IPAC2019 - Classification: MC5: Beam Dynamics and EM Fields / D03 Calculations of EM Fields

Paper	Title	Page
MOPGW005	Space-Charge Potential for Elliptical Beams	69
	S.R. Koscielniak TRIUMF, Vancouver, Canada
	This work is motivated by the weak-strong beam-beam effect as occurs in colliding charged-particle beams. We consider beams with elliptical cross section and power law binomial forms for the density distribution. We demonstrate explicitly how to construct analytically the space-charge potential inside the ’strong’ beam. This is essential to the program of calculating beam-beam effects for non-gaussian beams.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW005
About •	paper received ※ 19 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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MOPGW006	Long Range Beam Beam: Towards Faster Computations	72
	S.R. Koscielniak TRIUMF, Vancouver, Canada
	We outline some features of a program of study toward faster computation of the cumulative effect of a sequence of beam-beam interactions across the interaction region.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW006
About •	paper received ※ 23 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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MOPGW007	Electromagnetic Impulse of Beam Density F(x, y)G(z)	75
	S.R. Koscielniak TRIUMF, Vancouver, Canada
	We calculate the transverse impulse on a test particle as a bunch of charged particles beam passes by. It is often assumed, but seldom proven, that the EM field from a beam density distribution factored into transverse and longitudinal parts, F and G respectively, has also a factored form P(x, y)Q(z). This factorization is not possible for stationary charges. Contrastingly, it becomes increasingly accurate for ultra-relativistic particle beams. We give a general analysis, show how to develop the corrections in terms of integrals of F and derivatives of G. What is significant is that if we integrate over longitudinal coordinate z to find the transverse impulse on a witness charge, the correction terms integrate to zero leading to the impulse P(x, y)Integral[Q(z)] independent of bunch shape. If this result is already known, this paper serves as a reminder.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW007
About •	paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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MOPGW011	Field-map and Beam Transport Calculations of the Magnetic Separator at ALTO Facility at Orsay	86
	L. Perrot, R. Ollier IPN, Orsay, France
	The Institute of Nuclear Physics at Orsay (IPN-Orsay) has always been a major player in building accelerators for nuclear physics. The ALTO facility is powered by a 50 MeV/10μA linear electron accelerator dedicated to the production of radioactive beams. The production mode is based on the photo-fission process of a thick UCx target heated up to 2000°C and using the ISOL technique. For the ionization of the released fission fragments, three ion source types can be coupled to the target: Febiad ion source, surface ion source, and laser ion source. The facility can deliver the radioactive ions beams to six different experimental set-ups. The mono-charged RIB exiting from the source must be separated using a magnetic dipole in order to select a nucleus before its transmission through electrostatic devices up to the experimental set-ups. This paper is focus on the separator which was build and exploited with success since 40 years. We propose to revisit this dipole with a precise field-map calculation and particles transport simulations. These results will be use as a first brick of the understanding and reliability of the transmission along the RIB lines at the ALTO facility.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW011
About •	paper received ※ 19 April 2019 paper accepted ※ 18 May 2019 issue date ※ 21 June 2019
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MOPGW030	New Analytical Derivation of Group Velocity in TW Accelerating Structures	155
SUSPFO035	use link to see paper's listing under its alternate paper code
	M. Behtouei, M. Migliorati, L. Palumbo Sapienza University of Rome, Rome, Italy L. Faillace Universita’ degli Studi di Milano & INFN, Milano, Italy B. Spataro INFN/LNF, Frascati, Italy
	Ultra high-gradient accelerating structures are needed for the next generation of compact light sources. In the framework of the Compact Light XLS project, we are studying a high harmonic traveling-wave accelerating structure operating at a frequency of 35.982 GHz, in order to linearize the longitudinal space phase. In this paper, we propose a new analytical approach for the estimation of the group velocity in the structure and we compare it with numerical electromagnetic simulations that are carried out by using the code HFSS in the frequency domain.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW030
About •	paper received ※ 08 April 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPGW047	Analysis and Simulation of the "After-Pulse" RF Breakdown	196
	X. Lin, H.B. Chen, Z.N. Liu, J. Shi, H. Zha TUB, Beijing, People’s Republic of China X.W. Wu CERN, Meyrin, Switzerland
	During the high power experiment of a single-cell standing-wave accelerating structure, it was observed that many RF breakdowns happen when the field inside cavity is decaying after the input rf pulse is off. The distribution of breakdown timing shows a peak at the moment of RF power switches off. A series of simulation was performed to study the after-pulse breakdown effect in such a standing-wave structure. A method of calculating poynting vector over time is proposed in this article to study the modified poynting vector at critical points in the cavity. Field simulation and thermal simulation were also carried out to analyse possible reasons for the after-pulse breakdown effect.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW047
