IPAC2018 - List of Keywords (ECR)

Paper	Title	Other Keywords	Page
MOZGBF1	FRIB Front End Construction and Commissioning	rfq, MMI, operation, ion-source	58
	G. Pozdeyev FRIB, East Lansing, Michigan, USA
	The Facility for Rare Isotope Beams (FRIB) is based upon the CW, SC driver linac to accelerate all the stable isotopes up to more than 200 MeV/u with a beam power of 400 kW. The front end (FE) commissioning shall start in 2017. This invited talk presents the FRIB front end design, and current status of FRIB front end commissioning, including beam properties and energy, and their relationship to FRIB operational requirements.
	Slides MOZGBF1 [2.965 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOZGBF1
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TUPAL040	Ion Beam Studies in the FRIB Front End	ion-source, space-charge, coupling, optics	1094
	T. Yoshimoto, K. Fukushima, S.M. Lidia, T. Maruta, P.N. Ostroumov, G. Pozdeyev, H.T. Ren FRIB, East Lansing, USA
	Funding: Work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661 and the National Science Foundation under Cooperative Agreement PHY-1102511. The commissioning of the FRIB Front End with 12 keV/u argon beam started in the spring of 2017. Beam profile monitors were used to evaluate RMS Twiss parameters in various locations along the beam line. Beam dynamics in the LEBT was simulated using full 3D model of beam optics elements in the tracking codes. We found a good consistency between measured and simulated data. A beam image viewer was used to measure the beam density distribution in the real space. A hollow beam structure was observed in the Ar⁹⁺ beam with the current of ~20 eμA. Extensive beam dynamics study with 3D tracking code suggests that the hollow density distribution can be generated by space charge effects of the multi-component, multi-charge state ion beam just after the ECR ion source. This paper reports studies of a mechanism that can produce a hollow beam structure. E. Pozdeyev, invited talk at this conference
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAL040
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TUPMF073	Impedance Optimization of Small Gap Chambers for the High Single Bunch Current Operation at the Undulator Based Light Sources	impedance, lattice, undulator, simulation	1430
	Y.-C. Chae DESY, Hamburg, Germany
	In the undulator based light sources the intensity limit of single bunch is often determined by the strong vertical instability caused by the wakefield in the ring, where the undulator itself is large impedance source. The optimization of transition from the large aperture to undulator's small-gap chamber is on-going research topic in an effort to reduce the vertical impedance; at the same time, the demand on single-bunch current is high from the timing-mode x-ray user community. In this paper, after showing the results obtained by exploring the parameter space guided by Stupakov's formula, we propose the linearly-segmented transition which can reduce the impedance down to 60% or less of the original linear taper. The reduction can be utilized either to increase the bunch current substantially or to install a smaller gap chamber without impacting the bunch current limit. For the definite result we considered the transition between two ellipses, namely, (a, b) = (42 mm, 21 mm) and (18 mm, 4 mm) over the length 15-30 cm in beam direction.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF073
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TUPMK012	Acceleration of Charged Particles by Own Field in a Non-Stationary One-Dimensional Stream	interface, electron, acceleration, operation	1516
	A.S. Chikhachev Allrussian Electrotechnical Institute, Moskow, Russia
	The behavior of a non-stationary stream of the charged particles interacting with own field is studied. For the description the integral of the movement received in works * - Meshchersky's integral is used. The additional integral of the movement - interfaced to Meshchersky's integral, necessary for completely self-agreed description of a stream of the particles interacting with own field is constructed. The system of the equations reducing a problem to the solution of system of the ordinary differential equations is removed. Private decisions for potential, density of particles and density of current are provided. Earlier the problem was studied in work . Mestschersky J. Astronomische Nachrichten, 1893, T.132, N3153, p. 9. Nestschersky ibid, 1902, T.159, N3807, p. 15. * Chikhachev A.S., Technical Phisics, 2014, vol 59, N 4, pp 487-493.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMK012
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TUPML023	Amplitude Enhancement of the Self-Modulated Plasma Wakefields	proton, plasma, wakefield, focusing	1585
	Y. M. Li, G.X. Xia, Y. Zhao UMAN, Manchester, United Kingdom K.V. Lotov, A. Sosedkin Budker INP & NSU, Novosibirsk, Russia
	Seeded Self-modulation (SSM) has been demonstrated to transform a long proton bunch into many equidistant micro-bunches (e.g., the AWAKE case), which then resonantly excite strong wakefields. However, the wakefields in a uniform plasma suffer from a quick amplitude drop after reaching the peak. This is caused by a significant decrease of the wake phase velocity during self-modulation. A large number of protons slip out of focusing and decelerating regions and get lost, and thus cannot contribute to the wakefield growth. Previously suggested solutions incorporate a sharp or a linear plasma longitudinal density increase which can compensate the backward phase shift and therefore enhance the wakefields. In this paper, we propose a new plasma density profile, which can further boost the wakefield amplitude by 30%. More importantly, almost 24% of protons initially located along one plasma period survive in a micro-bunch after modulation. The underlying physics is discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML023
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WEPAL033	Development of Real-Time Mass Analysis System with Permanent Magnet for Ion Beam	ion-source, extraction, permanent-magnet, simulation	2236
	Y. Takeuchi, Y. Iwashita, H. Tongu Kyoto ICR, Uji, Kyoto, Japan
	In order to analyze time variation of the ion species in a pulse, we are developing a mass analysis system that has multiple collector electrodes to detect several ion species simultaneously. Strong permanent magnets can generate 1T magnetic field and the size of the analyzing magnet system can be compact. The detected signals are scanned by a fast multiplexer. The scanning rate is 2 MHz, so that all electrode signals of the 16 channels are scanned in 8 μs period. In this paper, details of the design of the analysis system, and preliminary beam extraction test results with prototype of the system are described.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAL033
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WEPAL049	Simulating Non-Relativistic Beams Using Helical Pulse Lines	impedance, simulation, site, GUI	2288
	C.J. Richard NSCL, East Lansing, Michigan, USA S.M. Lidia FRIB, East Lansing, USA
	Funding: Work supported by the US Department of Energy, Office of Science, High Energy Physics under Cooperative Agreement award number DE-SC0018362. Benchtop calibration of capacitive beam position monitors (BPMs) in low energy beamlines is challenging due to non-relativistic effects. Typical benchtop calibrations cannot account for these effects because they rely on speed of light fields transmitted along a straight wire. However, it is possible to replicate the electromagnetic fields generated by non-relativistic beams using a helical line pulse instead of a straight wire. In order to properly replicate the fields from a beam, a method must be developed for tailoring input pulses into the helical line to match bunch shape and a model of the impedance of the helix should be developed to assist with matching. This paper uses the sheath helix model to analyze signal propagation along a helical line in the time domain, with attention to dispersive effects and impedance matching. The results from this model are then compared to Microwave Studio simulations.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAL049
