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All SPIRAL2 cryomodules (twelve with one quarter wave resonator (QWR) at β=0.07 and seven with two QWRs at β=0.12) have been produced and qualified, and are now in installation phase on the LINAC at GANIL. After a general introduction on the LINAC, we will first remember and compare the different design choices taken for the two families of cryomodules. We will then present a summary of the techniques used for the preparation and integration of the cavities in the cryomodules, and compare the achieved performances with design parameters. At last, we describe the status of the LINAC installation as of end of August 2015., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

The publication will describe the comprehensive program and results of RF measurements taken during the mass production of superconducting cavities for the European XFEL., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

The most demanding component of a continuous wave (cw) injector is cw operating RF-gun, delivering highly populated low emittance bunches. RF-guns, both working at room temperature and superconducting, when they generate highly populated low emittance bunches have to be operated at high accelerating gradients to suppress space charge effects diluting emittance. Superconducting RF-guns are technically superior to the normal conducting devices because they dissipate orders of magnitude less power when operating at very high gradients in cw mode. In this contribution progress since 2013 in the R&D programs, designing and operation of the SRF-injectors at KEK, HZB, HZDR, PKU and DESY will be discussed., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

Recent results from the bulk niobium high-gradient cavity development program at CERN are presented, with particular focus on test results for the 704 MHz bulk niobium 5-cell elliptical cavity prototypes produced for the Superconducting Proton Linac (SPL) project. Successive cold tests of bare cavities have been used to refine the cavity preparation and testing process, with all steps done in-house at CERN. Current performance results are discussed with reference to observables such as ambient magnetic field, field emission levels, and quenches., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

The ARIEL e-Linac RF deflecting cavity is a 650 MHz superconducting deflecting mode cavity that will allow simultaneous beam delivery to both the Rare Isotope Beam program and an Energy Recovery Linac. The cavity will be operated at 4 K and with deflecting voltages of up 0.6 MV, resulting in a dissipated RF power of less than 1 W. Due to the modest performance requirements, alternative methods are being employed for the fabrication of this cavity. These include fabricating the entire cavity from reactor grade Niobium and welding the cavity using tungsten inert gas (TIG) welding in a high purity Argon environment. A post purification heat treatment will be performed in an RF induction oven to increase the cavity performance., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

INFN Milano – LASA is involved in the development and industrialization for the production of 704.4 MHz medium beta (β = 0.67) cavities for the ESS project. In this framework, we are designing a medium beta prototype cavity exploring both Large Grain and Fine Grain Niobium for its production as well as a high beta (β = 0.86) Large Grain cavity. In the meanwhile, an activity is ongoing for upgrading the LASA test facility to be able to test these kind of resonators., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

For the European XFEL superconducting Cavity series production at both cavity vendors’ four manufacturing machines for production key functions, HAZEMEMA and CTM, are supplied by DESY. Among three years of cavity production in two companies a lot of experience is gathered about influence of surroundings and production quality on cycle times, machine drop outs, general stability time of machines and parts subject to wear. Significant factors on cycle time for tuning operation like temperature stability and drift during tuning and measurements, precision of cell trimming before welding and tuning and generally geometrical factors are shown. RF aspects of tuning and production quality control as additional measurements for TM011-mode to estimate quality of its damping is presented. Performed full Cavity RF measurements exceeds XFEL specifications gives a possibility for additional quality control on welding shrinkage stability and it’s homogeneously distribution. The use of HAZEMEMA and CTM to assess the impact of asymmetric trimming, including calculation of it’s influence on the higher-order modes, is shown., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

The Lorentz detuning is the resonant frequency change in an RF cavity due to the radiation pressure on the cavity walls. We present benchmarking studies of Lorentz detuning calculations for a Double-Quarter Wave Crab Cavity (DQWCC) using the codes ACE3P. The results are compared with the Lorentz detuning measurements performed during the cold tests of the Proof-of-Principle DQWCC at BNL., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

A 56 MHz superconducting RF cavity has been designed, fabricated and installed in the Relativistic Heavy Ion Collider (RHIC). The cavity operates at 4.4 K with a “quiet helium source” to isolate the cavity from environmental acoustic noise. The cavity is a beam driven quarter wave resonator. It is detuned and damped during injection and acceleration cycles and is brought to operation only at store energy. We have observed clear luminosity increase and bunch length reduction in the first operation of the cavity with Au + Au and Au + He3 collisions. The cavity voltage was limited by quenching in the Higher Order Mode coupler. This paper also discusses the cavity beam experiments with no higher order mode coupler in p + p and p + Au RHIC operation., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

Inspection of the inner cavity surface by an optical system is an inexpensive and useful means for surface control and identification of critical or suspicious features. Optical inspection of around 100 EXFEL series and ILC-HiGrade cavities has been performed recently using the high-resolution OBACHT system. It is a semi-automated tool based on the Kyoto camera. To gain information about the 3D topography of surface features or defects, a replica technique has been applied additionally. This is a non-destructive surface-study method reaching resolution down to 1 μm by imprinting the details of the surface onto a hardened rubber. The footprint is subsequently investigated with a microscope or profilometer. Based on these studies, several defects on the surface have been found and classified. Most of the cavity failures leading e.g. to field limitations below 20 MV/m have been identified and corresponding feedback given to the production cycle. Typical surface features and defects as well as their influence on the cavity performance will be presented and discussed., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

In order to guaranty a sufficient High Order Modes (HOM) damping in the European XFEL cavities, a detailed analysis of the mechanical cavity production was performed. The mechanical measurements are precise enough to control the shape of cavity parts, but cannot be used for a welded cavity. To estimate the shape deformation during equator welding, the eigenfrequencies of cavity cells are compared with frequencies of cavity parts. This simple RF analysis can indicate irregularity of 9 equator welds and was used in addition to control of mean values for longitudinal and transverse deformations., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

In KEK-CFF, L-band SRF cavity fabrication studies have been actively proceeded. Main target of the R&D is investigation of cavity fabrication methods using different Nb materials. In this talk, we report mainly focus on the experiences obtained from single cell cavity fabrications. First, different Nb materials are compared, between fine grain Nb and large grain(LG) Nb from different vendors including low RRR LG Nb, in which, cavities were fabricated by electron beam welding method. Difficulty on LG cavity fabrication come from deformation due to stressed grain boundaries. In addition to nominal electron beam welded cavities, hydro-formed seamless cavities have been fabricated. Relatively large difference of equator and iris ratio cause difficulty on expansion of Nb pipes. Good qualified Nb pipe is essential and control of hydro-forming steps including annealing of materials is also important. In order to evaluate these cavity performances, vertical tests were carried out. Generally, they showed good performances. In this presentation, fabrication processes, technical difficulties, mitigation strategies and vertical test results are presented., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

Quench location detection has provided valuable insight in SRF cavity operation since two decades. While in earlier days temperature maps were used the state of the art technique nowadays is detecting the second sound wave, excited by a quench, using oscillating super-leak detector (OSTs). Typically, many OSTs surround the cavity and the quench location is determined by triangulation of the different OST signals. Convenient as the method is there is a mystery: taking the well-known velocity of the second sound wave, the quench seems to come from a place slightly above the cavity’s outer surface. In addition, not all triangulation spheres intersect in one point. We will present a model based on numerical quench propagation simulations that is able to fully explaining this discrepancy., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

An alternative fabrication method for superconducting radio frequency (SRF) cavities is presented. The novel fabrication method, based on 3D printing (or additive manufacturing, AM) technology capable of producing net-shape functional metallic parts of virtually any geometry, promises to greatly expand possibilities for advance cavity and end-group component designs. A description of the AM method and conceptual cavity designs are presented along with material analysis and RF measurement results of additively manufactured niobium samples., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

A full-scale model of the double-quarter-wave (DQW) cavity towards the High-Luminosity Large Hadron Collider (HL-LHC) upgrade was built in aluminum to characterize the deflecting mode. Field strength measurements have been carried out for both the transverse and longitudinal electromagnetic fields, by using the bead-pull technique. Perturbation objects of different shapes and material were used to separate the electric and magnetic field components. A reasonably good agreement was found between numerical simulation and measurements, which confirm the reliability and accuracy of the measurements done., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

The development of an x-ray fluorescence probe for detection of foreign material inclusions of the inner surface of 1.3 GHz tesla-type Niobium cavities is here presented. The setup dimensions are minimized so to access the inner cavity volume and focus on the surface of equator. Preliminary tests confirmed the system capability to detect and localize with good precision small metal inclusions of few micrograms. The results obtained from the inspection of some 1.3 GHz XFEL series production cavities are also pointed out., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

Three proof-of-principle compact crab cavity designs have been fabricated in bulk niobium and cold tested at their home labs, as a first validation step towards the High Luminosity LHC project. As a cross check, all three bare cavities have been retested at CERN, in order to cross check their performance, and cross-calibrate the CERN SRF cold test facilities. While achievable transverse deflecting voltage is the key performance indicator, secondary performance aspects derived from multiple cavity monitoring systems are also discussed. Temperature mapping profiles, quench detection, material properties, and trapped magnetic flux effects have been assessed, and the influence on performance discussed. The significant effort invested in developing expertise in preparation and testing of these crab cavities has already been fruitful for all partners, and more is to come within this ongoing program., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

We have designed, fabricated and tested two new half-wave resonators following the successful development of a series of niobium superconducting quarter-wave cavities. The half-wave resonators are optimized for β = 0.11 ions, operate at 162.5 MHz and are intended to provide up to 2 MV effective voltage for particles with the optimal velocity. Testing of the first two half-wave resonators is complete with both reaching accelerating voltages greater than 3.5 MV with low-field residual resistances of 1.7 and 2.3 nΩ respectively. The intention of this paper is to provide insight into how Argonne achieves low-residual resistances and high surface fields in low-beta cavities by describing the cavity design, fabrication, processing and testing., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

New auxiliary components have been designed and fabricated for the 1.3 GHz SRF cavities comprising the LCLS-II linac. In particular, the LCLS-II cavity’s helium vessel, high-power input coupler, higher-order mode (HOM) feedthroughs, magnetic shielding, and cavity tuning system were all designed to meet LCLS-II specifications. Integrated tests of the cavity and these components were done at Fermilab’s Horizontal Test Stand (HTS) using several kilowatts of continuous-wave (CW) RF power. The results of the tests are summarized here., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

The proposed design of the 0.8 GeV PIP-II SC Linac employs two families of 650 MHz 5-cell elliptical cavities with 2 different beta. The β=0.61 will cover the 185-500 MeV range and the β=0.92 will cover the 500-800 MeV range. In this paper we will present update of RF and mechanical design of dressed high beta cavity (β=0.92) for pulse regime of operation at 2 mA beam current. In previous CW version of PIP-II project the mechanical design was concentrated on minimization of frequency shift due to helium pressure fluctuation. In current case of pulse regime operation the main goal was Lorentz force detuning minimization. We present the scope of coupled RF-Mechanical issues and their resolution. Also detailed stress analysis of dresses cavity will be presented., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

The 10 cavities of the EXFEL 3rd Harmonic Cryomodule have been tested and qualified, before integration in the He-tank, in our upgraded Vertical Test stand. In this paper, we report the measured RF performance of these cavities together with the main features of the test facility., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

Serious albeit tiny surface defects can remain on the surface of superconducting radio frequency (SRF) cavities after polishing and cleaning. These defects reduce the efficiency of cavities and often limit the maximum attainable fields. We applied a Haar cascade artificial vision technique for automated identification, counting, and sizing of defects induced on niobium surface by Nb-H precipitates formed at cryogenic temperatures. The defects were counted and sized by a computer program and also counted and measured manually to estimate detection rate and accuracy of sizing. The overall detection rate was 53%, and the overall false positive rate was 29%. The technique that was used to automatically size the features was found to oversize the features, but oversize them consistently, resulting in a size histogram that represents the defect size distribution on the sample. After scaling the histogram data, the average defect area was found to be 90 square micrometers with the standard deviation of 70 square micrometers., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

17th International Conference on RF Superconductivity, SRF2015, Whistler, Canada, 13 Sep 2015 - 18 Sep 2015 ; 316-318(2015)., The main part of the su­per­con­duct­ing Eu­ro­pean XFEL lin­ear ac­cel­er­a­tor con­sists of 100 ac­cel­er­a­tor mod­ules each con­tain­ing eight RF-cav­i­ties. Be­fore the in­stal­la­tion to a mod­ule, all of these cav­i­ties will be tested at cryo­genic tem­per­a­tures in a ver­ti­cal cryo­stat in the ac­cel­er­a­tor mod­ule test fa­cil­ity (AMTF) at DESY. This paper dis­cusses the av­er­age ver­ti­cal test rate at the pre­sent sta­tus. It should be 1 in the ideal case, but ac­tu­ally it’s ob­served to be ap­prox­i­mately 1.5. Clas­si­fi­ca­tion and analy­sis con­cern­ing the rea­sons for this de­vi­a­tion are given as well as sug­ges­tions for a re­duc­tion of the test rate for fu­ture pro­duc­tion cy­cles.

The series production by two industrial vendors of the 800 1.3-GHz superconducting cavities for the European XFEL has been on-going since the beginning of 2013 and will conclude towards the end of this year. As of publication some 740 cavities (~93%) have been produced at an average rate of 6 cavities per week. As part of the acceptance testing, all cavities have undergone at least one vertical RF test at 2K at the AMTF facility at DESY. The acceptance criterion for module assembly is based on the concept of a “usable gradient”, which is defined as the maximum field taking into account Q0 performance and allowed thresholds for field emission, as well as breakdown limits. Approximate 20% of the cavities have undergone further surface treatment in the DESY infrastructure to improve their usable gradient performance. In this paper we present the performance statistics of the vertical test results, as well as an analysis of the limiting criteria for the usable gradient, and finally the impact of the surface retreatment on both usable gradient and Q0., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

For the application of high intensity continuous wave (CW) proton beam acceleration, a new superconducting accelerating structure for extremely low β proton working in TE210 mode has been proposed at Peking University. The cavity consists of eight electrodes and eight accelerating gaps. The RF frequency is 162.5MHz, and the designed proton input energy is 200keV. A peak field optimization has been performed for the lower surface field. The accelerating gaps are adjusted by phase sweeping based on KONUS beam dynamics. Solenoids are placed outside the cavity to provide transverse focusing. Numerical calculation shows that the transverse defocusing of the KONUS phase is about three times smaller than that of the conventional negative synchronous RF phase. The beam dynamics of a 10mA CW proton beam is simulated by the TraceWin code. The simulation results show that the beam’s size is under effective control. Both the simulation and the numerical calculation show that the cavity has a relatively high effective accelerating gradient of 2.6MV/m. Our results show that this new accelerating structure may be a possible candidate for superconducting operation at such a low energy range., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

In this paper we propose a high-precision method of measuring Q0 of SRF cavities. A common way to study the performance of an SRF cavity is to build an oscillator around it that is referred to as a self-exciting loop. In the standard approach, by tuning the loop phase for a maximum field level in the cavity and measuring forward and reflected waves, one finds the cavity coupling. Then, performing a time-decay measurement and finding the total quality factor, one gets Q0. However, this approach suffers from a deficiency originating from a single data-point measurement of the reflection coefficient. In our method by varying the loop phase shift, one obtains amplitudes of the reflection coefficient of the cavity as a function of its phases. The complex reflection coefficient describes a perfect circle in polar coordinates. Fitting the overdetermined set of data to that circle allows more accurate calculation of Q0 via the least-squares procedure. The method has been tested at the FREIA Laboratory on two cavities from IPN Orsay: a single spoke and a prototype ESS double spoke., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

3D simulations have been performed for a variety of SRF cavities which incorporate Higher Order Mode dampers, either in form of coaxial couplers or waveguide dampers. Instead of utilizing the rather standard approach of matching the output port of the dampers with a broadband coaxial or waveguide port, dissipative materials are modelled for RF field absorption. This for instance not only avoids the otherwise required definition of the number of modes considered for damping, which has an impact on the computational time, but also allows tailoring the load material to conform with experimental data of e.g. non-perfect absorbers. The new calculation scheme is presented. Findings are partially compared with those achieved with the standard waveguide port approach by means of external quality factors. CPU speeds are briefly discussed for both approaches., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

In order to validate the cavity package concept before the module preparation for the European XFEL Injector, one 3.9 GHz cavity, complete with magnetic shielding, power coupler and frequency tuner was tested in a specially designed single cavity cryomodule in one of the caves of the DESY Accelerator Module Test Facility (AMTF). The cavity was tested in high power pulsed operation up to the quench limit of 24 MV/m, above the vertical test qualifications and all subsystems under test (coupler, tuner, waveguide tuners, LLRF system) were qualified to design performances., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

DAE laboratories in India are involved in R&D activities on SRF cavity technology for the proposed high intensity proton linacs for ISNS/IADS and also FERMILAB PIP-II program under IIFC. VECC is responsible for design, analysis and development of a 650 MHz, β=0.61, 5-cell elliptical cavity. This paper describes the novel design of the cavity, with different aperture and wall angle, having better field flatness and mechanical stability, reliable surface processing facility and less beam loss. The cavity geometry has been optimized to get acceptable values of field enhancement factors, R/Q, Geometric factor, cell-to-cell coupling etc. The effective impedance of transverse and longitudinal HOMs are low enough to get rid of HOM damper for low beam current. 2-D analysis shows no possibility of multipacting. However, 3-D analysis using CST Particle Studio code confirms its presence and it can be suppressed by introducing a small convexity in the equator region. Two niobium half cells and beam pipes for the single cell cavity have been fabricated. Measurement and RF characterisation of half cells, prototype 1-cell and 5-cell and also 1-cell niobium cavities have been carried out., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

As part of the development of the ESS spoke linac, the FREIA Laboratory at Uppsala University, Sweden, has been equipped with a superconducting cavity test facility. The cryogenic tests of a single and double spoke cavity developed by IPN Orsay have been performed in the new HNOSS horizontal cryostat system. The cavities are equipped with a low power input antenna and a pick-up antenna. Different measurement methods were investigated to measure the RF signal coupling from the cavity. Results from the tests confirm the possibility to transport the cavities from France to Sweden without consequences. We present the methods and preliminary study results of the cavity performance., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

The ESS elliptical superconducting linac consists of two types of 704.42 MHz cavities, medium and high beta, to accelerate the beam from 216 MeV (spoke cavity linac) up to the full energy at 2 GeV. The last linac optimization, called Optimus+, has been carried out taking into account the limitations of SRF cavity performance (field emission). The medium and high-beta parts of the linac are composed of 36 and 84 elliptical cavities, with geometrical beta values of 0.67 and 0.86 respectively. We describe here the procedures and numerical analysis leading from half-cells to a complete medium cavity assembly, which take into account not only the frequency of the fundamental accelerating mode but also the higher order modes near the machine line. The half cell selection process to form dumb bells will be described, as well as the reshaping and trimming procedure., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

Final tuning and field profile characterization of SRF cavities always takes place at room temperature. However, important questions remains as to what happens when the cavity is cooled to LHe temperature, in particular with multi cell systems. To enable the characterization of cavities in the cold, we have designed and commissioned a "cold bead-pull" test stand at HZB. The present test stand is designed to be integrated in HoBiCaT (Horizontal bi-cavity testing facility) with the ability to provide electric field profile measurements under realistic superconducting conditions (T=1.8K). In this paper mechanical and operational details of the apparatus will be described as well as future plans for the development and usage of this facility., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

SRF Gun Cavity is an ongoing accelerator R&D project at DESY, being developed since several years. Currently several SRF Gun cavity prototypes were simulated, built and tested in our Lab and elsewhere. Lately the 1.6 cells Pb thin film cathode niobium cavity was tested in a vertical cryostat with a different cathode plug configurations. Cathode plug design was improved, as well as SRF Gun Cavity cleaning procedures. Results of the last cavity performance tests are presented and discussed., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

A compact detector and numerical algorithm for second sound measurements has been developed. The detector allows precise 3D quench localisation within a single unit and can be used even for cavities with mounted helium tank. The compact device is easily mounted and requires minimum space. It can be used as a part of the standard cold test of cavities. The results obtained with the new detector and a 3D algorithm have been cross-checked by optical inspection and resistor-based temperature mapping. The resolution of the detector is seen to be limited by the sampling rate and the lateral extent of the quench induced heated area on the Nb superconductor., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

For different design of ESS superconducting cavities, the higher order modes (HOM's) of monopoles, dipoles, quadrupoles and sextupoles are found. Their R/Q values are also calculated. Main HOM related issues are the beam instabilities and the HOM induced power especially from TM monopoles. The analysis for the beam induced HOM voltage and power in this paper showed that, if the HOM frequency is a few kHz away from the beam spectrum, it is not a problem. In order to understand the effects of the beam structure, analytic expressions are developed. With these expressions, the induced HOM voltage and power were calculated by assuming external Q for each HOM. Our analysis confirm that, with thebeam structure of ESS and a good cavity design, no special tight tolerances are required for cavity fabrication and no HOM couplers in the cavity beam pipes are planned., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

Currently most of Niobium (Nb) cavities are manufactured from fine grain Nb sheets. As-cast ingots go through a series of steps including forging, milling, rolling, and intermediate annealing, before they are deep-drawn into a half-cell shape and subsequently electron beam welded to make a full cavity. Tube hydroforming, a manufacturing technique where a tube is deformed using a pressurized fluid, is an alternative to the current costly manufacturing process. A whole cavity can be made from a tube using tube hydroforming. This study focuses on deformation of large grain Nb tubes during hydroforming. The crystal orientation of the grains is recorded. The tube is marked with a square-circle-grid which is used to measure the strain after deformation. The deformation of the tube is going to be modeled with crystal plasticity finite element and compared with experiments. This paper only covers the characterization of the tube and the hydroforming process., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

We report results of high-gradient testing of the first 5- cell superconducting radio frequency (SRF) module with a photonic band gap cell (PBG). Higher order mode (HOM) damping is vital for preserving the quality of high-current electron beams in novel SRF accelerators. Because HOMs are not confined by the PBG array, they can be effectively damped in order to raise the current threshold for beam instabilities. The PBG design increases the real-estate gradient of the linac because both HOM damping and the fundamental power coupling can be done through the PBG cell instead of via the beam pipe at the ends of the cavity. A superconducting multi-cell cavity with a PBG damping cell is therefore an attractive option for high-current linacs. The first-ever SRF multi-cell cavity incorporating a PBG cell was designed a LANL and built at Niowave Inc. The cavity was tuned to a desired gradient profile and underwent surface treatment at Niowave. A vertical test (VTS) was then performed at LANL, demonstrating an abnormally low cavity quality factor in the accelerating mode of 1.6*10⁶. Future tests are proposed to determine the source of the losses and resolve the problem., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

A 650 MHz SRF deflecting mode cavity has been designed for the ARIEL e-Linac to separate interleaved beams heading towards either Rare Ion Beam production or a recirculation loop for energy recovery, allowing the e-Linac to provide beam delivery to multiple users simultaneously. The cavity geometry has been optimized for the ARIEL specifications, resulting in a very compact cavity with high shunt impedance and low dissipated power. Analyses have been performed on the susceptibility to multipacting, input coupling considering beam loading and microphonics, and extensive studies into the damping of transverse and longitudinal higher order modes. The pressure sensitivity, frequency tuning, and thermal behaviour have also been studied using ANSYS. The cavity design resulting from these considerations will be discussed here., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

A 112 MHz superconducting RF photoemission gun was designed, fabricated and installed in RHIC for the Coherent electron Cooling Proof-of-Principle (CeC PoP) experiment at BNL. The gun was commissioned first without beam. This was followed by generating the first photoemission beam from a multi-alkali cathode. The paper presents the commissioning results., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

Multi-cell temperature mapping (T-map) system has been developed and applied on SRF Nb cavities vertical tests (VT) at Cornell. It has nearly two thousand thermometers and achieved a 1mK resolution of niobium surface temperature rinsing in superfluid helium . We have upgraded the system to be capable of monitoring the temperature profiles of quench spot on cavity. The recent results of T-map during cavity tests and details will be reported., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

The design of a compact superconducting crab-cavity for LHC using Nb-on-Cu-coating technique is presented. The cavity shape is based on the ridged waveguide resonator with wide open apertures to provide access to the inner surface of the cavity for coating. It also provides natural damping for HOMs and rather low longitudinal and transverse impedances. The results of the cavity shape optimization taking into account RF performance, coating, and thermo-mechanical considerations as well as the design and fabrication plans of the first prototype for coating and cold tests are presented., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

Cornell University treated five LCLS-II 9-cell cavities by nitrogen-doping recipe. In this paper, we reported the performance of these 9-cell cavities. In the treatments, the nitrogen recipes are slightly different. The cavities have been firstly doped under high nitrogen pressure; after the vertical tests some of the cavities has been reset the surface and re-doped under light nitrogen pressure. The detail of the cavity preparation and test results will be shown. The comparison of the different recipes will be discussed., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

The authors are developing the manufacturing method for super conducting radio frequency (SRF) cavities by using a hydroforming instead of an electron beam welding, which is the major manufacturing method. We expect a cost reduction by hiring the hydroforming. To realize this development, getting a high-purity seamless niobium tube with good forming ability and an advancement of hydroforming technique are necessary. We got the seamless niobium tube made by ATI Wah Chang with the cooperation of Fermilab, and succeeded to manufacture the 1-cell cavity by hydroforming. The accelerating gradient attained to 36 MV/m, and we confirmed it was available to use as the SRF cavity., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

In the framework of many accelerator projects relying on RF superconducting technology, shape conformity and processing time are key aspects for the optimization of niobium cavity fabrication. An alternative technique to traditional shaping methods, such as deep-drawing and spinning, is Electro-Hydraulic Forming (EHF). In EHF, cavities are obtained through ultra-high-speed deformation of blank sheets, using shockwaves induced in water by a pulsed electrical discharge. With respect to traditional methods, such a highly dynamic process can yield valuable results in terms of effectiveness, repeatability, final shape precision, higher formability and reduced spring-back. In this paper, the first results of EHF on copper prototypes and ongoing developments for niobium for the Superconducting Proton Linac studies at CERN are discussed. The simulations performed in order to master the embedded multi-physics phenomena and to steer process parameters are also presented., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

The FNAL designed 3.9 GHz third harmonic cavity for XFEL will be used in LCLS-II for linearizing the longitudinal beam profile. The 3.9 GHz SRF cavity is scaled down from the 1.3 GHz TESLA cavity shape, but has a disproportionately large beampipe radius for better higher-order mode (HOM) damping. The HOM and fundamental power (FPC) couplers will generate asymmetric field in the beam region, and thereby dilute the beam emittance. Meanwhile, due to the large beampipe, all but a few of the HOMs are above the beampipe cutoff. Thus the HOM damping analyses need to be performed in a full cryomodule, rather than in an individual cavity. The HOM damping in a 4-cavity cryomodule was investigated to determine possible trapped modes using the parallel electromagnetic code suite ACE3P developed at SLAC. The coupler RF kicks induced by the HOM and FPC couplers in the 3.9 GHz cavity were evaluated. A possible cavity-to-cavity arrangement is proposed which could provide effective cancellation of these RF kicks. In this paper we present and discuss the RF simulation results in the 3.9 GHz third harmonic cavity cryomodule., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

eRHIC project requires construction of a FFAG ring to accelerate electrons and connect to the existing ion ring of Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. This new ring will have the same radius as the RHIC ring. Synchrotron radiation lost in the electron ring should be compensated by a CW superconducting radio frequency (SRF) cavity. Here we propose an 845 MHz single cell harmonic cavity. This cavity will experience a high average current (∼0.7 A) passing through it. With this consideration, this cavity design requires optimization to reduce higher order mode power. On the other hand, the cavity will operate at relatively high gradient up to 18 MV/m. Current design requires fundamental couplers to handle 400 kW forward RF power and HOM couplers to extract 2.5 kW HOM power., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

The 3 cell superconducting TW accelerating structure was developed to experimentally demonstrate and to study tuning issues for a new experimental device - the superconducting traveling wave accelerator (STWA), a technology that may prove of crucial importance to the high energy SRF linacs by raising the effective gradient and therefore reducing the overall cost. Recently, a STWA structure with a feedback waveguide has been suggested. The structure was optimized and has phase advance per cell of 105° which provide 24% higher accelerating gradient than in SW cavities. Also STWA structure has no strong sensitivity of the field flatness and its length may be much longer than SW structure. With this presentation, we discuss the current status of a 3-cell L-band SC traveling wave along with the analysis of its tuning issues. Special attention will be paid to feedback loop operation with the two-coupler feed system. We also report on the development and fabrication of a niobium prototype 3-cell SC traveling wave structure to be tested at 2°K in fall 2015., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

The talk shall cover two SRF photoemission electron guns under commissioning at BNL: a 704 MHz elliptical ERL gun and a 112 MHz quarter-wave gun for coherent electron cooling experiment. In particular, the speaker shall report on generating first photoemission beam current from the 704 MHz SRF gun, multipacting issues in the SRF guns, photocathode behavior as well as other commissioning experiences and results., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

The beam crabbing proposed for the LHC High Luminosity Upgrade requires two crabbing systems operating in both horizontal and vertical planes. In addition, the crabbing cavity design needs to meet strict dimensional constraints and functional specifications of the cavities. This paper presents the detailed electromagnetic design including em properties, multipole analysis, multipacting levels of the 400 MHz rf-dipole crabbing cavity., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

As the Facility for Rare Isotope Beams (FRIB) project ramps into production, vendor relations, cavity quality, and schedule become critical to success. The driver linac will be constructed of 332 cavities housed in 48 cryomodules and designed with two cavity classes (quarter-wave and half-wave) and four different betas (0.041, 0.085, 0.29, and 0.53). The cavities will be supplied to FRIB from awarded industrial vendors. FRIB’s experience with SRF cavity fabrication will be presented including acceptance inspections, test results, technical issues, and mitigation strategies., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada