PAC2013 - Table of Session: WEPAC (Poster Session)

Paper	Title	Page
WEPAC01	Time-Resolved Temperature Mapping System for the APS Deflecting Cavity	784
	Y. Yang TUB, Beijing, People's Republic of China P. Dhakal, J.D. Mammosser, H. Wang JLAB, Newport News, Virginia, USA J.D. Fuerst, J.P. Holzbauer, J.A. Kaluzny, A. Nassiri, G. Wu, Y. Yang ANL, Argonne, USA
	Time-resolved temperature mapping of a superconducting cavity can give valuable information on the limiting process of the cavity performance. A fast temperature mapping system has been developed at Argonne National Laboratory (ANL) for a superconducting deflecting cavity test. The time resolution of the temperature mapping could be up to 50 us. Not only the spatial distribution of surface heating but also the thermodynamics can be recorded, which helps to understand the limitation mechanism. This new temperature mapping system has helped us to understand the rf performance limitations during the cavity vertical tests. Based on the findings from the temperature mapping, proper cavity treatment has been applied and the cavity performances have been improved.

WEPAC02	Mode Damping Measurement for the APS Deflecting Cavity	787
	Y. Yang, A. Nassiri, T.L. Smith, G.J. Waldschmidt, G. Wu ANL, Argonne, USA H. Wang JLAB, Newport News, Virginia, USA Y. Yang TUB, Beijing, People's Republic of China
	The Advanced Photon Source has considered using a deflecting-cavity-based scheme to produce short pulse xrays. A deflecting cavity design has been completed. To verify the simulation result on this cavity, a copper prototype of the design has been fabricated for bench measurement. In this paper, we report our measurement results on this cavity. All the cavity modes below 5 GHz were identified by comparing the field distributions with calculations along different beam paths. After adding the damper, the measured Qexts of those modes were consistent with calculated values, which demonstrated that the cavity damping scheme was sufficient to reduce the wake impedances well below the safety thresholds.

WEPAC03	Electro-Magnetic Optimization and Analysis of a Quarter Wave Resonator	790
	Z. Zheng, Z.Q. He TUB, Beijing, People's Republic of China A. Facco INFN/LNL, Legnaro (PD), Italy A. Facco, Z.Q. He, Z. Liu, J. Wei, Y. Xu, Y. Zhang, Z. Zheng FRIB, East Lansing, USA
	Funding: Work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661 A β=0.085 quarter wave resonator (QWR) with resonant frequency=80.5 MHz is used in the Facility of Rare Isotope Beam (FRIB). Its baseline structure is designed to achieve the FRIB specifications with optimum cost to performance ratio. Electro-magnetic optimization is introduced in this paper to modify its internal geometry to reach instead maximum accelerating gradient, while preserving the original flange to flange length. Reduced peak magnetic field and increased shunt impedance are well achieved in the optimization while keeping the same stored energy. The maximum accelerating voltage is raised accordingly. Multipacting and steering are also analyzed for the optimized cavity. This resonator could be used in the ReA linac at MSU and in all applications where the maximum accelerating voltage should be achieved in a limited space, or where the accelerator cost is mainly driven by the resonator gradient.

WEPAC04	Hydrogen Degassing Study During the Heat Treatment of 1.3-GHz SRF Cavities	793
	M.J. Joung, H.J. Kim IBS, Daejeon, Republic of Korea A.M. Rowe, M. Wong Fermilab, Batavia, USA
	Funding: IBS (Institute for Basic Science) Superconducting radio frequency (SRF) cavities undergo a number of processes as part of its manufacturing procedure in order to optimize their performance. Among these processes is a high temperature hydrogen degas heat treatment used to prevent 'Q' disease. The heat treatment occurs in the processing sequence after either chemically or mechanically polishing the cavity. This paper summarizes the hydrogen measurements during the heat treatment of a sample of chemically and mechanically polished single-cell and nine-cell 1.3-GHz cavities. The hydrogen measurements are analyzed according the polishing method, the polishing history, the amount of time that the cavity was baked at 800°C, and the temperature ramp rate.

WEPAC05	Measurement of a Superconducting Solenoid with Applications to Low-beta SRF Cryomodules	796
	S.H. Kim, Z.A. Conway, M.P. Kelly, P.N. Ostroumov ANL, Argonne, USA E. Burkhardt Cryomagnetics, Inc., Tennessee, USA
	Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics and Nuclear Physics, under Contract DE-AC02-76CH03000 and DE-AC02-06CH11357. Proton and heavy-ion linacs with superconducting cavities require compact lattices to suppress emittance growth in the low-velocity region. For beam focusing superconducting solenoids are superior in this regard to normal conducting quadrupoles. A superconducting solenoid with integral x-y steering coils has been fabricated for the Project-X Injector Experiment (PXIE) half-wave resonator cryomodule. It is capable of generating 6 T solenoidal fields and dipole steering fields of 30 T•mm field integrals in both of transverse directions. We experimentally investigated issues for practical use of this solenoid in cryomodules including: 1) the superposition of dipole steering fields on solenoidal fields, 2) the magnetic axis of the solenoid with respect to the mechanical references in cryogenic temperatures, and 3) the residual magnetic field generated by the solenoid on the superconducting RF cavity surfaces even after degaussing; a 72 MHz quarter wave resonator was used for this experiment. In this paper, we present details of experimental setup and results.

WEPAC06	Mechanical Design of the 704 MHz 5-cell SRF Cavity Cold Mass for CeC PoP Experiment	799
	J.C. Brutus, S.A. Belomestnykh, I. Ben-Zvi, Y. Huang, V. Litvinenko, I. Pinayev, J. Skaritka, L. Snydstrup, R. Than, J.E. Tuozzolo, W. Xu BNL, Upton, Long Island, New York, USA T.L. Grimm, R. Jecks, J.A. Yancey Niowave, Inc., Lansing, Michigan, USA
	Funding: Work is supported by Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 with the US DOE. A 5-cell SRF cavity operating at 704 MHz will be used for Coherent Electron Cooling Proof of Principle (CeC PoP) system under development for the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. The CeC PoP experiment will demonstrate the ability of relativistic electrons to cool a single bunch of heavy ions in RHIC. The cavity will accelerate 2 MeV electrons from a 112 MHz SRF gun up 22 MeV. Novel mechanical designs, including the super fluid heat exchanger, helium vessel, vacuum vessel, tuner mechanism, and FPC are presented. Structural and modal analysis, using ANSYS were performed to confirm the cavity chamber and He vessel structural stability and to calculate the tuning sensitivity of the cavity. This paper provides an overview of the design, the project status and schedule of the 704 MHz 5-cell SRF for CeC PoP experiment.

WEPAC07	Mechanical Design of 112 MHz SRF Gun FPC for CeC PoP Experiment	802
	J.C. Brutus, S.A. Belomestnykh, Y. Huang, V. Litvinenko, G.J. Mahler, I. Pinayev, J. Skaritka, L. Snydstrup, R. Than, J.E. Tuozzolo, Q. Wu, T. Xin BNL, Upton, Long Island, New York, USA
	Funding: Work is supported by Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 with the US DOE. A Quarter-Wave Resonator (QWR) type SRF gun operating at 112 MHz will be used for Coherent Electron Cooling Proof of Principle (CeC PoP) system under development for the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. The CeC PoP experiment will demonstrate the ability of relativistic electrons to cool a single bunch of heavy ions in RHIC. This cavity is designed to generate a 2 MeV, high charge (several nC), low repetition rate (78 kHz) electron beam using a new fundamental power coupler (FPC) design approach. Structural and thermal analysis, using ANSYS were performed to confirm the FPC structural stability and to calculate the deflection due to heat load from RF power generation. This paper provides an overview of the design, structural and thermal analysis, test results, and FPC tuning drive system for the 112 MHz gun.

WEPAC09	A Temperature-Mapping System for Multi-Cell SRF Accelerator Cavities	805
	G.M. Ge, G.H. Hoffstaetter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	A Temperature mapping (T-map) system for Superconducting Radio Frequency (SRF) cavities consists of a thermometer array positioned precisely on an exterior cavity wall, capable of detecting small increases in temperature; therefore it is a powerful tool for research on the quality factor (Q0) of SRF cavities. A new multi-cell T-mapping system is has been developed at Cornell University. The system has nearly two thousand thermometers to cover 7-cell SRF cavities for Cornell’s ERL project. A new multiplexing scheme was adopted to reduce number of wires. A 1mK resolution of the temperature increase ΔT is achieved. A 9-cell cavity of TESLA geometry was tested with the T-map system. By converting ΔT to power loss and quality factor, it has been found that for this cavity, most surface losses were generated by the first cell when the accelerating gradient is increased above 15MV/m. Effective and intuitive ways of displaying surface properties of the cavity interior, e.g. the residual resistivity, will be shown.

