IPAC2017 - List of Keywords (accelerating-gradient)

Paper	Title	Other Keywords	Page
MOPVA055	Upgrade of the Capture Section of the S-DALINAC Injector	cavity, SRF, electron, operation	993
	D.B. Bazyl, H. De Gersem, W.F.O. Müller TEMF, TU Darmstadt, Darmstadt, Germany
	Funding: This work is supported by the DFG through GRK 2128. In order to reduce the energy spread of the recirculated beam, the injector of the S-DALINAC needs to be optimized, because the non-isochronous recirculation cannot correct for errors originating from the injector linac. For the S-DALINAC, spatial restrictions suggest the use of SRF technology for the capture section. In this work, we consider various SRF cavities with an operating frequency of 3 GHz for a possible upgrade of the capture section of the S-DALINAC. The first results of the RF and beam dynamics simulations for the proposed options are presented in this paper.
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MOPVA063	Vertical Tests of ESS Medium Beta Prototype Cavities at LASA	cavity, vacuum, operation, radiation	1015
	A. Bosotti, A. Bellandi, M. Bertucci, A. Bignami, J.F. Chen, C.G. Maiano, P. Michelato, L. Monaco, R. Paparella, P. Pierini, D. Sertore INFN/LASA, Segrate (MI), Italy C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy S. Pirani ESS, Lund, Sweden
	In the framework of the INFN activity related to the European Spallation Source collaboration, the LASA infrastructure has been renewed to allow the qualification, in its vertical cryostat, of the 704 MHz medium beta cavity prototypes. A new cryogenic insert has been realized, fully equipped with dedicated mechanical supports, vacuum, thermal sensors and quench diagnostic systems. The RF test station has been upgraded as well with a new PLL electronics rack. The first beta 0.67 cavity prototype designed and produced by INFN Milano has been successfully cold tested at 2.0 K temperature, outperforming the ESS specifications. The technical features of LASA infrastructure, the design of novel components and the experimental results of cavities cold-tests are thoroughly described in this paper.
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MOPVA082	PLASMA PROCESSING R&D OF THE 1.3 GHZ SINGLE-CELL SRF CAVITY AT IMP	plasma, cavity, SRF, electromagnetic-fields	1055
	L. Yang, L. Chen, Y. He, S.C. Huang, C.X. Li, C.L. Li, Y.M. Li, L. Lu, A. Shi, L.P. Sun, A.D. Wu, S.H. Zhang IMP/CAS, Lanzhou, People's Republic of China
	The China-Accelerator Driven Sub-critical System (C-ADS) injector II has already commissioned with a CW 1 mA and a pulsed 10 mA proton beam. The beam energy achieved 10 MeV. The superconducting linac (SCL) is routinely operating at 4.7 MV/m average accelerating gradient in the low-beta cryomodules. Field emission and surface contaminants of the SCL limit the gradient in-crease in the beam commissioning. Hence, in order to increase the SCL accelerating gradient, reduce field emis-sion and remove surface pollutants, in-situ plasma pro-cessing R&D in a 1.3 GHz single-cell SRF cavity has being studied. In this paper, the current effort of plasma processing R&D in a 1.3 GHz single-cell SRF cavity will be presented in details and the future plan will be also reported.
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MOPVA087	Low Betta Superconducting Cavity for the New Injector Linac for Nuclotron-NICA	cavity, linac, simulation, multipactoring	1058
	M. Gusarova, T.A. Bakhareva, M.V. Lalayan, S.V. Matsievskiy, N.P. Sobenin, D.V. Surkov, K.V. Taletskiy, V. Zvyagintsev MEPhI, Moscow, Russia A.A. Bakinowskaya, V.S. Petrakovsky, A.I. Pokrovsky, D.A. Shparla Physical-Technical Institute of the National Academy of Sciences of Belarus, Minsk, Belarus A.V. Butenko, G.V. Trubnikov JINR/VBLHEP, Dubna, Moscow region, Russia V. Zvyagintsev TRIUMF, Vancouver, Canada
	The results of the RF, mechanical and multipactor discharge simulations of the 162 MHz quarter wave resonator (QWR) for New Superconducting Injector Linac for Nuclotron-NICA are presented. Cavity design in conjunction with manufacturing features is discussed.
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MOPVA088	Medium Betta Superconducting Cavity for the New Injector Linac for Nuclotron-NICA	cavity, simulation, linac, multipactoring	1061
	M. Gusarova, M.V. Lalayan, N.P. Sobenin, D.V. Surkov, K.V. Taletskiy MEPhI, Moscow, Russia A.A. Bakinowskaya, V.S. Petrakovsky, A.I. Pokrovsky, D.A. Shparla Physical-Technical Institute of the National Academy of Sciences of Belarus, Minsk, Belarus A.V. Butenko, G.V. Trubnikov JINR/VBLHEP, Dubna, Moscow region, Russia
