CLIC accelerating structures and NiZn ferrite used for kicker magnets
RF Design of the X-band Linac for the EuPRAXIA@SPARC_LAB Project
We illustrate the RF design of the X-band linac for the upgrade of the SPARC_LAB facility at INFN-LNF (EuPRAXIA@SPARC_LAB). The structures are travelling wave (TW) cavities, working on the 2Ď€/3 mode, fed by klystrons with pulse compressor systems. The tapering of the cells along the structure and the cell profiles have been optimized to maximize the effective shunt impedance keeping under control the maximum value of the modified Poynting vector, while the couplers have been designed to have a symmetric feeding and a reduced pulsed heating. In the paper we also present the RF power distribution layout of the accelerating module and a preliminary mechanical design
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