WEPAC10	Investigation of the Surface Resistivity of SRF Cavities via theHEAT and SRIMP Program as well as the Multi-cell T-Map System	808
	G.M. Ge, G.H. Hoffstaetter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	A high-sensitive temperature mapping system for multi-cell SRF cavities has been constructed at Cornell University. The resolution of the system is 1mK. Hence it’s able to detect small temperature increases when cavities reach at low accelerating gradients e.g. 3MV/m. The surface resistivity of superconductor under radio-frequency electromagnetic field can be calculated from the temperature increases. In this contribution, the surface resistance map of multi-cell SRF cavities is shown. The temperature mapping result is possible to establish a relationship between the surface resistivity and the magnetic field as well. Unlike the RF method which is average value of the surface resistance, the T-map results give local surface resistivity versus magnetic field. BCS theory assumes the surface resistivity is independent to the magnetic field. The T-map results, however, suggest that the surface resistance at high-loss region is field dependent and caused Q-slope.

WEPAC11	Cornell's Main Linac Cryo-module Prototype	811
	R.G. Eichhorn, G.M. Ge, Y. He, G.H. Hoffstaetter, M. Liepe, T. O'Connel, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: Supported by NSF award DMR-0807731 In preparation to built an energy-recovery linac (ERL) based synchrotron-light facility at Cornell University which can provide greatly improved X-ray beams due to the high electron-beam quality that is available from a linac, a phase 1 R&D program was launched, adressing critical challenges in the design. One of them being a full linac cryo-module, housing 6 superconducting cavities (operated at 1.8 K in cw mode), 7 HOM absorbers and 1 magnet/ BPM section. The final design will be presented and a report on the fabrication status that started in late 2012 will be given

WEPAC12	Theoretical Description of SIS Multilayer Films for SRF Cavities	814
	S. Posen, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA G. Catelani Forschungszentrum Jülich, Peter Gruenberg Institut (PGI-2), Jülich, Germany J.P. Sethna Cornell University, Ithaca, New York, USA M.K. Transtrum M.D.A.C.C., Houston, Texas, USA
	As surface magnetic fields in niobium superconducting RF (SRF) cavities prepared with modern techniques approach the fundamental limit of niobium’s superheating field, SRF researchers are looking to alternative superconductors to sustain even higher fields. However, the short coherence length of these superconductors may represent a critical vulnerability to vortex penetration at very small defects in the surface. A. Gurevich has proposed* a method of defeating this vulnerability: coating a bulk superconducting cavity with a series of very thin insulating and superconducting films. In this work, we present a thorough mathematical description of the SIS thin films proposed by Gurevich in the language of the accelerator community, to help researchers to optimize cavities made from alternative superconductors. * A. Gurevich, Appl. Phys. Lett. 88, 012511 (2006)

WEPAC13	Achieving High Accuracy in Cornell's ERL Cavity Production	817
	R.G. Eichhorn, B. Bullock, B. Clasby, J.J. Kaufman, B.M. Kilpatrick, S. Posen, J. Sears, V.D. Shemelin Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA T. Kürzeder TU Darmstadt, Darmstadt, Germany
	Funding: Supported by NSF award DMR-0807731 The phase 1 R&D program launched in preparation to building a 5 GeV Enery Recovery Linac (ERL) at Cornell, a full main linac cryomodule is currently built, housing six 7-cell cavities. In order to control the beam break-up limit, the shape of the cavity was highly optimized and stringent tolerances on the cavity production were targeted. We will report on the details of the cavity production, the accuracy of the cups forming the individual cells, the trimming procedure for the dumbbells, the cavity tuning and final accuracy of the cavity concerning field flatness, resonant frequency and overall length within this small series production.

WEPAC14	Studies of the Superconducting Traveling Wave Cavity for High Gradient Linac	820
	P.V. Avrakhov, A. Kanareykin, R.A. Kostin Euclid TechLabs, LLC, Solon, Ohio, USA N. Solyak, V.P. Yakovlev Fermilab, Batavia, USA
	Use of a traveling wave (TW) accelerating structure with a small phase advance per cell rather than a standing wave structure may provide a significant increase of the accelerating gradient in superconducting linacs. For the same surface electric and magnetic fields the TW achieves an accelerating gradient 1.2/1.4 larger than TESLA-like standing wave cavities [1]. Recent tests of L-band model of a single-cell cavity with waveguide feedback [2] demonstrated an accelerating gradient comparable to the gradient in a single-cell ILC-type cavity from the same manufacturer. This article presents the next stage of development of the TW resonance ring with 3-cell accelerating cavity which supposed to test in traveling wave regime. The main simulation results of the microphonics and Lorentz force detuning are also considered.

WEPAC17	Study on Particulate Retention on Polished Niobium Surfaces after BCP Etching	823
	I.M. Malloch, C. Compton, L. Popielarski FRIB, East Lansing, Michigan, USA
	Funding: This material is based upon work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE SC0000661, the State of Michigan and Michigan State University. Niobium surface defects and inclusions can be introduced during the manufacturing processes used in the production of SRF cavities. Bulk removal methods (sanding, polishing, etc…) are frequently utilized to remove or smooth away these defects on the surface of the niobium metal. It is hypothesized that these mechanical removal methods are capable of trapping performance-degrading particulates, which are then exposed during subsequent chemical processing, potentially contaminating the cavity prior to RF testing. This paper summarizes results of a series of surface roughness and etching experiments performed to determine the relationship between the extent of polishing and trapped particulate, and to determine a method for mitigating this particulate contamination through BCP etching. The relationship between these experiments and RF cavity performance will be explored as well.

WEPAC18	SRF Cavity Etching Developments for FRIB Cavity Processing	826
	K. Elliott NSCL, East Lansing, Michigan, USA I.M. Malloch, L. Popielarski, N. Putnam FRIB, East Lansing, Michigan, USA
	Funding: This material is based upon work supported by the U.S. Department of Energy Office of Science under cooperative agreement DE-SC0000661. Updates to the FRIB β=0.53 half wave resonator (HWR) design have provided an opportunity to test new buffered chemical polish (BCP) flow control techniques. New processing fixtures have been fabricated and used to process the FRIB β=0.53 HWR. This paper will present details of the fixture mechanical design iterations, the resulting BCP flow simulations, a qualitative evaluation of the agreement between simulations and measured results, and developments in process validation techniques.

WEPAC20	Magnetic Shield Optimization for the FRIB Superconducting Quarter-Wave Resonator Cryomodule	829
	Y. Xu, A.D. Fox, M.J. Johnson, M. Leitner, S.J. Miller, K. Saito FRIB, East Lansing, Michigan, USA
	The Facility for Rare Isotope Beams (FRIB) requires 49 cryomodules containing 330 superconducting low-beta cavities, which have to be shielded from the earth magnetic field. Comprehensive magnetic shielding simulations have been conducted for 80.5 MHz β=0.085 cryomodules exposed to earth fields of 0.5 Gauss in different coordinate directions. The magnetic shield has to attenuate the earth magnetic field by a minimum factor of 33 (to less than 15 milli Gauss) in order to limit flux trapping in the cavities during cool-down. In the reported optimization studies, the permeability of the magnetic shielding material, shield thickness, and number of magnetic shield layers have been varied. Different design concepts including global and local magnetic shielding have been evaluated. In addition, the design concepts are compared based on the cost of material, fabrication and assembly, the design complexity and compatibility with the overall cryomodule design to obtain an optimum solution.

WEPAC21	Tuning Process of SSR1 Cavity for Project X at FNAL	832
	P. Berrutti, M.H. Awida, T.N. Khabiboulline, D. Passarelli, L. Ristori, V.P. Yakovlev Fermilab, Batavia, USA
	SSR1 is a family of single spoke resonators to be used in Project X at Fermi National Laboratory. These cavities operate in CW regime having nominal frequency of 325 MHz and optimal beta of 0.22. SSR1 cavities will accelerate H⁻ ions after the Half Wave Resonator (HWR) section from 9 MeV to 32 MeV. In the near future this cavity will be used in Project X Injector Experiment (PXIE), which contains the ion source, the LEBT, the MEBT, the RFQ of Project X, and a cryogenic temperature section, having one HWR and one SSR1 cryomodule. SSR1 cavities have been built and tested at FNAL, the preparation of these resonators includes RF tuning which is the main focus of this paper. The frequency of the cavity is carefully chosen prior to the vertical test, and it is adjusted before welding the helium vessel to obtain 325 MHz nominal frequency for the dressed cavity in operating conditions. Several SSR1 cavities have been tuned at FNAL, the procedure, the hardware and the data are presented.

