DESY, Hamburg
JLAB, Newport News, Virginia
The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock
In this contribution, we report progress on the development of a hybrid lead/niobium superconducting RF (SRF) photoinjector. The goal of this effort is to build a Nb injector with the superconducting cathode made of lead, which demonstrated in the past superior quantum efficiency (QE) compared to Nb Three prototype hybrid devices, consisting of an all-niobium cavity with an arc-deposited spot of lead in the cathode region, have been constructed and tested. We present the cold test results of these cavities with and without lead.
JLAB, Newport News, Virginia
A major portion of the ILC R&D effort is focused on increasing the sustainable gradients in the baseline TESLA-shape SC cavities. This is a world-wide effort with major contributions from DESY (in parallel with their XFEL program), JLAB, FNAL and KEK. During the past year, the work in the US and Japan has ramped up considerably, and PAC09 is an opportune time to review the contributions from the groups in these regions, as well as at DESY.
IHEP Beijing, Beijing
KEK, Ibaraki
TIPC, BeiJing
Funding: Supported by National Natural Science Foundation of China (10525525)
1.3 GHz single cell large grain (LG) cavities have been studied in our research programs on the superconducting cavity for the International Linear Collider (ILC) in the last three years and five LG cavities were fabricated at IHEP and KEK. Three cavities were dealt with by surface treatments based on electro polishing (EP) and the maximum gradient of 47.90 MV/m was achieved. The other two cavities were treated based on chemical polishing (CP) and both reached the accelerating gradients higher than 35 MV/m with the maximum gradient of 40.27 MV/m. In this paper, the performance comparison of the large grain cavities will be presented and discussed.
ANL, Argonne
CEA, Gif-sur-Yvette
JLAB, Newport News, Virginia
Fermilab, Batavia
NHMFL, Tallahassee, Florida
IIT, Chicago, Illinois
Funding: DOE/OHEP
We have begun using Atomic Layer Deposition (ALD) to synthesize a variety of surface coatings on coupons and cavities as part of an effort to produce rf structures with significantly better performance and yield than those obtained from bulk niobium, The ALD process offers the possibility of conformally coating complex cavity shapes with precise layered structures with tightly constrained morphology and chemical properties. Our program looks both at the metallurgy and superconducting properties of these coatings, and also their performance in working structures. Initial results include: 1) evidence from point contact tunneling showing magnetic oxides can be a significant limitation to high gradient operation, 2) experimental results showing the production sharp niobium/oxide interfaces from a high temperature bake of ALD coated Al2O3 on niobium surfaces, 3) results from ALD coated structures.
BNL, Upton, Long Island, New York
Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
A beam excited 56 MHz RF Niobium Quarter Wave Resonator has been proposed to enhance RHIC beam luminosity and bunching. As multipacting is expected, an extensive study was carried out with the Multipac 2.1 code, looking for a way to suppress it. Multipacting bands were found. Discharge occurred at cavity’s top corner above beam gap and on outer conductor up to more than half its length, moving towards the end of the cavity. We find single-point multipacting, with emission from the outer conductor, as well as two-point multipacting involving both inner and outer conductor. We found a geometric approach to suppressing multipacting. The most promising method was ripples in outer conductor. Ripples’ depth, width and gap were optimized. In shallow depth of 1 cm, electrons multiply, drift further, however they are stopped by 2 cm ripples. Width of 1 and 3 cm didn’t work as in 1 cm electrons emerge out of it, whereas, in 3 cm, they resonate and trap inside. A 2 cm wide was found good. Likewise, 2 cm gap was valuable. Finally, we find that ripples of 2 cm deep, 2 cm wide spaced by 2 cm completely suppressed multipacting, and were adopted for fabrication.
IHEP Beijing, Beijing
TIPC, BeiJing
Funding: NSFC 10525525
With the aim to develop 1.3 GHz superconducting radio-frequency (SCRF） technology in the frame of ILC collaboration, IHEP has started a program to build a SCRF Accelerating Unit. This unit contains a 9-cell 1.3 GHz superconducting cavity, a short cryomodule, a high power input coupler, a tuner, a low level RF system and a high power RF source, etc. This program also includes the SCRF laboratory upgrade, which will permit the unit to be built and tested at IHEP. We will use this unit as a horizontal test stand for many 9-cell cavities and other components (e.g. input couplers, tuners), as in Europe and North America. In this paper, we report the recent R&D status and the future plan of this program.
CLASSE, Ithaca, New York
Funding: Work Supported by the U.S. Department of Energy
Cornell University’s superconducting niobium nine-elliptical-cell cavity testing and repair program is one contributor to the collaborative effort on critical SRF R&D for the ILC. The Cornell University program benefits from several unique features which provide for the rapid testing and, if necessary, repair of ILC nine-cell cavities: a continuous vertical electropolish procedure, superfluid helium second sound defect location, and tumble polishing. First, we report on the cavity 2K RF performance and the effect of micro-EP preceding the cavity test. Single-cell results at KEK have shown that micro-EP as a final surface treatment reduces the spread in gradients, but micro-EP has not yet been tried with multi-cell cavities. Secondly, we report on the highly efficient method of detecting defects using a few He-II second sound wave detectors and powering several modes of the 1.3GHz TM010 passband.
CLASSE, Ithaca, New York
Funding: Work Supported by the NSF and the DOE
An innovative reentrant cavity design instigated the initial, highly successful, superconducting niobium reentrant-single-cell cavity tests at Cornell and KEK. Prompted by the success of the single cell program a joint effort of Cornell University and Advanced Energy Systems (AES) fabricated two multiple-cell reentrant cavities: a three-cell and a nine-cell cavity. This paper reports the development status of these two cavities. First, the results of cold tests, superfluid helium defect location and repair work on the reentrant nine-cell cavity will be presented. Second, the results of cold tests, including defect location and repair efforts of the reentrant three-cell cavity will be presented.
CLASSE, Ithaca, New York
The superheating magnetic field of a superconducting niobium 1.3 GHz reentrant cavity was measured at several points in the temperature range from (1.7 to 4.4) K. This experimental data is used to discriminate between two competing theoretical s for the temperature dependent behavior of the RF superheating field. Measurements were made with <250 us high power pulses (HPP, ~1MW) to avoid defect initiated thermal breakdown from contaminating the data. Our test incorporated oscillating superleak transducers to determine the cavity quench locations and characterize changes and the migrations of the quench locations during processing. This information provides insight into the factors which limit the ultimate achievable RF surface magnetic field.
DESY, Hamburg
ACCEL, Bergisch Gladbach
W.C. Heraeus GmbH, Materials Technology Dept., Hanau
A test program of 1.3 GHz TESLA shape 9-cell large grain (LG) resonators for the European XFEL project was started at DESY. The main aim is to find out whether or not the choice of LG material could be an option for the fabrication of approx. 800 XFEL resonators. Several aspects are under investigation and will be compared with the conventional polycrystalline material option. One of the aspects is the material issue: could the required amount of LG niobium be produced at industry in a cost effective and reliable manner? The second issue is the fabrication of cavities: could the series production of resonators be done on the level of required accuracy and costs? The third one is the performance issue: what is the appropriate treatment for reproducibly achieving the specified XFEL accelerating gradients? Development of the LG disc production was done within the framework of the R&D program of DESY and W. C. HERAEUS. Eleven resonators are produced at the company ACCEL. Up to now three resonators are RF-tested vertically. The He-vessel was welded onto one of the resonators which passed the horizontal RF-test. The data and perspectives of the LG cavity application are discussed.
DESY, Hamburg
JLAB, Newport News, Virginia
Technological aspects of seamless tube fabrication and multi-cell cavity production by hydroforming will be discussed. Problems related to the fabrication of seamless cavities from bulk niobium are mainly solved. Several two cell- and three cell- niobium cavities have been produced by hydroforming at DESY. A 9-cell cavity of the TESLA shape has been completed from three sub-sections at company ZANON. The cavity was treated by electropolishing (EP) and successfully RF-tested. Two 3-cell units equipped with niobium beam pipes are being RF-tested after BCP surface treatment. The temperature mapping method with Jlab’s two-cell thermometry system is applied for performance analysis. It is of particular interest to compare the seamless cavity quench locations to those from standard cavities. The cryogenic test results and the T-mapping findings will be discussed. Of special interest is the combination of the seamless technique with NbCu cladding, i.e. the fabrication of cavity from bimetallic clad NbCu tube by hydroforming. Fabrication of single-cell and multi-cell NbCu clad cavities by hydroforming from bimetallic tubes is proven. Some test results will be presented.
Fermilab, Batavia
Combined temperature mapping and optical inspection of SRF cavities has revealed defects near the edge of the heat affected zone (HAZ) of numerous welds. We have re-created similar defects on welded coupons that were electropolished in the lab and characterized by a variety of tools. Several features that may have bearing on the origin of these defects are discussed, such as their location relative to grain boundaries, the strain state of the niobium prior to welding and etching, the electropolishing parameters, and so forth. Since coupons are useful for distribution to academic researchers, we also describe other detailed characterizations.
FZJ, Jülich
Forschungszentrum Jülich GmbH, Institut fur Nuklearchemie (INC), Jülich
The paper describes the design, fabrication and first test results of the triple-spoke cavity (resonant frequency 352 MHz, beta=0.48) developed at Forschungszentrum Jülich in the frame of High Intensity Pulsed Proton Injector project. The cavity has 5 cm diameter beam aperture, a transverse radius of 21.7 cm and the whole length of 78 cm. An initial wall thickness of niobium sheets used for cavity fabrication was around 4 mm. The RF cavity design has been adapted to two main goals - the simplest technology of cavity manufacture and for the prime goal of the project to achieve the best possible structural parameters (Lorenz force frequency shift and a resonant frequency pressure dependence). Intense cavity structural analyses have been conducted and the further prospectives on cavity developments are also presented. Construction of the niobium cavity prototype has been completed, the cavity has been chemically processed. Results of initial cold test are discussed.
KEK, Ibaraki
KAKEN Inc., Mito
Sokendai, Ibaraki
In order to achieve higher and more stable performance of super conducting radio-frequency (SRF) cavities, extensive effort in development and application has been done for surface treatment and conditioning methods. Those methods have been evaluated with vertical tests showing lots of remarkable results in cavity performance. However it cannot be well understood yet how surface treatment or conditioning contributed to the results and which step of process in the treatment or conditioning affected the results. In this article, we describe our try to understand those questions focusing on the surface analyses with scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) for electro-polishing (EP) processed niobium sample coupons.
KEK, Ibaraki
JLAB, Newport News, Virginia
The Electro-polishing process is the best candidate of final surface treatment for the production of ILC cavities. Nevertheless, the broad distribution of the gradient caused by field emitters in cavities is sitll a serious problem for the EP process. Ethanole- and degreaser-rinse processes after the EP process were found to be effective to decrease the field emmitter in recent studies, however, these are not perfect yet. We tried to test the sponge cleaning as the post EP process to remove the field emitter inside the cavcity. This article describe the results of series tests with a proto-type sponge-cleaning tool for single-cell cavity at KEK.
Plansee Metall GmbH, Reutte
W.C. Heraeus GmbH, Materials Technology Dept., Hanau
Sheet material made of high-purity Niobium (Nb-RRR) is the key component for future linear accelerators based on the superconducting radio-frequency technology. To be prepared for large production scale quantities, which are demanded for the upcoming projects like XFEL and ILC respectively, W.C. Heraeus (D) and Plansee SE (A) joined there competencies in the field of Nb-RRR. In 2007 the qualification procedure as material supplier for the XFEL project could be successfully finished and a complete product and technology package for products made of Nb-RRR was established. Based on the combination of the high expertise and long-term experience in electron beam melting of different Nb-RRR qualities; the knowledge and availability of various processing technologies for manufacturing of semi-finished and ready to assemble components; and the unique analytical capabilities for advanced quality control along the process chain customized product solutions can be realized for the accelerator industry. Beside a general overview about the production capabilities a strategy for installation of a Quality-Assurance-Management system for large production scale quantities are presented.
INFN/LASA, Segrate (MI)
Funding: Work partially supported by the FP6 EU programs EUROTRANS (Contract FI6KW-CT-2004-516520) and CARE/HIPPI (Contract RII3-CT-2003-506395).
The two TRASCO elliptical superconducting cavities for low energy (100-200 MeV) protons have been completed with equipping them with cold tuner and a magnetic shield internal to the helium tank. One of the two structures is now available for significative tests of Lorentz Force Detuning control of these low beta structures under pulsed conditions for future high intensity linac programs, as SPL or the ESS. The second structure will be integrated in a single cavity cryomodule under fabrication for the prototypical activities of the EUROTRANS program for nuclear waste trasmutation in accelerator driven systems.
LANL, Los Alamos, New Mexico
JLAB, Newport News, Virginia
Funding: DTRA
805 MHz elliptical SRF cavities have been used for SNS as the first application for protons. At LANL, an R&D started to explore a capability of getting high-gradient cavities (40-50 MV/m) at this frequency for the future applications such as proton and muon based interrogation testing facility added to the LANSCE accelerator and a power upgrade of the LANSCE accelerator for the fission and fusion material test station. Optimized cell designs for “standard”, “low-loss” and “re-entrant” shapes, cavity test results for “standard” single-cell cavities with temperature mapping as well as surface inspection results will be presented.
NSCL, East Lansing, Michigan
A medium-velocity half wave resonator has been designed and prototyped at the National Superconducting Cyclotron Laboratory for use in a heavy ion linac. The cavity is designed to provide 3.7 MV of accelerating voltage at an optimum beta = v/c = 0.53, with peak surface electric and magnetic fields of 32.5 MV/m and 79 mT, respectively. The resonant frequency is 322 MHz. The cavity was designed to reduce sensitivity to bath pressure fluctuations while maintaining a structure that can be easily fabricated, cleaned, and tuned. Deep draw forming dies and a copper cavity prototype were fabricated to confirm tolerances and formability. A prototype tuner was built; the helium vessel and power coupler have been designed. Measurements were performed to confirm finite element predictions for the mechanical modes, bath pressure sensitivity, tuner stiffness, and tuning range.
MHI, Kobe
We report on the activities and achievements at MHI about cavity fabrication for ILC. Some new procedures of cavity fabrication for industrialization are reported.
SINAP, Shanghai
SSRF, Shanghai
RF system for SSRF (Shanghai Synchrotron Radiation Facility) Storage Ring consists of three RF stations, each of which has a klystron, one superconducting RF module and its low level RF feedback control. A 300kW klystron will feed the RF power to the superconducting cavity via a circulator and waveguides. Three CESR type 499.654MHz superconducting modules with tuning range ±150kHz are now in operation. A digitalized I/Q technology based on FPGA is adopted in its low level control. The commissioning and the performance of whole RF system will be described in details in this paper.
JLAB, Newport News, Virginia
Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
The great majority of experience in niobium SRF cavity processing at Jefferson Lab is with BCP etching. This has been used on CEBAF cavities and others totaling over 500 in number. With improved process quality control, field emission is now largely controlled and other factors limit performance. All of the prototype cavities developed for the 12 GeV upgrade, although meeting minimum requirements, have demonstrated a Q-drop in the 17 23 MV/m range that is not remedied by 120 C bake. Most of these cavities received >250 micron removal by BCP etch. Three of these cavities are being electropolished using the protocol under development within ILC R&D activities. The first such cavity was transformed from Q = 3 ·1010 at 17 MV/m to quench from 1010 at 35 MV/m. The details of this and two subsequent electropolished JLab 7-cell cavities will be reported.
JLAB, Newport News, Virginia
The College of William and Mary, Williamsburg
North Carolina State University, Raleigh, North Carolina
Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
As SRF cavities approach fundamental material limits, there is increased interest in understanding the details of topographical influences on performance limitations. Micro-and nano-roughness are implicated in direct geometrical field enhancements and complications of the composition of the 50 nm surface layer in which the super-currents flow. Interior surface etching (BCP/EP) to remove mechanical damage leaves surface topography, including pits and protrusions of varying sharpness. These may promote RF magnetic field entry, locally quenching superconductivity, so as to degrade cavity performance. A more incisive analysis of surface topography than the widely-used average roughness is needed. In this study, a power spectral density (PSD) approach based on Fourier analysis of surface topography data acquired by both stylus profilometry and atomic force microscopy (AFM) is being used to distinguish the scale-dependent smoothing effects. The topographical evolution of the varied starting state Nb surface (CBP/ EBW) as a function of applied etching, polishing steps and conditions is reported, resulting in a novel qualitative and quantitative description of Nb surface topography.
JLAB, Newport News, Virginia
The College of William and Mary, Williamsburg
Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Future accelerators require unprecedented cavity performance, which is strongly influenced by interior surface nanosmoothness. Electropolishing is the technique of choice to be developed for high-field superconducting radiofrequency cavities. Electrochemical impedance spectroscopy (EIS) and related techniques point to the electropolishing mechanism of Nb in a sulfuric and hydrofluoric acid electrolyte of controlled by a compact surface salt film under F- diffusion-limited mass transport control. These and other findings are currently guiding a systematic characterization to form the basis for cavity process optimization, such as flowrate, electrolyte composition and temperature. This integrated analysis is expected to provide optimum EP parameter sets for a controlled, reproducible and uniform surface leveling for Nb SRF cavities.
JLAB, Newport News, Virginia
The College of William and Mary, Williamsburg
Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Much remains to be learned regarding the details of SRF performance effects with material variation, including niobium treated in different ways, and different bulk/thin film materials that are fabricated under different conditions. A facility that can measure small samples’ RF properties in a range of 0~180mT magnetic field and 2~20k temperature is necessary in order to answer this question. The Jefferson Lab surface impedance characterization (SIC) system has been designed to attempt to meet this requirement. The SIC system uses a sapphire-loaded cylindrical Nb cavity at 7.5GHz with 50mm diameter flat sample placed on a non-contacting end plate and a calorimetric technique to directly measure the rf dissipation in the sample in response to known rf fields over ~1 cm2. We report on the commissioning of this system and its first uses for characterizing materials. Preliminary tests with Nb thin film sample sputtered on Cu substrate, and bulk Nb sample have been done at low field. The presently available hardware is expected to enable tests up to 20 mT peak magnetic field on the sample CW. Paths to higher field tests have been identified.
JLAB, Newport News, Virginia
Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
SRF cavities are observed to be limited by non-linear localized effects. The variation of local material parameters between "hot" and "cold" spots is thus of intense interest. Such locations were identified in a BCP etched large-grain single-cell cavity and removed for examination by high resolution electron microscopy (SEM), electron-back scattering diffraction microscopy (EBSD), and scanning Auger electron spectroscopy (SAM). Pits with clear crystal facets were observed on both "Hotspot" and "Coldspot" specimens. The pits were found in-grain and on "Y"-shaped junction of three crystals. They are interpreted as etch pits induced by surface crystal defects (e.g., dislocations). All "Coldspots" examined had obvious low density of etching pits or very shallow tri-crystal boundary junction. EBSD revealed crystal structure surrounding the pits via crystal phase orientation mapping. This study suggests a mechanism by which BCP etching creates pits on large-grain Nb cavity surfaces and sharp-edged topography in fine-grain Nb. Field enhancements at very deep, sharp and densely populated etching pits may then cause distributed hotspots and limit cavity performance.
University of Pennsylvania, Philadelphia, Pennsylvania
TRIUMF, Vancouver
The quality factor of superconducting radio-frequency cavities typically degrades with increasing field at moderate gradients before the on-set of field emission. The origin of the so called medium field Q-slope is not fully described and understanding it would be important in order to develop a cavity design or treatment which minimizes this effect, allowing us to produce cavities with reduced cryogenic losses. This paper will present an analysis of the medium field Q-slope data measured on cavities at different frequencies treated with buffered chemical polishing (BCP) at TRIUMF. The data is compared with existing models and agreements-discrepancies will be highlighted.
AES, Medford, NY
Funding: Work supported by The Department of Energy under SBIR Contract DE-FG02-08ER85054
From past work we found that within the cost of the String Assembly that dominates the overall cost of the cryomodules for ILC, the greatest cost elements are the helium vessel with the 2 phase pipe assembly, the niobium material, and the SRF cavity fabrication*. The cost of niobium is dependant upon market supply and demand and is essentially out of our control. We have carried out an aggressive study to reduce the cost of cavity fabrication in a high production environment**, which leaves the helium vessel for further investigation. It is recognized that significant cost savings may be realized if the helium vessel could be constructed of stainless steel instead of titanium material as is currently planned. To facilitate this change (AES) has designed a niobium to stainless steel transition assembly that will interface the helium vessel to the SRF Cavity at each end. Details of the design and analysis of the low cost helium vessel assembly are discussed along with potential cost reductions for the ILC high production run.
*E. Bonnema, J. Sredniawski,"ILC RF Unit Industrial Cost Study Methodology & Results"
**A. Favale, J. Sredniawski, M. Calderaro, E. Peterson,"ILC Cavity Fabrication Optimization for High Production"