About •	paper received ※ 14 May 2019 paper accepted ※ 17 May 2019 issue date ※ 21 June 2019
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MOPGW060	Cherenkov Radiation at Off-Axis Bunch Passage Through Dielectric Concentrator	225
	S.N. Galyamin, A.V. Tyukhtin, V.V. Vorobev Saint Petersburg State University, Saint Petersburg, Russia
	Funding: Work supported by the Grant from Russian Foundation for Basic Research (No. 17-52-04107). Development of tunable systems for non-invasive bunch diagnostics is a modern trend in accelerator physics. Certain dielectric targets are considered in this context, for example, dielectric cones or prisms. Moreover, all-dielectric target which increase the radiated Cherenkov field near the predetermined focus up to several orders of magnitude has been described* and field near its focus and sensitivity of this target have been analyzed*. Here we consider a non-symmetrical case where charge trajectory has a shift with respect to structure axis. We develop analytical approach for description of Cherenkov radiation, perform three-dimensional simulations and compare the results. S.N. Galyamin and A.V. Tyukhtin, Phys. Rev. Lett., 113, 064802 (2014). ** S.N. Galyamin and A.V. Tyukhtin, Nucl. Instr. Meth. Phys. Res. B. 2017. V. 402. P.185-189.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW060
About •	paper received ※ 14 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPGW061	Radiation from a Dielectrically Loaded Waveguide with Open End	228
	S.N. Galyamin, A.A. Grigoreva, A.V. Tyukhtin, V.V. Vorobev Saint Petersburg State University, Saint Petersburg, Russia A. Aryshev KEK, Ibaraki, Japan
	Funding: Work supported by Russian Science Foundation (Grant No. 18-72-10137). Open-ended waveguide structures with dielectric loading excited by specially prepared electron bunches are considered as promising candidates for development of contemporary sources of Terahertz (THz) radiation. Despite of the fact that both ordinary vacuum THz devices (e.g., backward wave oscillator) are widely available and other mechanisms for THz generation are discussed, beam driven sources are still extremely attractive due to the extraordinary peak power of THz radiation. In this report, we study electromagnetic (EM) field produced by a charged particle bunch exiting an open-ended circular waveguide with dielectric filling placed inside collinear vacuum waveguide of a larger radius. Based on the previously developed theory, we mainly investigate Cherenkov radiation generated penetrated vacuum regions of the structure due to the diffraction mechanism. We pay attention to the case of a train of short bunches resulting in high-order Cherenkov modes excitation. We also develop analytical procedure allowing performing the limiting process to the case of infinite radius of the outer waveguide. B.D. O’Shea et al., Nature Communications, Vol. 7, P. 12763, (2016). ** S.N. Galyamin et al., J. Instrumentation, Vol. 13, P. C02012 (2018).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW061
About •	paper received ※ 15 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPGW062	Radiation of a Charge Moving in a Wire Structure	231
	S.N. Galyamin, A.V. Tyukhtin, V.V. Vorobev Saint Petersburg State University, Saint Petersburg, Russia A.I. Benediktovitch EuXFEL, Hamburg, Germany A.I. Benediktovitch BSU, Minsk, Belarus, Belarus
	Funding: This work is supported by the grant from Russian Foundation for Basic Research (No. 17-52-04107). In the X-ray frequency region, interaction of relativistic electrons with crystals results in parametric X-ray radiation (PXR), with its frequency being determined by distance between crystallographic planes and direction of electron motion. If instead of crystal one considers an artificial periodic structure with periods of the order of mm, one can expect emission of radiation of a similar nature at terahertz (THz) frequencies. This frequency range is of significant interest during last decade due to its prospective applications. Moreover, artificial wire-like structures are considered as a promising alternative to conventional dielectric structures for wakefield acceleration. Here we consider electromagnetic (EM) field produced by a charged particle bunch moving through a lattice of parallel conducting wires. We present several approaches for analysis of EM field in the described wire structure. First, conventional two-wave approximation for describing the "short-wave response" is developed. Second, we use the effective medium approach and describe the "long-wave" part of the spectrum. Third, we develop a method based on vibrator antenna theory which can be useful for finite length wire structure. P.D. Hoang, et al., Phys. Rev. Lett., V. 120, P. 164801 (2018).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW062
About •	paper received ※ 14 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPGW064	On Wakefield in Dielectric Waveguide with Shallow Corrugation of Metallic Wall	237
	A.V. Tyukhtin, E.R. Akhmatova, T.Yu. Alekhina, S.N. Galyamin, V.V. Vorobev Saint Petersburg State University, Saint Petersburg, Russia