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WEPMF041	Insights into the Role of C, N, and O Introduced by Low Temperature Baking on Niobium Cavity Performance	cavity, niobium, experiment, superconductivity	2455
	P.N. Koufalis, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Previous experiments have shown that introducing nitrogen gas during low temperature bakes (120-160 C) of niobium cavities introduces C, N, and O impurities to the first 10-100 nm of the surface. This new treatment results in higher quality factors and even 'anti-Q-slope' in some cases. However, it is not entirely clear the role that each of these impurities plays in the performance enhancement of the cavities. It has been suggested that interstitial N within the first few nm of the surface is solely responsible for the observed enhancement, but little work has been done on the role of C and O. Because both C and O are abundant in much higher quantities than N near the surface, it is important to understand whether they are beneficial or detrimental to cavity performance. We provide further insight into the effects of C and O on cavity performance by baking in an ambient atmosphere rich in CO2 as opposed to N2.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF041
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WEPMF046	Modeling of the Frequency and Field Dependence of the Surface Resistance of Impurity-Doped Niobium	cavity, niobium, experiment, SRF	2471
	J.T. Maniscalco, P.N. Koufalis, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The anti-Q-slope, a field-dependent decrease in surface resistance observed in impurity-doped niobium, has been investigated extensively in 1.3 GHz cavities. New early research into this effect has recently been performed at higher and lower frequencies, revealing an additional dependence on frequency: the anti-Q-slope is stronger at higher frequencies and weaker at lower frequencies. Several models have been proposed to explain the anti-Q-slope, with varying success in this new frequency-dependent regime. In this work, we analyze recent experimental data from a low-temperature-doped 1.3 GHz cavity and a high-temperature nitrogen-doped 2.6 GHz cavity and discuss the implications of these results on the proposed models.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF046
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WEPML013	Anti-Q-slope enhancement in high-frequency niobium cavities	cavity, niobium, SRF, experiment	2707
	M. Martinello, S. Aderhold, S.K. Chandrasekaran, M. Checchin, A. Grassellino, O.S. Melnychuk, S. Posen, A.S. Romanenko, D.A. Sergatskov Fermilab, Batavia, Illinois, USA
	N-doped 1.3 GHz niobium cavities showed for the first time the so-called anti-Q-slope, i.e. the increasing of the Q-factor as a function of the accelerating field. It was verified that the anti-Q-slope is consequence of the decreasing of the temperature-dependent component of the surface resistance as a function of the field. This trend is opposite compared to the increasing of the surface resistance previously observed in 1.3 GHz standard (EP, BCP, 120 C baked) niobium cavities. The effect of the different state-of-the-art surface treatments on the field dependence of the surface resistance is studied for 650 MHz, 1.3 GHz, 2.6 GHz and 3.9 Ghz cavities. This proceeding shows that the field dependence of the temperature-dependent component of the surface resistance has a strong frequency dependence and that the anti-Q-slope may appear even in clean niobium cavities if the resonant frequency is high enough, suggesting new routes toward the understanding of the anti-Q-slope effect.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML013
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THYGBF4	Accelerator Physics Advances in FRIB (Facility for Rare Isotope Beams)	cavity, linac, MMI, ECRIS	2950
	P.N. Ostroumov, N.K. Bultman, M. Ikegami, S.M. Lidia, S.M. Lund, G. Machicoane, T. Maruta, A.S. Plastun, G. Pozdeyev, X. Rao, J. Wei, T. Xu, T. Yoshimoto, Q. Zhao FRIB, East Lansing, USA C.Y. Wong NSCL, East Lansing, Michigan, USA
	Funding: Work supported by the U.S. DOE Office of Science under Cooperative Agreement DE-SC0000661 and the NSF under Cooperative Agreement PHY-1102511, the State of Michigan and Michigan State University. This paper presents recent developments of accelerator physics related topics for the Facility for Rare Isotope Beams (FRIB) being built at Michigan State University. While extensive beam dynamics simulations including all known errors do not show uncontrolled beam losses in the linac, ion beam contaminants extracted from the ECR ion source together with main ion beam can produce significant losses after the charge stripper. These studies resulted in development of beam collimation system at relatively low energy of 16 MeV/u and room temperature bunchers instead of originally planned superconducting ones. Commissioning of the Front End enabled detailed beam physics studies accompanied with the simulations using several beam dynamics codes. Settings of beam optics devices from the ECR to MEBT has been developed and applied to meet important project milestones. Similar work is planned for the beam commissioning of the first 3 cryomodules in the superconducting linac.
	Slides THYGBF4 [11.092 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THYGBF4
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THPAK068	Fringe Field Effect of Solenoids	solenoid, optics, neutron, quadrupole	3385
	T.V. Gorlov, J.A. Holmes ORNL, Oak Ridge, Tennessee, USA
	Funding: This work has been supported by Oak Ridge National Laboratory, man-aged by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy. We derive a precise analytical nonlinear transverse map for single particle transport through a solenoid with hard edge fringe fields. The transfer map is two dimensional for transverse coordinates and momenta with fixed longitudinal momentum. Because it is an accurate analytic map, it is also symplectic. The transfer map is compared with ex-act numerical tracking.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK068
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THPAL044	The Permanent Magnets Magnetic Characteristics Change Under Effect of 10 MeV Beam	radiation, electron, experiment, permanent-magnet	3742
	I.S. Guk, O.M. Bovda, V.O. Bovda, A.N. Dovbnya, A.I. Kalinichenko, S.S. Kandybey, V.N. Ljashchenko, A. Mytsykov, L.V. Onishchenko, O.A. Repikhov, A.Y. Zelinsky NSC/KIPT, Kharkov, Ukraine
	Magnets of applied electron accelerators are under direct effect of electrons and bremsstrahlung radiation stipulated by the electron beam. The choice of the materials for the rare elements alloy accelerator magnets has the decisive importance for the long term magnet parameters keeping. The experimental studies of the magnetic fields around the Nd-Fe-B and Sm2Co17 alloy magnets under effect of the electron beam have been done. The samples of 30х24х12 mm geometrical sizes were bombarded by electron beam of applied NSC KIPT accelerator KUT-1 with electron energy of 10 MeV and were irradiated by correspondent bremsstrahlung. The magnetic field value around Nd-Fe-B alloy samples was decreased nonlineary under electron beam bombarding with change of irradiation doze from 16 to 160 GRad. Under effect of bremsstrahlung the magnetic field value around samples was not changed. The repeated sample magnetizations allowed to restore the initial magnetic field distribution around magnets. The magnetic field distribution around Sm2Co17 alloy samples was not changed under effect of the electron beam and bremsstrahlung within irradiation dozes mentioned above. The induced activity in the Nd-Fe-B and Sm2Co17 alloy samples was changed slightly during the experiments.
