IPAC2021 - Classification: MC5: Beam Dynamics and EM Fields / D03 Calculations of EM Fields

Paper	Title	Page
TUPAB225	3D Magnetic Field Analysis of LHC Final Focus Quadrupoles with Beam Screen	1952
	T. Pugnat, B. Dalena, C. Lorin CEA-IRFU, Gif-sur-Yvette, France S. Bagnis CEA-DRF-IRFU, France
	During the LHC commissioning, a discrepancy in the non-linear corrector strengths between the model and the beam-based values has been observed. This has motivated the reconstruction of the 3D finite element model for the LHC final focusing MQXA type magnet. The longitudinal higher orders magnetic field pseudo-harmonics are computed taking into account ovalization of the magnet, interconnections design, and beam screens. The effect of this 3D field on the computation of the nonlinear correctors is evaluated and compared with beam-based corrector values. E. H. Maclean et al., "New approach to LHC optics commissioning for the nonlinear era", Phys. Rev. Acc. B, vol. 22, pp. 061004, June 2019.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB225
About •	paper received ※ 18 May 2021 paper accepted ※ 08 July 2021 issue date ※ 12 August 2021
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TUPAB238	Algorithm to Analyze Complex Magnetic Structures Using a Tube Approach	1995
	B. Riemann, M. Aiba PSI, Villigen PSI, Switzerland
	Modern synchrotron light sources often require sophisticated multipole field distributions that need to be realized by complex magnet structures. To pre-validate these magnet structures via simulations, the extraction procedure needs to output standard multipoles as well as fringe effects. The approach presented in this manuscript uses a volumetric grid map of the magnetic flux density as input. After computation of the reference trajectory (leapfrog integration), a large linear system is solved to compute transverse polynomial coefficients of the magnetic scalar potential in a series of interconnected thin cylinders (linear basis functions) along with that reference. The import of these coefficients into a lattice simulation is discussed using a modification of the tracking code Tracy. The shown approach is routinely used to check models of SLS 2.0 magnets for their properties.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB238
About •	paper received ※ 18 May 2021 paper accepted ※ 17 June 2021 issue date ※ 31 August 2021
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TUPAB239	Radiation of a Charged Particle Bunch Moving Along a Deep Corrugated Surface with a Small Period	1999
	E.S. Simakov, A.V. Tyukhtin Saint Petersburg State University, Saint Petersburg, Russia
	Funding: This work was supported by the Russian Science Foundation (Grant No. 18-72-10137). We investigate the electromagnetic radiation of a bunch moving along a corrugated conductive surface. It is assumed that wavelengths under consideration are much more than the period of the corrugation. In this case, the corrugated structure can be replaced with a smooth surface on which so-called equivalent boundary conditions (EBC) are fulfilled. In fact, we deal with anisotropic surface characterized by certain matrix impedance. Here, we consider the case of deep corrugation, i.e. we assume that the depth of the structure is much more than its period (the case of shallow corrugation was studied earlier). Using the EBC we obtain electromagnetic field components which are presented in form of spectral integrals. It is shown that the bunch generates surface waves propagating in the plane of the structure, whereas volume radiation is absent at the frequencies under consideration. We also consider the energy losses of the bunch. Typical dependences of a spectral density of the energy losses on corrugation parameters are obtained and analyzed. It is demonstrated that the features of the surface waves can be used for the bunch diagnostics. E.I. Nefedov, A.N. Sivov. Electrodynamics of periodic structures. Moscow, Nauka, 1977, 208 p. (in Russian). ** E.S. Simakov, A.V. Tyukhtin, S.N. Galyamin, Phys. Rev. AB, 22, 061301 (2019).
	Poster TUPAB239 [0.637 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB239
About •	paper received ※ 19 May 2021 paper accepted ※ 21 June 2021 issue date ※ 23 August 2021
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TUPAB240	The Impact of Trajectory-Shaped Coil on the Beam Dynamics in the SC230 Superconducting Cyclotron	2002
