IPAC2016 - List of Keywords (radio-frequency)

Paper	Title	Other Keywords	Page
MOPMR012	Studies of Buffer Gas Cooling of Ion Beams in an RFQ Cooler and Their Transport to the EBIS Charge Breeder	ion, rfq, simulation, emittance	248
	K.H. Yoo, M. Chung UNIST, Ulsan, Republic of Korea H.J. Son IBS, Daejeon, Republic of Korea
	In rare isotope accelerator facilities, an RFQ cooler is often used to manipulate ions. The RFQ cooler is a de-vice to effectively cool and confine ions in gaseous envi-ronment. The RFQ cooler provides a radial electric force to the beam by applying RF voltages to the quadrupole electrode structures, and axial force by applying different DC voltages to the segmented electrodes. The ions are trapped inside the potential well of the RFQ cooler formed by the DC fields, so that they have more colli-sions with the buffer gas. Several important parameters such as transverse emittance can be improved when ion beams are extracted from the RFQ cooler. In order to design an efficient RFQ cooler, which can properly match the ion beams into the EBIS charge breeder, it is essential to analyze evolutions of the transverse emittance and transmission efficiency through the RFQ cooler. Moreo-ver, to minimize emittance growth and maximize trans-mission efficiency, the beam transport line to the EBIS charge breeder needs to be optimized. In this work, we study the methods to apply the mechanism of buffer gas cooling in RFQ cooler to G4beamline and the beam transport line to EBIS charge breeder to TRACK.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPMR012
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MOPMR023	Surface Characterization and Field Emission Measurements of Copper Samples inside a Scanning Electron Microscope	electron, controls, vacuum, experiment	283
	J. Ögren, V.G. Ziemann Uppsala University, Uppsala, Sweden S.H.M. Jafri, K. Leifer Uppsala University, Department of Engineering Sciences, Uppsala, Sweden
	Vacuum breakdown in normal-conducting accelerating structures is a limiting factor for high gradient acceleration. Many aspects of the physics governing the breakdown process and its onset are yet to be fully understood. At Uppsala University we address these questions with an in-situ experimental setup mounted in an environmental scanning electron microscope. It consists of a piezo motor driven tungsten needle and a sample surface mounted on a piezo stage, allowing for nano-meter 3D-position control. One of the piezo motors controls the needle-sample gap while the two other scan across the surface. A DC-voltage up to 1 kV is applied across the gap and field emission currents from a copper surface are measured with an electrometer. Here we present the setup and some initial results.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPMR023
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MOPMR059	Development of S-band High Power Load	vacuum, klystron, radiation, electron	383
	X.C. Meng, H.B. Chen, C. Cheng, Y.-C. Du, Q. Gao, J. Shi, P. Wang, Z.F. Xiong TUB, Beijing, People's Republic of China
	Several types of S-band high power loads have been designed, manufactured and tested successfully in Tsinghua University. The high power loads, which work at 2856 MHz for 10 MW~100 MW range, are made of all stainless steel. In this paper, we will present the design, fabrication and the high power test results.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPMR059
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MOPMW030	High Powered Tests of Dielectric Loaded High Pressure RF Cavities for Use in Muon Cooling Channels	accelerating-gradient, cavity, plasma, experiment	460
	B.T. Freemire IIT, Chicago, Illinois, USA D.L. Bowring, A. Moretti, D.W. Peterson, A.V. Tollestrup, Y. Torun, K. Yonehara Fermilab, Batavia, Illinois, USA A.V. Kochemirovskiy University of Chicago, Chicago, Illinois, USA Y. Torun Illinois Institute of Technology, Chicago, Illlinois, USA
	Funding: This work is supported by the Fermilab Research Alliance, LLC under Contract No. DE-AC02-07CH11359. Bright muon sources require six dimensional cooling to achieve acceptable luminosities. Ionization cooling is the only known method able to do so within the muon lifetime. One proposed cooling channel, the Helical Cooling Channel, utilizes gas filled radio frequency cavities to both mitigate RF breakdown in the presence of strong, external magnetic fields, and provide the cooling medium. Engineering constraints on the diameter of the magnets within which these cavities operate dictate the radius of the cavities be decreased at their nominal operating frequency. To accomplish this, one may load the cavities with a larger dielectric material. Alumina of purities ranging from 96 to 99.8% was tested in a high pressure RF test cell at the MuCool Test Area at Fermilab. The results of breakdown studies with pure nitrogen gas, and oxygen-doped nitrogen gas indicate the peak surface electric field on the alumina ranges between 10 and 15 MV/m. How these results affect the design of a prototype cooling channel cavity will be discussed.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPMW030
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MOPMY016	Quadrature Directional Coupling Method for Precise RF Power Measurement	coupling, feedback, controls, experiment	549
	B. Du, G. Huang, L. Lin, Y.T. Liu, Z. Zhao USTC/NSRL, Hefei, Anhui, People's Republic of China
	The directional coupler is used in the RF transmission and distribution system of accelerator, to measure the forward and backward power. Due to the finite directional isolation of the coupler (20-30dB normally), the crosstalk exists between the bi-directional coupling output signals. For the typical isolation of 26dB, if the bi-directional crosstalk signals are in- or anti- phase, the error of input or reflected power measurement is 10% in case of total reflection, whilst the error of reflected power measurement is 100% in case of VSWR 1.1. A method of quadrature directional coupling measurement is developed to solve the isolation problem. A pair of directional couplers with 90° phase difference are employed to measure the RF power. The influence of the directional crosstalk would be reduced significantly by processing the measurement data. The prototype of quadrature directional couplers is constructed to verify this method. The results showed that the measurement accuracy of quadrature coupler pair after data process is better than 2% for forward measurement, even if the error of single coupler is over 6%. The paper also analyses the error caused by non-ideal quadrature.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPMY016