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THPAL058	Effect of Ozonated Water Cleaning on Photon Stimulated Desorption in a Stainless Steel Chamber	photon, vacuum, experiment, radiation	3778
	C.M. Cheng, C.K. Chan, C.-C. Chang, Y.T. Cheng, J. -Y. Chuang, G.-Y. Hsiung, L.H. Wu, Y.C. Yang NSRRC, Hsinchu, Taiwan
	Aluminium vacuum chambers cleaned with ozonated water show a reduction of residual carbon and lower surface outgassing rate after baking. We would like to investigate if stainless steel chambers show similar ef-fects. A stainless steel test chamber was cleaned by stand-ard chemical cleaning only and then compared with an-other one after immersion in 30ppm ozonated water for thirty minutes. Both samples were baked, then photon exposed and the photon desorption yields were deter-mined by vacuum gauges and residual gas analysers at the TLS 19B beamline. The test results on photon stimulated desorption yields and partial pressure variations with and without ozonated water cleaning of the stainless steel tubes will be discussed in some detail.
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THPAL092	Test Particle Monte Carlo Simulation of NEG Coated Narrow Tubular Samples	vacuum, experiment, simulation, SRF	3862
	O. Seify, A.N. Hannah, O.B. Malyshev, Sirvinskaite, R. Sirvinskaite, R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom Sirvinskaite, R. Sirvinskaite Loughborough University, Loughborough, Leicestershire, United Kingdom
	The pumping properties of the NEG coated vacuum chambers play an important role in the efficiency of vac-uum system of accelerators. The sticking probability of the NEG films is one the most important parameters to characterise the pumping properties of the NEG coated vacuum chambers. In order to investigate the NEG film sticking probability, Test Particle Monte-Carlo (TPMC) models were used. The models were based on the design of the installed experimental setup in ASTeC Vacuum Science group laboratory at Daresbury Laboratory (DL). The results of the simulations have been used for inter-preting the results of the measurements in the experi-mental setup.
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THPAL127	Structural Investigations of Nitrogen-Doped Niobium for Superconducting RF Cavities	niobium, cavity, vacuum, experiment	3940
	M. Major, L. Alff, M. Arnold, J. Conrad, S. Flege, R. Grewe, M. Mahr, N. Pietralla TU Darmstadt, Darmstadt, Germany F. Hug KPH, Mainz, Germany
	Funding: Work supported by the German Federal Ministry for Education and Research (BMBF) through grant 05H15RDRBA. Niobium is the standard material for superconducting RF (SRF) cavities. Superconducting materials with higher critical temperature or higher critical magnetic field allow cavities to work at higher operating temperatures or higher accelerating fields, respectively. Enhancing the surface properties of the superconducting material in the range of the penetration depth is also beneficial. One direction of search for new materials with better properties is the modification of bulk niobium by nitrogen doping. In the Nb-N phase diagram the cubic delta-phase of NbN has the highest critical temperature (16 K). Already slight nitrogen doping of the alpha-Nb phase results in higher quality factors.* Nb samples were N-doped at the refurbished UHV furnace at IKP Darmstadt. Reference samples were annealed in 1 bar nitrogen atmosphere at different temperatures. In this contribution the results on the structural investigations (x-ray diffraction and pole figure, secondary ion mass spectroscopy, scanning electron microscopy) at the Materials Research Department of TU Darmstadt will be presented. *Grassellino et al., Proc. SRF2015, MOBA06, 48.
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THPAL154	High-Gradient Performance of X-Band Choke-Mode Structures	GUI, experiment, HOM, damping	4011
	X.W. Wu, D.Z. Cao, H.B. Chen, J. Shi, H. Zha TUB, Beijing, People's Republic of China T. Abe, T. Higo, S. Matsumoto KEK, Ibaraki, Japan
	Funding: National Natural Science Foundation of China (Grant No. 11135004) The choke-mode accelerating structure is one of the higher-order-mode (HOM) damping structures. It has the advantage of relatively simple fabrication and low surface magnetic field. C-band choke-mode accelerating structures have been successfully applied in multibunch XFEL. However, the X-band choke-mode study remains in the theoretical design stage. The high-gradient performance of the choke is still unknown. Five different single-cell choke-mode accelerating structures were designed, fabricated and high-gradient tested to study the related RF breakdown characteristics. It was observed that high electric field and small choke dimension caused serious breakdowns in the choke which was the main limitation of the high-gradient performance. The Choke-mode accelerating structures reached 130 MV/m by decreasing the electric field and increasing the choke gap. A new quantity was proposed to give the high-gradient performance limit of choke-mode accelerating structures due to RF breakdown. The new quantity was obtained from the summary of the high-gradient experiments and could be used to guide high-gradient choke-mode accelerating structure design.
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THPMF012	Tapered Flying Radiofrequency Undulator	undulator, electron, FEL, simulation	4059
	S.P. Antipov, S.V. Kuzikov, A. Liu Euclid TechLabs, LLC, Solon, Ohio, USA S.V. Kuzikov, A.V. Savilov, A.A. Vikharev IAP/RAS, Nizhny Novgorod, Russia
	Funding: DOE SBIR DE-SC0017145 The x-ray free electron laser (x-FEL) efficiency, measured as a fraction of the electron beam power converted into light, is typically below 0.1% for most of the x-FEL facilities presently in operation. Undulator tapering techniques can be used to improve the conversion efficiency by 1-2 orders of magnitude. However at present there are no robust tapered undulator x-FEL schemes operating at 10% efficiency. In this paper we report on the development of tapered radiofrequency (RF) undulator. An RF undulator is a microwave waveguide in which strong RF field is excited that interacts with a charged particle beam forcing it to radiate coherent x-rays while undergoing a wiggling motion. RF undulators are attractive for use in x-FELs due to their large beam aperture and a short undulator period. Strongly tapered RF undulators (with tapering of a wavelength) due to non-resonant trapping regime allow keeping high overall XFEL efficiency being driven by laser plasma accelerated beams usually having high enough current but large energy spread (1-10%).
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THPMF046	Precision Charge Measurement of 40~MeV Electron-Beam to Calibrate Air Fluorescence Telescope for Cosmic Ray Observation	electron, vacuum, injection, ISOL	4163
	T. Shibata KEK, Ibaraki, Japan O.C. Shin OCU, Osaka, Japan
