LINAC2016 - Table of Session: MOP106 (Poster Session)

Paper	Title	Page
MOP106001	Energy Stability of ERLs and Recirculating Linacs	304
	R.G. Eichhorn, J. Hoke, Z. Mayle Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Energy recovery linacs can be seen as a hybrid between a linear and a circular accelerator. It has been shown in the past that an appropriate choice of the longitudinal working point can significantly improve the energy stability of a recirculating linac. In this contribution we will expand the concept of energy recovery linacs and investigate the energy spread of the beam as well as the recovery efficiency stability which can be a more demanding quantity in a high current ERL.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106001
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MOP106002	X-Band Photonic Band Gap Accelerating Structures with Improved Wakefield Suppression	307
	E.I. Simakov LANL, Los Alamos, New Mexico, USA
	Funding: This work is supported by U.S. Department of Energy (DOE) Office of High Energy Physics. We present the design of a novel photonic band gap (PBG) accelerating structure with elliptical rods and improved wakefields suppression. It has been long recognized that PBG structures have great potential in reducing long-range wakefields in accelerators. The first ever demonstration of acceleration in room-temperature PBG structures was conducted at MIT in 2005. The experimental characterization of the wakefield spectrum in a beam test was performed at Argonne Wakefield Accelerator facility in 2015, and the superior wakefield suppression properties of the PBG structure were demonstrated. In 2013 the team from MIT and SLAC demonstrated that the X-band PBG structures with elliptical rods have reduced breakdown rate compared to PBG structures with round rods, presumably due to the reduced surface magnetic fields. However, the structure with elliptical rods designed by MIT confined the dipole higher order mode in addition to the accelerating mode and thus did not have superior wakefield suppression properties. We demonstrate that PBG resonators can be designed with 40% smaller peak surface magnetic fields while preserving and even improving their wakefield suppression properties as compared to the structure with round rods. The design of the new structure is presented. The structure will be fabricated, tuned, and tested for high gradients and for wakefield suppression.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106002
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MOP106006	Electro-Mechanical Modeling of the LCLS-II Superconducting Cavities	310
	O. Kononenko, C. Adolphsenpresenter, Z. Li, T.O. Raubenheimer, C.H. Rivetta SLAC, Menlo Park, California, USA
	Funding: Work supported by the Department of Energy, Office of Science, Office of Basic Energy Science, under Contract No. DEAC0276SF00515 The 4 GeV LCLS-II superconducting linac will contain 280, 1.3 GHz TESLA-style cavities operated CW at 16 MV/m. Because of the low beam current, the cavity bandwidth will be fairly small, about 32 Hz, which makes the field stability sensitive to detuning from external vibrations and He pressure fluctuations. Piezo-electric actuators will be used to compensate for the detuning, which historically has been difficult at frequencies above a few Hz due to excitation of cavity mechanical resonances. To understand this interaction better, we have been doing extensive modeling of the cavities including mapping out the mechanical modes and computing their coupling to pressure changes, Lorentz forces and piezo actuator motion. One goal is to reproduce the measured detuning response of the piezo actuators up to 1 kHz, which is sensitive to how the cavities are constrained within a cryomodule. In this paper, we summarize these results and their implications for suppressing higher frequency detuning.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106006
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MOP106012	MESA - an ERL Project for Particle Physics Experiments	313
	F. Hug, K. Aulenbacher, R.G. Heine, B. Ledroit, D. Simon IKP, Mainz, Germany
	The Mainz Energy-recovering Superconducting Accelerator (MESA) will be constructed at the Institut für Kernphysik of the Johannes Gutenberg University of Mainz. The accelerator is a low energy continuous wave (CW) recirculating electron linac for particle physics experiments. MESA will be operated in two different modes serving mainly two experiments: the first is the external beam (EB) mode, where the beam is dumped after being used with the external fixed target experiment P2, whose goal is the measurement of the weak mixing angle with highest accuracy. The required beam current for P2 is 150 μA with polarized electrons at 155 MeV. In the second operation mode MESA will be run as an energy recovery linac (ERL). The experiment served in this mode is a (pseudo) internal fixed target experiment named MAGIX. It demands an unpolarized beam of 1 mA at 10⁵ MeV. In a later construction stage of MESA the achievable beam current in ERL-mode shall be upgraded to 10 mA. Within this contribution an overview of the MESA project will be given highlighting the latest accelerator layout and the challenges of operation with high density internal gas targets. Work supported by DFG through cluster of excellence PRISMA, CRC 1044 and RTG 2128
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106012
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MOP106015	Commissioning Status of the Chopper System for the MAX IV Injector	316
	D. Olsson, J. Andersson, F. Curbis, L. Isaksson, L. Malmgren, E. Mansten, S. Thorin MAX IV Laboratory, Lund University, Lund, Sweden
	The MAX IV facility in Lund, Sweden consists of two storage rings for production of synchrotron radiation. The two rings are designed for 1.5 GeV and 3 GeV, respectively, where the former is under construction, and the latter is undergoing beam commissioning. Both rings will be operating with top-up injections delivered by a full-energy injector that consists of 39 traveling-wave S-band LINAC structures. In order to reduce losses of high-energy electrons along the injector and in the rings during injection, only electrons that are within an allowed time structure are accelerated. This time structure depends on several parameters such as the available RF voltage and the radiation losses in the ring that is about to be injected, but also on the momentum acceptance of the transport lines in the injector. The electrons that are outside the allowed time structure are dumped when they have energies below 3 MeV by a chopper system that is located between a thermionic RF gun and the first LINAC structure. Basically, the chopper system consists of two planar striplines and a variable aperture, and the first stripline is fed with a superposed RF signal and the second one with HV pulses. The performance of the chopper system during commissioning of the 3 GeV ring is presented in this article.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106015
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MOP106016	High Power RF Requirements for Driving Discontinuous Bunch Trains in the MaRIE Linac	320
	J.T. Bradley III, D. Rees, A. Scheinker, R.L. Sheffield LANL, Los Alamos, New Mexico, USA
	Funding: Work supported by the US Department of Energy. The MaRIE project will use a superconducting linac to provide 12 GeV electron bunches to drive an X-ray FEL and to do electron radiography. Dynamic experiments planned for MaRIE require that the linac produce a series of micropulses that can be irregularly spaced within the macropulse, and these patterns can change from macropulse to macropulse. Irregular pulse structures create a challenge to optimizing the design of the RF and cryogenic systems. General formulas for cavities with beam loading can overestimate the power required for our irregular beam macropulse. The differing beam energy variations allowed for the XFEL and eRad micropulses produce cavity voltage control requirements that also vary within the macropulse. The RF pulse driving the cavities can be tailored to meet the needs of that particular beam macropulse because the macropulse structure is known before the pulse starts. We will derive a toolkit that can be used to determine the required RF power waveforms for arbitrary macropulse structures. We will also examine how the irregular RF power waveforms can impact RF and cryogenic system cost tradeoffs.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106016
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MOP106018	Measurement of the Transverse Beam Dynamics in a TESLA-type Superconducting Cavity	323
SPWR025	use link to see paper's listing under its alternate paper code
	A. Halavanau, P. Piot Northern Illinois University, DeKalb, Illinois, USA N. Eddy, D.R. Edstrom, A. Lunin, P. Piot, J. Ruan, N. Solyak Fermilab, Batavia, Illinois, USA
	Funding: US Department of Energy (DOE) under contract DE-SC0011831 with Northern Illinois University. Fermilab is operated by the Fermi Research Alliance LLC under US DOE contract DE-AC02-07CH11359. Superconducting linacs are capable of producing intense, ultra-stable, high-quality electron beams that have widespread applications in Science and Industry. Many project are based on the 1.3-GHz TESLA-type superconducting cavity. In this paper we provide an update on a recent experiment aimed at measuring the transfer matrix of a TESLA cavity at the Fermilab Accelerator Science and Technology (FAST) facility. The results are discussed and compared with analytical and numerical simulations.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106018
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MOP106021	Superconducting Traveling Wave Cavity Tuning Studies	327
	R.A. Kostin LETI, Saint-Petersburg, Russia P.V. Avrakhov, A. Kanareykin Euclid TechLabs, LLC, Solon, Ohio, USA N. Solyak, V.P. Yakovlev Fermilab, Batavia, Illinois, USA
	Funding: Work supported by US DOE SBIR # DE-SC0006300 Superconducting traveling wave cavity (SCTW) can provide 1.2-1.4 times larger accelerating gradient than conventional standing wave SRF cavities [1]. Firstly, traveling wave opens the way to use other than Pi-mode phase advance per cell which increase transit time factor. Secondly, traveling wave is not so sensitive to cavity length as standing wave, which length is limited to 1 meter because of field flatness degradation. 3 cell SCTW cavity was proposed [2] and built for high gradient traveling wave demonstration and tuning studies. This paper describes analytical model that was used for cavity development. Tuning properties and requirements are also discussed. ' r.kostin@euclidtechlabs.com
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106021
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MOP106022	Generation of Coherent Undulator Radiation at ELPH, Tohoku University	330
	S. Kashiwagi, T. Abe, H. Hama, F. Hinode, T. Muto, I. Nagasawa, K. Nanbu, H. Saito, Y. Saito, Y. Shibasaki, K. Takahashi Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
	A test accelerator as a coherent terahertz source (t-ACTS) has been under development at Tohoku University, in which an intense coherent terahertz (THz) radiation generated by an extremely short electron bunch. Velocity bunching scheme in a traveling accelerating structure is employed to generate femtosecond electron bunches. Spatial and temporal coherent radiation in THz region can be produced by the electron bunches with small transverse emittance. A long-period undulator, which has 25 periods with a period length of 10 cm and a peak magnetic field of 0.41 T, has been also developed and installed to provide intense coherent THz undulator radiation. By optimizing the bunch length, we found that it is possible to generate a coherent undulator radiation that contain only the fundamental wave from numerical studies. We are planning an experiment with 30 MeV beam to generate a coherent undulator radiation of 2.5THz. In the conference, we will report the preliminary experimental results.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106022
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MOP106023	Intra Bunch Train Transverse Dynamics in the Superconducting Accelerators FLASH and European XFEL	333
SPWR039	use link to see paper's listing under its alternate paper code
	T. Hellert, W. Decking, M. Dohlus DESY, Hamburg, Germany
	At FLASH and the European XFEL accelerator superconducting 9-cell TESLA cavities accelerate long bunch trains at high gradients in pulsed operation. Several RF cavities with individual operating limits are supplied by one RF power source. Within the bunch train, the low-level-RF system is able to restrict the variation of the vector sum voltage and phase of one control line below 3·10^-4 and 0.06 degree, respectively. However, individual cavities may have a significant spread of amplitudes and phases. Misaligned cavities in combination with variable RF parameters will cause significant intra-pulse orbit distortions, leading to an increase of the multi-bunch emittance. An efficient model including coupler kicks was developed to describe the effect at low beam energies. Comparison with start-to-end tracking and experimental data will be shown.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106023
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Paper