	I.D. Lyapin, O. Karamyshev, V. Malinin, D. Popov JINR/DLNP, Dubna, Moscow region, Russia G.A. Karamysheva JINR, Dubna, Moscow Region, Russia
	In this paper, we compared the effect of the cyclotron coil shape on the beam dynamics. Two models were created. The first has a conventional round coil, the second has a coil that follows the trajectory of the protons. Parameters of extracted beams are discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB240
About •	paper received ※ 19 May 2021 paper accepted ※ 27 May 2021 issue date ※ 21 August 2021
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TUPAB241	Characterization of the RF-Cavities geometry in Order to Optimize the Beam Parameters in S-Band On-Axis LINACs	2005
	A. Khosravi, B. Shokri LAPRI, Tehran, Iran N. Khosravi ILSF, Tehran, Iran
	The RF characteristics of an accelerating tube are primarily assigned to geometrical features of a cavity. As a consequence of this geometry, the final electric field will make the shape of our Gaussian bunch and the final dose. The accelerating field can be studied considering the nose cone, gap, and bore radius. In dual electron linacs, the role of input power and bunch current is inevitable. Therefore, the geometrical issues of RF-cavities are studied in a 6MeV electron on-axis SW tube. To make an accurate comparison, each RF-cavity is designed and optimized by POISSON SU-PERFISH. The optimized cavities are imported to the PIC solver of CST. Then the beam characteristics are studied on a predefined target.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB241
About •	paper received ※ 18 May 2021 paper accepted ※ 14 June 2021 issue date ※ 30 August 2021
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TUPAB242	The Beam-Study of the Side and On-Axis RF Cavities in S-Band 6 MeV LINACs	2008
	A. Khosravi, B. Shokri LAPRI, Tehran, Iran N. Khosravi ILSF, Tehran, Iran
	The geometry of side and on-axis RF cavities are two magnetic-coupled designs for the different LINAC applications. The electromagnetic fields, RF power, beam parameters, thermal stability, and manufacturing costs are the most critical factors in cavity type selection in each application. In this article, both RF-cavities are optimized in POISSON SUPERFISH code to compare the beam parameters accurately. Then the optimized cavities are making a tube and compare in ASTRA 1D code and CST 3D software. At last, the thermal sensitivity of both models is studied in MPHYSICS module of the CST. As a result, the final decision can be achieved on the side or on-axis cavities considering the input power, costs, beam properties, and thermal stability for the different applications of the LINACs
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB242
About •	paper received ※ 18 May 2021 paper accepted ※ 21 June 2021 issue date ※ 30 August 2021
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TUPAB243	Investigation of the Buncher Effect on Beam Properties in SW 3-6 MeV LINACs	2012
	A. Khosravi, B. Shokri LAPRI, Tehran, Iran N. Khosravi ILSF, Tehran, Iran
	The best quality of an electron beam is the primary goal of a linear accelerator design. Beam-study on a buncher section can lead us to a better perspective of the modulation and acceleration of a beam to optimize the final Gaussian beam. Five setups of different bunchers are designed, optimized, and presented in this article. A more brilliant and converged beam with a higher current, transverse emittance and smaller beam size is the study’s goal.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB243
About •	paper received ※ 18 May 2021 paper accepted ※ 14 June 2021 issue date ※ 26 August 2021
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TUPAB246	Numerical Simulation and Beam-Dynamics Study of a Hollow-Core Woodpile Coupler for Dielectric Laser Accelerators	2022
	G.S. Mauro, D. Mascali, G. Sorbello, G. Torrisi INFN/LNS, Catania, Italy A. Bacci INFN/LASA, Segrate (MI), Italy C. De Angelis, A. Locatelli University of Brescia, Brescia, Italy A.R. Rossi INFN-Milano, Milano, Italy G. Sorbello University of Catania, Catania, Italy