	The Telescope Array (TA) is ultra-high energy cosmic ray observation (UHECR). TA is using the fluorescence detectors (FD) for observation the air fluorescence(AFY) which are emitted in the cascade generated by an UHECR in atmosphere. One of the important observables is primary energy of UHECR, however it has 21% systematic uncertainty. For reduction of the uncertainty, we have been operated an 40-MeV electron linear accelerator from 2010 which we have constructed for absolute energy calibration. The accelerator is located at 100 m from FD station, and can shot electron beam which the direction is vertical into the air, the energy is 40-MeV, the pulse width is 1 micro-second, and the beam charge is 160 pC. The AFY efficiency and FD calibration parameters can be calibrated, which means energy scale of UHECR, by observation of the AFY which are generated by the electron beam in the air. The most important beam parameter is beam charge. The requirement of the accuracy of charge measurement is a few %, then we have developed the double faraday cups and one current transfer system. We calibrated the current transfer by the double faraday cups, and we could achieve about 1% accuracy.
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THPMK103	Initial Testing of Techniques for Large Scale Rf Conditioning for the Compact Linear Collider	linac, operation, linear-collider, collider	4548
	T.G. Lucas, M.J. Boland, P.J. Giansiracusa, R.P. Rassool, M. Volpi The University of Melbourne, Melbourne, Victoria, Australia N. Catalán Lasheras, A. Grudiev, T. Lefèvre, G. McMonagle, I. Syratchev, B.J. Woolley, W. Wuensch, V. del Pozo Romano CERN, Geneva, Switzerland J. Paszkiewicz University of Oxford, Oxford, United Kingdom C. Serpico Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy A. Vnuchenko IFIC, Valencia, Spain R. Zennaro PSI, Villigen PSI, Switzerland
	Nominal operating conditions for the Compact Linear Collider (CLIC) 380 GeV requires 72 MV/m loaded accelerating gradients for a 180 ns flat-top pulse. Achieving this requires extensive RF conditioning which past tests have demonstrated can take several months per structure, when conditioned at the nominal repetition rate of 50 Hz. At CERN there are three individual X-band test stands currently operational, testing up to 6 structures concurrently. For CLIC's 380 GeV design, 28,000 accelerating structures will make up the main linac. For a large scale conditioning programme, it is important to understand the RF conditioning process and to optimise the time taken for conditioning. In this paper, we review recent X-band testing results from CERN's test stands. With these results we investigate how to optimise the conditioning process and demonstrate the feasibility of pre-conditioning the structures at a higher repetition rate before installation into the main linac.
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THPMK116	NEA Surface Activation of GaAs Photocathode with CO2	cathode, experiment, electron, emittance	4590
	L.Guo. Guo UVSOR, Okazaki, Japan H. Iijima Tokyo University of Science, Tokyo, Japan M. Kuriki HU/AdSM, Higashi-Hiroshima, Japan K. Uchida Cosylab Japan, Ibaraki, Japan
	NEA (negative electron affinity)-GaAs cathode is able to generate highly spin polarized electron beam more than 90%. The NEA activation is performed usually with Cs and O2 or NF3, but the exact structure of the NEA surface is not known. In this paper, we performed the NEA activation on a cleaned GaAs surface with CO2, CO, N2, and O2 gases and compared the results to improve our understanding on the NEA surface. We found that CO2 activated the cathode, but N2 and CO did not. By analyzing CO2 activation, we found that atomic oxygen activates the NEA surface and CO degrades the NEA surface simultaneously. We found that the NEA activation ability of atomic oxygen is almost a half of that of O2 molecule.* *L. Guo, M. Kuriki, H. Iijima, K. Uchida. "NEA surface activation of GaAs photocathode with different gases", Surface Science 664C (2017) pp. 65-69.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK116
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THPML002	Emittance Preservation in Plasma-Based Accelerators with Ion Motion	emittance, plasma, wakefield, background	4654
	C. Benedetti, E. Esarey, W. Leemans, T.J. Mehrling, C.B. Schroeder LBNL, Berkeley, California, USA
	Funding: This work was supported by the Director, Office of Science, Office of High Energy Physics, of the U.S. DOE under Contract No. DE-AC02-05CH11231. In a plasma-accelerator-based linear collider, the density of matched, low-emittance, high-energy particle bunches required for collider applications can be orders of magnitude above the background ion density, leading to ion motion, perturbation of the focusing fields, and, hence, to beam emittance growth. By analyzing the response of the background ions to an ultrahigh density beam, analytical expressions, valid for non-relativistic ion motion, are obtained for the perturbed focusing wakefield. Initial beam distributions are derived that are equilibrium solutions, which require head-to-tail bunch shaping, enabling emittance preservation with ion motion.
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THPML052	Excitation of Plasma Wave by Lasers Beating in a Collisional and Mild-Relativistic Plasma	plasma, laser, electron, damping	4752
	M. Kaur, D.N. Gupta University of Delhi, Delhi, India
	Funding: Work supported by Department of Science and Technology (DST), Government of India. Excitation of plasma wave by two lasers beating in a collisional dominated relativistic plasma is investigated. We study the energy exchange between a plasma wave and two co-propagating lasers in plasma including the effect of relativistic mass change and electron-ion collisions. Two lasers, having frequency difference equal to the plasma frequency, excite a plasma beat wave resonantly by the ponderomotive force, which obeys the energy and momentum conservation. The relativistic effect and the electron-ion collision both contribute in energy exchange between the interacting waves in the beat-wave acceleration mechanism. Our study shows that the initial phase difference between interacting waves generates a phase mismatch between lasers and plasma wave, which alters the rate of amplitude variations of the interacting waves and, hence, affects the energy exchange between the interacting waves. This study may be crucial to design a compact plasma accelerator in low-intensity regime*. T. Tajima, and J. Dawson, Phys. Rev.Lett. 43, 267(1979) D. N. Gupta, M. S. Hur, and H. Suk, J.Appl. Phys. 100, 103101 (2006) *M. Kaur and D. N. Gupta, EuroPhysics letter 116, 35001 (2016).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML052
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FRXGBF3	Perspectives in High Intensity Heavy Ion Sources for Future Heavy Ion Accelerators	ion-source, heavy-ion, ECRIS, electron	5047
	L.T. Sun IMP/CAS, Lanzhou, People's Republic of China
	Driven by the development of next generation heavy ion accelerators such as IMP-HIAF, GSI-FAIR, RIKEN-RIBF, SPIRAL 2, JLEIC and so on that need very intense highly charged heavy ion beam injectors working at either pulsed or CW modes, intense research and development work towards more powerful ion sources have been made in different laboratories, which likewise has stimulated obvious advancement of the performances in recent years. However, even the best performing ion sources can't meet all the requirements. While the ion source researchers are tackling the next generation ion sources development, it is worth investigating the possibilities of other solutions, especially when very intense heavy ion beams are needed for the more intense and powerful heavy ion accelerators, for instance the driver accelerator to study inertial confinement fusion with heavy ion. This invited talk presents recent advancements of highly charged heavy ion sources, and discusses the other possible approaches for intense highly charged heavy ion beams for future heavy ion accelerators.
	Slides FRXGBF3 [10.014 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-FRXGBF3
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Paper

Title

Other Keywords

Page

MOZGBF1

FRIB Front End Construction and Commissioning

rfq, MMI, operation, ion-source

58

G. Pozdeyev
FRIB, East Lansing, Michigan, USA

The Facility for Rare Isotope Beams (FRIB) is based upon the CW, SC driver linac to accelerate all the stable isotopes up to more than 200 MeV/u with a beam power of 400 kW. The front end (FE) commissioning shall start in 2017. This invited talk presents the FRIB front end design, and current status of FRIB front end commissioning, including beam properties and energy, and their relationship to FRIB operational requirements.

Slides MOZGBF1 [2.965 MB]

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TUPAL040

Ion Beam Studies in the FRIB Front End

ion-source, space-charge, coupling, optics

1094

T. Yoshimoto, K. Fukushima, S.M. Lidia, T. Maruta, P.N. Ostroumov, G. Pozdeyev, H.T. Ren
FRIB, East Lansing, USA

Funding: Work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661 and the National Science Foundation under Cooperative Agreement PHY-1102511.
The commissioning of the FRIB Front End with 12 keV/u argon beam started in the spring of 2017*. Beam profile monitors were used to evaluate RMS Twiss parameters in various locations along the beam line. Beam dynamics in the LEBT was simulated using full 3D model of beam optics elements in the tracking codes. We found a good consistency between measured and simulated data. A beam image viewer was used to measure the beam density distribution in the real space. A hollow beam structure was observed in the Ar⁹⁺ beam with the current of ~20 eμA. Extensive beam dynamics study with 3D tracking code suggests that the hollow density distribution can be generated by space charge effects of the multi-component, multi-charge state ion beam just after the ECR ion source. This paper reports studies of a mechanism that can produce a hollow beam structure.
*E. Pozdeyev, invited talk at this conference

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TUPMF073

Impedance Optimization of Small Gap Chambers for the High Single Bunch Current Operation at the Undulator Based Light Sources

impedance, lattice, undulator, simulation

1430

Y.-C. Chae
DESY, Hamburg, Germany

In the undulator based light sources the intensity limit of single bunch is often determined by the strong vertical instability caused by the wakefield in the ring, where the undulator itself is large impedance source. The optimization of transition from the large aperture to undulator's small-gap chamber is on-going research topic in an effort to reduce the vertical impedance; at the same time, the demand on single-bunch current is high from the timing-mode x-ray user community. In this paper, after showing the results obtained by exploring the parameter space guided by Stupakov's formula, we propose the linearly-segmented transition which can reduce the impedance down to 60% or less of the original linear taper. The reduction can be utilized either to increase the bunch current substantially or to install a smaller gap chamber without impacting the bunch current limit. For the definite result we considered the transition between two ellipses, namely, (a, b) = (42 mm, 21 mm) and (18 mm, 4 mm) over the length 15-30 cm in beam direction.

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TUPMK012

Acceleration of Charged Particles by Own Field in a Non-Stationary One-Dimensional Stream

interface, electron, acceleration, operation

1516

A.S. Chikhachev
Allrussian Electrotechnical Institute, Moskow, Russia

The behavior of a non-stationary stream of the charged particles interacting with own field is studied. For the description the integral of the movement received in works * ** - Meshchersky's integral is used. The additional integral of the movement - interfaced to Meshchersky's integral, necessary for completely self-agreed description of a stream of the particles interacting with own field is constructed. The system of the equations reducing a problem to the solution of system of the ordinary differential equations is removed. Private decisions for potential, density of particles and density of current are provided. Earlier the problem was studied in work ***.
* Mestschersky J. Astronomische Nachrichten, 1893, T.132, N3153, p. 9.
** Nestschersky ibid, 1902, T.159, N3807, p. 15.
*** Chikhachev A.S., Technical Phisics, 2014, vol 59, N 4, pp 487-493.

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TUPML023

Amplitude Enhancement of the Self-Modulated Plasma Wakefields

proton, plasma, wakefield, focusing

1585

Y. M. Li, G.X. Xia, Y. Zhao
UMAN, Manchester, United Kingdom
K.V. Lotov, A. Sosedkin
Budker INP & NSU, Novosibirsk, Russia

Seeded Self-modulation (SSM) has been demonstrated to transform a long proton bunch into many equidistant micro-bunches (e.g., the AWAKE case), which then resonantly excite strong wakefields. However, the wakefields in a uniform plasma suffer from a quick amplitude drop after reaching the peak. This is caused by a significant decrease of the wake phase velocity during self-modulation. A large number of protons slip out of focusing and decelerating regions and get lost, and thus cannot contribute to the wakefield growth. Previously suggested solutions incorporate a sharp or a linear plasma longitudinal density increase which can compensate the backward phase shift and therefore enhance the wakefields. In this paper, we propose a new plasma density profile, which can further boost the wakefield amplitude by 30%. More importantly, almost 24% of protons initially located along one plasma period survive in a micro-bunch after modulation. The underlying physics is discussed.

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WEPAL033

Development of Real-Time Mass Analysis System with Permanent Magnet for Ion Beam

ion-source, extraction, permanent-magnet, simulation

2236

Y. Takeuchi, Y. Iwashita, H. Tongu
Kyoto ICR, Uji, Kyoto, Japan

In order to analyze time variation of the ion species in a pulse, we are developing a mass analysis system that has multiple collector electrodes to detect several ion species simultaneously. Strong permanent magnets can generate 1T magnetic field and the size of the analyzing magnet system can be compact. The detected signals are scanned by a fast multiplexer. The scanning rate is 2 MHz, so that all electrode signals of the 16 channels are scanned in 8 μs period. In this paper, details of the design of the analysis system, and preliminary beam extraction test results with prototype of the system are described.

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WEPAL049

Simulating Non-Relativistic Beams Using Helical Pulse Lines

impedance, simulation, site, GUI

2288

C.J. Richard
NSCL, East Lansing, Michigan, USA
S.M. Lidia
FRIB, East Lansing, USA

Funding: Work supported by the US Department of Energy, Office of Science, High Energy Physics under Cooperative Agreement award number DE-SC0018362.
Benchtop calibration of capacitive beam position monitors (BPMs) in low energy beamlines is challenging due to non-relativistic effects. Typical benchtop calibrations cannot account for these effects because they rely on speed of light fields transmitted along a straight wire. However, it is possible to replicate the electromagnetic fields generated by non-relativistic beams using a helical line pulse instead of a straight wire. In order to properly replicate the fields from a beam, a method must be developed for tailoring input pulses into the helical line to match bunch shape and a model of the impedance of the helix should be developed to assist with matching. This paper uses the sheath helix model to analyze signal propagation along a helical line in the time domain, with attention to dispersive effects and impedance matching. The results from this model are then compared to Microwave Studio simulations.