Title

Page

Energy Stability of ERLs and Recirculating Linacs

304

R.G. Eichhorn, J. Hoke, Z. Mayle
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Energy recovery linacs can be seen as a hybrid between a linear and a circular accelerator. It has been shown in the past that an appropriate choice of the longitudinal working point can significantly improve the energy stability of a recirculating linac. In this contribution we will expand the concept of energy recovery linacs and investigate the energy spread of the beam as well as the recovery efficiency stability which can be a more demanding quantity in a high current ERL.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106001

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MOP106002

X-Band Photonic Band Gap Accelerating Structures with Improved Wakefield Suppression

307

E.I. Simakov
LANL, Los Alamos, New Mexico, USA

Funding: This work is supported by U.S. Department of Energy (DOE) Office of High Energy Physics.
We present the design of a novel photonic band gap (PBG) accelerating structure with elliptical rods and improved wakefields suppression. It has been long recognized that PBG structures have great potential in reducing long-range wakefields in accelerators. The first ever demonstration of acceleration in room-temperature PBG structures was conducted at MIT in 2005. The experimental characterization of the wakefield spectrum in a beam test was performed at Argonne Wakefield Accelerator facility in 2015, and the superior wakefield suppression properties of the PBG structure were demonstrated. In 2013 the team from MIT and SLAC demonstrated that the X-band PBG structures with elliptical rods have reduced breakdown rate compared to PBG structures with round rods, presumably due to the reduced surface magnetic fields. However, the structure with elliptical rods designed by MIT confined the dipole higher order mode in addition to the accelerating mode and thus did not have superior wakefield suppression properties. We demonstrate that PBG resonators can be designed with 40% smaller peak surface magnetic fields while preserving and even improving their wakefield suppression properties as compared to the structure with round rods. The design of the new structure is presented. The structure will be fabricated, tuned, and tested for high gradients and for wakefield suppression.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106002