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MOPOR026	Measurement of the Energy Distribution Function of Electrons Generated by Radio-frequency Induced Multipacting in a Beam Pipe	electron, multipactoring, gun, diagnostics	664
	M. Van Gompel, F. Caspers, P. Costa Pinto, R. Leber, A. Romano, R. Salemme, M. Taborelli CERN, Geneva, Switzerland
	The development of Electron Multipacting (EM) in high intensity particle accelerators depends, amongst others, on the Secondary Electron Yield (SEY) of surfaces facing the beam. In-situ studies of electron clouds in particle accelerators must cope with operation schedule and other technical constrains. To overcome these difficulties, CERN implemented a Multipactor test bench, where EM is generated by Radio-Frequency (RF), using the beam pipes as a coaxial resonators. This tool was already successfully used to assess the effectiveness of low SEY carbon coatings on dipoles of the SPS at CERN and to study the conditioning dynamics of beam pipes. In this paper we present the development of an in-house built Retarding Field Energy Analyser (RFEA) to measure the Electrons Energy Distribution Function (EEDF) in the Multipactor test bench. The design of the electrodes was based on simulations in order to optimize sensitivity and energy resolution. The setup was tested with an electron gun at different energies before insertion in the Multipactor test bench. The evolution of the EEDF is measured at different RF powers. Feasibility to perform measurements in the machine is discussed.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR026
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MOPOY056	Development of a Neutronics Facility using Radio Frequency Quadrupole for Characterization of Fusion Grade Materials	rfq, ion, neutron, quadrupole	981
	R. Bahl, S.K. Kumar, M. Mittal, B. Sarkar, A. Shyam Institute for Plasma Research, Bhat, Gandhinagar, India
	Qualification of the materials is among the important challenges for a fusion reactor. Working in tandem with the present need that recognizes the value of evaluating fusion reactor materials, Institute for Plasma Research has initiated the 'Development of RFQ for Accelerators' project, which will provide a neutronic facility for material qualification in a relatively larger scale. The facility will consist of an high intensity ECR ion (H⁺/D⁺) source coupled to Radio Frequency Quadrupole (RFQ) Accelerator through a LEBT system to produce 5 MeV, 40 mA deuterium ions to fulfil the objectives. Further upgrade in the beam energy and current is also foreseen to suit the facility requirement. A four vane type copper RFQ @352.2 MHz frequency with transmission efficiency of ≈ 96% has been designed to accelerate deutrons upto 1 MeV energy as a demonstration of the RFQ functioning and controls. Through LEBT system, deuterons are then focused into RFQ using weak beam focalization method. The harmonization of the vane tips design and manufacturing constraints has been part of the study to have a near realistic engineering design. Design and analysis of RFQ will be discussed.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOY056
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TUOAB03	Transverse Coherent Instabilities in Storage Rings with Harmonic Cavities	synchrotron, impedance, cavity, simulation	1061
	F.J. Cullinan, R. Nagaoka SOLEIL, Gif-sur-Yvette, France G. Skripka, P.F. Tavares MAX IV Laboratory, Lund University, Lund, Sweden
	Many current and future synchrotron light sources employ harmonic cavities to lengthen the electron bunches in order to reduce the emittance dilution caused by intrabeam scattering. In some cases, the harmonic cavities may be tuned to fulfill the flat potential condition. For this condition, a large increase in the threshold currents of transverse coupled-bunch instabilities has been predicted and recently, the physical content behind this stabilization has been better understood. With this in mind, an investigation is made into the effectiveness of harmonic cavities for different machines. Frequency domain computations employing Laclare's eigenvalue method have been used to investigate the influence of several machine parameters and the results are presented.
	Slides TUOAB03 [14.037 MB]
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUOAB03
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TUPMB047	Tracking the Helium Balance in FREIA	EPICS, database, controls, hardware	1202
	V.G. Ziemann, L. Hermansson Uppsala University, Uppsala, Sweden
	In the FREIA laboratory at Uppsala University we test the super-conducting spoke-cavities for the European Spallation Source. Liquid Helium for cooling the cavities is provided by a liquefaction plant from which also a local user community at the University is served. Recently we encountered a leak due to a faulty valve which went undetected for some time and caused significant loss of Helium. In order to prevent such mishaps in the future we implemented a Helium tracking system that includes detailed accounting of Helium leaving and entering the closed system as well as all volumes containing Helium in the system. We describe the technical implementation and experience to date.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPMB047
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WEPMB034	Analysis of Niobium Quality Control for SRF Cavity	cavity, niobium, SRF, controls	2197
	M.J. Joung IBS, Daejeon, Republic of Korea