WEPAC22	Single Spoke Resonator Inner Electrode Optimization Driven by Reduction of Multipoles	835
	P. Berrutti, T.N. Khabiboulline, L. Ristori, N. Solyak, V.P. Yakovlev Fermilab, Batavia, USA
	Accelerating cavities based on coaxial resonators, half wave and spoke resonators for example, do not have azimuthal symmetry. This lack of symmetry introduces a transverse field perturbation which affects the beam dynamic, since the particles traveling through the structure are crossing two accelerating gaps separated by the inner electrode. The field asymmetry induces an asymmetric transverse momentum gain which, once expanded in multipoles, appears to be due to a quadrupole perturbation. Depending on the cavity geometry and particle velocity, the influence of electric and magnetic fields may vary quite significantly. A way of having symmetric transverse fields in spoke resonators consists in modifying the inner electrode from a pole to an X or Y shape. The application of these changes symmetrizes both electric and magnetic fields and reduces the multipoles amplitudes to negligible values. This paper presents the study aimed to reduce the multi-poles amplitudes of SSR2 cavity for Project X; the presented procedure, in general, is valid for any spoke cavity.

WEPAC23	Multipacting Simulations of SSR2 Cavity at FNAL	838
	P. Berrutti, T.N. Khabiboulline, L. Ristori, G.V. Romanov, A.I. Sukhanov, V.P. Yakovlev Fermilab, Batavia, USA
	SSR2 is the second family of single spoke resonator under development at Fermi National Accelerator Laboratory (FNAL). These cavities will be placed in Project X front-end after SSR1 spoke resonators, which have already been built and tested and FNAL. Spoke cavities are affected by multipacting and the nature of their 3D geometry does not allow simulating the multipactor process using 2D tools. 3D tracking simulations, of electrons inside the cavity volume, have been carried out using CST Particle Studio. Different Secondary Emission Coefficients have been applied to the cavity walls in order to understand how strongly the multipacting depends on material properties. The power levels used in simulations cover the whole operating gradient range of SSR2 cavity. Results of these simulations are compared to the one given by SSR1 model, which demonstrated good agreement with experimental data. The purposes of this paper are to present the results gotten from the tracking solver, to give a prediction of what will be the multipacting scenario for SSR2 cavity and if there will be any dangerous zone for operation.

WEPAC25	New Helium Vessel and Lever Tuner Designs for the 650 MHz Cavities for Project X	841
	I.V. Gonin, M.H. Awida, E. Borissov, M.H. Foley, C.J. Grimm, T.N. Khabiboulline, M. Merio, Y.M. Pischalnikov, L. Ristori, V.P. Yakovlev Fermilab, Batavia, USA
	The design of 5-cell elliptical 650 MHz β=0.9 cavities to accelerate H⁻ beam of 1 mA average current in the range 467-3000 MeV for the Project X Linac is currently under development at Fermilab. A new design of the Helium Vessel (HV) was developed for these cavities with the main goal of optimizing the frequency sensitivity df/dP by keeping the cavity stiffness reasonably small. We also present a design of the new lever tuner system. The HV in the new design is equipped with the tuner located at the end of the cavity instead of the initially proposed blade tuner located in the middle. We will present mechanical design results and ANSYS analyses for both the slow and fast tuners.

WEPAC29	CM2, Second 1.3GHz Cryomodule Fabrication at Fermilab	844
	T.T. Arkan, M.H. Awida, P. Berrutti, E. Borissov, C.M. Ginsburg, C.J. Grimm, E.R. Harms, A. Hocker, T.N. Khabiboulline, Y.O. Orlov, T.J. Peterson, R.V. Pilipenko, Y.M. Pischalnikov, K.S. Premo, L. Ristori, W. Schappert, V.P. Yakovlev Fermilab, Batavia, USA
	Funding: US Department of Energy CM2 is the second 1.3GHz Cryomodule assembled at the Cryomodule Assembly Facility (CAF) in Fermi National Accelerator Laboratory. The string has a doublet magnet, beam position monitor and eight cavities. All the cavities are qualified at 35 MV / m gradient at the Horizontal Test Facility before assembly. The dressed cavities were outfitted with magnetic shielding, blade tuner, and the cold mass was assembled based on the Tesla TTF Type III+ cryomodule design. CM2 is currently being installed into the test stand in NML where it will be cooled down and high power tested. CM2 will also be the first cryomodule that an electron beam will be put through at the NML facility. This will be a proof of principle for the planned Advanced Superconducting Test Accelerator (ASTA) facility at NML. This paper describes the assembly steps, the quality assurance methods and the challenges that we experienced during assembly and qualification steps at CAF. De

WEPAC32	Wakefield Loss Analysis of the Elliptical 3.9 GHz Third Harmonic Cavity	847
	M.H. Awida, P. Berrutti, T.N. Khabiboulline, A. Saini, V.P. Yakovlev Fermilab, Batavia, USA
	Third harmonic 3.9 GHz elliptical cavities are planned to be used in many particle accelerator projects such as XFEL, NGLS, and ASTA. In this paper, the wakefield losses due to single bunch passage are analysed considering bunches of RMS length 8 mm down to ultra short ones of 10 μm length. Both the loss and kick factors are numerically calculated for bunches of relatively long length (>1 mm) using CST wakefield solver. The data is then used to extrapolate asymptotically the values for ultra-short bunches by finding the wake functions. These calculations are essential to estimate the cryogenic losses in cryomodules and for beam dynamic analysis.

WEPAC33	Results of the New High Power Tests of Superconducting Photonic Band Gap Structure Cells	850
	E.I. Simakov, S. Arsenyev, W.B. Haynes, S.S. Kurennoy, D. C. Lizon, J.F. O'Hara, E.R. Olivas, D.Y. Shchegolkov, N.A. Suvorova, T. Tajima LANL, Los Alamos, New Mexico, USA S. Arsenyev MIT/PSFC, Cambridge, Massachusetts, USA C.H. Boulware, T.L. Grimm Niowave, Inc., Lansing, Michigan, USA
	Funding: This work is supported by the Department of Defense High Energy Laser Joint Technology Office through the Office of Naval Research. We present an update on the 2.1 GHz superconducting rf (SRF) photonic band gap (PBG) resonator experiment in Los Alamos. The new SRF PBG cell was designed with the particular emphasis on changing the shape of PBG rods to reduce the peak magnetic fields and at the same time to preserve its effectiveness for suppression of the higher order modes (HOMs). The new PBG cells have great potential for outcoupling long-range wakefields in SRF accelerator structures without affecting the fundamental accelerating mode. Using PBG structures in superconducting particle accelerators will allow operation at higher frequencies and moving forward to significantly higher beam luminosities thus leading towards a completely new generation of colliders for high energy physics. Here we report the results of our efforts to fabricate 2.1 GHz PBG cells with elliptical rods and to test them with high power in a liquid helium bath at the temperature of 2 Kelvin. The high gradient performance of the cells will be evaluated and the results will be compared to electromagnetic and thermal simulations.

WEPAC34	Update on the Design of a Five-Cell Superconducting RF Module with a PBG Coupler Cell	853
	S. Arsenyev MIT/PSFC, Cambridge, Massachusetts, USA E.I. Simakov LANL, Los Alamos, New Mexico, USA
	Funding: This work is supported by the U.S. Department of Energy (DOE) Office of Science Early Career Research Program. We present a complete design of the 5-cell superconducting accelerating module incorporating a Photonic Band Gap (PBG) cell with couplers. The purpose of the PBG cell is to achieve better Higher Order Mode (HOM) damping which is vital for preserving the quality of high-current electron beams in novel linear accelerators. The PBG technology can therefore be used for X-band free electron lasers. We first discuss the engineering aspects of incorporating a PBG cell in a superconducting PBG module. The main concern is to ensure the equal probability of quench is in each of the five cells, which leads to significant geometry modifications. We then present the simulation data on the HOM damping. Particularly, we calculate the external quality factors for the 10 most dangerous HOMs for this particular structure. Performance of different couplers and different modifications of the PBG lattice are discussed. Thermal analysis of the structure is also discussed briefly.

WEPAC35	Initial Studies of Multipactor Suppression Via TE and TM Modes	856
	S.A. Rice, J.P. Verboncoeur Michigan State University, East Lansing, USA
	Funding: Work supported by U.S. Air Force Office of Scientific Research (AFOSR) grant on the Basic Physics of Distributed Plasma Discharges. The formation of multipactor is strongly dependent upon the secondary electron yield (SEY) of a surface, and the emission velocities of the emitted electrons, in addition to the electric field. Since the secondary electron yield (SEY) of a material is dependent upon the kinetic energy and impact angle of the incident electron, we investigate use TE and TM coaxial cavity modes to modify the impacting electron velocities to reduce the average SEY and suppress multipactor, which builds upon our previous work examining TEM modes.