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MOP106006

Electro-Mechanical Modeling of the LCLS-II Superconducting Cavities

310

O. Kononenko, C. Adolphsenpresenter, Z. Li, T.O. Raubenheimer, C.H. Rivetta
SLAC, Menlo Park, California, USA

Funding: Work supported by the Department of Energy, Office of Science, Office of Basic Energy Science, under Contract No. DEAC0276SF00515
The 4 GeV LCLS-II superconducting linac will contain 280, 1.3 GHz TESLA-style cavities operated CW at 16 MV/m. Because of the low beam current, the cavity bandwidth will be fairly small, about 32 Hz, which makes the field stability sensitive to detuning from external vibrations and He pressure fluctuations. Piezo-electric actuators will be used to compensate for the detuning, which historically has been difficult at frequencies above a few Hz due to excitation of cavity mechanical resonances. To understand this interaction better, we have been doing extensive modeling of the cavities including mapping out the mechanical modes and computing their coupling to pressure changes, Lorentz forces and piezo actuator motion. One goal is to reproduce the measured detuning response of the piezo actuators up to 1 kHz, which is sensitive to how the cavities are constrained within a cryomodule. In this paper, we summarize these results and their implications for suppressing higher frequency detuning.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106006

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MOP106012

MESA - an ERL Project for Particle Physics Experiments

313

F. Hug, K. Aulenbacher, R.G. Heine, B. Ledroit, D. Simon
IKP, Mainz, Germany

The Mainz Energy-recovering Superconducting Accelerator (MESA) will be constructed at the Institut für Kernphysik of the Johannes Gutenberg University of Mainz. The accelerator is a low energy continuous wave (CW) recirculating electron linac for particle physics experiments. MESA will be operated in two different modes serving mainly two experiments: the first is the external beam (EB) mode, where the beam is dumped after being used with the external fixed target experiment P2, whose goal is the measurement of the weak mixing angle with highest accuracy. The required beam current for P2 is 150 μA with polarized electrons at 155 MeV. In the second operation mode MESA will be run as an energy recovery linac (ERL). The experiment served in this mode is a (pseudo) internal fixed target experiment named MAGIX. It demands an unpolarized beam of 1 mA at 10⁵ MeV. In a later construction stage of MESA the achievable beam current in ERL-mode shall be upgraded to 10 mA. Within this contribution an overview of the MESA project will be given highlighting the latest accelerator layout and the challenges of operation with high density internal gas targets.
Work supported by DFG through cluster of excellence PRISMA, CRC 1044 and RTG 2128

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reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106012

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MOP106015

Commissioning Status of the Chopper System for the MAX IV Injector

316

D. Olsson, J. Andersson, F. Curbis, L. Isaksson, L. Malmgren, E. Mansten, S. Thorin
MAX IV Laboratory, Lund University, Lund, Sweden

The MAX IV facility in Lund, Sweden consists of two storage rings for production of synchrotron radiation. The two rings are designed for 1.5 GeV and 3 GeV, respectively, where the former is under construction, and the latter is undergoing beam commissioning. Both rings will be operating with top-up injections delivered by a full-energy injector that consists of 39 traveling-wave S-band LINAC structures. In order to reduce losses of high-energy electrons along the injector and in the rings during injection, only electrons that are within an allowed time structure are accelerated. This time structure depends on several parameters such as the available RF voltage and the radiation losses in the ring that is about to be injected, but also on the momentum acceptance of the transport lines in the injector. The electrons that are outside the allowed time structure are dumped when they have energies below 3 MeV by a chopper system that is located between a thermionic RF gun and the first LINAC structure. Basically, the chopper system consists of two planar striplines and a variable aperture, and the first stripline is fed with a superposed RF signal and the second one with HV pulses. The performance of the chopper system during commissioning of the 3 GeV ring is presented in this article.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106015

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MOP106016

High Power RF Requirements for Driving Discontinuous Bunch Trains in the MaRIE Linac

320

J.T. Bradley III, D. Rees, A. Scheinker, R.L. Sheffield
LANL, Los Alamos, New Mexico, USA

Funding: Work supported by the US Department of Energy.
The MaRIE project will use a superconducting linac to provide 12 GeV electron bunches to drive an X-ray FEL and to do electron radiography. Dynamic experiments planned for MaRIE require that the linac produce a series of micropulses that can be irregularly spaced within the macropulse, and these patterns can change from macropulse to macropulse. Irregular pulse structures create a challenge to optimizing the design of the RF and cryogenic systems. General formulas for cavities with beam loading can overestimate the power required for our irregular beam macropulse. The differing beam energy variations allowed for the XFEL and eRad micropulses produce cavity voltage control requirements that also vary within the macropulse. The RF pulse driving the cavities can be tailored to meet the needs of that particular beam macropulse because the macropulse structure is known before the pulse starts. We will derive a toolkit that can be used to determine the required RF power waveforms for arbitrary macropulse structures. We will also examine how the irregular RF power waveforms can impact RF and cryogenic system cost tradeoffs.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106016

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MOP106018

Measurement of the Transverse Beam Dynamics in a TESLA-type Superconducting Cavity

323

SPWR025

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

A. Halavanau, P. Piot
Northern Illinois University, DeKalb, Illinois, USA
N. Eddy, D.R. Edstrom, A. Lunin, P. Piot, J. Ruan, N. Solyak
Fermilab, Batavia, Illinois, USA

Funding: US Department of Energy (DOE) under contract DE-SC0011831 with Northern Illinois University. Fermilab is operated by the Fermi Research Alliance LLC under US DOE contract DE-AC02-07CH11359.
Superconducting linacs are capable of producing intense, ultra-stable, high-quality electron beams that have widespread applications in Science and Industry. Many project are based on the 1.3-GHz TESLA-type superconducting cavity. In this paper we provide an update on a recent experiment aimed at measuring the transfer matrix of a TESLA cavity at the Fermilab Accelerator Science and Technology (FAST) facility. The results are discussed and compared with analytical and numerical simulations.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106018

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MOP106021

Superconducting Traveling Wave Cavity Tuning Studies

327

R.A. Kostin
LETI, Saint-Petersburg, Russia
P.V. Avrakhov, A. Kanareykin
Euclid TechLabs, LLC, Solon, Ohio, USA
N. Solyak, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA

Funding: Work supported by US DOE SBIR # DE-SC0006300
Superconducting traveling wave cavity (SCTW) can provide 1.2-1.4 times larger accelerating gradient than conventional standing wave SRF cavities [1]. Firstly, traveling wave opens the way to use other than Pi-mode phase advance per cell which increase transit time factor. Secondly, traveling wave is not so sensitive to cavity length as standing wave, which length is limited to 1 meter because of field flatness degradation. 3 cell SCTW cavity was proposed [2] and built for high gradient traveling wave demonstration and tuning studies. This paper describes analytical model that was used for cavity development. Tuning properties and requirements are also discussed.
' r.kostin@euclidtechlabs.com

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reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106021

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MOP106022

Generation of Coherent Undulator Radiation at ELPH, Tohoku University

330

S. Kashiwagi, T. Abe, H. Hama, F. Hinode, T. Muto, I. Nagasawa, K. Nanbu, H. Saito, Y. Saito, Y. Shibasaki, K. Takahashi
Tohoku University, Research Center for Electron Photon Science, Sendai, Japan

A test accelerator as a coherent terahertz source (t-ACTS) has been under development at Tohoku University, in which an intense coherent terahertz (THz) radiation generated by an extremely short electron bunch. Velocity bunching scheme in a traveling accelerating structure is employed to generate femtosecond electron bunches. Spatial and temporal coherent radiation in THz region can be produced by the electron bunches with small transverse emittance. A long-period undulator, which has 25 periods with a period length of 10 cm and a peak magnetic field of 0.41 T, has been also developed and installed to provide intense coherent THz undulator radiation. By optimizing the bunch length, we found that it is possible to generate a coherent undulator radiation that contain only the fundamental wave from numerical studies. We are planning an experiment with 30 MeV beam to generate a coherent undulator radiation of 2.5THz. In the conference, we will report the preliminary experimental results.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106022

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MOP106023

Intra Bunch Train Transverse Dynamics in the Superconducting Accelerators FLASH and European XFEL

333

SPWR039

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

T. Hellert, W. Decking, M. Dohlus
DESY, Hamburg, Germany

At FLASH and the European XFEL accelerator superconducting 9-cell TESLA cavities accelerate long bunch trains at high gradients in pulsed operation. Several RF cavities with individual operating limits are supplied by one RF power source. Within the bunch train, the low-level-RF system is able to restrict the variation of the vector sum voltage and phase of one control line below 3·10^-4 and 0.06 degree, respectively. However, individual cavities may have a significant spread of amplitudes and phases. Misaligned cavities in combination with variable RF parameters will cause significant intra-pulse orbit distortions, leading to an increase of the multi-bunch emittance. An efficient model including coupler kicks was developed to describe the effect at low beam energies. Comparison with start-to-end tracking and experimental data will be shown.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106023

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