	Hollow core dielectric microstructures powered by lasers represent a new and promising area of accelerator research thanks to the higher damage threshold and accelerating gradients with respect to metals at optical wavelengths. In this paper we present the design of a dielectric Electromagnetic Band Gap (EBG) mode converter for high-power coupling of the accelerating mode in Dielectric Laser Accelerators (DLAs). The design is wavelength-independent, and here we propose an implementation operating at 90.505 GHz (wavelength 3.3 mm) based on a silicon woodpile structure. The coupler is composed by two perpendicularly coupled hollow-core waveguides: a TE-like mode waveguide (excited from RF/laser power) and a TM-like mode accelerating waveguide. The structure has been numerically designed and optimized, presenting Insertion Losses (IL) < 0.3 dB and an efficient mode conversion in the operating bandwidth. The properties and effectiveness of the confined accelerating mode have been optimized in order to derive the needed accelerating gradient. The simulated electric field has been used as input for Astra beam-dynamics simulations in order to compute the beam properties.
	Poster TUPAB246 [2.209 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB246
About •	paper received ※ 18 May 2021 paper accepted ※ 27 July 2021 issue date ※ 13 August 2021
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TUPAB247	Influence of the Profile of the Dielectric Structure on the Electric Fields Excited by a Laser in Dielectric Accelerators Based on Chip	2026
	A. Vasyliev, O.O. Bolshov, K. Galaydych, A.I. Povrozin, G.V. Sotnikov NSC/KIPT, Kharkov, Ukraine
	Funding: The National Research Foundation of Ukraine, program "Leading and Young Scientists Research Support" (project # 2020.02/0299). To provide experimental researches at the NSC KIPT theoretical studies and computations of the electron acceleration in a dielectric laser accelerator have been carried out. Laser accelerator consists of two periodic quartz structures on diffraction gratings or Chips, symmetrically located along both sides of the vacuum accelerating channel. Using PIC numerical simulations, electromagnetic fields excited by laser radiation with a wavelength of 800 nm in dielectric laser accelerators were investigated. The influence of the shape and depth of the profile of diffraction gratings or Chip structures on the distribution of the electric field in the interaction space has been studied. For modeling, different types of profiles were taken, both in serial and a unique structure. In consequence of the analysis of the obtained results, estimated efficiency of acceleration was defined for each type of profile. The rectangular profile of the diffraction grating with the maximum accelerating gradient was selected as optimal for the next experiments.
	Poster TUPAB247 [1.195 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB247
About •	paper received ※ 19 May 2021 paper accepted ※ 31 May 2021 issue date ※ 11 August 2021
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TUPAB248	A Parallel Time Domain Thermal Solver for Transient Analysis of Accelerator Cavities	2030
	C.-K. Ng, L. Ge, Z. Li, L. Xiao SLAC, Menlo Park, California, USA
	Funding: Work supported by US DOE under contract AC02-76SF00515. Simulation of thermal effects in accelerator cavity is normally performed assuming steady state solution where a static thermal solver suffices to evaluate temperature gradients and impacts on mechanical design. However, during the rf pulse ramp up or the machine system cool-down process, when the field in the cavity changes rapidly, transient effects need to be taken into account. A parallel time domain thermal solver has been developed in the finite element multi-physics code suite ACE3P with integrated electromagnetic, thermal and mechanical modeling capabilities. The implementation takes advantage of the parallel computation infrastructure of ACE3P and shares most of the ingredients in mesh generation, matrix assembly, time advancement scheme and postprocessing. In this paper, we will outline the finite element formulation of the transient thermal problem and verify the implementation against analytical solutions and existing numerical results. The thermal solver has also been coupled to ACE3P mechanical solver, allowing stress and strain analysis during the transient stage. Application of the transient thermal solver to realistic accelerator cavities will be presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB248
About •	paper received ※ 19 May 2021 paper accepted ※ 25 August 2021 issue date ※ 02 September 2021
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TUPAB249	Diffraction at the Open-Ended Dielectric-Loaded Circular Waveguide	2033
	S.N. Galyamin, A.V. Tyukhtin, V.V. Vorobev Saint Petersburg State University, Saint Petersburg, Russia