	Funding: This work was supported by the Russian Science Foundation (Grant # 18-72-10137). Bunch radiation in periodical waveguides was mainly analyzed for situations when wavelengths are comparable to the structure period (Smith-Purcell emission). However, it is also of interest to study the "long-wave radiation" with wavelengths which are much larger than the structure period,. In such situation, the exact boundary conditions on the complicated periodic surface can be replaced with the equivalent boundary conditions (EBC) which must be fulfilled on the smooth surface. Earlier we considered with this approach radiation of the bunch moving along the axis of circular vacuum corrugated waveguide. Comparison of analytical results with COMSOL simulations showed high accuracy of the EBC method. Here we analyze an analogous problem for the waveguide with corrugated wall and dielectric filling under condition that Cherenkov effect takes place in the dielectric. Due to this fact the radiation differs radically from that in the vacuum waveguide. At the same time, the radiation has essential differences from the one in the usual dielectric waveguide. The radiation properties in the waveguide under consideration and its differences from the radiation in the waveguide with smooth wall are analyzed. G. Stupakov, K. Bane, Phys. Rev. ST-AB, 15 (2012) 124401. ** A.V. Tyukhtin et al, J. of Instrumentation, 13 (2018) C04009.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW064
About •	paper received ※ 15 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPGW081	Measurements of Stray Magnetic Fields at CERN for CLIC	289
SUSPFO099	use link to see paper's listing under its alternate paper code
	C. Gohil, N. Blaskovic Kraljevic, D. Schulte CERN, Meyrin, Switzerland P. Burrows JAI, Oxford, United Kingdom B. Heilig MFGI, Budapest, Hungary
	Simulations have shown that the Compact Linear Collider (CLIC) is sensitive to external dynamic magnetic fields (stray fields) to the nT level. Magnetic fields are not typically measured to this precision at CERN. Past measurements of the background magnetic field at CERN are limited. In this paper new measurements are presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW081
About •	paper received ※ 01 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPGW082	Mitigation of Stray Magnetic Field Effects in CLIC with Passive Shielding	293
	C. Gohil, N. Blaskovic Kraljevic, D. Schulte CERN, Meyrin, Switzerland P. Burrows JAI, Oxford, United Kingdom
	Simulations have shown the Compact Linear Collider (CLIC) is sensitive to external dynamic magnetic fields (stray fields) to the nT level. Due to these extremely tight tolerances, mitigation techniques will be required to prevent performance loss. A passive shielding technique is envisaged as a potential solution. A model for passive shielding is presented along with calculations of its transfer function. Measurements of the transfer function of a promising material (mu-metal) that can be used for passive shielding are presented. The validity of passive shielding models in small amplitude magnetic fields is also discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW082
About •	paper received ※ 01 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPTS016	Compression and Noise Reduction of Field Maps	875
	X. Du, L. Groening GSI, Darmstadt, Germany
	Errors from discretization and large data volume of field maps is a concern for beam dynamics simulations with respect to achievable accuracy and to the required amount of time. High-order singular value decomposition (HOSVD) has recently emerged as simple, effective, and adaptive tool to extract the essentials from multidimensional data. This paper is on the feasibility of compression and noise reduction of electromagnetic field map data with HOSVD. The method has been applied to an electric field map of a DTL cavity with 11 m in length comprising 55 rf-gaps. The original field map data of 220 MB was converted into practically noise-free data of just 20 KB. Noise was reduced by 95% as demonstrated using a cubic cavity for which the analytical field map is available.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPTS016
About •	paper received ※ 13 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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WEYYPLS3	Development of Methods for Calculation of Bunch Radiation in Presence of Dielectric Objects	2274
	A.V. Tyukhtin, E.S. Belonogaya, S.N. Galyamin, V.V. Vorobev Saint Petersburg State University, Saint Petersburg, Russia
	Funding: This work was supported by the Russian Science Foundation (Grant # 18-72-10137). Radiation of charged particles moving in presence of dielectric targets is of interests for various applications in accelerator and beam physics. Typically, the size of the target is much larger than the wavelengths under consideration. This fact gives us an obvious small parameter of the problem and allows developing approximate methods of analysis. We develop two methods: "ray-optical method" and "aperture method". These methods can be very effective for all situations where we can find the tangential field components on the "aperture" which is an object boundary illuminated by Cherenkov radiation. We apply the aperture method to different dielectric objects including a prism, a cone, and a ball. Electromagnetic field is analyzed on different distances from the objects. The special attention is given to investigation of the field in the far-field (Fraunhofer) area having large importance for various applications. We obtain analytical results for different objects, demonstrate typical radiation patterns and discuss new physical effects, in particular, the phenomenon of concentration of radiation and effect of "Cherenkov spotlight". Prospects of use of aperture method and ray-optical one for other objects are discussed as well. R.Kieffer et al, PRL, 121, 054802 (2018). ** E.S.Belonogaya et al, JOSA B, 32, 649 (2015); S.N.Galyamin, A.V.Tyukhtin, PRL, 113, 064802 (2014); A.V.Tyukhtin et al, J. Instrum., 13, C02033 (2018).
	Slides WEYYPLS3 [4.063 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEYYPLS3
About •	paper received ※ 14 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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Paper