	The results of the electrodynamical and multipactor discharge simulations of the medium betta superconducting cavity for New Superconducting Injector Linac for Nuclotron-NICA are presented. Different designs of CH and Spoke cavities are compared and the optimal one is chosen.
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MOPVA116	Quench Studies in Single-Cell Nb3Sn Cavities Coated Using Vapour Diffusion	cavity, radio-frequency, monitoring, niobium	1119
	D.L. Hall, M. Liepe, J.T. Maniscalco, R.D. Porter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA P. Cueva, D. Liarte, D.A. Muller, J.P. Sethna Cornell University, Ithaca, New York, USA
	The superconductor Nb3Sn is known to have a superheating field, Hsh, of approximately 400 mT. This critical field represents the ultimate achievable gradient in a superconducting cavity, and is equivalent to an accelerating gradient of 90 MV/m in an ILC single-cell cavity for this value of Hsh. However, the currently best performing Nb3Sn single-cell cavities remain limited to accelerating gradients of 17-18 MV/m, translating to a peak surface magnetic field of approx. 70 mT. In this paper, we consider theoretical models of candidate quench mechanisms, and compare them to experimental data from surface analysis and cavity tests.
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MOPVA128	RF Performance of Nitrogen-Doped Production SRF Cavities for LCLS-II	cavity, SRF, niobium, operation	1156
	D. Gonnella, A. Burrill, M.C. Ross SLAC, Menlo Park, California, USA S. Aderhold, A. Grassellino, C.J. Grimm, T.N. Khabiboulline, O.S. Melnychuk, S. Posen, D.A. Sergatskov Fermilab, Batavia, Illinois, USA E. Daly, G.K. Davis, F. Marhauser, K.M. Wilson JLab, Newport News, Virginia, USA
	Funding: DOE and the LCLS-II Project The Linac Coherent Light Source II (LCLS-II) requires 280 9-cell superconducting RF cavities for operation in continuous wave mode. Two vendors have previously been selected to produce the cavities, Research Instruments GmbH and Ettore Zanon S.p.a. Here we present results from manufacturing and cavity preparation for the cavities constructed at these two vendors for LCLS-II. We show how the cavity preparation method has been changed mid-production in order to improve flux expulsion in the cavities and maintain high performance in realistic magnetic field environments (~5 mG). Additionally, we show that the nitrogen-doping process has been carried out successfully and repeatedly on over 70 cavities.
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TUPAB006	Achievement of Stable Pulsed Operation at 31 MV/m in the STF-2 Cryomodule for the ILC	cavity, cryomodule, operation, radiation	1308
	Y. Yamamoto, T. Dohmae, M. Egi, K. Hara, T. Honma, E. Kako, Y. Kojima, T. Konomi, N. Kota, T. Kubo, T. Matsumoto, T. Miura, H. Nakai, K. Nakanishi, G.-T. Park, T. Saeki, H. Shimizu, T. Shishido, T. Takenaka, K. Umemori KEK, Ibaraki, Japan
	In the Superconducting RF Test Facility (STF) in KEK, the cooldown test for the STF-2 cryomodule with 12 cavities has been done totally three times since 2014. In 2016, the 3rd cooldown test for the STF-2 cryomodule including the capture cryomodule with 2 cavities, which was used for Quantum Beam Project in 2012, was successfully done. The main purpose is the vector-sum operation with 8 cavities at average accelerating gradient of 31 MV/m as the ILC specification, and the others are the measurement for Lorenz Force Detuning (LFD) and unloaded Q value, and Low Level RF (LLRF) study, etc. During 8 cavities operation, piezo actuators were used for the compensation of LFD, and the feed-forward and vector-sum control system by LLRF worked perfectly for keeping the lowest forward power and the stable flat-top of accelerating gradient. In this paper, the result for the STF-2 cryomodule in the 3rd cooldown test will be presented in detail.
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TUPAB070	S-Band Accelerating Structure for High-Gradient Upgrade of TTX	electron, impedance, simulation, linac	1485
	D.Z. Cao, H.B. Chen, Y.-C. Du, W. Gai, W.-H. Huang, X.C. Meng, J. Shi, C.-X. Tang, X.W. Wu, H. Zha TUB, Beijing, People's Republic of China
	Thomson scattering x-ray source is an indispensable scientific X-ray imaging tool in various research fields. The 3-meter S-band linac in Tsinghua Thomson scatter-ing X-ray source (TTX) has been running at an accelerat-ing gradient of 15 MV/m so far. The gradient will be upgraded to 30MV/m by replacing the old structure with a shorter linac. Detailed optimization of the RF design of the new S-band linac structure is presented in this paper. Finally, further research on energy upgrade with X-band structures are also discussed.
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WEPAB138	Prototyping High-Gradient mm-Wave Accelerating Structures	interface, experiment, cavity, RF-structure	2902
	E.A. Nanni, V.A. Dolgashev, A.A. Haase, J. Neilson, S.G. Tantawi SLAC, Menlo Park, California, USA S.C. Schaub MIT, Cambridge, Massachusetts, USA B. Spataro INFN/LNF, Frascati (Roma), Italy R.J. Temkin MIT/PSFC, Cambridge, Massachusetts, USA
	We present single-cell accelerating structures designed for high-gradient testing at 110 GHz. The purpose of this work is to study the basic physics of ultrahigh vacuum RF breakdown in high-gradient RF accelerators. The accelerating structures are pi-mode standing-wave cavities fed with a TM01 circular waveguide. The structures are fabricated using precision milling out of two metal blocks, and the blocks are joined with diffusion bonding and brazing. The impact of fabrication and joining techniques on the cell geometry and RF performance will be discussed. First prototypes had a measured Qo of 2800, approaching the theoretical design value of 3300. The geometry of these accelerating structures are as close as practical to single-cell standing-wave X-band accelerating structures more than 40 of which were tested at SLAC. This wealth of X-band data will serve as a baseline for these 110 GHz tests. The structures will be powered with short pulses from a MW gyrotron oscillator. RF power of 1 MW may allow us to reach an accelerating gradient of 400 MeV/m.
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WEPVA019	Group Velocity Matching in Dielectric-Lined Waveguides and its Role in Electron-THz Interaction	electron, acceleration, simulation, interface	3296
	A.L. Healy, G. Burt Cockcroft Institute, Lancaster University, Lancaster, United Kingdom D.M. Graham The University of Manchester, The Photon Science Institute, Manchester, United Kingdom S.P. Jamison STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	Terahertz(THz)-driven dielectric-lined waveguides have applications in electron manipulation, particularly acceleration, as the use of dielectric allows for phase velocities below the speed of light. However matching a single frequency to the correct velocity does not maximise electron-THz interaction; waveguide dispersion typically results in an unmatched group velocity and so the pulse envelope of a short THz pulse changes along the length of the structure. This reduces field amplitude and therefore accelerating gradient as the envelope propagates at a different velocity to the electron. Presented here is an analysis of the effect of waveguide dispersion on THz-electron interaction and its influence on structure dimensions and choice of THz pulse generation. This effect on net acceleration is demonstrated via an example of a structure excited by a single-cycle THz pulse, with a comparison of multi-cycle, lower intensity THz pulses on net acceleration.
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WEPVA020	Dual-Grating Dielectric Accelerators Driven by A Pulse-Front-Tilted Laser	laser, electron, simulation, vacuum	3299
	Y. Wei, C.P. Welsch The University of Liverpool, Liverpool, United Kingdom M.M. Dehler, E. Ferrari, N. Hiller, R. Ischebeck PSI, Villigen PSI, Switzerland J.D.A. Smith TXUK, Warrington, United Kingdom C.P. Welsch Cockcroft Institute, Warrington, Cheshire, United Kingdom G.X. Xia UMAN, Manchester, United Kingdom
	Dual-grating Dielectric Laser-driven Accelerators (DLAs) are considered to be one of the most promising technologies to miniaturize future particle accelerators. Accelerating gradients in the GV/m range seem accessible and 690 MV/m has been demonstrated in fused silica structures. However, the increase in beam energy is limited by the short interaction length between the laser pulses and the electron bunch. In this contribution, a pulse-front-tilt operation for a laser beam is studied to extend the interaction length, resulting in a greater energy gain for a dual-grating DLA. The VSIM code is used to compare this new scheme with the commonly used approach of a normally incident laser beam and advantages are summarized. [1]T. Plettner, et al., Phys. Rev. ST Accel. Beams 9, 111301 (2006) [2]K. P. Wootton, et al., Opt. Lett., 41, 2696 (2016). [3]E. A. Peralta, et al., Nature 503, 91 (2013)
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WEPVA022	RECENT TWO-BEAM ACCELERATION ACTIVITIES AT ARGONNE WAKEFIELD ACCELERATOR FACILITY	acceleration, experiment, wakefield, impedance	3305
	J.H. Shao, S.P. Antipov, M.E. Conde, W. Gai, Q. Gao, G. Ha, W. Liu, N.R. Neveu, J.G. Power, Y.R. Wang, E.E. Wisniewski, L.M. Zheng ANL, Argonne, Illinois, USA C.-J. Jing, J.Q. Qiu Euclid TechLabs, LLC, Solon, Ohio, USA J. Shi, D. Wang TUB, Beijing, People's Republic of China