	Funding: Work supported by Russian Science Foundation (Grant No. 18-72-10137). Contemporary beam and THz technologies are tightly interlaced during last years. Strong THz fields allow realization of THz driven electron guns, THz bunch compression, streaking* and THz driven wakefield acceleration. Inversely, dielectric capillaries similar to those used for THz bunch manipulation can be in turn utilized for development of high-power narrow-band THz sources. Mentioned cases involve interaction of THz waves and particle bunches with an open end of certain dielectric loaded waveguide structure, most frequently a circular capillary. For further development of the discussed prospective topics a rigorous approach allowing analytical investigation of both radiation from open-ended capillaries and their excitation by external source would be extremely useful. We present an elegant and efficient rigorous method for solving circular open-ended dielectric-loaded waveguide diffraction problems based on Wiener-Hopf technique. We deal with the case of uniform dielectric loading and internal excitation by a waveguide mode. S-parameters, near-field and far-field distributions are presented. The obtained results can be also applied to the narrow band wakefield. L. Zhao et al., Phys. Rev. Lett., 124, 054802 (2020). M.T. Hibberd et al., Nat. Photonics, 14, 755-759 (2020). * D. Wang et al., Rev. Sci. Instr., 89(9), 093301 (2018).
	Poster TUPAB249 [2.160 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB249
About •	paper received ※ 19 May 2021 paper accepted ※ 21 June 2021 issue date ※ 21 August 2021
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TUPAB250	Axicon-Based Concentrator for Cherenkov Radiation	2036
	S.N. Galyamin, A.V. Tyukhtin Saint Petersburg State University, Saint Petersburg, Russia
	Funding: Work supported by Russian Science Foundation (Grant No. 18-72-10137). We propose a new type of axisymmetric dielectric target - an "axicon-based concentrator" - which effectively concentrates generated Cherenkov radiation (CR) into a small vicinity of a focus point. It consists of two "glued" bodies of revolution: a hollow axicon and a hollow "lens." A theoretical investigation of the radiation field produced by a charge moving through the discussed radiator is performed for the general case where a charge trajectory is shifted with respect to the structure axis. The idea of a dielectric target with a specific profile of the outer surface and suitable analytical methods were presented and developed in our preceding papers , . An essential advantage of the current version of the device is that it allows the efficient concentration of CR energy from relativistic particles, making this device extremely prospective for various applications such as beam-driven THz sources and bunch diagnostic systems. S.N. Galyamin et al., Phys. Rev. Accel. Beams 22, 083001 (2019); 22, 109901 (2019). ** A.V. Tyukhtin et al., Phys. Rev. A 102, 053514 (2020).
	Poster TUPAB250 [1.255 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB250
About •	paper received ※ 24 May 2021 paper accepted ※ 21 June 2021 issue date ※ 12 August 2021
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THPAB245	A Simulation Study of Beam Pipe Eddy Current Effects on Beam Optics	4288
	T. Asami, T. Koseki The University of Tokyo, Graduate School of Science, Tokyo, Japan S. Igarashi, T. Koseki, Y. Kurimoto, Y. Sato KEK, Ibaraki, Japan
	In synchrotrons, fast changes of magnetic field induce eddy currents at the wall of beam pipes. The eddy currents cause a phase delay between excitation currents of the magnets and the magnetic field. The undesired magnetic field affected by eddy currents might be a serious obstacle in controlling beam optics precisely. In fact, in the operation of a high-intensity proton synchrotron J-PARC MR, the largest beam loss is observed at the beginning of acceleration when the magnetic field starts to vary in time. Therefore, it is important to estimate and understand the effects of eddy currents on beam optics. In this study, we have calculated the effect of eddy currents on magnetic field for some magnets in J-PARC MR, using electromagnetic simulation software. In this paper, we would like to report the details and results of the simulation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB245
About •	paper received ※ 19 May 2021 paper accepted ※ 26 July 2021 issue date ※ 17 August 2021
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Paper

Title

Page

3D Magnetic Field Analysis of LHC Final Focus Quadrupoles with Beam Screen

1952

T. Pugnat, B. Dalena, C. Lorin
CEA-IRFU, Gif-sur-Yvette, France
S. Bagnis
CEA-DRF-IRFU, France

During the LHC commissioning, a discrepancy in the non-linear corrector strengths between the model and the beam-based values has been observed*. This has motivated the reconstruction of the 3D finite element model for the LHC final focusing MQXA type magnet. The longitudinal higher orders magnetic field pseudo-harmonics are computed taking into account ovalization of the magnet, interconnections design, and beam screens. The effect of this 3D field on the computation of the nonlinear correctors is evaluated and compared with beam-based corrector values.
*E. H. Maclean et al., "New approach to LHC optics commissioning for the nonlinear era", Phys. Rev. Acc. B, vol. 22, pp. 061004, June 2019.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB225

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paper received ※ 18 May 2021 paper accepted ※ 08 July 2021 issue date ※ 12 August 2021

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TUPAB238

Algorithm to Analyze Complex Magnetic Structures Using a Tube Approach

1995

B. Riemann, M. Aiba
PSI, Villigen PSI, Switzerland

Modern synchrotron light sources often require sophisticated multipole field distributions that need to be realized by complex magnet structures. To pre-validate these magnet structures via simulations, the extraction procedure needs to output standard multipoles as well as fringe effects. The approach presented in this manuscript uses a volumetric grid map of the magnetic flux density as input. After computation of the reference trajectory (leapfrog integration), a large linear system is solved to compute transverse polynomial coefficients of the magnetic scalar potential in a series of interconnected thin cylinders (linear basis functions) along with that reference. The import of these coefficients into a lattice simulation is discussed using a modification of the tracking code Tracy. The shown approach is routinely used to check models of SLS 2.0 magnets for their properties.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB238

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paper received ※ 18 May 2021 paper accepted ※ 17 June 2021 issue date ※ 31 August 2021

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TUPAB239

Radiation of a Charged Particle Bunch Moving Along a Deep Corrugated Surface with a Small Period

1999

E.S. Simakov, A.V. Tyukhtin
Saint Petersburg State University, Saint Petersburg, Russia

Funding: This work was supported by the Russian Science Foundation (Grant No. 18-72-10137).
We investigate the electromagnetic radiation of a bunch moving along a corrugated conductive surface. It is assumed that wavelengths under consideration are much more than the period of the corrugation. In this case, the corrugated structure can be replaced with a smooth surface on which so-called equivalent boundary conditions (EBC) are fulfilled*. In fact, we deal with anisotropic surface characterized by certain matrix impedance. Here, we consider the case of deep corrugation, i.e. we assume that the depth of the structure is much more than its period (the case of shallow corrugation was studied earlier**). Using the EBC we obtain electromagnetic field components which are presented in form of spectral integrals. It is shown that the bunch generates surface waves propagating in the plane of the structure, whereas volume radiation is absent at the frequencies under consideration. We also consider the energy losses of the bunch. Typical dependences of a spectral density of the energy losses on corrugation parameters are obtained and analyzed. It is demonstrated that the features of the surface waves can be used for the bunch diagnostics.
* E.I. Nefedov, A.N. Sivov. Electrodynamics of periodic structures. Moscow, Nauka, 1977, 208 p. (in Russian).
** E.S. Simakov, A.V. Tyukhtin, S.N. Galyamin, Phys. Rev. AB, 22, 061301 (2019).

