Z.L. Thune, N. Fleming, C. McKinney, E.M. Nicometo
MSU, East Lansing, USA
S. Balachandran
NHMFL, Tallahassee, Florida, USA
T.R. Bieler
Michigan State University, East Lansing, Michigan, USA
Funding:US Dept. of Energy award DE-SC0009960 The consistent production of high-purity niobium cavities for superconducting radiofrequency (SRF) applications is crucial for enabling improvements in accelerator performance. Recent work has shown that dislocations and grain boundaries trap magnetic flux which dissipates energy and degrades cavity performance. We hypothesize that the current heating rate used in production is too slow and therefore facilitates recovery rather than recrystallization. Recovery, unlike recrystallization, does not reduce the number of geometrically necessary dislocations (GNDs) that are strongly correlated to trapped magnetic flux. Using excess high-purity niobium saved from the production of a cavity, the material was divided into two groups and rolled to ~30% reduction with half rolled parallel to the original rolling direction, and the other half rolled perpendicular. To examine the effect of heating rate, samples were encapsulated in quartz tubes and placed into either a preheated furnace or a cold furnace to allow for heat treatments at different rates. Then using ex-situ electron backscatter diffraction (EBSD) mapping, the extent of recrystallization was determined.
A. Tsymbaliuk, D. Bortolato, F. Chiurlotto, E. Chyhyrynets, G. Keppel, E. Munaron, C. Pira, F. Stivanello
INFN/LNL, Legnaro (PD), Italy
E. Chyhyrynets
Università degli Studi di Padova, Padova, Italy
A. Tsymbaliuk
UNIFE, Ferrara, Italy
The SPES project is based at INFN LNL and covers basic research in nuclear physics, radionuclide production, materials science research, nuclear technology and medicine. The Radioactive Ion Beam (RIB) produced by SPES will be accelerated by ALPI, which is a linear accelerator, equipped with superconducting quarter wave resonators (QWRs) and operating at LNL since 1990. For RIB acceleration it is mandatory to perform an upgrade of ALPI which consists of the implementation of two additional cryostats, containing 4 accelerating cavities each, in the high-ß section. The QWRs production technology is well established. The production technology of Nb/Cu QWRs should be adjusted for high-ß cavities production. In the framework of the upgrade, several vacuum systems were refurbished, optimal parameters of the biased sputtering processes of copper QWR cavities and plates were defined. The process of mechanical and chemical preparation, sputtering and cryogenic measurement of the high-ß Nb/Cu QWR cavities were adjusted. Several QWR cavities were already produced and measured. Currently, the production of the Nb/Cu sputtered QWR cavities and plates is ongoing.
V.A. Garcia Diaz, O. Azzolini, E. Chyhyrynets, G. Keppel, C. Pira, F. Stivanello, M. Zanierato
INFN/LNL, Legnaro (PD), Italy
E. Chyhyrynets
Università degli Studi di Padova, Padova, Italy
D. Fonnesu
CERN, Meyrin, Switzerland
O. Kugeler, D.B. Tikhonov
HZB, Berlin, Germany
R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
M. Vogel
University Siegen, Siegen, Germany
Funding:European Union’s H2020 Framework Programme under Grant Agreement no. 764879 Thick films deposited in long pulse DCMS mode onto 6 GHz copper cavities have demonstrated the mitigation of the Q-slope at low accelerating fields. The Nb thick films (~40 microns) show the possibility to reproduce the bulk niobium superconducting properties and morpholo-gy characterizations exhibited dense and void-free films that are encouraging for the scaling of the process to 1.3 GHz cavities. In this work a full characterization of thick films by DC magnetometry, computer tomography, SEM and RF characterizations are presented.
E.A.S. Viklund, D.N. Seidman
NU, Evanston, Illinois, USA
L. Grassellino, S. Posen, T.J. Ring
Fermilab, Batavia, Illinois, USA
To improve the superconducting performance of niobium SRF cavities, electropolishing (EP) with a sulfuric and hydroflouric acid mixture is used. The chemistry of this reaction is complex due to the interactions between diffusion mechanisms, surface oxide structure, and multiple chemical species. Past studies on the EP process have produced a certain set of optimum parameters that have been used successfully for a long time. However, two recent developments have called the efficacy of the existing EP process into question. Since the introduction of nitrogen doping the surface quality of some cavities has been very poor. Also, EP performed at colder than standard temperatures leads to an increase in the cavity performance. To understand these questions, we perform a multivariate study on the EP process using niobium test samples electropolished at different temperatures and potentials. We find that electropolishing at lower potentials leads to rough surface features such as pitting and grain etching. Some of the surface features show similarities to features seen in niobium cavities. The effect of electropolishing temperature is not clear based on the results of this study.
C. Bate, A. Dangwal Pandey, A. Ermakov, B. Foster, T.F. Keller, D. Reschke, J. Schaffran, S. Sievers, H. Weise, M. Wenskat
DESY, Hamburg, Germany
B. Foster
Oxford University, Physics Department, Oxford, Oxon, United Kingdom
W. Hillert, M. Wenskat
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
Many accelerator projects such as the European XFEL cw upgrade or the ILC, would benefit from cavities with reduced surface resistance (high Q-values) while maintaining a high accelerating gradient. A possible way to meet the requirements is the so-called nitrogen-infusion procedure on Niobium cavities. However, a fundamental understanding and a theoretical model of this method are still missing. The approach shown here is based on R\&D using small samples, with the goal of identifying all key parameters of the process and establishing a stable, reproducible recipe. To understand the underlying processes of the surface evolution that give improved cavity performance, advanced surface-analysis techniques (e.g. SEM/EDX, TEM, XPS, TOF-SIMS) are utilized and several kinds of samples are analyzed. Furthermore, parameters such as RRR and the surface critical magnetic field denoted as Hc3 have been investigated. For this purpose, a small furnace dedicated to sample treatment was set up to change and explore the parameter space of the infusion recipe. Results of these analyses and their implications for the R\&D on cavities are presented.
M.M. Kelley, T. Arias, N. Sitaraman
Cornell University, Ithaca, New York, USA
Funding:This work was supported by the US National Science Foundation under award PHY-1549132, the Center for Bright Beams. For over 50 years experiments have repeatedly demonstrated that the superconducting performance of Nb3Sn is profoundly sensitive to grain boundaries (GBs), but only recently has a microscopic theory emerged. Here we present the first comprehensive, ab initio study of GBs in Nb3Sn*. While most conventional superconductors, such as Nb, are not significantly impacted by GBs, Nb3Sn is much more sensitive to defects and disorder owing to its short coherence length of ~3 nm. Indeed, experiments suggest a link between GB stoichiometry and the performance of Nb3Sn superconducting radio frequency (SRF) cavities, and mesoscopic simulations point to GBs as a candidate mechanism that lowers the vortex-entry field in Nb3Sn SRF cavities. Our density-functional theory (DFT) calculations on tilt and twist GBs provide direct insight into antisite defect formation near GBs and how local electronic properties are impacted by clean GBs and by GBs with added point defects. Ultimately, we will show how GB composition affects the local Tc around GBs in Nb3Sn to elucidate recent SRF experiments and provide insight on promising modifications to the growth procedure of Nb3Sn to optimize its SRF performance. [*] Michelle M Kelley et al 2021 Supercond. Sci. Technol. 34 015015
I.P. Parajuli, G. Ciovati, J.R. Delayen, A.V. Gurevich
ODU, Norfolk, Virginia, USA
G. Ciovati, J.R. Delayen
JLab, Newport News, Virginia, USA
One of the building blocks of modern particle accelerators is superconducting radiofrequency (SRF) cavities. Niobium is the material of choice to build such cavities, which operate at liquid helium temperature (2 - 4 K) and have some of the highest quality factors found in Nature. There are several sources of residual losses, one of them is trapped magnetic flux, which limits the quality factor in SRF cavities. The flux trapping mechanism depends on different niobium surface preparations and cool-down conditions. Suitable diagnostic tools are not yet available to study the effects of such conditions on magnetic flux trapping. A magnetic field scanning system (MFSS) for SRF cavities using Hall probes and Fluxgate magnetometer has been designed, built, and is commissioned to measure the local magnetic field trapped in 1.3 GHz single-cell SRF cavities at 4 K. In this contribution, we will present the preliminary results from MFSS for a single cell niobium cavity.
D.J. Seal
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
G. Burt, P. Goudket, O.B. Malyshev, B.S. Sian, R. Valizadeh
Cockcroft Institute, Warrington, Cheshire, United Kingdom
G. Burt, B.S. Sian
Lancaster University, Lancaster, United Kingdom
J.A. Conlon, P. Goudket, O.B. Malyshev, R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
A low-power SRF test facility is being upgraded at Daresbury Laboratory as part of the superconducting thin film testing programme. The facility consists of a bulk niobium test cavity operating at 7.8 GHz, surrounded by RF chokes, and can be run with input RF powers up to 1 W. It is housed within a liquid helium free cryostat and is able to test thin film planar samples up to 100 mm in diameter with a thickness between 1 and 20 mm. The RF chokes allow the cavity to be physically and thermally isolated from the sample, thus reducing the need for complicated sample mounting, whilst minimising field leakage out of the cavity. This allows for a fast turnaround time of two to three days per sample. Initial tests using a newly designed sample holder have shown that an RF-DC compensation method can be used successfully to calculate the surface resistance of samples down to 4 K. Potential upgrades include a pick-up antenna for direct measurements of stored energy and the addition of a self-excited loop to mitigate the effects of microphonics. Details of this facility and preliminary results are described in this paper.
D. Fonnesu, J. Bremer, T. Koettig, L. Laín-Amador, C. Pereira Carlos, G.J. Rosaz, A.P.O. Vaaranta
CERN, Meyrin, Switzerland
Funding:EASITrain - European Advanced Superconductivity Innovation and Training. This MSCA ITN has received funding from the European Union’s H2020 Framework Programme under GA no. 764879. In the framework of The Future Circular Collider (FCC) Study, the development of thin-film coated superconducting radio-frequency (SRF) cavities capable of providing higher accelerating fields (10 to 20 MV/m against 5 MV/m of LHC) represents a major challenge. In this work, we present the development of a test stand commissioned at CERN for the inductive measurement of the critical temperature (Tc) of SC thin-film deposited on copper samples for SRF applications. Based on new studies for the production of Non Evaporable Getters (NEG) coated chambers [1], we also present the first results of an alternative forming method for seamless copper cavities with niobium layer integrated in the production process. [1] doi:10.1116/1.4999539
I.H. Senevirathne, J.R. Delayen, A.V. Gurevich
ODU, Norfolk, Virginia, USA
J.R. Delayen, A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA
Funding:NSF Grants PHY-1734075 and PHY-1416051, and DOE Awards DE-SC0010081 and DE-SC0019399 The SIS structure which consists of alternative thin layers of superconductors and insulators on a bulk niobium has been proposed to shield niobium cavity surface from high magnetic field and hence increase the accelerating gradient. The study of the behavior of multilayer super-conductors in an external magnetic field is essential to optimize their SRF performance. In this work we report the development of a simple and efficient technique to measure penetration of magnetic field into bulk, thin film and multilayer superconductors. Experimental setup contains a small superconducting solenoid which can produce a parallel surface magnetic field up to 0.5 T and Hall probes to detect penetrated magnetic field across the superconducting sample. This system was calibrated and used to study the effect of niobium sample thickness on the field of full magnetic flux penetration. We determined the optimum thickness of the niobium substrate to fabricate the multilayer structure for the measurements in our setup. This technique was used to measure penetration fields of Nb3Sn thin films and Nb3Sn/Al2O3 multi-layers deposited on Al2O3 wafers.
J.K. Tiskumara, J.R. Delayen
ODU, Norfolk, Virginia, USA
G.V. Eremeev
Fermilab, Batavia, Illinois, USA
U. Pudasaini, C.E. Reece
JLab, Newport News, Virginia, USA
The twin axis cavity with two identical accelerating beams has been proposed for energy recovery linac (ERL) applications. Nb3Sn is a superconducting material with a higher critical temperature and a higher critical field as compared to Nb, which promises a lower operating cost due to higher quality factors. Two niobium twin axis cavities were fabricated at JLab and were proposed to be coated with Nb3Sn. Due to their more complex geometry, the typical coating process used for basic elliptical cavi-ties needs to be improved to coat these cavities. This development advances the current coating system at JLab for coating complex cavities. Two twin axis cavities were coated recently for the first time. This contribution dis-cusses initial results from coating of twin axis cavities, RF testing and witness sample analysis with an overview of the current challenges towards high performance Nb3Sn coated twin axis cavities.
A.L. Prudnikava, J. Knobloch, O. Kugeler, Y. Tamashevich
HZB, Berlin, Germany
V. Aristov, O. Molodtsova
DESY, Hamburg, Germany
S. Babenkov
LIDYL, Gif sur Yvette, France
A. Makarova
FUB, Berlin, Germany
D. Smirnov
Technische Universität Dresden, Dresden, Germany
Processing of niobium cavities with the so-called ni-trogen infusion treatment demonstrates the improve-ment of efficiency and no degradation of maximal accelerating gradients. However, the chemical compo-sition of the niobium surface and especially the role of nitrogen gas in this treatment has been the topic of many debates. While our study of the infused niobium using synchrotron X-ray Photoelectron Spectroscopy (XPS) showed modification of the surface sub-oxides surprisingly there was no evidence of nitrogen con-centration build up during the 120°C baking step, irre-spectively of N2 supply. Noteworthy, that the niobium contamination with carbon and nitrogen took place during a prolonged high-temperature anneal even in a high vacuum condition (10-8-10-9 mbar). Evidently, the amount of such contamination appears to play a key role in the final cavity performance
F. Furuta, D.J. Bice, M. Martinello, T.J. Ring
Fermilab, Batavia, Illinois, USA
FNAL has established a cold Electro-Polishing (EP) method which maintains the outer surface temperature of cavity cell around 12~15°C during EP process. Cold EP has been applied on the various SRF cavities and contributed to achieve high RF performances with them. To investigate more feasibility and capability of EP at lower temperature, the FNAL EP temperature control tool was recently improved. Extra-cold EP process below 0°C at cavity cell region was successfully performed on 1.3 GHz 1-cell cavity. A compatible RF performance with cold EP method was also demonstrated during the cavity vertical testing. The details of extra-cold EP process and the cavity test results will be presented.
A. Kumar, K. Abe, T. Dohmae, S. Michizono, T. Saeki, Y. Watanabe, A. Yamamoto, M. Yamanaka
KEK, Ibaraki, Japan
A. Fajardo, N. Lannoy
ATI, Albany, Oregon, USA
G.R. Myneni
JLab, Newport News, Virginia, USA
G.R. Myneni
BSCE, Yorktown, Virginia, USA
At KEK, research is being conducted to manufacture cost-effective 1.3 GHz superconducting radio frequency cavities based on the fine grain (FG) and large grain (LG) Niobium (Nb) materials. Medium grain (MG) Nb has been proposed and developed as an alternative to the FG and LG Nb, being expected to have better mechanical stability with a cost-effective and clean manufacturing approach. MG Nb has an average grain size of 200 - 300 µm, which is approximately 100 times smaller than the LG Nb, however, there are occasional grains as large as 1-2 mm. As such, it is expected to have isotropic properties rather than the anisotropic properties of LG Nb. In this paper, we will outline the mechanical properties of the directly sliced high RRR MG Nb material (manufactured by ATI), and a comparative study will be presented with respect to FG and LG Nb. Moreover, the viability of MG Nb for the global high-pressure regulation for 1.3 GHz SRF cavity will be presented.
R. Katayama, A. Araki, H. Ito, E. Kako, T. Konomi, S. Michizono, M. Omet, K. Umemori
KEK, Ibaraki, Japan
We will report on the current progress of High-Q/High-G R&D using three 1.3 GHz 9-cell TESLA shape niobium superconducting cavities at the High Energy Accelerator Research Organization (KEK). These cavities are made of bulk niobium of fine grain material with RRR >300 and have been annealed at 900 degrees for 3 hours. The cavity performances were evaluated at the Superconducting RF Test Facility at KEK (KEK-STF) after 2-step bake (70-75°C 4 h + 120°C 48 h), electropolishing at low temperature, and fast cooling procedure were applied to these cavities. In this study, obtained results will be compared with the baseline measurement for the standard recipe at KEK.
M. Cavellier
Omega Physics, St Gildas de Rhuys, France
Nitrogen-doping of Niobium cavities is now well known and industrialization of this process is emerging. However, the current process, based on thermal treatment in Nitrogen atmosphere leads to various inaccuracies (what is the concentration of Nitrogen in the Nb material? Penetration depth, created phases, …) and some post-treatment like chemical-mechanical polishing of the inner surface. This work presents a new and more accurate patented process based on nitrogen ion beam implantation into the inner surface of Nb cavities. Ion implantation is a well-known, controlled, accurate and reproducible process that does not require post-treatment. For these reasons, the industrialization of Nitrogen-doping Nb cavities will be improved through ion implantation.
M.O. Hyun, J. Joo, H.C. Jung, Y. Kim
IBS, Daejeon, Republic of Korea
Funding:This paper was supported by the Rare Isotope Science Project (RISP), which is funded by the Ministry of Science and ICT (MSIT) and National Research Foundation (NRF) of the Republic of Korea. Rare Isotope Science Project (RISP) in the Institute of Basic Science (IBS), South Korea, is now constructing superconducting linear accelerator 3 (SCL3) for low-energy beam experiment and also making prototypes of superconducting cavity, RF power coupler, tuner, and cryomodule of superconducting (SC) linear accelerator 2 (SCL2) for high-energy beam experiment. Single spoke resonator type-1 (SSR1) and type-2 (SSR2) superconducting cavities are now on the prototyping stage. This paper explains about SSR2 fabrication process from press-forming to electron beam welding (EBW) with RRR300 niobium sheets.
T. Dohmae, K. Abe, H. Inoue, A. Kumar, S. Michizono, T. Saeki, K. Umemori, Y. Watanabe, A. Yamamoto, M. Yamanaka, K. Yoshida
KEK, Ibaraki, Japan
A. Fajardo, N. Lannoy
ATI, Albany, Oregon, USA
G.R. Myneni
JLab, Newport News, USA
Medium grain (MG) niobium disc which is directly sliced from forged ingot is newly investigated for the cavity material. An effective cost reduction can be achieved using MG niobium since rolling process which is necessary for typical niobium sheet can be skipped during MG niobium production. Grain size of MD niobium is 200-300 um which is much smaller than large grain (LG) niobium directly sliced from melted niobium ingot. Hence, the formability of MG niobium is expected to be much better than LG niobium. KEK has started fabrication of cavity using MG niobium. In this talk, characteristic of MG niobium during fabrication will be reported.
S. Barrière, S. Atieh, B. Bulat, R. Calaga, S.J. Calvo, O. Capatina, T. Demazière, G. Favre, A. Gallifa Terricabras, M. Garlasché, J.-M. Geisser, J.A. Mitchell, E. Montesinos, F. Motschmann, P. Naisson, R. Ninet, L. Prever-Loiri, L.R.A. Renaglia, K. Scibor, N. Villanti
CERN, Meyrin, Switzerland
Superconducting RF crab cavities are being manufactured as part of the HL-LHC upgrade at CERN. Amongst its related ancillaries, radiofrequency HOM (High Order Modes) suppressors and field antennas are essential for reaching nominal performance during operation with high energy beams, as they monitor and control the electromagnetic fields in the cavities. Several concepts of such equipment have been engineered and manufactured, for both design validation and RF performance assessment. The following paper highlights manufacturing process definition, its challenges and the assembly strategies focusing on the ongoing RFD prototypes for the SPS beam tests. Specific tooling development and test campaigns are also described.
O. Hryhorenko, D. Longuevergne
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
C.Z. Antoine
CEA-IRFU, Gif-sur-Yvette, France
F. Brisset
ICMMO, Orsay, France
T. Dohmae
KEK, Ibaraki, Japan
The preparation of SRF cavities includes a lengthy, costly, and safety issued electrochemical polishing (EP or BCP) step to remove the damaged layer coming from the cavity fabrication. We have shown that most of the damage layer is originated from the rolling process during the preparation of the sheet material, while subsequent deep drawing tends to leave only µm thick damage layer. We propose a 2-steps mechanical process that allows us to easily get rid of the thick damage layer on the sheets before cavity forming. The process has been established on samples and extended to large disks ready for 1.3 GHz half-cell forming. The polished sheets will be then sent to KEK for half-cell forming and subsequent surface and material analysis before proceeding to half-cell welding. Former studies on the sample demonstrated that damages induced by forming can successfully be removed by recrystallization and less than 10 µm final chemistry.
P. Dhakal, B.J. Kross, F. Marhauser, J.E. McKisson, J. Musson, H. Wang, A. Weisenberger, W.Z. Xi
JLab, Newport News, Virginia, USA
Funding:This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences & Office of Nuclear Physics. A proposal has been conceived to levitate and trap mesoscopic particles using radio frequency (RF) fields in a superconducting RF(SRF) cavity. Exploiting the intrinsic characteristics of an SRF cavity, this proposal aims at overcoming a major limit faced by state-of-the-art laser trapping techniques. The goal of the proposal is to establish a foundation to enable observation of quantum phenomena of an isolated mechanical oscillator interacting with microwave fields. An experiment supported by LDRD funding at JLab has started to address R&D issues relevant to these new research directions using existing SRF facilities at JLab. The success of this experiment would establish its groundbreaking relevance to quantum information science and technology, which may lead to applications in precision force measurement sensors, quantum memories, and alternative quantum computing implementations with promises for superior coherence characteristics and scalability well beyond the start-of-the-art. In this contribution, we will introduce the proposal and basic consideration of the experiment.
A. Cano, D. Bafia, A. Grassellino, J. Lee, M. Martinello, A.S. Romanenko, T. Spina, Z-H. Sung
Fermilab, Batavia, Illinois, USA
E.A. Karapetrova
ANL, Lemont, Illinois, USA
We have mapped microstructural changes in the near-surface region of Nb from SRF cavity-cutouts upon thermal cycles in the range from 300 to 30 K using grazing incidence synchrotron X-Ray diffraction (GIXRD). Segregation of secondary phases was observed after the thermal cycle, and their nature has been clarified and discussed in view of previous studies on hydrides formation in SRF bulk Nb cavities. The temperature dependence of the relative population of these formed phases was obtained from GIXRD patterns profile fitting. Both, Nb bulk matrix and the new phases formed after cool-down show specific structural features as thermal contraction/expansion, structural transitions, and Nb lattice variation due to the induced strain by precipitates formation. The information derived from this structural study can explain some phenomena as the dissipation at high accelerating field (i.e. High Field Q Slope, HFQS) in the Nb SRF performance as well as new mechanisms never addressed in previous studies. A Romanenko, F Barkov, LD Cooley, A Grassellino, Proximity breakdown of hydrides in superconducting niobium cavities, Superconductor Science and Technology, 2013
M. Wenskat, C. Bate, D. Reschke, J. Schaffran, L. Steder, H. Weise
DESY, Hamburg, Germany
C. Bate, G.D.L. Semione, A. Stierle
University of Hamburg, Hamburg, Germany
M. Butterling, E. Hirschmann, M.O. Liedke, A. Wagner
HZDR, Dresden, Germany
J. Cizek
Charles University, Prague, Czech Republic
W. Hillert
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
Positron annihilation measurements allow to study the hydrogen interaction with vacancies in a crystal lattice. Furthermore, the 3/2 ratio of the positronium annihilation can be used to identify local magnetic impurities in thin layers. Dynamic studies of these properties in annealing studies up to 300°C will be presented. The discussion is accompanied by X-ray reflectivity studies performed on single crystal samples to study the niobium oxide dissolution. The dynamics of magnetic impurities during a Mid-T bake will be presented, put into the context of cavity studies and a potential link to rf properties will be discussed.
T.E. Oseroff, M. Liepe, Z. Sun
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
With the increasing worldwide focus on the development of new surfaces for SRF cavities, exploring alternative materials and multilayer structures, test systems that allow measuring the RF performance of simple sample geometries (e.g., flat samples) become increasingly essential. These systems provide RF performance results that are needed to guide the development of these surfaces. This contribution gives an overview of sample test systems currently available, including the improved Cornell sample host cavity. Recent advances in this important technology, performance specifications, and current limitations are discussed. In addition, an overview is given of interesting recent RF performance results on samples coated with non-niobium bulk and multilayer films.
E. Thoeng, J.R. Adelman, A. Chatzichristos, M. Dehn, D. Fujimoto, V.L. Karner, R. Kiefl, W.A. MacFarlane, J.O. Ticknor
UBC & TRIUMF, Vancouver, British Columbia, Canada
M. Asaduzzaman, T. Junginger
UVIC, Victoria, Canada
D.L. Cortie
University of Wollongong, Institute of Superconducting and Electronic Materials, Wollongong, New South Wales, Australia
S.R. Dunsiger, T. Junginger, P. Kolb, R.E. Laxdal, C.D.P. Levy, R. Li, R.M.L. McFadden, I. McKenzie, G. Morris, M. Stachura
TRIUMF, Vancouver, Canada
The \betaNMR (\beta-detected nuclear magnetic resonance) facility at TRIUMF offers the possibility of depth-resolved probing of the Meissner state over the first §I{100}{\nano\meter} below a sample surface. The measurement can give the attenuation of the applied magnetic field, as a function of depth. The technique can be especially important when probing layered systems like the dirty/clean S-S (superconductor-superconductor) bi-layer and S-I-S (Superconductor-Insulator-Superconductor) structures. The TRIUMF SRF (Superconducting RF) group has recently completed first measurements at beta-NMR on Nb samples with various treatments. The results and method will be reported.
L.M.A. Ferreira, N.S. Chritin, R. Ferreira, V. Gerbet
CERN, Meyrin, Switzerland
A new SRF cavity polishing facility which covers the needs for present projects like the HL-LHC and its CRAB cavities as well as ongoing and future activities in the frame of the FCC study was commissioned at CERN in 2019. This facility can handle chemical and electrochemical polishing baths, can process both niobium and copper-based cavities on a wide range of geometries, starting at 400 MHz up to 1.3 GHz for elliptical type of cavities and more complex shapes as defined by the DQW and RFD CRAB design. The main subassemblies of this facility are presented. Some important design details and materials choices of the facility will be briefly discussed together with the range of operational parameters. First results on different substrates and geometries are discussed in terms of surface finishing and polishing rate uniformity.
T.R. Bieler, D. Kang
Michigan State University, East Lansing, Michigan, USA
R. Rodríguez-Desconocido, M. Terol-Sánchez
UPM, Madrid, Spain
N. Fleming, C. McKinney, Z.L. Thune, K. Zheng
MSU, East Lansing, USA
A.A. Kolka
Niowave, Inc., Lansing, Michigan, USA
Funding:Supported by US Dept. of Energy award DE-SC0009960. The performance of niobium cavities in superconducting radiofrequency particle accelerators requires nearly defect-free inner surfaces. While methods to obtain smooth inner surfaces are established, the role of metallurgical defects on superconducting performance is also important, as defects such as grain boundaries and dislocations are known to trap flux that dissipates energy and reduces efficiency. Variable microstructure and texture gradients may account for the observed variability in cavity performance, so it is hypothesized that the texture and microstructure gradients originate from the large grain size of ingots, whose influence is not completely erased in the process of making sheet metal. To examine the evolution of microstructure and texture gradients, the crystal orientations present in a cylindrical cap rolled to ~90% reduction were heat treated. Initial crystal orientations were measured before rolling, and before and after slow and rapid heating rate vacuum heat treatments.
J.W. Angle, M.J. Kelley
Virginia Polytechnic Institute and State University, Blacksburg, USA
M.J. Kelley, E.M. Lechner, A.D. Palczewski, C.E. Reece
JLab, Newport News, Virginia, USA
F.A. Stevie
NCSU AIF, Raleigh, North Carolina, USA
SIMS analyses for ’N-doped’ materials are becoming increasingly important. A major hurdle to acquiring quantitative SIMS results for these materials is the uncertainty of instrument calibration due to changes in sample height either from sample topography or from the sample holder itself. The CAMECA sample holder design allows for many types of samples to be analyzed. However, the cost is that the holder faceplate can bend, introducing uncertainty into the SIMS results. Here we designed and created an improved sample holder which is reinforced to prevent faceplate deflection and thereby reduce uncertainty. Simulations show that the new design significantly reduces deflection from 10 µm to 5 nm. Measurements show a reduction of calibration (RSF) uncertainty from this source from 4.1% to 0.95%. Grain orientation has long been suspected to affect RSF determination as well. A bicrystal implant standard consisting of [111] and [001] grains were repeatedly rotated 15° in between analyses. It was observed that 20% of the analyses performed on [111] grains exhibited anomalously high RSF values likely due to the changing of the grain normal with respect to the primary Cs+ beam.
J.W. Angle, M.J. Kelley
Virginia Polytechnic Institute and State University, Blacksburg, USA
M.J. Kelley, E.M. Lechner, A.D. Palczewski, C.E. Reece
JLab, Newport News, Virginia, USA
F.A. Stevie
NCSU AIF, Raleigh, North Carolina, USA
Detection of surface contamination for SRF material is difficult due to the miniscule quantities and near atomic resolution needed. Visual inspection of samples known to have experienced surface contamination were found to have inconsistent nitride coverage after nitrogen doping. EBSD analysis suggest that nitride suppression tends to be most prevalent when deviating from the [111] and [001] zone axes. XPS suggested that tin was present as a contaminant on the surface with SIMS mass spectra also confirming its presence. SIMS depth profiles show a depletion of nitrogen content as well as an increase in car-bon content for contaminated samples.
N. Sitaraman, T. Arias, Z. Baraissov, M.M. Kelley, D.A. Muller
Cornell University, Ithaca, New York, USA
M. Liepe, R.D. Porter, Z. Sun
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Funding:This work was supported by the U.S. National Science Foundation under Award No. PHY-1549132, the Center for Bright Beams The properties of niobium oxide are of critical importance for a wide range of topics, from the behavior of nitrogen during infusion treatments, to the nucleation of Nb3Sn, to the superconducting properties of the surface. However, the modeling of the oxide is often much simplified, ignoring the variety of niobium oxide phases and the extremely different properties of these phases in the presence of impurities and defects. We use density functional theory (DFT) to investigate how electrochemical treatments and gas infusion procedures change the properties of niobium oxide, and to investigate how these properties could be optimized for Nb3Sn nucleation and for niobium SRF performance.
F. Éozénou, M. Baudrier, E. Cenni, E. Fayette, L. Maurice, C. Servouin
CEA-DRF-IRFU, France
V. Chouhan, Y.I. Ida, K. Nii, T.Y. Yamaguchi
MGH, Hyogo-ken, Japan
H. Hayano, H. Ito, S. Kato, T. Kubo, H. Monjushiro, T. Saeki
KEK, Ibaraki, Japan
G. Jullien
CEA-IRFU, Gif-sur-Yvette, France
Vertical Electro-Polishing (VEP) of elliptical cavities using rotating Ninja cathodes (Marui Company patented technology) has continually been improved since 2012 and successfully applied for 1300MHz multicell ILC-type resonators. The goal of the presented study is to apply this technology to 704 MHz ESS-type resonators with both better Q0 and accelerating gradients in mind. We intend to demonstrate the superiority of VEP compared to standard Buffer Chemical Polishing (BCP), for possible applications such as MYRRHA accelerator. We describe here the promising results achieved on β=0.86 single-cell cavity after 200 µm uniform removal. The cavity quenched at 27 MV/m without any heat treatment. The surface resistance achieved was less than 5nΩ at 1.8K. Substantial performance improvement is expected after heat treatment of the cavity and additional 20 µm VEP sequence. A cathode for 5-Cell ESS cavity is concomitantly under design stage.
M. Zanierato, O. Azzolini, E. Chyhyrynets, V.A. Garcia Diaz, G. Keppel, C. Pira, F. Stivanello
INFN/LNL, Legnaro (PD), Italy
The deposition of Nb3Sn on copper cavities is inter-esting for the higher thermal conductivity of copper compared to common Nb substrates. The better heat exchange would allow the use of cryocoolers reducing cryogenic costs and the risk of thermal quench [1]. Magnetron sputtering technology allows the deposi-tion of Nb3Sn on substrates different than Nb, however the coating of substrates with complex geometry (such as elliptical cavities) may require targets with non-planar shape, difficult to realize with classic powder sintering techniques. In this work, the possibility of using the Liquid Tin Diffusion (LTD) technique to produce sputtering targets is explored. The LTD tech-nique is a wire fabrication technology, already devel-oped in the past at LNL for SRF applications [2], that allows the deposition of very thick and uniform coat-ing on Nb substrates even with complex geometry [3]. Improvements in LTD process, proof of concept of a single use LTD target production, and characterization of the Nb3Sn film coated by DC magnetron sputtering with these innovative targets are reported in this work.
C.S. Narug, M. Parise, D. Passarelli
Fermilab, Batavia, Illinois, USA
Funding:This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. Jacketed Superconducting Radio Frequency (SRF) cavities structurally comprise of an inner niobium vessel surrounded by a liquid helium containment vessels. The pressure of the helium bath and/or its volume might be such that a jacketed SRF cavity shall be considered a system of pressure vessels. Thus, methods described in the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC) should be used to analyze the structural soundness of jacketed SRF cavities. This paper will report the use of the set of rules developed at Fermilab for the design of SRF cavities, such as jacketed 1.3 GHz cavities for LCLS-II HE and jacketed Single Spoke Resonator type~2 (SSR2) for PIP-II, to ensure a similar level of safety as prescribed by the ASME BPVC.
L. Vega Cid, S. Atieh, L.M.A. Ferreira, L. Laín-Amador, C. Pereira Carlos, G.J. Rosaz, K. Scibor, W. Venturini Delsolaro, P. Vidal García
CERN, Meyrin, Switzerland
S.B. Leith
University Siegen, Siegen, Germany
A necessary condition for high SRF performances in thin film coated cavities is the absence of substrate defects. For instance, in the past, defects originated around electron beam welds in high magnetic field areas have been shown to be the cause of performance limitations in Nb/Cu cavities. Seamless cavities are therefore good candidates to allow an optimization of the coating parameters without the pitfalls of a changing substrate. In this work, we present the first results of two different methods to produce seamless cavities applied to 1.3 GHz copper single cells coated with thin Nb films by means of HIPIMS. A first method consists in electroplating the copper resonator on precisely machined aluminum mandrels, which are then dissolved chemically. As an alternative and a cross check, one cavity was machined directly from the bulk. Both cavities were coated with HIPIMS Nb films using the same coating parameters and the SRF performance was measured down to 1.8 K with a variable coupler to minimize the measurement uncertainty.
U. Pudasaini, C.E. Reece
JLab, Newport News, Virginia, USA
J.K. Tiskumara
ODU, Norfolk, Virginia, USA
Funding:Authored by Jefferson Science Associates under contract no. DE¬AC05¬06OR23177 Nb3Sn promises better RF performance (Q and Eacc) than niobium at any given temperature because of superior superconducting properties. Nb3Sn-coated SRF cavities are now produced routinely by growing a few microns thick Nb3Sn films inside Nb cavities via the tin vapor diffusion technique. Sn evaporation and consumption during the growth process notably affect the quality of the coating. Aiming at favorable surface characteristics that could enhance the RF performance, many coatings were produced by varying Sn sources and temperature profiles. Coupon samples were examined using different material characterization techniques, and a selected few sets of coating parameters were used to coat 1.3 GHz single-cell cavities for RF testing. The Sn supply’s careful tuning is essential to manage the microstructure, roughness, and overall surface characteristics of the coating. We summarize the material analysis of witness samples and discuss the performance of several Nb3Sn-coated single-cell cavities linked to Sn-source characteristics and observed Sn consumption during the film growth process.
Tensile tests at liquid He temperature were performed using specimen taken from high purity large grain niobium ingot produced by CBMM. The measured RRR is 242. The ingot is 260 mm in diameter and sliced by a multi wire saw to 2.8 thickness. 5 specimens were cut off from one sliced disk. 3 disks were set in same phase to obtain same grain distribution. 3 specimens each of 5 grain patterns 5, 15 in total were used for the tensile test. The tensile test stand using a cryostat and liquid He was manufactured by ourselves. The measured tensile strength varied 379 to 808 MPa. The average value is 611 MPa. The tensile strength at room temperature is 84 MPa. The strength becomes high at low temperature like a fine grain niobium. The specimen includes a grain boundary, and causes the variation of strength. The different result was obtained in same grain patterns. The relationship between crystal orientation and strength is discussed.
G. Ciovati, P. Dhakal
JLab, Newport News, Virginia, USA
I.P. Parajuli, M.R.P. Walive Pathiranage
ODU, Norfolk, Virginia, USA
T. Saeki
KEK, Ibaraki, Japan
Funding:U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177. Superconducting radio-frequency (SRF) cavities made of high-purity bulk niobium are widely used in modern particle accelerators. The development of metallic outer coatings with high thermal conductivity would have a beneficial impact in terms of improved thermal stability, reduced material cost and for the development of conduction-cooled, cryogenic-free SRF cavities. Several high-purity, fine-grain Nb samples have been coated with 2’4 mm thick copper by electroplating. Measurements of the thermal conductivity of the bimetallic Nb/Cu samples in the range 2’7 K showed values of the order of 1 kW/(m K) at 4.3 K. Very good adhesion between copper and niobium was achieved by depositing a thin Cu layer by cold spray on the niobium, prior to electroplating the bulk Cu layer.
M. Major, L. Alff, M. Arnold, J. Conrad, S. Flege, R. Grewe, N. Pietralla
TU Darmstadt, Darmstadt, Germany
Funding:Work supported by the German Federal Ministry for Education and Research (BMBF) through grant 05H18RDRB2 and the German Research Foundation (DFG) via the AccelencE Research Training Group (GRK 2128). Niobium is the standard material for superconducting RF (SRF) cavities for particle acceleration. Superconducting materials with higher critical temperature or higher critical magnetic field allow cavities to work at higher operating temperatures or higher accelerating fields, respectively. One direction of search for new materials with better properties is the modification of bulk niobium by nitrogen doping. In the Nb-N phase diagram, the cubic delta-phase of NbN has the highest critical temperature. Niobium samples were annealed and doped with nitrogen in the high-temperature furnace at TU Darmstadt and investigated at its Materials Research Department with respect to structural modifications. X-ray diffraction (XRD) confirmed the appearance of Nb4N3 and Nb2N phases on the surface of the samples. A single cell cavity was annealed under optimized doping conditions. The test samples treated together with the cavity showed almost single Nb4N3 phase. XRD pole figures also showed grain growth during sample annealing.
B. Giaccone, M. Martinello
Fermilab, Batavia, Illinois, USA
B. Giaccone, J. Zasadzinski
IIT, Chicago, Illinois, USA
A study of the niobium oxide structure is presented here, with particular focus on the niobium suboxides. Multiple steps of argon sputtering and XPS measurements were carried out until the metal surface was exposed. The sample was then exposed to air and the oxide regrowth was studied. In addition, three Nb samples prepared with different surface treatments were studied before and after being subjected to plasma processing. The scope is investigating the microscopic effect that the reactive oxygen contained in the glow discharge may have on the niobium surface. This study suggests that the Nb2O5 thickness may increase, although no negative change in the cavity performance is measured since the pentoxide is a dielectric.
J. Demercastel-Soulier, P. Duchesne, D. Longuevergne, G. Olry, T. Pépin-Donat, F. Rabehasy, D. Reynet, S. Roset, L.M. Vogt
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
Buffered chemical polishing (BPC) is the reference surface polishing adopted for ESS and MYRRHA SRF spoke resonators at IJCLab. This chemical treatment, in addition to improving the RF performance, fits into the frequency adjustment strategy of the jacketed cavity during its preparation phase. In the framework of the collaboration with Fermilab for PIP-II project, IJCLab has developed a new setup to perform rotational BCP. The implementation of a rotation during chemical etching improves significantly the homogeneity and quality of surface polishing. In this paper, we present the numerical analysis based on a fluid dynamics model. The goal is to estimate the acid flow characteristics inside the cavity, determine the influence of several parameters as mass flow rate and rotation speed and propose the best configuration for the new experimental setup
Y.L. Huang, H. Guo, Y. He, C.L. Li, T. Liu, R.X. Wang, Z.J. Wang, M. Xu, Z.Q. Yang, S.X. Zhang
IMP/CAS, Lanzhou, People’s Republic of China
Funding:Large Research Infrastructures "China initiative Accelerator Driven System"(Grant No.2017-000052-75-01-000590 ) and National Natural Science Foundation of China (Grant NO. 11805249) 650MHz multi-cell superconducting elliptical cavities with optimum beta equal to 0.62 and 0.82 were adopted in the driver linac of Chinese initiative Accelerator Driven Subcritical System (CiADS) to accelerate the 10 mA proton beam from 175 MeV up to 500 MeV, with the possibility to upgrade the energy to 1 GeV and higher. Mechanical design and optimization of the niobium cavity-titanium helium vessel assembly will be summarized in this paper. Vertical test results of three single cell prototype cavities will also be discussed, with comparisons with the simulation values. *Work supported by Large Research Infrastructures "China initiative Accelerator Driven System’(Grant No.2017-000052-75-01-000590 ) and National Natural Science Foundation of China (Grant NO. 11805249)
D. Bychanok, V. Bayev, S. Huseu, S.A. Maksimenko, A.E. Sukhotski, E. Vasilevich
INP BSU, Minsk, Belarus
A.V. Butenko, E. Syresin
JINR, Dubna, Moscow Region, Russia
M. Gusarova, M.V. Lalayan, S.M. Polozov
MEPhI, Moscow, Russia
V.S. Petrakovsky, A.I. Pokrovsky, A. Shvedov, S.V. Yurevich
Physical-Technical Institute of the National Academy of Sciences of Belarus, Minsk, Belarus
Y. Tamashevich
HZB, Berlin, Germany
The main fabrication stages of niobium and copper prototypes of coaxial half-wave resonators (HWR) operating at frequency 325 MHz for the Nuclotron-based Ion Collider fAcility (NICA) injector are presented and discussed. Results of intermediate measurements and electromagnetic properties control for niobium and copper cavities of equivalent geometrical characteristics are compared and analyzed. The comparison of electromagnetic properties of Cu- and Nb-prototypes allows estimating specific features and differences of intermediate "warm" measurements of niobium and copper cavities. The presented results will be used for further development and production of superconductive niobium cavities with a similar design for the NICA-project.
J. Tamura, Y. Kondo, F. Maekawa, S.I. Meigo, B. Yee-Rendón
JAEA/J-PARC, Tokai-mura, Japan
T. Dohmae, E. Kako, H. Sakai, K. Umemori
KEK, Ibaraki, Japan
The Japan Atomic Energy Agency (JAEA) is proposing an accelerator-driven subcritical system (ADS) for efficient reduction of high-level radioactive waste generated in nuclear power plants. One of the challenging R¥&Ds for ADS is the reliability of the accelerator. In preparation for the full-scale design of the proton linac for the JAEA-ADS, we are now prototyping a single-spoke cavity for low-beta (around 0.2) beam acceleration. As there is no experience of manufacturing a superconducting spoke cavity in Japan, the cavity prototyping and performance testing are essential to ensure the feasibility of the JAEA-ADS linac. To proceed to an actual cavity fabrication, we have carefully reviewed the fabrication process. And then, we examined the electron-beam welding using niobium test pieces and investigated the welding condition for realizing the smooth underbead. We have finally started the press forming of niobium sheets and the machine work to shape the cavity parts. Now, we are parparing for the electron-beam welding of the shaped niobium parts.
J. Völker, A. Frahm, S. Keckert, J. Knobloch, A.N. Matveenko, A. Neumann, H. Plötz, Y. Tamashevich
HZB, Berlin, Germany
J. Knobloch
University of Siegen, Siegen, Germany
Frequently SRF modules require strong focusing magnets close to SRF cavities. The shielding of those magnetic fields to avoid flux trapping, for example during a quench, is a challenge. At HZB, the bERLinPro photo-injector module includes a 1.4 cell SRF cavity placed in close proximity to a superconducting (SC) focusing solenoid. At full solenoid operation, parts of the double mu-metal shield are expected to saturate. To prevent saturation, we developed a new superconducting Meissner-Shield. Several tests of different designs were performed both in the injector module and in the HoBiCaT test facility. The measured results of the final design show a significant shielding that are in good agreement with calculations. Based on these results, a reduction of the magnetic flux density in the mu-metal shields of almost one order of magnitude is expected The design has now been incorporated in the injector module. In this paper we will present the design, the setup and results of the final testing of the superconducting shield.
H. Padamsee
Cornell University, Ithaca, New York, USA
H. Padamsee, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA
The Standing Wave TESLA Niobium-based structure is limited to a gradient of about 50 MV/m by the critical RF magnetic field. To break through this barrier, we explore the option of Niobium-based traveling wave (TW) structures. Optimization of TW structures was done taking into account experimentally known limiting electric and magnetic fields. It is shown that a TW structure can have an accelerating gradient above 70 MeV/m that is about 1.5 times higher than contemporary standing wave structures with the same critical magnetic field. The other benefit of TW structures shown is R/Q about 2 times higher than TESLA structure that reduces 2 times the dynamic heat load. A method is proposed how to make TW structures multipactor-free. Some design proposals can be realized to facilitate fabrication. Further increase of the real-estate gradient (equivalent to 80 MV/m active gradient) is also possible by increasing the length of the accelerating structure because of higher group velocity and cell-to-cell coupling. Realization of this work opens paths to ILC energy upgrades beyond 1 TeV to 3 TeV in competition with CLIC. The paper will discuss corresponding opportunities and challenges.
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Funding:Department of Atomic Energy, India This talk is a summary talk of the recent progress of SRF activities in India including RRCAT, BARC, VECC, IUAC. The latest SRF activities for several national accelerator projects and international projects like PIP-II in FNAL are presented. RRCAT in Indore has been pursuing a complete chain of fabrication, RF tests and characterization at various stages including the SCRF infrastructure facilities, processing, HPR, vertical test stand and Horizontal Test Stand. Several cavities have been successfully tested in the vertical test stand and the Horizontal Test Stand has been commissioned and ready to test the cavities. BARC in Mumbai has developed low beta single spoke cavities for PIP-II R & D in collaboration with IUAC. VECC is pursuing development of single cell and five cell low beta SCRF cavities for PIP-II R &D. IUAC in New Delhi have developed SRF cavities in their infrastructure facilities and has supported institutes in India towards 1.3 GHz cavities, single cell LB and HB cavities and development of SSR1 cavities. Status of the SRF cavity development and the latest results of cavity performance qualification should be presented in this talk
C. Pira, O. Azzolini, R. Caforio, E. Chyhyrynets, V.A. Garcia, G. Keppel, F. Stivanello
INFN/LNL, Legnaro (PD), Italy
Superconducting radio frequency (SRF) cavities performances strongly depend on the substrate preparation. Currently, the conventional protocol of SRF surface preparation includes electropolishing (EP) as the main treatment achieving low roughness, clean and non-contaminated surfaces, both for bulk Nb and Cu substrates. Harsh and non-environmentally friendly solutions are typically used: HF and H2SO4 mixture for Nb, and H3PO4 with Butanol mixtures for EP of Cu. This research is focused on the application of a relatively new technique "Plasma Electrolytic Polishing" (PEP) for the SRF needs. PEP technology is an evolution of EP with a list of advantages that SRF community can benefit from. PEP requires diluted salt solutions moving to a greener approach in respect to EP. PEP can in principle substitute, or completely eliminate, intermediate steps, like mechanical and/or (electro) chemical polishing. Thanks to the superior removing rate in the field (up to 3.5 µm/min of Nb, and 10 µm/min of Cu) in one single treatment roughness below 100 nm Ra has been obtained both for Nb and Cu. In the present work a proof of concept is shown on Nb and Cu planar samples.
E.M. Lechner, M.J. Kelley, A.D. Palczewski, C.E. Reece
JLab, Newport News, Virginia, USA
J.W. Angle, M.J. Kelley
Virginia Polytechnic Institute and State University, Blacksburg, USA
F.A. Stevie
NCSU AIF, Raleigh, North Carolina, USA
Funding:U.S. DOE Contract No. DE-AC05-06OR23177 Results recently published by Ito et al. showed that "furnace baking" Nb SRF cavities after electropolishing yields high quality factors and anti-Q-slopes resembling that of N doped cavities. Small Nb samples were prepared following the recipe outlined by Ito. These samples were measured by SIMS to examine impurity contributions to the RF penetration layer. These diffusion profiles are modeled, and their consequences on RF properties discussed.
M. Ge, A.T. Holic, M. Liepe, J. Sears
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Reducing thermoelectric currents during cooldown is important to maintain high-quality factors (Q0) of the cavities in the LCLS-II HE cryomodules. The temperature-dependent Seebeck coefficients of the materials used in the cryomodules are needed for quantitative estimations of thermoelectric currents. In this work, we present a setup for cryogenic Seebeck coefficient measurements as well as the measured Seebeck coefficients of high-pure niobium at cryogenic temperatures between 4K and 200K.
Y. Jung, H. Jang, H. Kim, H. Kim, J.W. Kim, M.S. Kim, J. Lee, M. Lee
IBS, Daejeon, Republic of Korea
S. Jeon
Kyungpook National University, Daegu, Republic of Korea
Institute for Basic Science have been constructing Superconducting LINAC composed of quarter wave resonator (QWR) and half wave resonator (HWR). All QWR cavities have been completely fabricated and successfully tested to be assembled in QWR cryomodules. For now, we have been testing HWR cavities over 50%. For the testing period, the success rate experienced up and downs like we went through during the QWR tests. In many cases, we observed that some cavities did not reach requirement performance 2K although they showed high performance at 4K. We increased the temperature of heat treatment to cure the rapid Q drop at the high gradient and observed most cavities passed the test after heat treatment.
K. Nii, V. Chouhan, Y.I. Ida, T.Y. Yamaguchi
MGH, Hyogo-ken, Japan
H. Hayano, S. Kato, H. Monjushiro, T. Saeki
KEK, Ibaraki, Japan
We have been developing a vertical electropolishing (VEP) method for niobium superconducting RF cavities using a novel setup that allows periodic flipping of the cavity to put it upside down in the VEP process. The purpose of using the novel setup named as flipping system is to achieve uniform removal and smooth surface of the cavity. Previously, we have already introduced the VEP system and showed the preliminary results of VEP performed with the flipping system. In this article, we report VEP results obtained with a nine-cell coupon cavity. The results include detail on coupon currents with I-V curves for coupons, and impact of the cavity flipping on removal uniformity and surface morphology of the cavity.
M. Omet, R. Katayama, K. Umemori
KEK, Ibaraki, Japan
In this contribution we report on two topics regarding recent activities on 9-cell TESLA-type cavities at the High Energy Accelerator Research Organization (KEK). First, we give an overview of the inner surface treatments and vertical test (VT) results of four fine grain 9-cell TESLA-type cavities over the last one and a half years. Secondly, we report on the upgrade of the VT DAQ system at the Superconducting RF Test Facility (STF) at KEK. In this upgrade, most components of the VT system were integrated in an EPICS control system. Based on Control System Studio (CSS) and Python a new user interface was created, improving the workflow during and after VTs at STF.
J.D. Mammosser, B.E. Robertson
ORNL RAD, Oak Ridge, Tennessee, USA
R. Afanador, M.S. Champion, M.N. Greenwood, M.P. Howell, S.-H. Kim, S.E. Stewart, D.J. Vandygriff
ORNL, Oak Ridge, Tennessee, USA
A. Bitter, K.B. Bolz, A. Navitski, L. Zweibäumer
RI Research Instruments GmbH, Bergisch Gladbach, Germany
E. Daly, G.K. Davis, P. Dhakal, D. Forehand, K. Macha, C.E. Reece, K.M. Wilson
JLab, Newport News, Virginia, USA
Funding:UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE) The Proton Power Upgrade (PPU) Project at Oak Ridge National Lab’s Spallation Neutron Source (SNS) is currently under construction. The project will double the beam power from 1.4 to 2.8 MW. This is accomplished by increasing the beam current and adding seven new Superconducting Radio Frequency (SRF) cryomodules. Each new cryomodule will contain four six-cell, beta 0.81, PPU style cavities. A quality assurance plan was developed and implemented for the procurement of 32 PPU cavities. As part of this plan, reference cavities were qualified and sent to Research Instruments Co. for the development and verification of process steps. Here we present the results from this plan to date.
M. Bertucci, A. Bosotti, A. D’Ambros, A.T. Grimaldi, P. Michelato, L. Monaco, C. Pagani, R. Paparella, D. Sertore
INFN/LASA, Segrate (MI), Italy
A. Gresele, A. Torri
Ettore Zanon S.p.A., Nuclear Division, Schio, Italy
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy
M. Rizzi
Ettore Zanon S.p.A., Schio, Italy
INFN-LASA is currently involved in the production of PIP-II low-beta cavity prototypes. The main challenge of this activity is to develop a state-of-the art surface treatment recipe on such cavity geometry, to achieve the high-Q target required for cavity operation in the linac. This paper reports the status of cavity treatments development and the first cold test results of a single-cell cavity. This cavity has undergone a baseline treatment based on Electropolishing as bulk removal step. Being this test successful, a strategy for pushing the cavities towards higher performances is here proposed.
Z. Sun, M. Liepe, T.E. Oseroff, R.D. Porter
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
T. Arias, Z. Baraissov, D.A. Muller, N. Sitaraman
Cornell University, Ithaca, New York, USA
C. Dukes
University of Virginia, Charlottesville, Virginia, USA
D. Johnson-McDaniel, M. Salim
CCMR, Ithaca, New York, USA
Surface oxides on Nb and Nb3Sn SRF cavities, as a thin ’dirty’ layer, could be critical to their performance as suggested by recent theory. Although these oxides have been studied in the past, we intend here to provide a deeper understanding based on a systematic study on coupon samples that have been processed under the different conditions currently used in SRF cavity treatments. Our aim is to obtain a more complete picture of the oxide evolution. This then might help to explain the observed cavity performance variation, and might allow designing a process to achieve a designed, optimized surface with controlled oxides types and thickness. We find that the surface oxides are in amorphous phase that exhibits normal conducting behaviors, while the pentoxide further degrades with time. Also, we observed a thin hydroxide layer on the outermost surface and possibly Nb(OH)x motifs in the bulk. Moreover, distinctive oxide structures were found in Nb3Sn samples from vapor diffusion, electroplating, and sputtering. The semiconducting SnOx appeared through the oxide depth in vapor diffused Nb3Sn, while a ~1 nm SnOx layer merely exists at the outermost surface of electroplated Nb3Sn.
G.H. Biallas
Hyperboloid LLC, Yorktown, Virginia, USA
E. Daly, K. Macha, C.E. Reece
JLab, Newport News, Virginia, USA
Funding:Funding supplied by US Department of Energy SBIR Grant #DE-SC0019579 Hyperboloid LLC developed and successfully tested a System of High Force Spring Clamps to substitute, one for one, for bolts on the flanges of SRF Cavities. The Clamps are like exceptionally forceful binder clips. The System, that includes the Hydraulic Openers that apply the clamps, minimizes generation of particulates when sealing cavity flanges. Hyperboloid LLC used ANSYS to design the titanium clamps that generate the force to seal the hexagonal cross section, relatively hard aluminum gasket developed for TESLA and used at JLab and other accelerators. The System is developed to be suitable for use in SRF Clean Rooms. Results of particle counter readings during bolt and clamp installation and superfluid helium challenges to the sealed flanges are discussed. Results of a half-size clamp that could seal a soft aluminum gasket and the attempt to seal a gasket made of niobium are also discussed. L. Monaco, P. Michelato, C. Pagani, N. Panzeri, Experimental and Theoretical Analysis of Tesla-like SFRF Cavity Flanges, INFN Milano- LASA, I-20090 Segrate (MI), Italy. Proc. EPAC 2006, Edinburgh, SC
D. Bafia, A. Grassellino, A.S. Romanenko
Fermilab, Batavia, Illinois, USA
We studied the role of O concentration with depth in the performance of Nb SRF cavities. An ensemble of electropolished 1.3 GHz cavities, which initially showed high field Q-slope (HFQS), was subjected to sequential testing and treatment with in-situ low temperature baking at various temperatures. We find that increasing the bake duration causes (i) an increase in the onset of HFQS until it is absent up to quench (ii) a non-monotonic relationship with the quench field (iii) an evolution of the RBCS toward a non-equilibrium behavior that drives anti-Q slope. Our data is qualitatively explained by assuming an O diffusion model and suggests that the mitigation of HFQS that arises from 120°C in-situ LTB is mediated by the diffusion of O from the native oxide which prevents the precipitation of proximity-coupled Nb nano-hydrides, in turn enabling higher quench fields. The decrease in quench field for cavities in which O has been diffused >90 nm from the RF surface may be due to a reduction of the field limit in the SS bilayer structure. We also suggest that the evolution of the RBCS occurs due to the absence of proximity coupled inclusions, bringing about non-equilibrium effects.
We report on an investigation of the effect of a new baking process called "furnace baking" on the quality factor. Furnace baking is performed as the final step of the cavity surface treatment; the cavities are heated in a vacuum furnace in a temperature range of 200-800C for 3 h, followed by high-pressure rinsing and radio-frequency measurement. We find the anti-Q-slope for cavities furnace-baked at a temperature range of 250 to 400C and a reduction in the residual resistance for all cavities. In particular, an extremely high Q value of 5·1010 at 16 MV/m and 2.0 K is obtained for cavities furnace-baked at 300C.
D. Bafia, M. Checchin, A. Grassellino, A.S. Romanenko
Fermilab, Batavia, Illinois, USA
J. Zasadzinski
IIT, Chicago, Illinois, USA
We report recent studies on the anomalous frequency variations of 1.3 GHz Nb SRF cavities near the transition temperature Tc and use them to investigate the underlying physics of state-of-the-art surface treatments. One such feature, a dip in frequency, correlates directly with the quality factor at 16 MV/m and the anti-Q slope that arise in cavities with dilute concentrations of N interstitial in the RF layer achieved via N-doping and mid temperature baking. For N interstitial, we find that the dip magnitude and Tc follow exponential relationships with the electronic mean free path. We present the first observation of the frequency dip near Tc in a cavity baked at 200 C in-situ for 11 hours, which is concurrent with the anti-Q slope, and may be driven by oxygen diffused from the native oxide, thus suggesting the possibility of ‘‘O-doping.’’ We also investigate the conductivities of two cavities that display different resonant frequency behaviors near Tc and suggest that the anti-Q slope and frequency dip phenomena may occur in the presence of interstitial N or possibly O that inhibit the formation of proximity coupled Nb nano-hydrides.
G.B.G. Stenning
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
A. Sublet, G. Vandoni, L. Vega Cid, W. Venturini Delsolaro, P. Vidal García
CERN, Meyrin, Switzerland
"Bulk niobium (Nb) has been the material of choice for superconducting RF (SRF) cavities but for further improvement in cavity RF performance, one may have to turn to films of Nb and to other superconducting materials deposited on copper as thermal and mechanical support. Other materials known as A15, such as Nb3Sn or V3Si and B1 such as NbTiN and NbN are much easier to synthesise in thin films rather than being made as bulk cavity. The potential benefits of using materials other than Nb would be a higher Tc, a potentially higher critical held Hc, leading to potentially significant cryogenics cost reduction if the cavity operation temperature is 4.2 K or higher. We report on optimising deposition parameters and effect of substrate treatment prior to deposition for successful synthesising of Nb and the alternative superconducting thin film with high superconducting properties (Tc and Hsh) on flat substrates and QPR samples in single layer. The DC and RF SC properties have been tested using PPMS and QPR measurements. This work is part of the H2020 ARIES collaboration. We further report on preparation of RF cavities employing these alternative material for future cavity production."