	The Two-Beam Acceleration (TBA) is a modified approach to the structure-based wakefield acceleration which may meet the luminosity, efficiency, and cost requirement of a future linear collider. Recently, various TBA experiments have been carried out at the Argonne Wakefield Accelerator Facility (AWA). With X-band metallic power extractors and accelerators, a 70 MeV/m average accelerating gradient has been demonstrated in two stages while a 150 MeV/m gradient as well as 300 MW extracted power have been achieved in a single stage. In addition, low cost K-band dielectric power extractor and accelerator have also been developed. The preliminary results show power extraction of 55 MW and an average accelerating gradient of 28 MeV/m.
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THOBB3	ESS SRF Linear Accelerator Components Preliminary Results and Integration	cavity, SRF, cryomodule, linac	3666
	C. Darve, N. Elias, C.G. Maiano, F. Schlander ESS, Lund, Sweden C. Arcambal, G. Devanz, F. Peauger CEA/DRF/IRFU, Gif-sur-Yvette, France E. Cenni CEA/IRFU, Gif-sur-Yvette, France G. Costanza Lund University, Lund, Sweden P. Duthil, G. Olry, D. Reynet IPN, Orsay, France L. Hermansson Uppsala University, Uppsala, Sweden P. Michelato, D. Sertore INFN/LASA, Segrate (MI), Italy
	The European Spallation Source (ESS) is a pan-European project and one of world's largest research infrastructures based on neutron sources. This collaborative project is funded by a collaboration of 17 European countries and is under construction in Lund, Sweden. The 5 MW, 2.86 ms long pulse proton accelerator has a repetition frequency of 14 Hz (4 % duty cycle), and a beam current of 62.5 mA. The Superconducting Radio-Frequency (SRF) linac is composed of three families of Superconducting Radio-Frequency (SRF) cavities, which are being prototyped, counting the spoke resonators with a geometric beta of 0.5, medium-beta elliptical cavities (beta_g=0.67) and high-beta elliptical cavities (beta_g=0.86). After a description of the ESS linear accelerator layout, this article will focus on the recent progress towards integration of the first test results of the main critical components to be assembled in cryomodules, then in the ESS tunnel.
	Slides THOBB3 [25.611 MB]
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THPIK070	Localization of RF Breakdown Point in a Coaxially Loaded LINAC Cavity	linac, cavity, electron, operation	4254
	Q.S. Chen, T. Hu, B. Qin HUST, Wuhan, People's Republic of China Y.J. Pei USTC/NSRL, Hefei, Anhui, People's Republic of China
	Here we report how the RF breakdown point (RFBP) can be localized in a coaxially loaded linac cavity with just the forward and the reflected power signal. The cavity uses 4 load cells instead of output coupler to absorb remanent power, so no transmitted power signal could be recorded. We propose two methods to analyze the measured signals and localize the RFBP. One method focuses on the time delay of the two signals while the other one focuses on the amplitude. Quantitative analysis showed the two methods were well consistent with each other and indicated the RFBP located at the end of the linac cavity.
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THPIK125	Ultra High Gradient Breakdown Rates in X-Band Cryogenic Normal Conducting Rf Accelerating Cavities	cryogenics, cavity, experiment, electron	4395
	A.D. Cahill, J.B. Rosenzweig UCLA, Los Angeles, California, USA V.A. Dolgashev, S.G. Tantawi, S.P. Weathersby SLAC, Menlo Park, California, USA
	Funding: Work Supported by DOE/SU Contract DE-AC02-76-SF00515, US NSF Award PHY-1549132, the Center for Bright Beams, and DOE SCGSR Fellowship. RF breakdown is one of the major factors limiting the operating accelerating gradient in rf particle accelerators. We conjecture that the breakdown rate is linked to the movements of crystal defects induced by periodic mechanical stress. Pulsed surface heating possibly creates a major part of this stress. By decreasing crystal mobility and increasing yield strength we hope to reduce the breakdown rate for the same accelerating gradient. We can achieve these properties by cooling a copper accelerating cavity to cryogenic temperatures. We tested an 11.4 GHz cryogenic copper accelerating cavity at high power and observed that the rf and dark current signals are consistent with Q₀ changing during rf pulses. To take this change in Q₀ into account, we created a non-linear circuit model in which the Q₀ is allowed to vary inside the pulse. We used this model to process the data obtained from the high power test of the cryogenic accelerating structure. We present the results of measurements with low rf breakdown rates for surface electric fields near 500 MV/m for a shaped rf pulse with 150 ns of flat gradient.
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Paper