Poster TUPAB239 [0.637 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB239

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paper received ※ 19 May 2021 paper accepted ※ 21 June 2021 issue date ※ 23 August 2021

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TUPAB240

The Impact of Trajectory-Shaped Coil on the Beam Dynamics in the SC230 Superconducting Cyclotron

2002

I.D. Lyapin, O. Karamyshev, V. Malinin, D. Popov
JINR/DLNP, Dubna, Moscow region, Russia
G.A. Karamysheva
JINR, Dubna, Moscow Region, Russia

In this paper, we compared the effect of the cyclotron coil shape on the beam dynamics. Two models were created. The first has a conventional round coil, the second has a coil that follows the trajectory of the protons. Parameters of extracted beams are discussed.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB240

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paper received ※ 19 May 2021 paper accepted ※ 27 May 2021 issue date ※ 21 August 2021

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TUPAB241

Characterization of the RF-Cavities geometry in Order to Optimize the Beam Parameters in S-Band On-Axis LINACs

2005

A. Khosravi, B. Shokri
LAPRI, Tehran, Iran
N. Khosravi
ILSF, Tehran, Iran

The RF characteristics of an accelerating tube are primarily assigned to geometrical features of a cavity. As a consequence of this geometry, the final electric field will make the shape of our Gaussian bunch and the final dose. The accelerating field can be studied considering the nose cone, gap, and bore radius. In dual electron linacs, the role of input power and bunch current is inevitable. Therefore, the geometrical issues of RF-cavities are studied in a 6MeV electron on-axis SW tube. To make an accurate comparison, each RF-cavity is designed and optimized by POISSON SU-PERFISH. The optimized cavities are imported to the PIC solver of CST. Then the beam characteristics are studied on a predefined target.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB241

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paper received ※ 18 May 2021 paper accepted ※ 14 June 2021 issue date ※ 30 August 2021

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TUPAB242

The Beam-Study of the Side and On-Axis RF Cavities in S-Band 6 MeV LINACs

2008

A. Khosravi, B. Shokri
LAPRI, Tehran, Iran
N. Khosravi
ILSF, Tehran, Iran

The geometry of side and on-axis RF cavities are two magnetic-coupled designs for the different LINAC applications. The electromagnetic fields, RF power, beam parameters, thermal stability, and manufacturing costs are the most critical factors in cavity type selection in each application. In this article, both RF-cavities are optimized in POISSON SUPERFISH code to compare the beam parameters accurately. Then the optimized cavities are making a tube and compare in ASTRA 1D code and CST 3D software. At last, the thermal sensitivity of both models is studied in MPHYSICS module of the CST. As a result, the final decision can be achieved on the side or on-axis cavities considering the input power, costs, beam properties, and thermal stability for the different applications of the LINACs

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB242

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paper received ※ 18 May 2021 paper accepted ※ 21 June 2021 issue date ※ 30 August 2021

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TUPAB243

Investigation of the Buncher Effect on Beam Properties in SW 3-6 MeV LINACs

2012

A. Khosravi, B. Shokri
LAPRI, Tehran, Iran
N. Khosravi
ILSF, Tehran, Iran

The best quality of an electron beam is the primary goal of a linear accelerator design. Beam-study on a buncher section can lead us to a better perspective of the modulation and acceleration of a beam to optimize the final Gaussian beam. Five setups of different bunchers are designed, optimized, and presented in this article. A more brilliant and converged beam with a higher current, transverse emittance and smaller beam size is the study’s goal.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB243

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paper received ※ 18 May 2021 paper accepted ※ 14 June 2021 issue date ※ 26 August 2021

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TUPAB246

Numerical Simulation and Beam-Dynamics Study of a Hollow-Core Woodpile Coupler for Dielectric Laser Accelerators

2022

G.S. Mauro, D. Mascali, G. Sorbello, G. Torrisi
INFN/LNS, Catania, Italy
A. Bacci
INFN/LASA, Segrate (MI), Italy
C. De Angelis, A. Locatelli
University of Brescia, Brescia, Italy
A.R. Rossi
INFN-Milano, Milano, Italy
G. Sorbello
University of Catania, Catania, Italy

Hollow core dielectric microstructures powered by lasers represent a new and promising area of accelerator research thanks to the higher damage threshold and accelerating gradients with respect to metals at optical wavelengths. In this paper we present the design of a dielectric Electromagnetic Band Gap (EBG) mode converter for high-power coupling of the accelerating mode in Dielectric Laser Accelerators (DLAs). The design is wavelength-independent, and here we propose an implementation operating at 90.505 GHz (wavelength 3.3 mm) based on a silicon woodpile structure. The coupler is composed by two perpendicularly coupled hollow-core waveguides: a TE-like mode waveguide (excited from RF/laser power) and a TM-like mode accelerating waveguide. The structure has been numerically designed and optimized, presenting Insertion Losses (IL) < 0.3 dB and an efficient mode conversion in the operating bandwidth. The properties and effectiveness of the confined accelerating mode have been optimized in order to derive the needed accelerating gradient. The simulated electric field has been used as input for Astra beam-dynamics simulations in order to compute the beam properties.

Poster TUPAB246 [2.209 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB246

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paper received ※ 18 May 2021 paper accepted ※ 27 July 2021 issue date ※ 13 August 2021

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TUPAB247

Influence of the Profile of the Dielectric Structure on the Electric Fields Excited by a Laser in Dielectric Accelerators Based on Chip

2026

A. Vasyliev, O.O. Bolshov, K. Galaydych, A.I. Povrozin, G.V. Sotnikov
NSC/KIPT, Kharkov, Ukraine

Funding: The National Research Foundation of Ukraine, program "Leading and Young Scientists Research Support" (project # 2020.02/0299).
To provide experimental researches at the NSC KIPT theoretical studies and computations of the electron acceleration in a dielectric laser accelerator have been carried out. Laser accelerator consists of two periodic quartz structures on diffraction gratings or Chips, symmetrically located along both sides of the vacuum accelerating channel. Using PIC numerical simulations, electromagnetic fields excited by laser radiation with a wavelength of 800 nm in dielectric laser accelerators were investigated. The influence of the shape and depth of the profile of diffraction gratings or Chip structures on the distribution of the electric field in the interaction space has been studied. For modeling, different types of profiles were taken, both in serial and a unique structure. In consequence of the analysis of the obtained results, estimated efficiency of acceleration was defined for each type of profile. The rectangular profile of the diffraction grating with the maximum accelerating gradient was selected as optimal for the next experiments.

Poster TUPAB247 [1.195 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB247

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paper received ※ 19 May 2021 paper accepted ※ 31 May 2021 issue date ※ 11 August 2021

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TUPAB248

A Parallel Time Domain Thermal Solver for Transient Analysis of Accelerator Cavities

2030

C.-K. Ng, L. Ge, Z. Li, L. Xiao
SLAC, Menlo Park, California, USA

Funding: Work supported by US DOE under contract AC02-76SF00515.
Simulation of thermal effects in accelerator cavity is normally performed assuming steady state solution where a static thermal solver suffices to evaluate temperature gradients and impacts on mechanical design. However, during the rf pulse ramp up or the machine system cool-down process, when the field in the cavity changes rapidly, transient effects need to be taken into account. A parallel time domain thermal solver has been developed in the finite element multi-physics code suite ACE3P with integrated electromagnetic, thermal and mechanical modeling capabilities. The implementation takes advantage of the parallel computation infrastructure of ACE3P and shares most of the ingredients in mesh generation, matrix assembly, time advancement scheme and postprocessing. In this paper, we will outline the finite element formulation of the transient thermal problem and verify the implementation against analytical solutions and existing numerical results. The thermal solver has also been coupled to ACE3P mechanical solver, allowing stress and strain analysis during the transient stage. Application of the transient thermal solver to realistic accelerator cavities will be presented.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB248

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paper received ※ 19 May 2021 paper accepted ※ 25 August 2021 issue date ※ 02 September 2021

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TUPAB249

Diffraction at the Open-Ended Dielectric-Loaded Circular Waveguide

2033

S.N. Galyamin, A.V. Tyukhtin, V.V. Vorobev
Saint Petersburg State University, Saint Petersburg, Russia