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WEPMF041

Insights into the Role of C, N, and O Introduced by Low Temperature Baking on Niobium Cavity Performance

cavity, niobium, experiment, superconductivity

2455

P.N. Koufalis, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Previous experiments have shown that introducing nitrogen gas during low temperature bakes (120-160 C) of niobium cavities introduces C, N, and O impurities to the first 10-100 nm of the surface. This new treatment results in higher quality factors and even 'anti-Q-slope' in some cases. However, it is not entirely clear the role that each of these impurities plays in the performance enhancement of the cavities. It has been suggested that interstitial N within the first few nm of the surface is solely responsible for the observed enhancement, but little work has been done on the role of C and O. Because both C and O are abundant in much higher quantities than N near the surface, it is important to understand whether they are beneficial or detrimental to cavity performance. We provide further insight into the effects of C and O on cavity performance by baking in an ambient atmosphere rich in CO2 as opposed to N2.

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WEPMF046

Modeling of the Frequency and Field Dependence of the Surface Resistance of Impurity-Doped Niobium

cavity, niobium, experiment, SRF

2471

J.T. Maniscalco, P.N. Koufalis, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

The anti-Q-slope, a field-dependent decrease in surface resistance observed in impurity-doped niobium, has been investigated extensively in 1.3 GHz cavities. New early research into this effect has recently been performed at higher and lower frequencies, revealing an additional dependence on frequency: the anti-Q-slope is stronger at higher frequencies and weaker at lower frequencies. Several models have been proposed to explain the anti-Q-slope, with varying success in this new frequency-dependent regime. In this work, we analyze recent experimental data from a low-temperature-doped 1.3 GHz cavity and a high-temperature nitrogen-doped 2.6 GHz cavity and discuss the implications of these results on the proposed models.

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WEPML013

Anti-Q-slope enhancement in high-frequency niobium cavities

cavity, niobium, SRF, experiment

2707

M. Martinello, S. Aderhold, S.K. Chandrasekaran, M. Checchin, A. Grassellino, O.S. Melnychuk, S. Posen, A.S. Romanenko, D.A. Sergatskov
Fermilab, Batavia, Illinois, USA

N-doped 1.3 GHz niobium cavities showed for the first time the so-called anti-Q-slope, i.e. the increasing of the Q-factor as a function of the accelerating field. It was verified that the anti-Q-slope is consequence of the decreasing of the temperature-dependent component of the surface resistance as a function of the field. This trend is opposite compared to the increasing of the surface resistance previously observed in 1.3 GHz standard (EP, BCP, 120 C baked) niobium cavities. The effect of the different state-of-the-art surface treatments on the field dependence of the surface resistance is studied for 650 MHz, 1.3 GHz, 2.6 GHz and 3.9 Ghz cavities. This proceeding shows that the field dependence of the temperature-dependent component of the surface resistance has a strong frequency dependence and that the anti-Q-slope may appear even in clean niobium cavities if the resonant frequency is high enough, suggesting new routes toward the understanding of the anti-Q-slope effect.

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THYGBF4

Accelerator Physics Advances in FRIB (Facility for Rare Isotope Beams)

cavity, linac, MMI, ECRIS

2950

P.N. Ostroumov, N.K. Bultman, M. Ikegami, S.M. Lidia, S.M. Lund, G. Machicoane, T. Maruta, A.S. Plastun, G. Pozdeyev, X. Rao, J. Wei, T. Xu, T. Yoshimoto, Q. Zhao
FRIB, East Lansing, USA
C.Y. Wong
NSCL, East Lansing, Michigan, USA

Funding: Work supported by the U.S. DOE Office of Science under Cooperative Agreement DE-SC0000661 and the NSF under Cooperative Agreement PHY-1102511, the State of Michigan and Michigan State University.
This paper presents recent developments of accelerator physics related topics for the Facility for Rare Isotope Beams (FRIB) being built at Michigan State University. While extensive beam dynamics simulations including all known errors do not show uncontrolled beam losses in the linac, ion beam contaminants extracted from the ECR ion source together with main ion beam can produce significant losses after the charge stripper. These studies resulted in development of beam collimation system at relatively low energy of 16 MeV/u and room temperature bunchers instead of originally planned superconducting ones. Commissioning of the Front End enabled detailed beam physics studies accompanied with the simulations using several beam dynamics codes. Settings of beam optics devices from the ECR to MEBT has been developed and applied to meet important project milestones. Similar work is planned for the beam commissioning of the first 3 cryomodules in the superconducting linac.

Slides THYGBF4 [11.092 MB]

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THPAK068

Fringe Field Effect of Solenoids

solenoid, optics, neutron, quadrupole

3385

T.V. Gorlov, J.A. Holmes
ORNL, Oak Ridge, Tennessee, USA

Funding: This work has been supported by Oak Ridge National Laboratory, man-aged by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.
We derive a precise analytical nonlinear transverse map for single particle transport through a solenoid with hard edge fringe fields. The transfer map is two dimensional for transverse coordinates and momenta with fixed longitudinal momentum. Because it is an accurate analytic map, it is also symplectic. The transfer map is compared with ex-act numerical tracking.

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THPAL044

The Permanent Magnets Magnetic Characteristics Change Under Effect of 10 MeV Beam

radiation, electron, experiment, permanent-magnet

3742

I.S. Guk, O.M. Bovda, V.O. Bovda, A.N. Dovbnya, A.I. Kalinichenko, S.S. Kandybey, V.N. Ljashchenko, A. Mytsykov, L.V. Onishchenko, O.A. Repikhov, A.Y. Zelinsky
NSC/KIPT, Kharkov, Ukraine

Magnets of applied electron accelerators are under direct effect of electrons and bremsstrahlung radiation stipulated by the electron beam. The choice of the materials for the rare elements alloy accelerator magnets has the decisive importance for the long term magnet parameters keeping. The experimental studies of the magnetic fields around the Nd-Fe-B and Sm2Co17 alloy magnets under effect of the electron beam have been done. The samples of 30х24х12 mm geometrical sizes were bombarded by electron beam of applied NSC KIPT accelerator KUT-1 with electron energy of 10 MeV and were irradiated by correspondent bremsstrahlung. The magnetic field value around Nd-Fe-B alloy samples was decreased nonlineary under electron beam bombarding with change of irradiation doze from 16 to 160 GRad. Under effect of bremsstrahlung the magnetic field value around samples was not changed. The repeated sample magnetizations allowed to restore the initial magnetic field distribution around magnets. The magnetic field distribution around Sm2Co17 alloy samples was not changed under effect of the electron beam and bremsstrahlung within irradiation dozes mentioned above. The induced activity in the Nd-Fe-B and Sm2Co17 alloy samples was changed slightly during the experiments.

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THPAL058

Effect of Ozonated Water Cleaning on Photon Stimulated Desorption in a Stainless Steel Chamber

photon, vacuum, experiment, radiation

3778

C.M. Cheng, C.K. Chan, C.-C. Chang, Y.T. Cheng, J. -Y. Chuang, G.-Y. Hsiung, L.H. Wu, Y.C. Yang
NSRRC, Hsinchu, Taiwan

Aluminium vacuum chambers cleaned with ozonated water show a reduction of residual carbon and lower surface outgassing rate after baking. We would like to investigate if stainless steel chambers show similar ef-fects. A stainless steel test chamber was cleaned by stand-ard chemical cleaning only and then compared with an-other one after immersion in 30ppm ozonated water for thirty minutes. Both samples were baked, then photon exposed and the photon desorption yields were deter-mined by vacuum gauges and residual gas analysers at the TLS 19B beamline. The test results on photon stimulated desorption yields and partial pressure variations with and without ozonated water cleaning of the stainless steel tubes will be discussed in some detail.

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THPAL092

Test Particle Monte Carlo Simulation of NEG Coated Narrow Tubular Samples

vacuum, experiment, simulation, SRF

3862

O. Seify, A.N. Hannah, O.B. Malyshev, Sirvinskaite, R. Sirvinskaite, R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
Sirvinskaite, R. Sirvinskaite
Loughborough University, Loughborough, Leicestershire, United Kingdom

The pumping properties of the NEG coated vacuum chambers play an important role in the efficiency of vac-uum system of accelerators. The sticking probability of the NEG films is one the most important parameters to characterise the pumping properties of the NEG coated vacuum chambers. In order to investigate the NEG film sticking probability, Test Particle Monte-Carlo (TPMC) models were used. The models were based on the design of the installed experimental setup in ASTeC Vacuum Science group laboratory at Daresbury Laboratory (DL). The results of the simulations have been used for inter-preting the results of the measurements in the experi-mental setup.

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THPAL127

Structural Investigations of Nitrogen-Doped Niobium for Superconducting RF Cavities

niobium, cavity, vacuum, experiment

3940

M. Major, L. Alff, M. Arnold, J. Conrad, S. Flege, R. Grewe, M. Mahr, N. Pietralla
TU Darmstadt, Darmstadt, Germany
F. Hug
KPH, Mainz, Germany

Funding: Work supported by the German Federal Ministry for Education and Research (BMBF) through grant 05H15RDRBA.
Niobium is the standard material for superconducting RF (SRF) cavities. Superconducting materials with higher critical temperature or higher critical magnetic field allow cavities to work at higher operating temperatures or higher accelerating fields, respectively. Enhancing the surface properties of the superconducting material in the range of the penetration depth is also beneficial. One direction of search for new materials with better properties is the modification of bulk niobium by nitrogen doping. In the Nb-N phase diagram the cubic delta-phase of NbN has the highest critical temperature (16 K). Already slight nitrogen doping of the alpha-Nb phase results in higher quality factors.* Nb samples were N-doped at the refurbished UHV furnace at IKP Darmstadt. Reference samples were annealed in 1 bar nitrogen atmosphere at different temperatures. In this contribution the results on the structural investigations (x-ray diffraction and pole figure, secondary ion mass spectroscopy, scanning electron microscopy) at the Materials Research Department of TU Darmstadt will be presented.
*Grassellino et al., Proc. SRF2015, MOBA06, 48.

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THPAL154

High-Gradient Performance of X-Band Choke-Mode Structures

GUI, experiment, HOM, damping

4011

X.W. Wu, D.Z. Cao, H.B. Chen, J. Shi, H. Zha
TUB, Beijing, People's Republic of China
T. Abe, T. Higo, S. Matsumoto
KEK, Ibaraki, Japan

Funding: National Natural Science Foundation of China (Grant No. 11135004)
The choke-mode accelerating structure is one of the higher-order-mode (HOM) damping structures. It has the advantage of relatively simple fabrication and low surface magnetic field. C-band choke-mode accelerating structures have been successfully applied in multibunch XFEL. However, the X-band choke-mode study remains in the theoretical design stage. The high-gradient performance of the choke is still unknown. Five different single-cell choke-mode accelerating structures were designed, fabricated and high-gradient tested to study the related RF breakdown characteristics. It was observed that high electric field and small choke dimension caused serious breakdowns in the choke which was the main limitation of the high-gradient performance. The Choke-mode accelerating structures reached 130 MV/m by decreasing the electric field and increasing the choke gap. A new quantity was proposed to give the high-gradient performance limit of choke-mode accelerating structures due to RF breakdown. The new quantity was obtained from the summary of the high-gradient experiments and could be used to guide high-gradient choke-mode accelerating structure design.

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THPMF012

Tapered Flying Radiofrequency Undulator

undulator, electron, FEL, simulation

4059

S.P. Antipov, S.V. Kuzikov, A. Liu
Euclid TechLabs, LLC, Solon, Ohio, USA
S.V. Kuzikov, A.V. Savilov, A.A. Vikharev
IAP/RAS, Nizhny Novgorod, Russia

Funding: DOE SBIR DE-SC0017145
The x-ray free electron laser (x-FEL) efficiency, measured as a fraction of the electron beam power converted into light, is typically below 0.1% for most of the x-FEL facilities presently in operation. Undulator tapering techniques can be used to improve the conversion efficiency by 1-2 orders of magnitude. However at present there are no robust tapered undulator x-FEL schemes operating at 10% efficiency. In this paper we report on the development of tapered radiofrequency (RF) undulator. An RF undulator is a microwave waveguide in which strong RF field is excited that interacts with a charged particle beam forcing it to radiate coherent x-rays while undergoing a wiggling motion. RF undulators are attractive for use in x-FELs due to their large beam aperture and a short undulator period. Strongly tapered RF undulators (with tapering of a wavelength) due to non-resonant trapping regime allow keeping high overall XFEL efficiency being driven by laser plasma accelerated beams usually having high enough current but large energy spread (1-10%).

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THPMF046

Precision Charge Measurement of 40~MeV Electron-Beam to Calibrate Air Fluorescence Telescope for Cosmic Ray Observation

electron, vacuum, injection, ISOL

4163

T. Shibata
KEK, Ibaraki, Japan
O.C. Shin
OCU, Osaka, Japan

The Telescope Array (TA) is ultra-high energy cosmic ray observation (UHECR). TA is using the fluorescence detectors (FD) for observation the air fluorescence(AFY) which are emitted in the cascade generated by an UHECR in atmosphere. One of the important observables is primary energy of UHECR, however it has 21% systematic uncertainty. For reduction of the uncertainty, we have been operated an 40-MeV electron linear accelerator from 2010 which we have constructed for absolute energy calibration. The accelerator is located at 100 m from FD station, and can shot electron beam which the direction is vertical into the air, the energy is 40-MeV, the pulse width is 1 micro-second, and the beam charge is 160 pC. The AFY efficiency and FD calibration parameters can be calibrated, which means energy scale of UHECR, by observation of the AFY which are generated by the electron beam in the air. The most important beam parameter is beam charge. The requirement of the accuracy of charge measurement is a few %, then we have developed the double faraday cups and one current transfer system. We calibrated the current transfer by the double faraday cups, and we could achieve about 1% accuracy.

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THPMK103

Initial Testing of Techniques for Large Scale Rf Conditioning for the Compact Linear Collider

linac, operation, linear-collider, collider

4548

T.G. Lucas, M.J. Boland, P.J. Giansiracusa, R.P. Rassool, M. Volpi
The University of Melbourne, Melbourne, Victoria, Australia
N. Catalán Lasheras, A. Grudiev, T. Lefèvre, G. McMonagle, I. Syratchev, B.J. Woolley, W. Wuensch, V. del Pozo Romano
CERN, Geneva, Switzerland
J. Paszkiewicz
University of Oxford, Oxford, United Kingdom
C. Serpico
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
A. Vnuchenko
IFIC, Valencia, Spain
R. Zennaro
PSI, Villigen PSI, Switzerland

Nominal operating conditions for the Compact Linear Collider (CLIC) 380 GeV requires 72 MV/m loaded accelerating gradients for a 180 ns flat-top pulse. Achieving this requires extensive RF conditioning which past tests have demonstrated can take several months per structure, when conditioned at the nominal repetition rate of 50 Hz. At CERN there are three individual X-band test stands currently operational, testing up to 6 structures concurrently. For CLIC's 380 GeV design, 28,000 accelerating structures will make up the main linac. For a large scale conditioning programme, it is important to understand the RF conditioning process and to optimise the time taken for conditioning. In this paper, we review recent X-band testing results from CERN's test stands. With these results we investigate how to optimise the conditioning process and demonstrate the feasibility of pre-conditioning the structures at a higher repetition rate before installation into the main linac.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK103

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THPMK116

NEA Surface Activation of GaAs Photocathode with CO2

cathode, experiment, electron, emittance

4590

L.Guo. Guo
UVSOR, Okazaki, Japan
H. Iijima
Tokyo University of Science, Tokyo, Japan
M. Kuriki
HU/AdSM, Higashi-Hiroshima, Japan
K. Uchida
Cosylab Japan, Ibaraki, Japan

NEA (negative electron affinity)-GaAs cathode is able to generate highly spin polarized electron beam more than 90%. The NEA activation is performed usually with Cs and O2 or NF3, but the exact structure of the NEA surface is not known. In this paper, we performed the NEA activation on a cleaned GaAs surface with CO2, CO, N2, and O2 gases and compared the results to improve our understanding on the NEA surface. We found that CO2 activated the cathode, but N2 and CO did not. By analyzing CO2 activation, we found that atomic oxygen activates the NEA surface and CO degrades the NEA surface simultaneously. We found that the NEA activation ability of atomic oxygen is almost a half of that of O2 molecule.*
*L. Guo, M. Kuriki, H. Iijima, K. Uchida. "NEA surface activation of GaAs photocathode with different gases", Surface Science 664C (2017) pp. 65-69.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK116

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THPML002

Emittance Preservation in Plasma-Based Accelerators with Ion Motion

emittance, plasma, wakefield, background

4654

C. Benedetti, E. Esarey, W. Leemans, T.J. Mehrling, C.B. Schroeder
LBNL, Berkeley, California, USA

Funding: This work was supported by the Director, Office of Science, Office of High Energy Physics, of the U.S. DOE under Contract No. DE-AC02-05CH11231.
In a plasma-accelerator-based linear collider, the density of matched, low-emittance, high-energy particle bunches required for collider applications can be orders of magnitude above the background ion density, leading to ion motion, perturbation of the focusing fields, and, hence, to beam emittance growth. By analyzing the response of the background ions to an ultrahigh density beam, analytical expressions, valid for non-relativistic ion motion, are obtained for the perturbed focusing wakefield. Initial beam distributions are derived that are equilibrium solutions, which require head-to-tail bunch shaping, enabling emittance preservation with ion motion.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML002

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THPML052

Excitation of Plasma Wave by Lasers Beating in a Collisional and Mild-Relativistic Plasma

plasma, laser, electron, damping

4752

M. Kaur, D.N. Gupta
University of Delhi, Delhi, India

Funding: Work supported by Department of Science and Technology (DST), Government of India.
Excitation of plasma wave by two lasers beating in a collisional dominated relativistic plasma is investigated. We study the energy exchange between a plasma wave and two co-propagating lasers in plasma including the effect of relativistic mass change and electron-ion collisions. Two lasers, having frequency difference equal to the plasma frequency, excite a plasma beat wave resonantly by the ponderomotive force, which obeys the energy and momentum conservation*. The relativistic effect and the electron-ion collision both contribute in energy exchange between the interacting waves in the beat-wave acceleration mechanism. Our study shows that the initial phase difference between interacting waves generates a phase mismatch between lasers and plasma wave, which alters the rate of amplitude variations of the interacting waves and, hence, affects the energy exchange between the interacting waves**. This study may be crucial to design a compact plasma accelerator in low-intensity regime***.
*T. Tajima, and J. Dawson, Phys. Rev.Lett. 43, 267(1979)
**D. N. Gupta, M. S. Hur, and H. Suk, J.Appl. Phys. 100, 103101 (2006)
***M. Kaur and D. N. Gupta, EuroPhysics letter 116, 35001 (2016).

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML052

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FRXGBF3

Perspectives in High Intensity Heavy Ion Sources for Future Heavy Ion Accelerators

ion-source, heavy-ion, ECRIS, electron

5047

L.T. Sun
IMP/CAS, Lanzhou, People's Republic of China

Driven by the development of next generation heavy ion accelerators such as IMP-HIAF, GSI-FAIR, RIKEN-RIBF, SPIRAL 2, JLEIC and so on that need very intense highly charged heavy ion beam injectors working at either pulsed or CW modes, intense research and development work towards more powerful ion sources have been made in different laboratories, which likewise has stimulated obvious advancement of the performances in recent years. However, even the best performing ion sources can't meet all the requirements. While the ion source researchers are tackling the next generation ion sources development, it is worth investigating the possibilities of other solutions, especially when very intense heavy ion beams are needed for the more intense and powerful heavy ion accelerators, for instance the driver accelerator to study inertial confinement fusion with heavy ion. This invited talk presents recent advancements of highly charged heavy ion sources, and discusses the other possible approaches for intense highly charged heavy ion beams for future heavy ion accelerators.

Slides FRXGBF3 [10.014 MB]

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