Title

Other Keywords

Page

MOPVA055

Upgrade of the Capture Section of the S-DALINAC Injector

cavity, SRF, electron, operation

993

D.B. Bazyl, H. De Gersem, W.F.O. Müller
TEMF, TU Darmstadt, Darmstadt, Germany

Funding: This work is supported by the DFG through GRK 2128.
In order to reduce the energy spread of the recirculated beam, the injector of the S-DALINAC needs to be optimized, because the non-isochronous recirculation cannot correct for errors originating from the injector linac. For the S-DALINAC, spatial restrictions suggest the use of SRF technology for the capture section. In this work, we consider various SRF cavities with an operating frequency of 3 GHz for a possible upgrade of the capture section of the S-DALINAC. The first results of the RF and beam dynamics simulations for the proposed options are presented in this paper.

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MOPVA063

Vertical Tests of ESS Medium Beta Prototype Cavities at LASA

cavity, vacuum, operation, radiation

1015

A. Bosotti, A. Bellandi, M. Bertucci, A. Bignami, J.F. Chen, C.G. Maiano, P. Michelato, L. Monaco, R. Paparella, P. Pierini, D. Sertore
INFN/LASA, Segrate (MI), Italy
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy
S. Pirani
ESS, Lund, Sweden

In the framework of the INFN activity related to the European Spallation Source collaboration, the LASA infrastructure has been renewed to allow the qualification, in its vertical cryostat, of the 704 MHz medium beta cavity prototypes. A new cryogenic insert has been realized, fully equipped with dedicated mechanical supports, vacuum, thermal sensors and quench diagnostic systems. The RF test station has been upgraded as well with a new PLL electronics rack. The first beta 0.67 cavity prototype designed and produced by INFN Milano has been successfully cold tested at 2.0 K temperature, outperforming the ESS specifications. The technical features of LASA infrastructure, the design of novel components and the experimental results of cavities cold-tests are thoroughly described in this paper.

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MOPVA082

PLASMA PROCESSING R&D OF THE 1.3 GHZ SINGLE-CELL SRF CAVITY AT IMP

plasma, cavity, SRF, electromagnetic-fields

1055

L. Yang, L. Chen, Y. He, S.C. Huang, C.X. Li, C.L. Li, Y.M. Li, L. Lu, A. Shi, L.P. Sun, A.D. Wu, S.H. Zhang
IMP/CAS, Lanzhou, People's Republic of China

The China-Accelerator Driven Sub-critical System (C-ADS) injector II has already commissioned with a CW 1 mA and a pulsed 10 mA proton beam. The beam energy achieved 10 MeV. The superconducting linac (SCL) is routinely operating at 4.7 MV/m average accelerating gradient in the low-beta cryomodules. Field emission and surface contaminants of the SCL limit the gradient in-crease in the beam commissioning. Hence, in order to increase the SCL accelerating gradient, reduce field emis-sion and remove surface pollutants, in-situ plasma pro-cessing R&D in a 1.3 GHz single-cell SRF cavity has being studied. In this paper, the current effort of plasma processing R&D in a 1.3 GHz single-cell SRF cavity will be presented in details and the future plan will be also reported.

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MOPVA087

Low Betta Superconducting Cavity for the New Injector Linac for Nuclotron-NICA

cavity, linac, simulation, multipactoring

1058

M. Gusarova, T.A. Bakhareva, M.V. Lalayan, S.V. Matsievskiy, N.P. Sobenin, D.V. Surkov, K.V. Taletskiy, V. Zvyagintsev
MEPhI, Moscow, Russia
A.A. Bakinowskaya, V.S. Petrakovsky, A.I. Pokrovsky, D.A. Shparla
Physical-Technical Institute of the National Academy of Sciences of Belarus, Minsk, Belarus
A.V. Butenko, G.V. Trubnikov
JINR/VBLHEP, Dubna, Moscow region, Russia
V. Zvyagintsev
TRIUMF, Vancouver, Canada

The results of the RF, mechanical and multipactor discharge simulations of the 162 MHz quarter wave resonator (QWR) for New Superconducting Injector Linac for Nuclotron-NICA are presented. Cavity design in conjunction with manufacturing features is discussed.

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MOPVA088

Medium Betta Superconducting Cavity for the New Injector Linac for Nuclotron-NICA

cavity, simulation, linac, multipactoring

1061

M. Gusarova, M.V. Lalayan, N.P. Sobenin, D.V. Surkov, K.V. Taletskiy
MEPhI, Moscow, Russia
A.A. Bakinowskaya, V.S. Petrakovsky, A.I. Pokrovsky, D.A. Shparla
Physical-Technical Institute of the National Academy of Sciences of Belarus, Minsk, Belarus
A.V. Butenko, G.V. Trubnikov
JINR/VBLHEP, Dubna, Moscow region, Russia

The results of the electrodynamical and multipactor discharge simulations of the medium betta superconducting cavity for New Superconducting Injector Linac for Nuclotron-NICA are presented. Different designs of CH and Spoke cavities are compared and the optimal one is chosen.