WEPAC39	Tests of an RF Dipole Crabbing Cavity for an Electron-Ion Collider	859
	A. Castilla, J.R. Delayen ODU, Norfolk, Virginia, USA A. Castilla, J.R. Delayen JLAB, Newport News, Virginia, USA A. Castilla DCI-UG, León, Mexico
	On the scheme of developing a medium energy electron-ion collider (MEIC) at Jefferson Lab, we have designed a compact superconducting rf dipole cavity at 750 MHz to crab both electron and ion bunches and increase luminosities at the interaction points (IP) of the machine. Following the design optimization and characterization of the electromagnetic properties such as peak surface fields and shunt impedance, along with field nonuniformities, multipole components content, higher order modes (HOM) and multipacting, a prototype cavity was built by Niowave Inc. The 750 MHz prototype crab cavity has been tested at 4 K and is ready for re-testing at 4 K and 2 K at Jefferson Lab. In this paper we present the detailed results of the rf tests performed on the 750 MHz crab cavity prototype.

WEPAC40	Mechanical Analysis of the 400 MHz RF-Dipole Crabbing Cavity Prototype for LHC High Luminosity Upgrade	862
	S.U. De Silva, J.R. Delayen, H. Park ODU, Norfolk, Virginia, USA S.U. De Silva, J.R. Delayen, H. Park JLAB, Newport News, Virginia, USA Z. Li SLAC, Menlo Park, California, USA
	The proposed LHC high luminosity upgrade requires two crabbing systems in increasing the peak luminosity, operating both vertically and horizontally at two interaction points of IP1 and IP5. The required system has tight dimensional constraints and needs to achieve higher operational gradients. A proof-of-principle 400 MHz crabbing cavity design has been successfully tested and has proven to be an ideal candidate for the crabbing system. The cylindrical proof-of-principle rf-dipole design has been adapted in to a square shaped design to further meet the dimensional requirements. The new rf-dipole design has been optimized in meeting the requirements in rf-properties, higher order mode damping, and multipole components. A crabbing system in a cryomodule is expected to be tested on the SPS beam line prior to the test at LHC. The new prototype is required to achieve the mechanical and thermal specifications of the SPS test followed by the test at LHC. This paper discusses the detailed mechanical and thermal analysis in minimizing Lorentz force detuning and sensitivity to liquid He pressure fluctuations.

WEPAC41	Comparison of Electromagnetic, Thermal and Mechanical Calculations with RF Test Results in RF-Dipole Deflecting/Crabbing Cavities	865
	H. Park, S.U. De Silva, J.R. Delayen JLAB, Newport News, Virginia, USA S.U. De Silva, J.R. Delayen, H. Park ODU, Norfolk, Virginia, USA
	The current requirements of higher gradients and strict dimensional constraints in the emerging applications have required the designing of compact deflecting and crabbing rf structures. The superconducting rf-dipole cavity is one of the first novel compact designs with attractive properties such as higher gradients, higher shunt impedance and widely separated higher order modes. The recent tests performed on proof-of-principle designs of the rf-dipole geometry at 4.2 K and 2.0 K in a vertical test assembly have proven the designs to achieve higher gradients with higher intrinsic quality factors and easily processed multipacting conditions. The design frequency sensitivity to pressure (df/dp) due to liquid He pressure fluctuations, Lorentz force detuning due to radiation pressure, and thermal and mechanical effects have also been measured during the tests. These effects lead to cavity frequency detuning while in operation and therefore needs to be reduced. This paper presents the detailed comparison of the measurement to the simulation results obtained from ANSYS.

WEPAC42	Geometry Effects on Multipole Components and Beam Optics in High-Velocity Multi-Spoke Cavities	868
	C.S. Hopper, K.E. Deitrick, J.R. Delayen ODU, Norfolk, Virginia, USA J.R. Delayen JLAB, Newport News, Virginia, USA
	Velocity-of-light, multi-spoke cavities are being proposed to accelerate electrons in a compact light-source [1]. There are strict requirements on the beam quality which require that the linac have only small non-uniformities in the accelerating field. Beam dynamics simulations have uncovered varying levels of focusing and defocusing in the proposed cavities, which is dependent on the geometry of the spoke in the vicinity of the beam path. Here we present results for the influence different spoke geometries have on the multipole components of the accelerating field and how these components, in turn, impact the simulated beam properties. * T. Satogata et al, “Compact Accelerator Design for a Compact Light Source,” IPAC13, Shanghai, China, May 2013.

WEPAC43	Study of Cavity Imperfection Impact on RF-Parameters and Multipole Components in a Superconducting RF-Dipole Cavity	871
	R.G. Olave, S.U. De Silva, J.R. Delayen ODU, Norfolk, Virginia, USA Z. Li SLAC, Menlo Park, California, USA
	Funding: This work is funded by the US/LHC LARP program. The ODU/SLAC superconducting rf-dipole cavity is under consideration for the crab-crossing system in the upcoming LHC luminosity upgrade. While the proposed cavity complies well within the rf-parameters and multipolar component restrictions for the LHC system, cavity imperfections arising from cavity fabrication, welding and frequency tuning may have a significant effect in these parameters. We report on an initial study of the impact of deviation from the ideal shape on the cavity’s performance in terms of rf-parameters and multipolar components.

WEPAC44	Higher Order Modes Damping and Multipacting Analysis for the SPX Deflecting Cavity in APS Upgrade	874
	C.-K. Ng, Z. Li, L. Xiao SLAC, Menlo Park, California, USA A. Nassiri, G.J. Waldschmidt, G. Wu ANL, Argonne, USA R.A. Rimmer, H. Wang JLAB, Newport News, Virginia, USA
	Funding: Work supported by US DOE under contract number DE-AC02-06CH11357. A single-cell superconducting deflecting cavity operating at 2.815 GHz has been proposed and designed for the Short Pulse X-ray (SPX) project for the Advanced Photon Source (APS) upgrade. Each deflecting cavity is equipped with one fundamental power coupler (FPC), one lower order mode (LOM) coupler, and two higher order mode (HOM) couplers to achieve the stringent damping requirements for the unwanted modes. Using the electromagnetic simulation suite ACE3P, HOM damping will be calculated for the cavity including the full engineering design waveguide configurations and rf windows. Trapped modes in the bellows located in the beampipes connecting the cavities in a cryomodule will be computed and their effects on heating evaluated. Furthermore, multipacting activities at the end groups of the cavity will be identified to assess possible problems during high power processing.

WEPAC46	Wakefield Computations for a Corrugated Pipe as a Beam Dechirper for FEL Applications	877
	C.-K. Ng, K.L.F. Bane SLAC, Menlo Park, California, USA
	Funding: Work supported by the US DOE under contract DE-AC02-76SF00515. A beam “dechirper” based on a corrugated, metallic vacuum chamber has been proposed recently to cancel residual energy chirp in a beam before it enters the undulator in a linac-based X-ray FEL. Rather than the round geometry that was originally proposed, we consider a pipe composed of two parallel plates with corrugations. The advantage is that the strength of the wake effect can be tuned by adjusting the separation of the plates. The separation of the plates is a few millimeters, and the corrugations are fractions of a millimeter in size. The dechirpers need to be meters long in order to provide sufficient longitudinal wakefield to cancel the beam chirp. Considerable computation resources are required to determine accurately the wakefield for such a long structure with small corrugation gaps. Combining the moving window technique and parallel computing using multiple processors, the parallel finite-element electromagnetic suite ACE3P allows efficient determination of the wakefield through convergence studies. In this paper, we will calculate the longitudinal, dipole and quadrupole wakefields for the dechirper and compare the results with those of analytical approaches. K.L.F. Bane, G. Stupakov, Nucl. Instrum. Meth. A690 (2012) 106-110.

WEPAC47	Mechanical Design of a New Injector Cryomodule 2-Cell Cavity at CEBAF	880
	G. Cheng, J. Henry, J.D. Mammosser, R.A. Rimmer, H. Wang, M. Wiseman, S. Yang JLAB, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. As a part of Jefferson Lab’s 12 GeV upgrade, a new injector superconducting RF cryomodule is required. This unit consists of a 2-cell and 7-cell cavity, with the latter being refurbished from an existing cavity. The new 2-cell cavity requires electromagnetic design and optimization followed by mechanical design analyses. The electromagnetic design is reported elsewhere. This paper aims to present the procedures and conclusions of the analyses on cavity tuning sensitivity, pressure sensitivity, upset condition pressure induced stresses, and structural vibration frequencies. The purposes of such analyses include: 1) provide reference data for cavity tuner design; 2) examine the structural integrity of the cavity; and 3) evaluate the 2-cell cavity’s resistance to microphonics. Design issues such as the location of stiffening rings, effect of tuner stiffness on cavity stress, choice of cavity wall thickness, etc. are investigated by conducting extensive finite element analyses. Progress in fabrication of the 2-cell cavity is also reported. The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes.