	Funding: the Ministry of Science, ICT and Future Planning (MSIP) and the National Research Foundation (NRF) of the Republic of Korea under Contract 2013M7A1A1075764. Clean and smooth surface is important to get low sur-face resistance for superconducting material. SRF (Super-conducting Radio Frequency) cavity made of niobium which is superconducting material and also one of the rare metal. The procedure of niobium quality control was set up to get high performance SRF cavity. The procedure consists of three parts; certificates check, Nb specification verification, and surface inspection and measurements of thickness, roughness, flatness. Three important properties which are RRR value, chemical composition and me-chanical properties were verified to conform Nb specifica-tion. The range of thickness, roughness and flatness for niobium as SRF cavity raw material were obtained by measurement.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMB034
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WEPMR023	Surface Analysis Studies of Nb3Sn Thin Films	cavity, niobium, SRF, electron	2316
	D.L. Hall, J.J. Kaufman, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	A recent study to optimise the coating of thin-film Nb3Sn cavities has resulted in coating procedures that can fabricate 1.3 GHz cavities capable of reproducibly achieving fields of >16 MV/m with record high Qs >10¹⁰ at 4.2 K. However, the performance of these next generation SRF cavities is as yet well below the theoretical maximum performance expected of Nb3Sn, thus giving ample room for further advancements. Current measurements strongly suggest that the current limits are due to local defects and irregularities in the coated surface. In this paper we analyse, using methods including SEM/EDS, TEM, XRD and EBSD, the surface of both sample coupons and cavity cut-outs, with a view to identifying and understanding the origin of surface non-uniformities that would lead to increased surface resistance and cavity quench.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR023
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WEPMR024	RF Measurements on High Performance Nb3Sn Cavities	cavity, niobium, SRF, accelerating-gradient	2320
	D.L. Hall, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	A single-cell 1.3 GHz ILC-shape thin-film Nb3Sn-on-Nb cavity recently achieved accelerating gradients of >16 MV/m with a record Q0 of approx. 2·10¹⁰ at 4.2 K, exceeding the power efficiency seen in the current most efficient niobium cavities. A concurrent study of the coating process has resulted in a coating procedure that is capable of replicating this performance in other single-cell cavities. In this paper we demonstrate the RF performance and behaviour of these next generation SRF cavities, with an emphasis on both the impact from both external magnetic fields and the cavity cool down procedure on cavity performance.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR024
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WEPMR025	Improved N-Doping Protocols for SRF Cavities	simulation, cavity, niobium, SRF	2323
	D. Gonnella, R.G. Eichhorn, F. Furuta, G.M. Ge, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF, DOE Nitrogen-doping has been shown to consistently produce better quality factors in SRF cavities than is achievable with standard preparation techniques. Unfortunately, nitrogen-doping typically brings with it lower quench fields and higher sensitivities of residual resistance to trapped magnetic flux. Here we present work to understand these effects in hopes of mitigating them while maintaining the high Q desired by future projects. Using a nitrogen diffusion simulation, material parameters of nitrogen-doped cavities can be predicted prior to doping. These simulations results are consistent with SIMS data taken from samples treated with cavities. The nature of doping's effect on quench field has also been studied using CW and pulsed measurements. These results have allowed us to better understand the nature of nitrogen-doping and its effect on cavity performance.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR025
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WEPMR027	Dependence of Surface Resistance on N-Doping Level	niobium, cavity, SRF, linac	2331
	D. Gonnella, F. Furuta, G.M. Ge, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF, DOE Nitrogen-doping has become a standard tool for reaching high quality factors in SRF cavities in the medium field region at 2 K. This high Q has been shown to be a result of lowering of the temperature dependent BCS resistance. Here we show that this lowering of the BCS resistance is due to interstitial nitrogen in the niobium lowering the mean free path. The BCS resistance extracted from experimental data is shown to be consistent with theoretical predictions from BCS theory; that there is an optimal doping of which the mean free path is lowered to about half the intrinsic coherence length. These results provide insight into understanding the mechanisms behind nitrogen-doping and allow us to more accurately predict doping parameters to reach optimal cavity performance.
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WEPMR028	Studies on the Field Dependence of the BCS Surface Resistance	cavity, SRF, experiment, niobium	2335
	J.T. Maniscalco, D. Gonnella, G.H. Hoffstaetter, P.N. Koufalis, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Experiments have shown that the temperature-dependent portion of the RF surface resistance of SRF materials also exhibits a dependence on the magnitude of the surface field, manifested as a "Q-slope" or "anti-Q-slope" in the medium field region. Recent theoretical work proposes an explanation of the anti-Q-slope in dirty-limit superconductors. In this report, we compare theoretical predictions with the results of systematic experimental studies on the RF field dependence of the surface resistance using 1.3 GHz niobium SRF cavities with a wide range of mean free paths. We find very good agreement between theory and experiment in the dirty limit, with some divergence as the cavities approach the clean limit.
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WEPOR034	Design and Evaluation of a Broad Band microTCA.4 Based Downconverter	LLRF, controls, laser, electron	2746
	N. Gan, Y.L. Chi, R.L. Liu, X. Ma IHEP, Beijing, People's Republic of China
	Modern low-level RF (LLRF) control systems of particle accelerators are designed to achieve extremely precise field amplitude and phase regulation inside the accelerating cavities, the RF field signal is usually converted to an intermediate frequency (IF) before being sampled by ADC. As the down-conversion is an important procedure of the digital signal processing in LLRF system, designing a high performance and broad band downconverter compatible with various accelerators will be significant. In this paper, the design of a MicroTCA based downconverter is presented, the major design objective of this module is wider operating frequency range and more flexibility in application. Several performance evaluations on different frequency points of this module have been conducted and the module presents a good performance in the operating frequency range.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPOR034
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THOBB02	Impurity Doping of Superconducting Radio Frequency Cavities	cavity, niobium, vacuum, SRF	3195
	P.N. Koufalis, F. Furuta, G.M. Ge, D. Gonnella, J.J. Kaufman, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF PHYS-1416318 Impurity doping of bulk-niobium superconducting radio frequency (SRF) cavities is a relatively new field of study and the underlying physics is not yet fully understood. Previous studies have shown an increase in the intrinsic quality factor and the corresponding decrease of the temperature-dependent component of the surface resistance of nitrogen-doped cavities with increasing accelerating field.* Here we investigate the effects of alternative inert dopants on the surface resistance and thus the intrinsic quality factor of SRF cavities in pursuit of the optimal dopant and doping level. A. Grassellino et al., Nitrogen and Argon Doping of Niobium for Superconducting Radio Frequency Cavities. Supercond. Sci. Technol., 26(102001), 2013
	Slides THOBB02 [4.048 MB]
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THOBB02
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THPMB038	Comparing RF-Cavity Phase-Scan Simulations in the ESS Linac Simulator with Measurements Taken in the Spallation Neutron Source Coupled-Cavity Linac	cavity, linac, neutron, controls	3317
	E. Laface, Y.I. Levinsen ESS, Lund, Sweden I. List Cosylab, Ljubljana, Slovenia T.A. Pelaia II ORNL, Oak Ridge, Tennessee, USA
	The ESS Linac Simulator (ELS) is the model that will be used at the European Spallation Source ERIC in Lund, Sweden, to simulate the transport of the beam envelope for the operations. During the machine restart in August 2015 at the Spallation Neutron Source (SNS) in Oak Ridge, USA, we were able to perform the first benchmarking studies of the ELS. In this paper, we present the results of the phase-scans performed in four RF cavities of the coupled-cavity linac at SNS compared with the same scans simulated in the ELS. The phase of the cavity was modified while the phase of the beam was recorded in two BPMs downstream from the cavity. This measurement was repeated for four independent cavities and the results are compared here with the model, which favourably reproduces the BPM response to the cavity scans.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPMB038
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THPMB039	Voltage Error Studies in the ESS RFQ	rfq, emittance, proton, linac	3320
	A. Ponton, Y.I. Levinsen, E. Sargsyan ESS, Lund, Sweden A.C. France, O. Piquet, B. Pottin CEA/IRFU, Gif-sur-Yvette, France
	During the fabrication of an RFQ, deviation from the perfect geometry will occur during assembling, brazing and machining the different parts. These geometrical defects will impact the theoretical inter-vane voltage, given by the beam dynamics, by altering the quadrupolar component as well as adding dipolar terms in the voltage function. Tuners can correct partially the effect of the manufacturing. The study summarizes the effects of the voltage errors on the beam quality in the case of the ESS RFQ with a harmonic analysis of the voltage function. We discuss the acceptable level of voltage errors and associated mechanical tolerances.
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THPMY024	Upgrade of a UHV Furnace for 1700 C Heat Treatment and Processing of Niobium Samples	vacuum, niobium, power-supply, radiation	3709
	J. Conrad, L. Alff, R. Grewe, T. Kürzeder, M. Major, N. Pietralla TU Darmstadt, Darmstadt, Germany F. Hug IKP, Mainz, Germany S.T. Sievers MIT, Marburg, Germany
	Funding: Supported by the German Federal Ministry for Education and Research (BMBF) under Grant No. 05H15RDRBA In 2005 a high temperature vacuum furnace was put into operation at the Institute for Nuclear Physics at the Technische Universität Darmstadt. It has been designed for firing pure Niobium at temperatures of up to 1870 C. Until now several Nb cavities have been heat treated at 850 C with a proven record of success. The current focus of research in improving the superconductive characteristics of accelerator cavities is on new materials such as Nb3Sn or NbN or on the doping of Nb surfaces with nitrogen, so called N2-Doping. The surface preparations generally take place at temperatures of not more than 1000 C. To study phenomena that occur at higher temperatures, like the formation of delta-phase NbN at 1300 to 1700 C, it is planned to refurbish the UHV furnace and use it for corresponding studies. We will report on the design of a new annealing pot and a sample holder and give a review on our first experiences with the upgraded furnace.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPMY024
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Paper

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Other Keywords

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MOPMR012

Studies of Buffer Gas Cooling of Ion Beams in an RFQ Cooler and Their Transport to the EBIS Charge Breeder

ion, rfq, simulation, emittance

248

K.H. Yoo, M. Chung
UNIST, Ulsan, Republic of Korea
H.J. Son
IBS, Daejeon, Republic of Korea

In rare isotope accelerator facilities, an RFQ cooler is often used to manipulate ions. The RFQ cooler is a de-vice to effectively cool and confine ions in gaseous envi-ronment. The RFQ cooler provides a radial electric force to the beam by applying RF voltages to the quadrupole electrode structures, and axial force by applying different DC voltages to the segmented electrodes. The ions are trapped inside the potential well of the RFQ cooler formed by the DC fields, so that they have more colli-sions with the buffer gas. Several important parameters such as transverse emittance can be improved when ion beams are extracted from the RFQ cooler. In order to design an efficient RFQ cooler, which can properly match the ion beams into the EBIS charge breeder, it is essential to analyze evolutions of the transverse emittance and transmission efficiency through the RFQ cooler. Moreo-ver, to minimize emittance growth and maximize trans-mission efficiency, the beam transport line to the EBIS charge breeder needs to be optimized. In this work, we study the methods to apply the mechanism of buffer gas cooling in RFQ cooler to G4beamline and the beam transport line to EBIS charge breeder to TRACK.

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MOPMR023

Surface Characterization and Field Emission Measurements of Copper Samples inside a Scanning Electron Microscope

electron, controls, vacuum, experiment

283

J. Ögren, V.G. Ziemann
Uppsala University, Uppsala, Sweden
S.H.M. Jafri, K. Leifer
Uppsala University, Department of Engineering Sciences, Uppsala, Sweden

Vacuum breakdown in normal-conducting accelerating structures is a limiting factor for high gradient acceleration. Many aspects of the physics governing the breakdown process and its onset are yet to be fully understood. At Uppsala University we address these questions with an in-situ experimental setup mounted in an environmental scanning electron microscope. It consists of a piezo motor driven tungsten needle and a sample surface mounted on a piezo stage, allowing for nano-meter 3D-position control. One of the piezo motors controls the needle-sample gap while the two other scan across the surface. A DC-voltage up to 1 kV is applied across the gap and field emission currents from a copper surface are measured with an electrometer. Here we present the setup and some initial results.

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MOPMR059

Development of S-band High Power Load

vacuum, klystron, radiation, electron

383

X.C. Meng, H.B. Chen, C. Cheng, Y.-C. Du, Q. Gao, J. Shi, P. Wang, Z.F. Xiong
TUB, Beijing, People's Republic of China

Several types of S-band high power loads have been designed, manufactured and tested successfully in Tsinghua University. The high power loads, which work at 2856 MHz for 10 MW~100 MW range, are made of all stainless steel. In this paper, we will present the design, fabrication and the high power test results.

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MOPMW030

High Powered Tests of Dielectric Loaded High Pressure RF Cavities for Use in Muon Cooling Channels

accelerating-gradient, cavity, plasma, experiment

460

B.T. Freemire
IIT, Chicago, Illinois, USA
D.L. Bowring, A. Moretti, D.W. Peterson, A.V. Tollestrup, Y. Torun, K. Yonehara
Fermilab, Batavia, Illinois, USA
A.V. Kochemirovskiy
University of Chicago, Chicago, Illinois, USA
Y. Torun
Illinois Institute of Technology, Chicago, Illlinois, USA

Funding: This work is supported by the Fermilab Research Alliance, LLC under Contract No. DE-AC02-07CH11359.
Bright muon sources require six dimensional cooling to achieve acceptable luminosities. Ionization cooling is the only known method able to do so within the muon lifetime. One proposed cooling channel, the Helical Cooling Channel, utilizes gas filled radio frequency cavities to both mitigate RF breakdown in the presence of strong, external magnetic fields, and provide the cooling medium. Engineering constraints on the diameter of the magnets within which these cavities operate dictate the radius of the cavities be decreased at their nominal operating frequency. To accomplish this, one may load the cavities with a larger dielectric material. Alumina of purities ranging from 96 to 99.8% was tested in a high pressure RF test cell at the MuCool Test Area at Fermilab. The results of breakdown studies with pure nitrogen gas, and oxygen-doped nitrogen gas indicate the peak surface electric field on the alumina ranges between 10 and 15 MV/m. How these results affect the design of a prototype cooling channel cavity will be discussed.

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MOPMY016

Quadrature Directional Coupling Method for Precise RF Power Measurement

coupling, feedback, controls, experiment

549

B. Du, G. Huang, L. Lin, Y.T. Liu, Z. Zhao
USTC/NSRL, Hefei, Anhui, People's Republic of China

The directional coupler is used in the RF transmission and distribution system of accelerator, to measure the forward and backward power. Due to the finite directional isolation of the coupler (20-30dB normally), the crosstalk exists between the bi-directional coupling output signals. For the typical isolation of 26dB, if the bi-directional crosstalk signals are in- or anti- phase, the error of input or reflected power measurement is 10% in case of total reflection, whilst the error of reflected power measurement is 100% in case of VSWR 1.1. A method of quadrature directional coupling measurement is developed to solve the isolation problem. A pair of directional couplers with 90° phase difference are employed to measure the RF power. The influence of the directional crosstalk would be reduced significantly by processing the measurement data. The prototype of quadrature directional couplers is constructed to verify this method. The results showed that the measurement accuracy of quadrature coupler pair after data process is better than 2% for forward measurement, even if the error of single coupler is over 6%. The paper also analyses the error caused by non-ideal quadrature.

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MOPOR026

Measurement of the Energy Distribution Function of Electrons Generated by Radio-frequency Induced Multipacting in a Beam Pipe

electron, multipactoring, gun, diagnostics

664

M. Van Gompel, F. Caspers, P. Costa Pinto, R. Leber, A. Romano, R. Salemme, M. Taborelli
CERN, Geneva, Switzerland

The development of Electron Multipacting (EM) in high intensity particle accelerators depends, amongst others, on the Secondary Electron Yield (SEY) of surfaces facing the beam. In-situ studies of electron clouds in particle accelerators must cope with operation schedule and other technical constrains. To overcome these difficulties, CERN implemented a Multipactor test bench, where EM is generated by Radio-Frequency (RF), using the beam pipes as a coaxial resonators. This tool was already successfully used to assess the effectiveness of low SEY carbon coatings on dipoles of the SPS at CERN and to study the conditioning dynamics of beam pipes. In this paper we present the development of an in-house built Retarding Field Energy Analyser (RFEA) to measure the Electrons Energy Distribution Function (EEDF) in the Multipactor test bench. The design of the electrodes was based on simulations in order to optimize sensitivity and energy resolution. The setup was tested with an electron gun at different energies before insertion in the Multipactor test bench. The evolution of the EEDF is measured at different RF powers. Feasibility to perform measurements in the machine is discussed.

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MOPOY056

Development of a Neutronics Facility using Radio Frequency Quadrupole for Characterization of Fusion Grade Materials

rfq, ion, neutron, quadrupole

981

R. Bahl, S.K. Kumar, M. Mittal, B. Sarkar, A. Shyam
Institute for Plasma Research, Bhat, Gandhinagar, India

Qualification of the materials is among the important challenges for a fusion reactor. Working in tandem with the present need that recognizes the value of evaluating fusion reactor materials, Institute for Plasma Research has initiated the 'Development of RFQ for Accelerators' project, which will provide a neutronic facility for material qualification in a relatively larger scale. The facility will consist of an high intensity ECR ion (H⁺/D⁺) source coupled to Radio Frequency Quadrupole (RFQ) Accelerator through a LEBT system to produce 5 MeV, 40 mA deuterium ions to fulfil the objectives. Further upgrade in the beam energy and current is also foreseen to suit the facility requirement. A four vane type copper RFQ @352.2 MHz frequency with transmission efficiency of ≈ 96% has been designed to accelerate deutrons upto 1 MeV energy as a demonstration of the RFQ functioning and controls. Through LEBT system, deuterons are then focused into RFQ using weak beam focalization method. The harmonization of the vane tips design and manufacturing constraints has been part of the study to have a near realistic engineering design. Design and analysis of RFQ will be discussed.

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TUOAB03

Transverse Coherent Instabilities in Storage Rings with Harmonic Cavities

synchrotron, impedance, cavity, simulation

1061

F.J. Cullinan, R. Nagaoka
SOLEIL, Gif-sur-Yvette, France
G. Skripka, P.F. Tavares
MAX IV Laboratory, Lund University, Lund, Sweden

Many current and future synchrotron light sources employ harmonic cavities to lengthen the electron bunches in order to reduce the emittance dilution caused by intrabeam scattering. In some cases, the harmonic cavities may be tuned to fulfill the flat potential condition. For this condition, a large increase in the threshold currents of transverse coupled-bunch instabilities has been predicted and recently, the physical content behind this stabilization has been better understood. With this in mind, an investigation is made into the effectiveness of harmonic cavities for different machines. Frequency domain computations employing Laclare's eigenvalue method have been used to investigate the influence of several machine parameters and the results are presented.

Slides TUOAB03 [14.037 MB]

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TUPMB047

Tracking the Helium Balance in FREIA

EPICS, database, controls, hardware

1202

V.G. Ziemann, L. Hermansson
Uppsala University, Uppsala, Sweden

In the FREIA laboratory at Uppsala University we test the super-conducting spoke-cavities for the European Spallation Source. Liquid Helium for cooling the cavities is provided by a liquefaction plant from which also a local user community at the University is served. Recently we encountered a leak due to a faulty valve which went undetected for some time and caused significant loss of Helium. In order to prevent such mishaps in the future we implemented a Helium tracking system that includes detailed accounting of Helium leaving and entering the closed system as well as all volumes containing Helium in the system. We describe the technical implementation and experience to date.

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WEPMB034

Analysis of Niobium Quality Control for SRF Cavity

cavity, niobium, SRF, controls

2197

M.J. Joung
IBS, Daejeon, Republic of Korea

Funding: the Ministry of Science, ICT and Future Planning (MSIP) and the National Research Foundation (NRF) of the Republic of Korea under Contract 2013M7A1A1075764.
Clean and smooth surface is important to get low sur-face resistance for superconducting material. SRF (Super-conducting Radio Frequency) cavity made of niobium which is superconducting material and also one of the rare metal. The procedure of niobium quality control was set up to get high performance SRF cavity. The procedure consists of three parts; certificates check, Nb specification verification, and surface inspection and measurements of thickness, roughness, flatness. Three important properties which are RRR value, chemical composition and me-chanical properties were verified to conform Nb specifica-tion. The range of thickness, roughness and flatness for niobium as SRF cavity raw material were obtained by measurement.

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WEPMR023

Surface Analysis Studies of Nb3Sn Thin Films

cavity, niobium, SRF, electron

2316

D.L. Hall, J.J. Kaufman, M. Liepe, J.T. Maniscalco
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

A recent study to optimise the coating of thin-film Nb3Sn cavities has resulted in coating procedures that can fabricate 1.3 GHz cavities capable of reproducibly achieving fields of >16 MV/m with record high Qs >10¹⁰ at 4.2 K. However, the performance of these next generation SRF cavities is as yet well below the theoretical maximum performance expected of Nb3Sn, thus giving ample room for further advancements. Current measurements strongly suggest that the current limits are due to local defects and irregularities in the coated surface. In this paper we analyse, using methods including SEM/EDS, TEM, XRD and EBSD, the surface of both sample coupons and cavity cut-outs, with a view to identifying and understanding the origin of surface non-uniformities that would lead to increased surface resistance and cavity quench.

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WEPMR024

RF Measurements on High Performance Nb3Sn Cavities

cavity, niobium, SRF, accelerating-gradient

2320

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

A single-cell 1.3 GHz ILC-shape thin-film Nb3Sn-on-Nb cavity recently achieved accelerating gradients of >16 MV/m with a record Q0 of approx. 2·10¹⁰ at 4.2 K, exceeding the power efficiency seen in the current most efficient niobium cavities. A concurrent study of the coating process has resulted in a coating procedure that is capable of replicating this performance in other single-cell cavities. In this paper we demonstrate the RF performance and behaviour of these next generation SRF cavities, with an emphasis on both the impact from both external magnetic fields and the cavity cool down procedure on cavity performance.

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WEPMR025

Improved N-Doping Protocols for SRF Cavities

simulation, cavity, niobium, SRF

2323

D. Gonnella, R.G. Eichhorn, F. Furuta, G.M. Ge, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: NSF, DOE
Nitrogen-doping has been shown to consistently produce better quality factors in SRF cavities than is achievable with standard preparation techniques. Unfortunately, nitrogen-doping typically brings with it lower quench fields and higher sensitivities of residual resistance to trapped magnetic flux. Here we present work to understand these effects in hopes of mitigating them while maintaining the high Q desired by future projects. Using a nitrogen diffusion simulation, material parameters of nitrogen-doped cavities can be predicted prior to doping. These simulations results are consistent with SIMS data taken from samples treated with cavities. The nature of doping's effect on quench field has also been studied using CW and pulsed measurements. These results have allowed us to better understand the nature of nitrogen-doping and its effect on cavity performance.

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WEPMR027

Dependence of Surface Resistance on N-Doping Level

niobium, cavity, SRF, linac

2331

D. Gonnella, F. Furuta, G.M. Ge, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: NSF, DOE
Nitrogen-doping has become a standard tool for reaching high quality factors in SRF cavities in the medium field region at 2 K. This high Q has been shown to be a result of lowering of the temperature dependent BCS resistance. Here we show that this lowering of the BCS resistance is due to interstitial nitrogen in the niobium lowering the mean free path. The BCS resistance extracted from experimental data is shown to be consistent with theoretical predictions from BCS theory; that there is an optimal doping of which the mean free path is lowered to about half the intrinsic coherence length. These results provide insight into understanding the mechanisms behind nitrogen-doping and allow us to more accurately predict doping parameters to reach optimal cavity performance.

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WEPMR028

Studies on the Field Dependence of the BCS Surface Resistance

cavity, SRF, experiment, niobium

2335

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

Experiments have shown that the temperature-dependent portion of the RF surface resistance of SRF materials also exhibits a dependence on the magnitude of the surface field, manifested as a "Q-slope" or "anti-Q-slope" in the medium field region. Recent theoretical work proposes an explanation of the anti-Q-slope in dirty-limit superconductors. In this report, we compare theoretical predictions with the results of systematic experimental studies on the RF field dependence of the surface resistance using 1.3 GHz niobium SRF cavities with a wide range of mean free paths. We find very good agreement between theory and experiment in the dirty limit, with some divergence as the cavities approach the clean limit.

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WEPOR034

Design and Evaluation of a Broad Band microTCA.4 Based Downconverter

LLRF, controls, laser, electron

2746

N. Gan, Y.L. Chi, R.L. Liu, X. Ma
IHEP, Beijing, People's Republic of China

Modern low-level RF (LLRF) control systems of particle accelerators are designed to achieve extremely precise field amplitude and phase regulation inside the accelerating cavities, the RF field signal is usually converted to an intermediate frequency (IF) before being sampled by ADC. As the down-conversion is an important procedure of the digital signal processing in LLRF system, designing a high performance and broad band downconverter compatible with various accelerators will be significant. In this paper, the design of a MicroTCA based downconverter is presented, the major design objective of this module is wider operating frequency range and more flexibility in application. Several performance evaluations on different frequency points of this module have been conducted and the module presents a good performance in the operating frequency range.

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THOBB02

Impurity Doping of Superconducting Radio Frequency Cavities

cavity, niobium, vacuum, SRF

3195

P.N. Koufalis, F. Furuta, G.M. Ge, D. Gonnella, J.J. Kaufman, M. Liepe, J.T. Maniscalco
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: NSF PHYS-1416318
Impurity doping of bulk-niobium superconducting radio frequency (SRF) cavities is a relatively new field of study and the underlying physics is not yet fully understood. Previous studies have shown an increase in the intrinsic quality factor and the corresponding decrease of the temperature-dependent component of the surface resistance of nitrogen-doped cavities with increasing accelerating field.* Here we investigate the effects of alternative inert dopants on the surface resistance and thus the intrinsic quality factor of SRF cavities in pursuit of the optimal dopant and doping level.
A. Grassellino et al., Nitrogen and Argon Doping of Niobium for Superconducting Radio Frequency Cavities. Supercond. Sci. Technol., 26(102001), 2013

Slides THOBB02 [4.048 MB]

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THPMB038

Comparing RF-Cavity Phase-Scan Simulations in the ESS Linac Simulator with Measurements Taken in the Spallation Neutron Source Coupled-Cavity Linac

cavity, linac, neutron, controls

3317

E. Laface, Y.I. Levinsen
ESS, Lund, Sweden
I. List
Cosylab, Ljubljana, Slovenia
T.A. Pelaia II
ORNL, Oak Ridge, Tennessee, USA

The ESS Linac Simulator (ELS) is the model that will be used at the European Spallation Source ERIC in Lund, Sweden, to simulate the transport of the beam envelope for the operations. During the machine restart in August 2015 at the Spallation Neutron Source (SNS) in Oak Ridge, USA, we were able to perform the first benchmarking studies of the ELS. In this paper, we present the results of the phase-scans performed in four RF cavities of the coupled-cavity linac at SNS compared with the same scans simulated in the ELS. The phase of the cavity was modified while the phase of the beam was recorded in two BPMs downstream from the cavity. This measurement was repeated for four independent cavities and the results are compared here with the model, which favourably reproduces the BPM response to the cavity scans.

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THPMB039

Voltage Error Studies in the ESS RFQ

rfq, emittance, proton, linac

3320

A. Ponton, Y.I. Levinsen, E. Sargsyan
ESS, Lund, Sweden
A.C. France, O. Piquet, B. Pottin
CEA/IRFU, Gif-sur-Yvette, France

During the fabrication of an RFQ, deviation from the perfect geometry will occur during assembling, brazing and machining the different parts. These geometrical defects will impact the theoretical inter-vane voltage, given by the beam dynamics, by altering the quadrupolar component as well as adding dipolar terms in the voltage function. Tuners can correct partially the effect of the manufacturing. The study summarizes the effects of the voltage errors on the beam quality in the case of the ESS RFQ with a harmonic analysis of the voltage function. We discuss the acceptable level of voltage errors and associated mechanical tolerances.

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THPMY024

Upgrade of a UHV Furnace for 1700 C Heat Treatment and Processing of Niobium Samples

vacuum, niobium, power-supply, radiation

3709

J. Conrad, L. Alff, R. Grewe, T. Kürzeder, M. Major, N. Pietralla
TU Darmstadt, Darmstadt, Germany
F. Hug
IKP, Mainz, Germany
S.T. Sievers
MIT, Marburg, Germany

Funding: Supported by the German Federal Ministry for Education and Research (BMBF) under Grant No. 05H15RDRBA
In 2005 a high temperature vacuum furnace was put into operation at the Institute for Nuclear Physics at the Technische Universität Darmstadt. It has been designed for firing pure Niobium at temperatures of up to 1870 C. Until now several Nb cavities have been heat treated at 850 C with a proven record of success. The current focus of research in improving the superconductive characteristics of accelerator cavities is on new materials such as Nb3Sn or NbN or on the doping of Nb surfaces with nitrogen, so called N2-Doping. The surface preparations generally take place at temperatures of not more than 1000 C. To study phenomena that occur at higher temperatures, like the formation of delta-phase NbN at 1300 to 1700 C, it is planned to refurbish the UHV furnace and use it for corresponding studies. We will report on the design of a new annealing pot and a sample holder and give a review on our first experiences with the upgraded furnace.

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