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MOPVA116

Quench Studies in Single-Cell Nb3Sn Cavities Coated Using Vapour Diffusion

cavity, radio-frequency, monitoring, niobium

1119

D.L. Hall, M. Liepe, J.T. Maniscalco, R.D. Porter
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
P. Cueva, D. Liarte, D.A. Muller, J.P. Sethna
Cornell University, Ithaca, New York, USA

The superconductor Nb3Sn is known to have a superheating field, Hsh, of approximately 400 mT. This critical field represents the ultimate achievable gradient in a superconducting cavity, and is equivalent to an accelerating gradient of 90 MV/m in an ILC single-cell cavity for this value of Hsh. However, the currently best performing Nb3Sn single-cell cavities remain limited to accelerating gradients of 17-18 MV/m, translating to a peak surface magnetic field of approx. 70 mT. In this paper, we consider theoretical models of candidate quench mechanisms, and compare them to experimental data from surface analysis and cavity tests.

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MOPVA128

RF Performance of Nitrogen-Doped Production SRF Cavities for LCLS-II

cavity, SRF, niobium, operation

1156

D. Gonnella, A. Burrill, M.C. Ross
SLAC, Menlo Park, California, USA
S. Aderhold, A. Grassellino, C.J. Grimm, T.N. Khabiboulline, O.S. Melnychuk, S. Posen, D.A. Sergatskov
Fermilab, Batavia, Illinois, USA
E. Daly, G.K. Davis, F. Marhauser, K.M. Wilson
JLab, Newport News, Virginia, USA

Funding: DOE and the LCLS-II Project
The Linac Coherent Light Source II (LCLS-II) requires 280 9-cell superconducting RF cavities for operation in continuous wave mode. Two vendors have previously been selected to produce the cavities, Research Instruments GmbH and Ettore Zanon S.p.a. Here we present results from manufacturing and cavity preparation for the cavities constructed at these two vendors for LCLS-II. We show how the cavity preparation method has been changed mid-production in order to improve flux expulsion in the cavities and maintain high performance in realistic magnetic field environments (~5 mG). Additionally, we show that the nitrogen-doping process has been carried out successfully and repeatedly on over 70 cavities.

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TUPAB006

Achievement of Stable Pulsed Operation at 31 MV/m in the STF-2 Cryomodule for the ILC

cavity, cryomodule, operation, radiation

1308

Y. Yamamoto, T. Dohmae, M. Egi, K. Hara, T. Honma, E. Kako, Y. Kojima, T. Konomi, N. Kota, T. Kubo, T. Matsumoto, T. Miura, H. Nakai, K. Nakanishi, G.-T. Park, T. Saeki, H. Shimizu, T. Shishido, T. Takenaka, K. Umemori
KEK, Ibaraki, Japan

In the Superconducting RF Test Facility (STF) in KEK, the cooldown test for the STF-2 cryomodule with 12 cavities has been done totally three times since 2014. In 2016, the 3rd cooldown test for the STF-2 cryomodule including the capture cryomodule with 2 cavities, which was used for Quantum Beam Project in 2012, was successfully done. The main purpose is the vector-sum operation with 8 cavities at average accelerating gradient of 31 MV/m as the ILC specification, and the others are the measurement for Lorenz Force Detuning (LFD) and unloaded Q value, and Low Level RF (LLRF) study, etc. During 8 cavities operation, piezo actuators were used for the compensation of LFD, and the feed-forward and vector-sum control system by LLRF worked perfectly for keeping the lowest forward power and the stable flat-top of accelerating gradient. In this paper, the result for the STF-2 cryomodule in the 3rd cooldown test will be presented in detail.

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TUPAB070

S-Band Accelerating Structure for High-Gradient Upgrade of TTX

electron, impedance, simulation, linac

1485

D.Z. Cao, H.B. Chen, Y.-C. Du, W. Gai, W.-H. Huang, X.C. Meng, J. Shi, C.-X. Tang, X.W. Wu, H. Zha
TUB, Beijing, People's Republic of China

Thomson scattering x-ray source is an indispensable scientific X-ray imaging tool in various research fields. The 3-meter S-band linac in Tsinghua Thomson scatter-ing X-ray source (TTX) has been running at an accelerat-ing gradient of 15 MV/m so far. The gradient will be upgraded to 30MV/m by replacing the old structure with a shorter linac. Detailed optimization of the RF design of the new S-band linac structure is presented in this paper. Finally, further research on energy upgrade with X-band structures are also discussed.