Paper

Title

Page

Time-Resolved Temperature Mapping System for the APS Deflecting Cavity

784

Y. Yang
TUB, Beijing, People's Republic of China
P. Dhakal, J.D. Mammosser, H. Wang
JLAB, Newport News, Virginia, USA
J.D. Fuerst, J.P. Holzbauer, J.A. Kaluzny, A. Nassiri, G. Wu, Y. Yang
ANL, Argonne, USA

Time-resolved temperature mapping of a superconducting cavity can give valuable information on the limiting process of the cavity performance. A fast temperature mapping system has been developed at Argonne National Laboratory (ANL) for a superconducting deflecting cavity test. The time resolution of the temperature mapping could be up to 50 us. Not only the spatial distribution of surface heating but also the thermodynamics can be recorded, which helps to understand the limitation mechanism. This new temperature mapping system has helped us to understand the rf performance limitations during the cavity vertical tests. Based on the findings from the temperature mapping, proper cavity treatment has been applied and the cavity performances have been improved.

WEPAC02

Mode Damping Measurement for the APS Deflecting Cavity

787

Y. Yang, A. Nassiri, T.L. Smith, G.J. Waldschmidt, G. Wu
ANL, Argonne, USA
H. Wang
JLAB, Newport News, Virginia, USA
Y. Yang
TUB, Beijing, People's Republic of China

The Advanced Photon Source has considered using a deflecting-cavity-based scheme to produce short pulse xrays. A deflecting cavity design has been completed. To verify the simulation result on this cavity, a copper prototype of the design has been fabricated for bench measurement. In this paper, we report our measurement results on this cavity. All the cavity modes below 5 GHz were identified by comparing the field distributions with calculations along different beam paths. After adding the damper, the measured Qexts of those modes were consistent with calculated values, which demonstrated that the cavity damping scheme was sufficient to reduce the wake impedances well below the safety thresholds.

WEPAC03

Electro-Magnetic Optimization and Analysis of a Quarter Wave Resonator

790

Z. Zheng, Z.Q. He
TUB, Beijing, People's Republic of China
A. Facco
INFN/LNL, Legnaro (PD), Italy
A. Facco, Z.Q. He, Z. Liu, J. Wei, Y. Xu, Y. Zhang, Z. Zheng
FRIB, East Lansing, USA

Funding: Work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661
A β=0.085 quarter wave resonator (QWR) with resonant frequency=80.5 MHz is used in the Facility of Rare Isotope Beam (FRIB). Its baseline structure is designed to achieve the FRIB specifications with optimum cost to performance ratio. Electro-magnetic optimization is introduced in this paper to modify its internal geometry to reach instead maximum accelerating gradient, while preserving the original flange to flange length. Reduced peak magnetic field and increased shunt impedance are well achieved in the optimization while keeping the same stored energy. The maximum accelerating voltage is raised accordingly. Multipacting and steering are also analyzed for the optimized cavity. This resonator could be used in the ReA linac at MSU and in all applications where the maximum accelerating voltage should be achieved in a limited space, or where the accelerator cost is mainly driven by the resonator gradient.

WEPAC04

Hydrogen Degassing Study During the Heat Treatment of 1.3-GHz SRF Cavities

793

M.J. Joung, H.J. Kim
IBS, Daejeon, Republic of Korea
A.M. Rowe, M. Wong
Fermilab, Batavia, USA

Funding: IBS (Institute for Basic Science)
Superconducting radio frequency (SRF) cavities undergo a number of processes as part of its manufacturing procedure in order to optimize their performance. Among these processes is a high temperature hydrogen degas heat treatment used to prevent 'Q' disease. The heat treatment occurs in the processing sequence after either chemically or mechanically polishing the cavity. This paper summarizes the hydrogen measurements during the heat treatment of a sample of chemically and mechanically polished single-cell and nine-cell 1.3-GHz cavities. The hydrogen measurements are analyzed according the polishing method, the polishing history, the amount of time that the cavity was baked at 800°C, and the temperature ramp rate.

WEPAC05

Measurement of a Superconducting Solenoid with Applications to Low-beta SRF Cryomodules

796

S.H. Kim, Z.A. Conway, M.P. Kelly, P.N. Ostroumov
ANL, Argonne, USA
E. Burkhardt
Cryomagnetics, Inc., Tennessee, USA

Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics and Nuclear Physics, under Contract DE-AC02-76CH03000 and DE-AC02-06CH11357.
Proton and heavy-ion linacs with superconducting cavities require compact lattices to suppress emittance growth in the low-velocity region. For beam focusing superconducting solenoids are superior in this regard to normal conducting quadrupoles. A superconducting solenoid with integral x-y steering coils has been fabricated for the Project-X Injector Experiment (PXIE) half-wave resonator cryomodule. It is capable of generating 6 T solenoidal fields and dipole steering fields of 30 T•mm field integrals in both of transverse directions. We experimentally investigated issues for practical use of this solenoid in cryomodules including: 1) the superposition of dipole steering fields on solenoidal fields, 2) the magnetic axis of the solenoid with respect to the mechanical references in cryogenic temperatures, and 3) the residual magnetic field generated by the solenoid on the superconducting RF cavity surfaces even after degaussing; a 72 MHz quarter wave resonator was used for this experiment. In this paper, we present details of experimental setup and results.

WEPAC06

Mechanical Design of the 704 MHz 5-cell SRF Cavity Cold Mass for CeC PoP Experiment

799

J.C. Brutus, S.A. Belomestnykh, I. Ben-Zvi, Y. Huang, V. Litvinenko, I. Pinayev, J. Skaritka, L. Snydstrup, R. Than, J.E. Tuozzolo, W. Xu
BNL, Upton, Long Island, New York, USA
T.L. Grimm, R. Jecks, J.A. Yancey
Niowave, Inc., Lansing, Michigan, USA

Funding: Work is supported by Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 with the US DOE.
A 5-cell SRF cavity operating at 704 MHz will be used for Coherent Electron Cooling Proof of Principle (CeC PoP) system under development for the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. The CeC PoP experiment will demonstrate the ability of relativistic electrons to cool a single bunch of heavy ions in RHIC. The cavity will accelerate 2 MeV electrons from a 112 MHz SRF gun up 22 MeV. Novel mechanical designs, including the super fluid heat exchanger, helium vessel, vacuum vessel, tuner mechanism, and FPC are presented. Structural and modal analysis, using ANSYS were performed to confirm the cavity chamber and He vessel structural stability and to calculate the tuning sensitivity of the cavity. This paper provides an overview of the design, the project status and schedule of the 704 MHz 5-cell SRF for CeC PoP experiment.

WEPAC07

Mechanical Design of 112 MHz SRF Gun FPC for CeC PoP Experiment

802

J.C. Brutus, S.A. Belomestnykh, Y. Huang, V. Litvinenko, G.J. Mahler, I. Pinayev, J. Skaritka, L. Snydstrup, R. Than, J.E. Tuozzolo, Q. Wu, T. Xin
BNL, Upton, Long Island, New York, USA

Funding: Work is supported by Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 with the US DOE.
A Quarter-Wave Resonator (QWR) type SRF gun operating at 112 MHz will be used for Coherent Electron Cooling Proof of Principle (CeC PoP) system under development for the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. The CeC PoP experiment will demonstrate the ability of relativistic electrons to cool a single bunch of heavy ions in RHIC. This cavity is designed to generate a 2 MeV, high charge (several nC), low repetition rate (78 kHz) electron beam using a new fundamental power coupler (FPC) design approach. Structural and thermal analysis, using ANSYS were performed to confirm the FPC structural stability and to calculate the deflection due to heat load from RF power generation. This paper provides an overview of the design, structural and thermal analysis, test results, and FPC tuning drive system for the 112 MHz gun.

WEPAC09

A Temperature-Mapping System for Multi-Cell SRF Accelerator Cavities

805

G.M. Ge, G.H. Hoffstaetter
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

A Temperature mapping (T-map) system for Superconducting Radio Frequency (SRF) cavities consists of a thermometer array positioned precisely on an exterior cavity wall, capable of detecting small increases in temperature; therefore it is a powerful tool for research on the quality factor (Q0) of SRF cavities. A new multi-cell T-mapping system is has been developed at Cornell University. The system has nearly two thousand thermometers to cover 7-cell SRF cavities for Cornell’s ERL project. A new multiplexing scheme was adopted to reduce number of wires. A 1mK resolution of the temperature increase ΔT is achieved. A 9-cell cavity of TESLA geometry was tested with the T-map system. By converting ΔT to power loss and quality factor, it has been found that for this cavity, most surface losses were generated by the first cell when the accelerating gradient is increased above 15MV/m. Effective and intuitive ways of displaying surface properties of the cavity interior, e.g. the residual resistivity, will be shown.

WEPAC10

Investigation of the Surface Resistivity of SRF Cavities via theHEAT and SRIMP Program as well as the Multi-cell T-Map System

808

G.M. Ge, G.H. Hoffstaetter
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

A high-sensitive temperature mapping system for multi-cell SRF cavities has been constructed at Cornell University. The resolution of the system is 1mK. Hence it’s able to detect small temperature increases when cavities reach at low accelerating gradients e.g. 3MV/m. The surface resistivity of superconductor under radio-frequency electromagnetic field can be calculated from the temperature increases. In this contribution, the surface resistance map of multi-cell SRF cavities is shown. The temperature mapping result is possible to establish a relationship between the surface resistivity and the magnetic field as well. Unlike the RF method which is average value of the surface resistance, the T-map results give local surface resistivity versus magnetic field. BCS theory assumes the surface resistivity is independent to the magnetic field. The T-map results, however, suggest that the surface resistance at high-loss region is field dependent and caused Q-slope.

WEPAC11

Cornell's Main Linac Cryo-module Prototype

811

R.G. Eichhorn, G.M. Ge, Y. He, G.H. Hoffstaetter, M. Liepe, T. O'Connel, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: Supported by NSF award DMR-0807731
In preparation to built an energy-recovery linac (ERL) based synchrotron-light facility at Cornell University which can provide greatly improved X-ray beams due to the high electron-beam quality that is available from a linac, a phase 1 R&D program was launched, adressing critical challenges in the design. One of them being a full linac cryo-module, housing 6 superconducting cavities (operated at 1.8 K in cw mode), 7 HOM absorbers and 1 magnet/ BPM section. The final design will be presented and a report on the fabrication status that started in late 2012 will be given

WEPAC12

Theoretical Description of SIS Multilayer Films for SRF Cavities

814

S. Posen, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
G. Catelani
Forschungszentrum Jülich, Peter Gruenberg Institut (PGI-2), Jülich, Germany
J.P. Sethna
Cornell University, Ithaca, New York, USA
M.K. Transtrum
M.D.A.C.C., Houston, Texas, USA

As surface magnetic fields in niobium superconducting RF (SRF) cavities prepared with modern techniques approach the fundamental limit of niobium’s superheating field, SRF researchers are looking to alternative superconductors to sustain even higher fields. However, the short coherence length of these superconductors may represent a critical vulnerability to vortex penetration at very small defects in the surface. A. Gurevich has proposed* a method of defeating this vulnerability: coating a bulk superconducting cavity with a series of very thin insulating and superconducting films. In this work, we present a thorough mathematical description of the SIS thin films proposed by Gurevich in the language of the accelerator community, to help researchers to optimize cavities made from alternative superconductors.
* A. Gurevich, Appl. Phys. Lett. 88, 012511 (2006)

WEPAC13

Achieving High Accuracy in Cornell's ERL Cavity Production

817

R.G. Eichhorn, B. Bullock, B. Clasby, J.J. Kaufman, B.M. Kilpatrick, S. Posen, J. Sears, V.D. Shemelin
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
T. Kürzeder
TU Darmstadt, Darmstadt, Germany

Funding: Supported by NSF award DMR-0807731
The phase 1 R&D program launched in preparation to building a 5 GeV Enery Recovery Linac (ERL) at Cornell, a full main linac cryomodule is currently built, housing six 7-cell cavities. In order to control the beam break-up limit, the shape of the cavity was highly optimized and stringent tolerances on the cavity production were targeted. We will report on the details of the cavity production, the accuracy of the cups forming the individual cells, the trimming procedure for the dumbbells, the cavity tuning and final accuracy of the cavity concerning field flatness, resonant frequency and overall length within this small series production.

WEPAC14

Studies of the Superconducting Traveling Wave Cavity for High Gradient Linac

820

P.V. Avrakhov, A. Kanareykin, R.A. Kostin
Euclid TechLabs, LLC, Solon, Ohio, USA
N. Solyak, V.P. Yakovlev
Fermilab, Batavia, USA

Use of a traveling wave (TW) accelerating structure with a small phase advance per cell rather than a standing wave structure may provide a significant increase of the accelerating gradient in superconducting linacs. For the same surface electric and magnetic fields the TW achieves an accelerating gradient 1.2/1.4 larger than TESLA-like standing wave cavities [1]. Recent tests of L-band model of a single-cell cavity with waveguide feedback [2] demonstrated an accelerating gradient comparable to the gradient in a single-cell ILC-type cavity from the same manufacturer. This article presents the next stage of development of the TW resonance ring with 3-cell accelerating cavity which supposed to test in traveling wave regime. The main simulation results of the microphonics and Lorentz force detuning are also considered.

WEPAC17

Study on Particulate Retention on Polished Niobium Surfaces after BCP Etching

823

I.M. Malloch, C. Compton, L. Popielarski
FRIB, East Lansing, Michigan, USA

Funding: This material is based upon work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE SC0000661, the State of Michigan and Michigan State University.
Niobium surface defects and inclusions can be introduced during the manufacturing processes used in the production of SRF cavities. Bulk removal methods (sanding, polishing, etc…) are frequently utilized to remove or smooth away these defects on the surface of the niobium metal. It is hypothesized that these mechanical removal methods are capable of trapping performance-degrading particulates, which are then exposed during subsequent chemical processing, potentially contaminating the cavity prior to RF testing. This paper summarizes results of a series of surface roughness and etching experiments performed to determine the relationship between the extent of polishing and trapped particulate, and to determine a method for mitigating this particulate contamination through BCP etching. The relationship between these experiments and RF cavity performance will be explored as well.

WEPAC18

SRF Cavity Etching Developments for FRIB Cavity Processing

826

K. Elliott
NSCL, East Lansing, Michigan, USA
I.M. Malloch, L. Popielarski, N. Putnam
FRIB, East Lansing, Michigan, USA

Funding: This material is based upon work supported by the U.S. Department of Energy Office of Science under cooperative agreement DE-SC0000661.
Updates to the FRIB β=0.53 half wave resonator (HWR) design have provided an opportunity to test new buffered chemical polish (BCP) flow control techniques. New processing fixtures have been fabricated and used to process the FRIB β=0.53 HWR. This paper will present details of the fixture mechanical design iterations, the resulting BCP flow simulations, a qualitative evaluation of the agreement between simulations and measured results, and developments in process validation techniques.

WEPAC20

Magnetic Shield Optimization for the FRIB Superconducting Quarter-Wave Resonator Cryomodule

829

Y. Xu, A.D. Fox, M.J. Johnson, M. Leitner, S.J. Miller, K. Saito
FRIB, East Lansing, Michigan, USA

The Facility for Rare Isotope Beams (FRIB) requires 49 cryomodules containing 330 superconducting low-beta cavities, which have to be shielded from the earth magnetic field. Comprehensive magnetic shielding simulations have been conducted for 80.5 MHz β=0.085 cryomodules exposed to earth fields of 0.5 Gauss in different coordinate directions. The magnetic shield has to attenuate the earth magnetic field by a minimum factor of 33 (to less than 15 milli Gauss) in order to limit flux trapping in the cavities during cool-down. In the reported optimization studies, the permeability of the magnetic shielding material, shield thickness, and number of magnetic shield layers have been varied. Different design concepts including global and local magnetic shielding have been evaluated. In addition, the design concepts are compared based on the cost of material, fabrication and assembly, the design complexity and compatibility with the overall cryomodule design to obtain an optimum solution.

WEPAC21

Tuning Process of SSR1 Cavity for Project X at FNAL

832

P. Berrutti, M.H. Awida, T.N. Khabiboulline, D. Passarelli, L. Ristori, V.P. Yakovlev
Fermilab, Batavia, USA

SSR1 is a family of single spoke resonators to be used in Project X at Fermi National Laboratory. These cavities operate in CW regime having nominal frequency of 325 MHz and optimal beta of 0.22. SSR1 cavities will accelerate H⁻ ions after the Half Wave Resonator (HWR) section from 9 MeV to 32 MeV. In the near future this cavity will be used in Project X Injector Experiment (PXIE), which contains the ion source, the LEBT, the MEBT, the RFQ of Project X, and a cryogenic temperature section, having one HWR and one SSR1 cryomodule. SSR1 cavities have been built and tested at FNAL, the preparation of these resonators includes RF tuning which is the main focus of this paper. The frequency of the cavity is carefully chosen prior to the vertical test, and it is adjusted before welding the helium vessel to obtain 325 MHz nominal frequency for the dressed cavity in operating conditions. Several SSR1 cavities have been tuned at FNAL, the procedure, the hardware and the data are presented.

WEPAC22

Single Spoke Resonator Inner Electrode Optimization Driven by Reduction of Multipoles

835

P. Berrutti, T.N. Khabiboulline, L. Ristori, N. Solyak, V.P. Yakovlev
Fermilab, Batavia, USA

Accelerating cavities based on coaxial resonators, half wave and spoke resonators for example, do not have azimuthal symmetry. This lack of symmetry introduces a transverse field perturbation which affects the beam dynamic, since the particles traveling through the structure are crossing two accelerating gaps separated by the inner electrode. The field asymmetry induces an asymmetric transverse momentum gain which, once expanded in multipoles, appears to be due to a quadrupole perturbation. Depending on the cavity geometry and particle velocity, the influence of electric and magnetic fields may vary quite significantly. A way of having symmetric transverse fields in spoke resonators consists in modifying the inner electrode from a pole to an X or Y shape. The application of these changes symmetrizes both electric and magnetic fields and reduces the multipoles amplitudes to negligible values. This paper presents the study aimed to reduce the multi-poles amplitudes of SSR2 cavity for Project X; the presented procedure, in general, is valid for any spoke cavity.

WEPAC23

Multipacting Simulations of SSR2 Cavity at FNAL

838

P. Berrutti, T.N. Khabiboulline, L. Ristori, G.V. Romanov, A.I. Sukhanov, V.P. Yakovlev
Fermilab, Batavia, USA

SSR2 is the second family of single spoke resonator under development at Fermi National Accelerator Laboratory (FNAL). These cavities will be placed in Project X front-end after SSR1 spoke resonators, which have already been built and tested and FNAL. Spoke cavities are affected by multipacting and the nature of their 3D geometry does not allow simulating the multipactor process using 2D tools. 3D tracking simulations, of electrons inside the cavity volume, have been carried out using CST Particle Studio. Different Secondary Emission Coefficients have been applied to the cavity walls in order to understand how strongly the multipacting depends on material properties. The power levels used in simulations cover the whole operating gradient range of SSR2 cavity. Results of these simulations are compared to the one given by SSR1 model, which demonstrated good agreement with experimental data. The purposes of this paper are to present the results gotten from the tracking solver, to give a prediction of what will be the multipacting scenario for SSR2 cavity and if there will be any dangerous zone for operation.

WEPAC25

New Helium Vessel and Lever Tuner Designs for the 650 MHz Cavities for Project X

841

I.V. Gonin, M.H. Awida, E. Borissov, M.H. Foley, C.J. Grimm, T.N. Khabiboulline, M. Merio, Y.M. Pischalnikov, L. Ristori, V.P. Yakovlev
Fermilab, Batavia, USA

The design of 5-cell elliptical 650 MHz β=0.9 cavities to accelerate H⁻ beam of 1 mA average current in the range 467-3000 MeV for the Project X Linac is currently under development at Fermilab. A new design of the Helium Vessel (HV) was developed for these cavities with the main goal of optimizing the frequency sensitivity df/dP by keeping the cavity stiffness reasonably small. We also present a design of the new lever tuner system. The HV in the new design is equipped with the tuner located at the end of the cavity instead of the initially proposed blade tuner located in the middle. We will present mechanical design results and ANSYS analyses for both the slow and fast tuners.

WEPAC29

CM2, Second 1.3GHz Cryomodule Fabrication at Fermilab

844

T.T. Arkan, M.H. Awida, P. Berrutti, E. Borissov, C.M. Ginsburg, C.J. Grimm, E.R. Harms, A. Hocker, T.N. Khabiboulline, Y.O. Orlov, T.J. Peterson, R.V. Pilipenko, Y.M. Pischalnikov, K.S. Premo, L. Ristori, W. Schappert, V.P. Yakovlev
Fermilab, Batavia, USA

Funding: US Department of Energy
CM2 is the second 1.3GHz Cryomodule assembled at the Cryomodule Assembly Facility (CAF) in Fermi National Accelerator Laboratory. The string has a doublet magnet, beam position monitor and eight cavities. All the cavities are qualified at 35 MV / m gradient at the Horizontal Test Facility before assembly. The dressed cavities were outfitted with magnetic shielding, blade tuner, and the cold mass was assembled based on the Tesla TTF Type III+ cryomodule design. CM2 is currently being installed into the test stand in NML where it will be cooled down and high power tested. CM2 will also be the first cryomodule that an electron beam will be put through at the NML facility. This will be a proof of principle for the planned Advanced Superconducting Test Accelerator (ASTA) facility at NML. This paper describes the assembly steps, the quality assurance methods and the challenges that we experienced during assembly and qualification steps at CAF. De

WEPAC32

Wakefield Loss Analysis of the Elliptical 3.9 GHz Third Harmonic Cavity

847

M.H. Awida, P. Berrutti, T.N. Khabiboulline, A. Saini, V.P. Yakovlev
Fermilab, Batavia, USA

Third harmonic 3.9 GHz elliptical cavities are planned to be used in many particle accelerator projects such as XFEL, NGLS, and ASTA. In this paper, the wakefield losses due to single bunch passage are analysed considering bunches of RMS length 8 mm down to ultra short ones of 10 μm length. Both the loss and kick factors are numerically calculated for bunches of relatively long length (>1 mm) using CST wakefield solver. The data is then used to extrapolate asymptotically the values for ultra-short bunches by finding the wake functions. These calculations are essential to estimate the cryogenic losses in cryomodules and for beam dynamic analysis.

WEPAC33

Results of the New High Power Tests of Superconducting Photonic Band Gap Structure Cells

850

E.I. Simakov, S. Arsenyev, W.B. Haynes, S.S. Kurennoy, D. C. Lizon, J.F. O'Hara, E.R. Olivas, D.Y. Shchegolkov, N.A. Suvorova, T. Tajima
LANL, Los Alamos, New Mexico, USA
S. Arsenyev
MIT/PSFC, Cambridge, Massachusetts, USA
C.H. Boulware, T.L. Grimm
Niowave, Inc., Lansing, Michigan, USA

Funding: This work is supported by the Department of Defense High Energy Laser Joint Technology Office through the Office of Naval Research.
We present an update on the 2.1 GHz superconducting rf (SRF) photonic band gap (PBG) resonator experiment in Los Alamos. The new SRF PBG cell was designed with the particular emphasis on changing the shape of PBG rods to reduce the peak magnetic fields and at the same time to preserve its effectiveness for suppression of the higher order modes (HOMs). The new PBG cells have great potential for outcoupling long-range wakefields in SRF accelerator structures without affecting the fundamental accelerating mode. Using PBG structures in superconducting particle accelerators will allow operation at higher frequencies and moving forward to significantly higher beam luminosities thus leading towards a completely new generation of colliders for high energy physics. Here we report the results of our efforts to fabricate 2.1 GHz PBG cells with elliptical rods and to test them with high power in a liquid helium bath at the temperature of 2 Kelvin. The high gradient performance of the cells will be evaluated and the results will be compared to electromagnetic and thermal simulations.

WEPAC34

Update on the Design of a Five-Cell Superconducting RF Module with a PBG Coupler Cell

853

S. Arsenyev
MIT/PSFC, Cambridge, Massachusetts, USA
E.I. Simakov
LANL, Los Alamos, New Mexico, USA

Funding: This work is supported by the U.S. Department of Energy (DOE) Office of Science Early Career Research Program.
We present a complete design of the 5-cell superconducting accelerating module incorporating a Photonic Band Gap (PBG) cell with couplers. The purpose of the PBG cell is to achieve better Higher Order Mode (HOM) damping which is vital for preserving the quality of high-current electron beams in novel linear accelerators. The PBG technology can therefore be used for X-band free electron lasers. We first discuss the engineering aspects of incorporating a PBG cell in a superconducting PBG module. The main concern is to ensure the equal probability of quench is in each of the five cells, which leads to significant geometry modifications. We then present the simulation data on the HOM damping. Particularly, we calculate the external quality factors for the 10 most dangerous HOMs for this particular structure. Performance of different couplers and different modifications of the PBG lattice are discussed. Thermal analysis of the structure is also discussed briefly.

WEPAC35

Initial Studies of Multipactor Suppression Via TE and TM Modes

856

S.A. Rice, J.P. Verboncoeur
Michigan State University, East Lansing, USA

Funding: Work supported by U.S. Air Force Office of Scientific Research (AFOSR) grant on the Basic Physics of Distributed Plasma Discharges.
The formation of multipactor is strongly dependent upon the secondary electron yield (SEY) of a surface, and the emission velocities of the emitted electrons, in addition to the electric field. Since the secondary electron yield (SEY) of a material is dependent upon the kinetic energy and impact angle of the incident electron, we investigate use TE and TM coaxial cavity modes to modify the impacting electron velocities to reduce the average SEY and suppress multipactor, which builds upon our previous work examining TEM modes.