Title

Page

Space-Charge Potential for Elliptical Beams

69

S.R. Koscielniak
TRIUMF, Vancouver, Canada

This work is motivated by the weak-strong beam-beam effect as occurs in colliding charged-particle beams. We consider beams with elliptical cross section and power law binomial forms for the density distribution. We demonstrate explicitly how to construct analytically the space-charge potential inside the ’strong’ beam. This is essential to the program of calculating beam-beam effects for non-gaussian beams.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW005

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paper received ※ 19 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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MOPGW006

Long Range Beam Beam: Towards Faster Computations

72

S.R. Koscielniak
TRIUMF, Vancouver, Canada

We outline some features of a program of study toward faster computation of the cumulative effect of a sequence of beam-beam interactions across the interaction region.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW006

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paper received ※ 23 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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MOPGW007

Electromagnetic Impulse of Beam Density F(x, y)G(z)

75

S.R. Koscielniak
TRIUMF, Vancouver, Canada

We calculate the transverse impulse on a test particle as a bunch of charged particles beam passes by. It is often assumed, but seldom proven, that the EM field from a beam density distribution factored into transverse and longitudinal parts, F and G respectively, has also a factored form P(x, y)Q(z). This factorization is not possible for stationary charges. Contrastingly, it becomes increasingly accurate for ultra-relativistic particle beams. We give a general analysis, show how to develop the corrections in terms of integrals of F and derivatives of G. What is significant is that if we integrate over longitudinal coordinate z to find the transverse impulse on a witness charge, the correction terms integrate to zero leading to the impulse P(x, y)Integral[Q(z)] independent of bunch shape. If this result is already known, this paper serves as a reminder.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW007

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paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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MOPGW011

Field-map and Beam Transport Calculations of the Magnetic Separator at ALTO Facility at Orsay