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WEPAB138

Prototyping High-Gradient mm-Wave Accelerating Structures

interface, experiment, cavity, RF-structure

2902

E.A. Nanni, V.A. Dolgashev, A.A. Haase, J. Neilson, S.G. Tantawi
SLAC, Menlo Park, California, USA
S.C. Schaub
MIT, Cambridge, Massachusetts, USA
B. Spataro
INFN/LNF, Frascati (Roma), Italy
R.J. Temkin
MIT/PSFC, Cambridge, Massachusetts, USA

We present single-cell accelerating structures designed for high-gradient testing at 110 GHz. The purpose of this work is to study the basic physics of ultrahigh vacuum RF breakdown in high-gradient RF accelerators. The accelerating structures are pi-mode standing-wave cavities fed with a TM01 circular waveguide. The structures are fabricated using precision milling out of two metal blocks, and the blocks are joined with diffusion bonding and brazing. The impact of fabrication and joining techniques on the cell geometry and RF performance will be discussed. First prototypes had a measured Qo of 2800, approaching the theoretical design value of 3300. The geometry of these accelerating structures are as close as practical to single-cell standing-wave X-band accelerating structures more than 40 of which were tested at SLAC. This wealth of X-band data will serve as a baseline for these 110 GHz tests. The structures will be powered with short pulses from a MW gyrotron oscillator. RF power of 1 MW may allow us to reach an accelerating gradient of 400 MeV/m.

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WEPVA019

Group Velocity Matching in Dielectric-Lined Waveguides and its Role in Electron-THz Interaction

electron, acceleration, simulation, interface

3296

A.L. Healy, G. Burt
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
D.M. Graham
The University of Manchester, The Photon Science Institute, Manchester, United Kingdom
S.P. Jamison
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

Terahertz(THz)-driven dielectric-lined waveguides have applications in electron manipulation, particularly acceleration, as the use of dielectric allows for phase velocities below the speed of light. However matching a single frequency to the correct velocity does not maximise electron-THz interaction; waveguide dispersion typically results in an unmatched group velocity and so the pulse envelope of a short THz pulse changes along the length of the structure. This reduces field amplitude and therefore accelerating gradient as the envelope propagates at a different velocity to the electron. Presented here is an analysis of the effect of waveguide dispersion on THz-electron interaction and its influence on structure dimensions and choice of THz pulse generation. This effect on net acceleration is demonstrated via an example of a structure excited by a single-cycle THz pulse, with a comparison of multi-cycle, lower intensity THz pulses on net acceleration.

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WEPVA020

Dual-Grating Dielectric Accelerators Driven by A Pulse-Front-Tilted Laser

laser, electron, simulation, vacuum

3299

Y. Wei, C.P. Welsch
The University of Liverpool, Liverpool, United Kingdom
M.M. Dehler, E. Ferrari, N. Hiller, R. Ischebeck
PSI, Villigen PSI, Switzerland
J.D.A. Smith
TXUK, Warrington, United Kingdom
C.P. Welsch
Cockcroft Institute, Warrington, Cheshire, United Kingdom
G.X. Xia
UMAN, Manchester, United Kingdom

Dual-grating Dielectric Laser-driven Accelerators (DLAs) are considered to be one of the most promising technologies to miniaturize future particle accelerators. Accelerating gradients in the GV/m range seem accessible and 690 MV/m has been demonstrated in fused silica structures. However, the increase in beam energy is limited by the short interaction length between the laser pulses and the electron bunch. In this contribution, a pulse-front-tilt operation for a laser beam is studied to extend the interaction length, resulting in a greater energy gain for a dual-grating DLA. The VSIM code is used to compare this new scheme with the commonly used approach of a normally incident laser beam and advantages are summarized.
[1]T. Plettner, et al., Phys. Rev. ST Accel. Beams 9, 111301 (2006)
[2]K. P. Wootton, et al., Opt. Lett., 41, 2696 (2016).
[3]E. A. Peralta, et al., Nature 503, 91 (2013)

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WEPVA022

RECENT TWO-BEAM ACCELERATION ACTIVITIES AT ARGONNE WAKEFIELD ACCELERATOR FACILITY

acceleration, experiment, wakefield, impedance

3305

J.H. Shao, S.P. Antipov, M.E. Conde, W. Gai, Q. Gao, G. Ha, W. Liu, N.R. Neveu, J.G. Power, Y.R. Wang, E.E. Wisniewski, L.M. Zheng
ANL, Argonne, Illinois, USA
C.-J. Jing, J.Q. Qiu
Euclid TechLabs, LLC, Solon, Ohio, USA
J. Shi, D. Wang
TUB, Beijing, People's Republic of China

The Two-Beam Acceleration (TBA) is a modified approach to the structure-based wakefield acceleration which may meet the luminosity, efficiency, and cost requirement of a future linear collider. Recently, various TBA experiments have been carried out at the Argonne Wakefield Accelerator Facility (AWA). With X-band metallic power extractors and accelerators, a 70 MeV/m average accelerating gradient has been demonstrated in two stages while a 150 MeV/m gradient as well as 300 MW extracted power have been achieved in a single stage. In addition, low cost K-band dielectric power extractor and accelerator have also been developed. The preliminary results show power extraction of 55 MW and an average accelerating gradient of 28 MeV/m.

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THOBB3

ESS SRF Linear Accelerator Components Preliminary Results and Integration

cavity, SRF, cryomodule, linac

3666

C. Darve, N. Elias, C.G. Maiano, F. Schlander
ESS, Lund, Sweden
C. Arcambal, G. Devanz, F. Peauger
CEA/DRF/IRFU, Gif-sur-Yvette, France
E. Cenni
CEA/IRFU, Gif-sur-Yvette, France
G. Costanza
Lund University, Lund, Sweden
P. Duthil, G. Olry, D. Reynet
IPN, Orsay, France
L. Hermansson
Uppsala University, Uppsala, Sweden
P. Michelato, D. Sertore
INFN/LASA, Segrate (MI), Italy

The European Spallation Source (ESS) is a pan-European project and one of world's largest research infrastructures based on neutron sources. This collaborative project is funded by a collaboration of 17 European countries and is under construction in Lund, Sweden. The 5 MW, 2.86 ms long pulse proton accelerator has a repetition frequency of 14 Hz (4 % duty cycle), and a beam current of 62.5 mA. The Superconducting Radio-Frequency (SRF) linac is composed of three families of Superconducting Radio-Frequency (SRF) cavities, which are being prototyped, counting the spoke resonators with a geometric beta of 0.5, medium-beta elliptical cavities (beta_g=0.67) and high-beta elliptical cavities (beta_g=0.86). After a description of the ESS linear accelerator layout, this article will focus on the recent progress towards integration of the first test results of the main critical components to be assembled in cryomodules, then in the ESS tunnel.

Slides THOBB3 [25.611 MB]

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THPIK070

Localization of RF Breakdown Point in a Coaxially Loaded LINAC Cavity

linac, cavity, electron, operation

4254

Q.S. Chen, T. Hu, B. Qin
HUST, Wuhan, People's Republic of China
Y.J. Pei
USTC/NSRL, Hefei, Anhui, People's Republic of China

Here we report how the RF breakdown point (RFBP) can be localized in a coaxially loaded linac cavity with just the forward and the reflected power signal. The cavity uses 4 load cells instead of output coupler to absorb remanent power, so no transmitted power signal could be recorded. We propose two methods to analyze the measured signals and localize the RFBP. One method focuses on the time delay of the two signals while the other one focuses on the amplitude. Quantitative analysis showed the two methods were well consistent with each other and indicated the RFBP located at the end of the linac cavity.

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THPIK125

Ultra High Gradient Breakdown Rates in X-Band Cryogenic Normal Conducting Rf Accelerating Cavities

cryogenics, cavity, experiment, electron

4395

A.D. Cahill, J.B. Rosenzweig
UCLA, Los Angeles, California, USA
V.A. Dolgashev, S.G. Tantawi, S.P. Weathersby
SLAC, Menlo Park, California, USA

Funding: Work Supported by DOE/SU Contract DE-AC02-76-SF00515, US NSF Award PHY-1549132, the Center for Bright Beams, and DOE SCGSR Fellowship.
RF breakdown is one of the major factors limiting the operating accelerating gradient in rf particle accelerators. We conjecture that the breakdown rate is linked to the movements of crystal defects induced by periodic mechanical stress. Pulsed surface heating possibly creates a major part of this stress. By decreasing crystal mobility and increasing yield strength we hope to reduce the breakdown rate for the same accelerating gradient. We can achieve these properties by cooling a copper accelerating cavity to cryogenic temperatures. We tested an 11.4 GHz cryogenic copper accelerating cavity at high power and observed that the rf and dark current signals are consistent with Q₀ changing during rf pulses. To take this change in Q₀ into account, we created a non-linear circuit model in which the Q₀ is allowed to vary inside the pulse. We used this model to process the data obtained from the high power test of the cryogenic accelerating structure. We present the results of measurements with low rf breakdown rates for surface electric fields near 500 MV/m for a shaped rf pulse with 150 ns of flat gradient.

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