Funding: Work supported by Russian Science Foundation (Grant No. 18-72-10137).
Contemporary beam and THz technologies are tightly interlaced during last years. Strong THz fields allow realization of THz driven electron guns, THz bunch compression, streaking* and THz driven wakefield acceleration**. Inversely, dielectric capillaries similar to those used for THz bunch manipulation can be in turn utilized for development of high-power narrow-band THz sources***. Mentioned cases involve interaction of THz waves and particle bunches with an open end of certain dielectric loaded waveguide structure, most frequently a circular capillary. For further development of the discussed prospective topics a rigorous approach allowing analytical investigation of both radiation from open-ended capillaries and their excitation by external source would be extremely useful. We present an elegant and efficient rigorous method for solving circular open-ended dielectric-loaded waveguide diffraction problems based on Wiener-Hopf technique. We deal with the case of uniform dielectric loading and internal excitation by a waveguide mode. S-parameters, near-field and far-field distributions are presented. The obtained results can be also applied to the narrow band wakefield.
* L. Zhao et al., Phys. Rev. Lett., 124, 054802 (2020).
** M.T. Hibberd et al., Nat. Photonics, 14, 755-759 (2020).
*** D. Wang et al., Rev. Sci. Instr., 89(9), 093301 (2018).

Poster TUPAB249 [2.160 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB249

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paper received ※ 19 May 2021 paper accepted ※ 21 June 2021 issue date ※ 21 August 2021

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TUPAB250

Axicon-Based Concentrator for Cherenkov Radiation

2036

S.N. Galyamin, A.V. Tyukhtin
Saint Petersburg State University, Saint Petersburg, Russia

Funding: Work supported by Russian Science Foundation (Grant No. 18-72-10137).
We propose a new type of axisymmetric dielectric target - an "axicon-based concentrator" - which effectively concentrates generated Cherenkov radiation (CR) into a small vicinity of a focus point. It consists of two "glued" bodies of revolution: a hollow axicon and a hollow "lens." A theoretical investigation of the radiation field produced by a charge moving through the discussed radiator is performed for the general case where a charge trajectory is shifted with respect to the structure axis. The idea of a dielectric target with a specific profile of the outer surface and suitable analytical methods were presented and developed in our preceding papers *, **. An essential advantage of the current version of the device is that it allows the efficient concentration of CR energy from relativistic particles, making this device extremely prospective for various applications such as beam-driven THz sources and bunch diagnostic systems.
* S.N. Galyamin et al., Phys. Rev. Accel. Beams 22, 083001 (2019); 22, 109901 (2019).
** A.V. Tyukhtin et al., Phys. Rev. A 102, 053514 (2020).

Poster TUPAB250 [1.255 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB250

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paper received ※ 24 May 2021 paper accepted ※ 21 June 2021 issue date ※ 12 August 2021

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THPAB245

A Simulation Study of Beam Pipe Eddy Current Effects on Beam Optics

4288

T. Asami, T. Koseki
The University of Tokyo, Graduate School of Science, Tokyo, Japan
S. Igarashi, T. Koseki, Y. Kurimoto, Y. Sato
KEK, Ibaraki, Japan

In synchrotrons, fast changes of magnetic field induce eddy currents at the wall of beam pipes. The eddy currents cause a phase delay between excitation currents of the magnets and the magnetic field. The undesired magnetic field affected by eddy currents might be a serious obstacle in controlling beam optics precisely. In fact, in the operation of a high-intensity proton synchrotron J-PARC MR, the largest beam loss is observed at the beginning of acceleration when the magnetic field starts to vary in time. Therefore, it is important to estimate and understand the effects of eddy currents on beam optics. In this study, we have calculated the effect of eddy currents on magnetic field for some magnets in J-PARC MR, using electromagnetic simulation software. In this paper, we would like to report the details and results of the simulation.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB245

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paper received ※ 19 May 2021 paper accepted ※ 26 July 2021 issue date ※ 17 August 2021

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