86

L. Perrot, R. Ollier
IPN, Orsay, France

The Institute of Nuclear Physics at Orsay (IPN-Orsay) has always been a major player in building accelerators for nuclear physics. The ALTO facility is powered by a 50 MeV/10μA linear electron accelerator dedicated to the production of radioactive beams. The production mode is based on the photo-fission process of a thick UCx target heated up to 2000°C and using the ISOL technique. For the ionization of the released fission fragments, three ion source types can be coupled to the target: Febiad ion source, surface ion source, and laser ion source. The facility can deliver the radioactive ions beams to six different experimental set-ups. The mono-charged RIB exiting from the source must be separated using a magnetic dipole in order to select a nucleus before its transmission through electrostatic devices up to the experimental set-ups. This paper is focus on the separator which was build and exploited with success since 40 years. We propose to revisit this dipole with a precise field-map calculation and particles transport simulations. These results will be use as a first brick of the understanding and reliability of the transmission along the RIB lines at the ALTO facility.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW011

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paper received ※ 19 April 2019 paper accepted ※ 18 May 2019 issue date ※ 21 June 2019

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MOPGW030

New Analytical Derivation of Group Velocity in TW Accelerating Structures

155

SUSPFO035

use link to see paper's listing under its alternate paper code

M. Behtouei, M. Migliorati, L. Palumbo
Sapienza University of Rome, Rome, Italy
L. Faillace
Universita’ degli Studi di Milano & INFN, Milano, Italy
B. Spataro
INFN/LNF, Frascati, Italy

Ultra high-gradient accelerating structures are needed for the next generation of compact light sources. In the framework of the Compact Light XLS project, we are studying a high harmonic traveling-wave accelerating structure operating at a frequency of 35.982 GHz, in order to linearize the longitudinal space phase. In this paper, we propose a new analytical approach for the estimation of the group velocity in the structure and we compare it with numerical electromagnetic simulations that are carried out by using the code HFSS in the frequency domain.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW030

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paper received ※ 08 April 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPGW047

Analysis and Simulation of the "After-Pulse" RF Breakdown

196

X. Lin, H.B. Chen, Z.N. Liu, J. Shi, H. Zha
TUB, Beijing, People’s Republic of China
X.W. Wu
CERN, Meyrin, Switzerland

During the high power experiment of a single-cell standing-wave accelerating structure, it was observed that many RF breakdowns happen when the field inside cavity is decaying after the input rf pulse is off. The distribution of breakdown timing shows a peak at the moment of RF power switches off. A series of simulation was performed to study the after-pulse breakdown effect in such a standing-wave structure. A method of calculating poynting vector over time is proposed in this article to study the modified poynting vector at critical points in the cavity. Field simulation and thermal simulation were also carried out to analyse possible reasons for the after-pulse breakdown effect.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW047

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paper received ※ 14 May 2019 paper accepted ※ 17 May 2019 issue date ※ 21 June 2019

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MOPGW060

Cherenkov Radiation at Off-Axis Bunch Passage Through Dielectric Concentrator

225

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

Funding: Work supported by the Grant from Russian Foundation for Basic Research (No. 17-52-04107).
Development of tunable systems for non-invasive bunch diagnostics is a modern trend in accelerator physics. Certain dielectric targets are considered in this context, for example, dielectric cones or prisms. Moreover, all-dielectric target which increase the radiated Cherenkov field near the predetermined focus up to several orders of magnitude has been described* and field near its focus and sensitivity of this target have been analyzed**. Here we consider a non-symmetrical case where charge trajectory has a shift with respect to structure axis. We develop analytical approach for description of Cherenkov radiation, perform three-dimensional simulations and compare the results.
* S.N. Galyamin and A.V. Tyukhtin, Phys. Rev. Lett., 113, 064802 (2014).
** S.N. Galyamin and A.V. Tyukhtin, Nucl. Instr. Meth. Phys. Res. B. 2017. V. 402. P.185-189.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW060

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paper received ※ 14 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPGW061

Radiation from a Dielectrically Loaded Waveguide with Open End

228

S.N. Galyamin, A.A. Grigoreva, A.V. Tyukhtin, V.V. Vorobev
Saint Petersburg State University, Saint Petersburg, Russia
A. Aryshev
KEK, Ibaraki, Japan

Funding: Work supported by Russian Science Foundation (Grant No. 18-72-10137).
Open-ended waveguide structures with dielectric loading excited by specially prepared electron bunches are considered as promising candidates for development of contemporary sources of Terahertz (THz) radiation. Despite of the fact that both ordinary vacuum THz devices (e.g., backward wave oscillator) are widely available and other mechanisms for THz generation are discussed, beam driven sources are still extremely attractive due to the extraordinary peak power of THz radiation*. In this report, we study electromagnetic (EM) field produced by a charged particle bunch exiting an open-ended circular waveguide with dielectric filling placed inside collinear vacuum waveguide of a larger radius. Based on the previously developed theory**, we mainly investigate Cherenkov radiation generated penetrated vacuum regions of the structure due to the diffraction mechanism. We pay attention to the case of a train of short bunches resulting in high-order Cherenkov modes excitation. We also develop analytical procedure allowing performing the limiting process to the case of infinite radius of the outer waveguide.
* B.D. O’Shea et al., Nature Communications, Vol. 7, P. 12763, (2016).
** S.N. Galyamin et al., J. Instrumentation, Vol. 13, P. C02012 (2018).

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW061

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paper received ※ 15 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPGW062

Radiation of a Charge Moving in a Wire Structure

231

S.N. Galyamin, A.V. Tyukhtin, V.V. Vorobev
Saint Petersburg State University, Saint Petersburg, Russia
A.I. Benediktovitch
EuXFEL, Hamburg, Germany
A.I. Benediktovitch
BSU, Minsk, Belarus, Belarus

Funding: This work is supported by the grant from Russian Foundation for Basic Research (No. 17-52-04107).
In the X-ray frequency region, interaction of relativistic electrons with crystals results in parametric X-ray radiation (PXR), with its frequency being determined by distance between crystallographic planes and direction of electron motion. If instead of crystal one considers an artificial periodic structure with periods of the order of mm, one can expect emission of radiation of a similar nature at terahertz (THz) frequencies. This frequency range is of significant interest during last decade due to its prospective applications. Moreover, artificial wire-like structures are considered as a promising alternative to conventional dielectric structures for wakefield acceleration*. Here we consider electromagnetic (EM) field produced by a charged particle bunch moving through a lattice of parallel conducting wires. We present several approaches for analysis of EM field in the described wire structure. First, conventional two-wave approximation for describing the "short-wave response" is developed. Second, we use the effective medium approach and describe the "long-wave" part of the spectrum. Third, we develop a method based on vibrator antenna theory which can be useful for finite length wire structure.
* P.D. Hoang, et al., Phys. Rev. Lett., V. 120, P. 164801 (2018).

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW062

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paper received ※ 14 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPGW064

On Wakefield in Dielectric Waveguide with Shallow Corrugation of Metallic Wall

237

A.V. Tyukhtin, E.R. Akhmatova, T.Yu. Alekhina, S.N. Galyamin, V.V. Vorobev
Saint Petersburg State University, Saint Petersburg, Russia

Funding: This work was supported by the Russian Science Foundation (Grant # 18-72-10137).
Bunch radiation in periodical waveguides was mainly analyzed for situations when wavelengths are comparable to the structure period (Smith-Purcell emission). However, it is also of interest to study the "long-wave radiation" with wavelengths which are much larger than the structure period*,**. In such situation, the exact boundary conditions on the complicated periodic surface can be replaced with the equivalent boundary conditions (EBC) which must be fulfilled on the smooth surface. Earlier we considered with this approach radiation of the bunch moving along the axis of circular vacuum corrugated waveguide**. Comparison of analytical results with COMSOL simulations showed high accuracy of the EBC method. Here we analyze an analogous problem for the waveguide with corrugated wall and dielectric filling under condition that Cherenkov effect takes place in the dielectric. Due to this fact the radiation differs radically from that in the vacuum waveguide. At the same time, the radiation has essential differences from the one in the usual dielectric waveguide. The radiation properties in the waveguide under consideration and its differences from the radiation in the waveguide with smooth wall are analyzed.
* G. Stupakov, K. Bane, Phys. Rev. ST-AB, 15 (2012) 124401.
** A.V. Tyukhtin et al, J. of Instrumentation, 13 (2018) C04009.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW064

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paper received ※ 15 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPGW081

Measurements of Stray Magnetic Fields at CERN for CLIC

289

SUSPFO099

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C. Gohil, N. Blaskovic Kraljevic, D. Schulte
CERN, Meyrin, Switzerland
P. Burrows
JAI, Oxford, United Kingdom
B. Heilig
MFGI, Budapest, Hungary

Simulations have shown that the Compact Linear Collider (CLIC) is sensitive to external dynamic magnetic fields (stray fields) to the nT level. Magnetic fields are not typically measured to this precision at CERN. Past measurements of the background magnetic field at CERN are limited. In this paper new measurements are presented.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW081

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paper received ※ 01 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPGW082

Mitigation of Stray Magnetic Field Effects in CLIC with Passive Shielding

293

C. Gohil, N. Blaskovic Kraljevic, D. Schulte
CERN, Meyrin, Switzerland
P. Burrows
JAI, Oxford, United Kingdom

Simulations have shown the Compact Linear Collider (CLIC) is sensitive to external dynamic magnetic fields (stray fields) to the nT level. Due to these extremely tight tolerances, mitigation techniques will be required to prevent performance loss. A passive shielding technique is envisaged as a potential solution. A model for passive shielding is presented along with calculations of its transfer function. Measurements of the transfer function of a promising material (mu-metal) that can be used for passive shielding are presented. The validity of passive shielding models in small amplitude magnetic fields is also discussed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW082

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paper received ※ 01 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPTS016

Compression and Noise Reduction of Field Maps

875

X. Du, L. Groening
GSI, Darmstadt, Germany

Errors from discretization and large data volume of field maps is a concern for beam dynamics simulations with respect to achievable accuracy and to the required amount of time. High-order singular value decomposition (HOSVD) has recently emerged as simple, effective, and adaptive tool to extract the essentials from multidimensional data. This paper is on the feasibility of compression and noise reduction of electromagnetic field map data with HOSVD. The method has been applied to an electric field map of a DTL cavity with 11 m in length comprising 55 rf-gaps. The original field map data of 220 MB was converted into practically noise-free data of just 20 KB. Noise was reduced by 95% as demonstrated using a cubic cavity for which the analytical field map is available.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPTS016

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paper received ※ 13 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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WEYYPLS3

Development of Methods for Calculation of Bunch Radiation in Presence of Dielectric Objects

2274

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

Funding: This work was supported by the Russian Science Foundation (Grant # 18-72-10137).
Radiation of charged particles moving in presence of dielectric targets is of interests for various applications in accelerator and beam physics*. Typically, the size of the target is much larger than the wavelengths under consideration. This fact gives us an obvious small parameter of the problem and allows developing approximate methods of analysis. We develop two methods: "ray-optical method" and "aperture method"**. These methods can be very effective for all situations where we can find the tangential field components on the "aperture" which is an object boundary illuminated by Cherenkov radiation. We apply the aperture method to different dielectric objects including a prism, a cone, and a ball. Electromagnetic field is analyzed on different distances from the objects. The special attention is given to investigation of the field in the far-field (Fraunhofer) area having large importance for various applications. We obtain analytical results for different objects, demonstrate typical radiation patterns and discuss new physical effects, in particular, the phenomenon of concentration of radiation and effect of "Cherenkov spotlight". Prospects of use of aperture method and ray-optical one for other objects are discussed as well.
* R.Kieffer et al, PRL, 121, 054802 (2018).
** E.S.Belonogaya et al, JOSA B, 32, 649 (2015); S.N.Galyamin, A.V.Tyukhtin, PRL, 113, 064802 (2014); A.V.Tyukhtin et al, J. Instrum., 13, C02033 (2018).

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEYYPLS3

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paper received ※ 14 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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