WEPAC39

Tests of an RF Dipole Crabbing Cavity for an Electron-Ion Collider

859

A. Castilla, J.R. Delayen
ODU, Norfolk, Virginia, USA
A. Castilla, J.R. Delayen
JLAB, Newport News, Virginia, USA
A. Castilla
DCI-UG, León, Mexico

On the scheme of developing a medium energy electron-ion collider (MEIC) at Jefferson Lab, we have designed a compact superconducting rf dipole cavity at 750 MHz to crab both electron and ion bunches and increase luminosities at the interaction points (IP) of the machine. Following the design optimization and characterization of the electromagnetic properties such as peak surface fields and shunt impedance, along with field nonuniformities, multipole components content, higher order modes (HOM) and multipacting, a prototype cavity was built by Niowave Inc. The 750 MHz prototype crab cavity has been tested at 4 K and is ready for re-testing at 4 K and 2 K at Jefferson Lab. In this paper we present the detailed results of the rf tests performed on the 750 MHz crab cavity prototype.

WEPAC40

Mechanical Analysis of the 400 MHz RF-Dipole Crabbing Cavity Prototype for LHC High Luminosity Upgrade

862

S.U. De Silva, J.R. Delayen, H. Park
ODU, Norfolk, Virginia, USA
S.U. De Silva, J.R. Delayen, H. Park
JLAB, Newport News, Virginia, USA
Z. Li
SLAC, Menlo Park, California, USA

The proposed LHC high luminosity upgrade requires two crabbing systems in increasing the peak luminosity, operating both vertically and horizontally at two interaction points of IP1 and IP5. The required system has tight dimensional constraints and needs to achieve higher operational gradients. A proof-of-principle 400 MHz crabbing cavity design has been successfully tested and has proven to be an ideal candidate for the crabbing system. The cylindrical proof-of-principle rf-dipole design has been adapted in to a square shaped design to further meet the dimensional requirements. The new rf-dipole design has been optimized in meeting the requirements in rf-properties, higher order mode damping, and multipole components. A crabbing system in a cryomodule is expected to be tested on the SPS beam line prior to the test at LHC. The new prototype is required to achieve the mechanical and thermal specifications of the SPS test followed by the test at LHC. This paper discusses the detailed mechanical and thermal analysis in minimizing Lorentz force detuning and sensitivity to liquid He pressure fluctuations.

WEPAC41

Comparison of Electromagnetic, Thermal and Mechanical Calculations with RF Test Results in RF-Dipole Deflecting/Crabbing Cavities

865

H. Park, S.U. De Silva, J.R. Delayen
JLAB, Newport News, Virginia, USA
S.U. De Silva, J.R. Delayen, H. Park
ODU, Norfolk, Virginia, USA

The current requirements of higher gradients and strict dimensional constraints in the emerging applications have required the designing of compact deflecting and crabbing rf structures. The superconducting rf-dipole cavity is one of the first novel compact designs with attractive properties such as higher gradients, higher shunt impedance and widely separated higher order modes. The recent tests performed on proof-of-principle designs of the rf-dipole geometry at 4.2 K and 2.0 K in a vertical test assembly have proven the designs to achieve higher gradients with higher intrinsic quality factors and easily processed multipacting conditions. The design frequency sensitivity to pressure (df/dp) due to liquid He pressure fluctuations, Lorentz force detuning due to radiation pressure, and thermal and mechanical effects have also been measured during the tests. These effects lead to cavity frequency detuning while in operation and therefore needs to be reduced. This paper presents the detailed comparison of the measurement to the simulation results obtained from ANSYS.

WEPAC42

Geometry Effects on Multipole Components and Beam Optics in High-Velocity Multi-Spoke Cavities

868

C.S. Hopper, K.E. Deitrick, J.R. Delayen
ODU, Norfolk, Virginia, USA
J.R. Delayen
JLAB, Newport News, Virginia, USA

Velocity-of-light, multi-spoke cavities are being proposed to accelerate electrons in a compact light-source [1]. There are strict requirements on the beam quality which require that the linac have only small non-uniformities in the accelerating field. Beam dynamics simulations have uncovered varying levels of focusing and defocusing in the proposed cavities, which is dependent on the geometry of the spoke in the vicinity of the beam path. Here we present results for the influence different spoke geometries have on the multipole components of the accelerating field and how these components, in turn, impact the simulated beam properties.
* T. Satogata et al, “Compact Accelerator Design for a Compact Light Source,” IPAC13, Shanghai, China, May 2013.

WEPAC43

Study of Cavity Imperfection Impact on RF-Parameters and Multipole Components in a Superconducting RF-Dipole Cavity

871

R.G. Olave, S.U. De Silva, J.R. Delayen
ODU, Norfolk, Virginia, USA
Z. Li
SLAC, Menlo Park, California, USA

Funding: This work is funded by the US/LHC LARP program.
The ODU/SLAC superconducting rf-dipole cavity is under consideration for the crab-crossing system in the upcoming LHC luminosity upgrade. While the proposed cavity complies well within the rf-parameters and multipolar component restrictions for the LHC system, cavity imperfections arising from cavity fabrication, welding and frequency tuning may have a significant effect in these parameters. We report on an initial study of the impact of deviation from the ideal shape on the cavity’s performance in terms of rf-parameters and multipolar components.

WEPAC44

Higher Order Modes Damping and Multipacting Analysis for the SPX Deflecting Cavity in APS Upgrade

874

C.-K. Ng, Z. Li, L. Xiao
SLAC, Menlo Park, California, USA
A. Nassiri, G.J. Waldschmidt, G. Wu
ANL, Argonne, USA
R.A. Rimmer, H. Wang
JLAB, Newport News, Virginia, USA

Funding: Work supported by US DOE under contract number DE-AC02-06CH11357.
A single-cell superconducting deflecting cavity operating at 2.815 GHz has been proposed and designed for the Short Pulse X-ray (SPX) project for the Advanced Photon Source (APS) upgrade. Each deflecting cavity is equipped with one fundamental power coupler (FPC), one lower order mode (LOM) coupler, and two higher order mode (HOM) couplers to achieve the stringent damping requirements for the unwanted modes. Using the electromagnetic simulation suite ACE3P, HOM damping will be calculated for the cavity including the full engineering design waveguide configurations and rf windows. Trapped modes in the bellows located in the beampipes connecting the cavities in a cryomodule will be computed and their effects on heating evaluated. Furthermore, multipacting activities at the end groups of the cavity will be identified to assess possible problems during high power processing.

WEPAC46

Wakefield Computations for a Corrugated Pipe as a Beam Dechirper for FEL Applications

877

C.-K. Ng, K.L.F. Bane
SLAC, Menlo Park, California, USA

Funding: Work supported by the US DOE under contract DE-AC02-76SF00515.
A beam “dechirper” based on a corrugated, metallic vacuum chamber has been proposed recently to cancel residual energy chirp in a beam before it enters the undulator in a linac-based X-ray FEL*. Rather than the round geometry that was originally proposed, we consider a pipe composed of two parallel plates with corrugations. The advantage is that the strength of the wake effect can be tuned by adjusting the separation of the plates. The separation of the plates is a few millimeters, and the corrugations are fractions of a millimeter in size. The dechirpers need to be meters long in order to provide sufficient longitudinal wakefield to cancel the beam chirp. Considerable computation resources are required to determine accurately the wakefield for such a long structure with small corrugation gaps. Combining the moving window technique and parallel computing using multiple processors, the parallel finite-element electromagnetic suite ACE3P allows efficient determination of the wakefield through convergence studies. In this paper, we will calculate the longitudinal, dipole and quadrupole wakefields for the dechirper and compare the results with those of analytical approaches.
* K.L.F. Bane, G. Stupakov, Nucl. Instrum. Meth. A690 (2012) 106-110.

WEPAC47

Mechanical Design of a New Injector Cryomodule 2-Cell Cavity at CEBAF

880

G. Cheng, J. Henry, J.D. Mammosser, R.A. Rimmer, H. Wang, M. Wiseman, S. Yang
JLAB, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
As a part of Jefferson Lab’s 12 GeV upgrade, a new injector superconducting RF cryomodule is required. This unit consists of a 2-cell and 7-cell cavity, with the latter being refurbished from an existing cavity. The new 2-cell cavity requires electromagnetic design and optimization followed by mechanical design analyses. The electromagnetic design is reported elsewhere. This paper aims to present the procedures and conclusions of the analyses on cavity tuning sensitivity, pressure sensitivity, upset condition pressure induced stresses, and structural vibration frequencies. The purposes of such analyses include: 1) provide reference data for cavity tuner design; 2) examine the structural integrity of the cavity; and 3) evaluate the 2-cell cavity’s resistance to microphonics. Design issues such as the location of stiffening rings, effect of tuner stiffness on cavity stress, choice of cavity wall thickness, etc. are investigated by conducting extensive finite element analyses. Progress in fabrication of the 2-cell cavity is also reported.
The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes.