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The concept of resonant coupling and the benefits that accrue from its application is well known in the world of room temperature coupled cavity linacs. Design studies show that it can be applied successfully between sections of conventional elliptical superconducting coupled cavity accelerator structures and internally to structures with spoked cavity resonators. The coupling mechanisms can be designed without creating problems with high field regions or multipactoring. The application of resonant coupling to superconducting accelerators eliminates the need for complex cryogenic mechanical tuners and reduces the time needed to bring a superconducting accelerator into operation.

The Canadian Light Source (CLS) is a third-generation synchrotron located inSaskatoon, Canada. A superconducting radio frequency (SRF) cavity contained in a 4.43 Kliquid helium I cryostat is used at the CLS to replenish energy loss in the electron beam. Adynamic simulation of this cryostat has been generated to examine pressure and levelfluctuations due to variations in heat loading or other system parameters. This simulatorhas led to some interesting observations in system behavior, which have been shown tooccur in the actual system as well. For example, mass rates of vaporization appear to dropas heat loading increases under certain conditions. Also, the relationship between pressureand SRF tuning characteristics is examined, and the abilities and limitations of thesimulator are presented.

Superconductor Technologies Inc. (STI) developed the Sapphire cryocooler specifically for the SuperLink® product; a high performance superconducting Radio Frequency (RF) front-end receiver used by wireless carriers such as Verizon Wireless and AT&T to improve network cell coverage and data speeds. STI has built and deployed over 6,000 systems operating 24 hours a day (24/7), 7 days a week in the field since 1999. Sapphire is an integrated free piston Stirling cycle cryocooler with a cooling capacity of 5 Watts at 77 Kelvin (K) with less than 100 Watts (W) input power. It has a field-proven Mean Time Between Failure (MTBF) of well over 1 million hours, requires zero maintenance and has logged over 250 million cumulative runtime hours. The Sapphire cooler is built on a scalable technology platform, enabling the design of machines with cooling capacities greater than 1 kilowatt (kW). This scalable platform also extends the same outstanding attributes as the Sapphire cooler, namely high reliability, zero main...

The Facility for Rare Isotope Beams (FRIB) will be a new User Facility for Nuclear Science. The facility is funded by the Department of Energy (DOE) Office of Science and Michigan State University (MSU) and will be constructed on the campus of MSU. The main accelerator for the FRIB project will be a superconducting linac constructed of 52 cryomodules, housing 344 superconducting radio frequency (SRF) cavities. All of the SRF cavities must be operated at superfluid helium temperatures of 2 K. During FRIB fabrication, and prior to the commissioning of the FRIB cryoplant, all cavities and cryomodules must be tested as part of the FRIB quality assurance program. To meet the requirements of FRIB production, upgrades to the existing SRF infrastructure at the National Superconducting Cyclotron Lab (NSCL) must be designed and commissioned. These upgrades include: two additional test Dewars, a FRIB cryomodule testing bay, and a cryogenic system capable of supporting the 2 K cryogenic load, including sub atmospheric pumps, heat exchangers, and JT valves. Transfer lines connecting these new additions will also be designed and fabricated. This paper describes these new systems and show that they will meet FRIB requirements as well as maintaining flexibility for future changes.

Superconducting radio frequency (SRF) cavities made from niobium and cooled with liquid helium are becoming key components of many particle accelerators. The helium vessels surrounding the RF cavities, portions of the niobium cavities themselves, and also possibly the vacuum vessels containing these assemblies, generally fall under the scope of local and national pressure vessel codes. In the U.S., Department of Energy rules require national laboratories to follow national consensus pressure vessel standards or to show "a level of safety greater than or equal to" that of the applicable standard. Thus, while used for its superconducting properties, niobium ends up being treated as a low-temperature pressure vessel material. Niobium material is not a code listed material and therefore requires the designer to understand the mechanical properties for material used in each pressure vessel fabrication; compliance with pressure vessel codes therefore becomes a problem. This report summarizes the approaches that various institutions have taken in order to bring superconducting RF cryomodules into compliance with pressure vessel codes.

Nominal 2-K helium refrigeration systems are frequently used for superconducting radio frequency and magnet string technologies used in accelerators. This paper examines the trade-offs and approximate performance of four basic types of processes used for the refrigeration of these technologies; direct vacuum pumping on a helium bath, direct vacuum pumping using full or partial refrigeration recovery, cold compression, and hybrid compression (i.e., a blend of cold and warm sub-atmospheric compression).

In recent years, single‐crystal/large‐grain niobium has received much attention [1]. It has the following advantages: rolling‐annealing is unnecessary, and superconducting cavities made from large‐grain niobium discs may not require electropolishing. However, to obtain a large‐grain disc, an ingot must be sliced using a saw and finished smooth by using a lathe. Slicing a disc takes several hours and produces niobium shavings. KEK, Tokyo Denkai, and TKX Corporation have developed a new niobium ingot slicing technique [2, 3], and Tokyo Denkai has installed the slicing machine. This study describes the new ingot slicing technology, which ensures state‐of‐the‐art productivity for the superconducting radio frequency (SRF) cavity material industry.

Superconducting radio frequency (SRF) niobium cavities are widely used in high‐energy physics to accelerate particle beams in particle accelerators. The performance of SRF cavities is affected by the microstructure and purity of the niobium sheet, surface quality, geometry, etc. Following optimum strain paths in the forming of these cavities can significantly control these parameters. To select these strain paths, however, information about the mechanical behavior, microstructure, and formability of the niobium sheet is required. In this study the Barlat 2000 yield function has been used as a yield function for high purity niobium. Results from this study showed that, due to intrinsic behavior, it is necessary to evolve the anisotropic coefficients of Barlat’s yield function in order to properly model the plastic behavior of the niobium sheet. The accuracy of the newly developed evolutionary yield function was verified by applying it to the modeling of the hydrostatic bulging of the niobium sheet. Also, i...

Superconducting Radio Frequency (SRF) cavities provide enhanced efficiency and reduced energy utilization in present day particle accelerators. Niobium (Nb) is the material of choice for these cavities due to its high critical temperature and critical magnetic field. In order to understand why certain treatments, especially a low temperature bake, improve performance, it is important to study Nb surface characteristics and identify elemental contamination that can affect the performance of the cavity. H, C, O, and N are of interest because they are interstitial impurities in Nb. In earlier work, SIMS analysis using a CAMECA IMS‐6F with Cs+ primary beam showed that C and N were probably not significant factors impacting performance but there was a very high level of H in the Nb. Ion implants of C, N, O, and D into Nb provided quantification of C, N, O and indicated that D is very mobile in the Nb. Further analyses showed that heat treated Nb has lower levels of surface H than non heat treated Nb and subseq...

Hydrogen is a difficult impurity to physically deal with in superconducting radio frequency (SRF) niobium, therefore, its properties in the metals should be well understood to allow the metal’s superconducting properties to be optimized for minimum loss in the construction of resonant accelerator cavities. It is known that hydrogen is a paramagnetic impurity in niobium from NMR studies. This paramagnetism and its effect on superconducting properties are important to understand. To that end analytical induction measurements aimed at isolating the magnetic properties of hydrogen in SRF niobium are introduced along with optical reflection spectroscopy which is also sensitive to the presence of hydrogen. From the variety, magnitude and rapid kinetics found in the optical and magnetic properties of niobium contaminated with hydrogen forced a search for an atomic model. This yielded quantum mechanical description that correctly generates the activation energy for diffusion of the proton and its isotopes not only in niobium but the remaining metals for which data is available. This interpretation provides a frame work for understanding the individual and collective behavior of protons in metals.

The properties and performance of the ultra high purity Nb used to fabricate superconducting radio frequency (SRF) particle accelerator cavities have been found to vary with processing conditions. One hypothesis for these variations is that hydrogen, absorbed during processing, is responsible for this behavior. The key assumption behind this hypothesis is that niobium can absorb hydrogen from one or more of the processing environments. This paper reviews work examining the validity of this assumption. It was determined that Nb will spontaneously react with water producing adsorbed atomic hydrogen that is readily absorbed into the metal. The passivating oxide film normally prevents this reaction, but this film is frequently removed during processing and it is attacked by the fluoride ion used in the polishing solutions for SRF cavities. However, during electropolishing that cathodic reduction of hydrogen is transferred to the auxiliary electrode and this should suppress hydrogen absorption.

We present a study of superconducting properties of both large grain (1 mm average grain size) and small grain (50 micron average grain size) Niobium materials containing varying amounts of Tantalum impurities that have been used in the fabrication of high accelerating gradient superconducting radio frequency cavities. We found that a buffered chemical polishing of these Niobium samples causes a distinct reduction in the superconducting parameters like TC, wt‐ ppm to 1300 wt‐ppm. Implications of these results on the performance of niobium superconducting radio frequency cavities are discussed, especially the anomalous high field RF losses that have been reported in the literature.

A new cryomodule containing seven low‐beta superconducting radio frequency (SRF) cavities has been added to the ATLAS heavy ion linac, providing an additional 15 MV accelerating potential to the existing accelerator. We describe the final stages of cryomodule assembly, commissioning, and installation in the ATLAS accelerator. The clean techniques used to achieve low‐particulate rf surfaces are presented, as are the module design features which enable clean assembly and reliable high‐gradient operation. The thermal performance of the cryomodule is described, along with performance data for the SRF cavities. Details on subsystem performance including helium and nitrogen systems, vacuum systems, thermal and magnetic shields, slow and fast tuners, and survey/alignment systems are given.

Physics laboratories around the world are developing niobium superconducting radio frequency (SRF) cavities for use in particle accelerators. These SRF cavities are typically cooled to low temperatures by direct contact with a liquid helium bath, resulting in at least part of the helium container being made from pure niobium. In the U.S., the Code of Federal Regulations allows national laboratories to follow national consensus pressure vessel rules or use of alternative rules which provide a level of safety greater than or equal to that afforded by ASME Boiler and Pressure Vessel Code. Thus, while used for its superconducting properties, niobium ends up also being treated as a material for pressure vessels. This report summarizes what we have learned about the use of niobium as a pressure vessel material, with a focus on issues for compliance with pressure vessel codes. We present results of a literature search for mechanical properties and tests results, as well as a review of ASME pressure vessel code requirements and issues.

At the Forschungszentrum Dresden‐Rossendorf the development and the setup of the 2nd superconducting radio frequency photo electron injector (SRF‐Photo‐Gun) is finished. This new injector is placed next to the existing thermionic gun of the superconducting linear accelerator ELBE. A connection between the accelerator and the SRF‐Gun will provide improved beam parameters for the users at the second half of 2009. At the moment the commissioning is fully under way. We will report on important results concerning cavity commissioning like measurements of: Q vs. E, microphonics, Lorentz detuning, tuner parameters, pressure sensibility and in‐situ fundamental mode field distribution calculated from measured pass band.

A helium cryogenic system with cooling capacity of 1 kW at 4.5 K was set up at Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing. This helium refrigeration system is dedicated for the cooling of two superconducting radio frequency (SRF) cavities, two interaction region superconducting quadrupole magnets (SCQ), the Beijing Spectrometer III (BESIII) solenoid magnet (SSM), which are the key items of the upgrade project of Beijing Electron-Positron Collider (BEPCII). Commissioning with the SSM and SCQ magnets has been carried out, which will be introduced in this paper. The cryogenic system of BESIII magnet showed very robust as SSM quenched. This paper presents the overall status and some test results of the cryogenic system.

Fermilab is heavily engaged and making strong technical contributions to the superconducting radio-frequency research and development program (SRF R&D). Four major SRF test areas are being constructed to enable vertical and horizontal cavity testing, as well as cryomodule testing. The existing Fermilab cryogenic infrastructure has been modified to service the SRF R&D needs. The project's first stage has been successfully completed, which allows for distribution of cryogens for a single-cavity cryomodule using the existing Cryogenic Test Facility (CTF) that houses three Tevatron satellite refrigerators. The cooling capacity available for cryomodule testing at Meson Detector Building (MDB) results from the liquefaction capacity of the CTF cryogenic system. The cryogenic system for a single 9-cell cryomodule is currently operational. The paper describes the status, challenges and operational experience of the initial phase of the project.

A new superconducting radio frequency (SRF) cavities test facility is now operational at Fermilab's Meson Detector Building (MDB). The facility is supplied cryogens from the Cryogenic Test Facility (CTF) located in a separate building 500-m away. The design incorporates ambient temperature pumping for super-fluid helium production, as well as three 0.6-kW at 4.5-K refrigerators, five screw compressors, a helium purifier, helium and nitrogen inventory, cryogenic distribution system, and a variety of test cryostats. To control and monitor the vastly distributed cryogenic system, a flexible scheme has been developed. Both commercial and experimental physics tools are used. APACS+{trademark}, a process automation control system from Siemens-Moore, is at the heart of the design. APACS+{trademark} allows engineers to configure an ever evolving test facility while maintaining control over the plant and distribution system. APACS+{trademark} nodes at CTF and MDB are coupled by a fiber optic network. DirectLogic205 PLC's by KOYO{reg_sign} are used as the field level interface to most I/O. The top layer of this system uses EPICS (Experimental Physics and Industrial Control System) as a SCADA/HMI. Utilities for graphical display, control loop setting, real time/historical plotting and alarming have been implemented by using the world-wide library of applications for EPICS. OPC client/server technology is used to bridge across each different platform. This paper presents this design and its successful implementation.

This work investigates properties of large grained, high purity niobium with respect to the forming of superconducting radio frequency (SRF) cavities from such large grained sheets. The yield stresses were examined using tensile specimens that were essentially single crystals in orientations evenly distributed in the standard projection triangle. No distinct yield anisotropy was found, however, vacuum annealing increased the yield strength by a factor 2…3. The deep drawing forming operation of the half cells raises the issues of elastic shape changes after the release of the forming tool (springback) and residual stresses, both of which are indicated to be negligible. This is a consequence of the low yield stress (< 100 MPa) and the large thickness (compared to typical thicknesses in sheet metal forming). However, the significant anisotropy of the transversal plastic strains after uniaxial deformation points to potentially critical thickness variations for large grained / single crystal half cells, thus r...

This paper reviews methods used to produce metallic single crystals. Methods are assessed in terms of being able to use the technique to produce RRR niobium single crystals for RF superconducting accelerator cavities.

As Superconducting Radio Frequency (SRF) technology is used in more accelerator designs, research has focused on increasing the efficiency of these accelerators by pushing gradients and investigating cost reduction options. Today, most SRF structures are fabricated from high purity niobium. Over years of research, a material specification has been derived that defines a uniaxial, fine grain structure for SRF cavity fabrication. Most recently a push has been made to investigate the merits of using single or large grain niobium as a possible alternative to fine grain niobium. Michigan State University (MSU), in collaboration with Fermi National Accelerator Laboratory (FNAL) and Thomas Jefferson National Accelerator Facility (JLAB), is researching large grain niobium via cavity fabrication processes and testing, as well as exploring materials science issues associated with recrystallization and heat transfer. Single‐cell 1.3 GHz (β=0.081) cavities made from both fine and large grain niobium were compared both in terms of fabrication procedures and performance. Two 7‐cell cavities are currently being fabricated.

The Spallation Neutron Source (SNS) is under construction at Oak Ridge National Laboratory. The cold section of the Linac consists of 81 superconducting radio frequency cavities cooled to 2.1K by a 2400 watt cryogenic refrigeration system. The major cryogenic system components include warm helium compressors with associated oil removal and gas management, 4.5K cold box, 7000L liquid helium dewar, 2.1K cold box (consisting of 4 stages of cold compressors), gaseous helium storage, helium purification and gas impurity monitoring system, liquid nitrogen storage and the cryogenic distribution transfer line system. The overall system commissioning and future plans will be presented.

Peking University Superconducting Accelerator Facility (PKU‐SCAF) will be constructed as a multi‐disciplinary integrated base for fundamental and application researches at Peking University in China since 2004. The main SC accelerator shall produce an electron beam of 20MeV for different kinds of experiments. Electrons from the source are being accelerated by two superconducting resonators, which are TESLA‐type 1.3GHz 9‐cell superconducting RF cavities operating at 2K and integrated in one cryostat. A superconducting 2.5‐cell resonator also working at 2K will serve as capture cavity. Consequently, a cryogenic system with the capacity of about 100W at 2K has to be designed, fabricated, tested and operated for the PKU‐SCAF. This paper presents the cryogenic design for PKU‐SCAF using computational process analysis software. The cryogenic characteristics of cryomodule, design concept and layout of overall system are discussed. The critical thermal parameters for major components in the superfluid system are given.

On August 20th 2004 the International Technology Recommendation Panel (ITRP) released its recommendation that the Linear Collider be based on Superconducting RF Technology. Following a request of the organizers of this conference we will summarise in this article the arguments worked out and presented by the ITRP, which led to this recommendation. The main features of both RF‐technologies, the favoured L‐band RF system of the superconducting version of the Linear Collider and the X‐band‐technology anticipated for the normal‐conducting alternative will be briefly described.

In light of the recent developments with the International Linear Collider (ILC), and the recommendation to utilize “Cold” technology for this future particle accelerator, this paper will present the lessons learned from the recently concluded Spallation Neutron Source (SNS) superconducting radio frequency (SRF) cryomodule production run at the Thomas Jefferson National Accelerator Facility (Jefferson Lab). Over the past twenty years Jefferson Lab has worked with industry to successfully design, manufacture, test and commission more SRF cryomodules than any other entity in the United States. The knowledge gained from the design and fabrication of the SNS prototype, eleven — 0.61 (medium) beta and the twelve — 0.81 (high) beta cryomodules, will prove to be an effective asset to the ILC project. After delivery of the final production cryomodule in March 2005, design and fabrication data will be collected, evaluated and presented to make this information beneficial for future particle accelerator projects. Recommendations with respect to these findings will also be presented as an integral part of this paper.

Electron beam (EB) welding in UHV (ultra-high vacuum, 10(-5) divided by 10(-8) mbar) is applied in the standard fabrication of high gradient niobium superconducting radio frequency (SRF) cavities of TESLA design. The quality of EB welding is critical for cavity performance. Experimental data of gas content (H-2, O-2, N-2) and RRR (residual resistivity ratio) measurements in niobium (Nb) welding seams are presented. EB welding in UHV conditions allow to preserve low gas content (1 divided by 3 wt. ppm hydrogen and 5 divided by 7 ppm. oxygen and nitrogen), essential for high values of RRR - 350 divided by 400 units. Gas content redistribution in the electron beam welded and heat affected region take place in the welding process. Correlation between gas solubility parameters, RRR and thermal conductivity are presented. Mechanisms of gas solubility in EB welding process are discussed.

Superconducting Radio Frequency (SRF) cavities are becoming the preferred method of particle acceleration for many new high energy physics projects around the world. These SRF cavities are assembled in series into a thermal structure known as a cryomodule (CM). Currently, Thomas Jefferson National Accelerator Facility (JLab) is providing the superconducting cryomodules for both the Spallation Neutron Source (SNS) and the prototype for the energy upgrade to the JLab Continuous Electron Beam Accelerator Facility (CEBAF). Once completed, the cryomodules are assembled in series to form a superconducting linear accelerator (LINAC) utilized primarily for particle physics research and development. During operation, the cryomodule maintains the temperature of the cavities at 2 K, while the external shell of the cryomodule is at ambient temperature (293 K). This paper will present the design, fabrication and assembly of the CM components in order to optimize thermal performance, which is vital to the SRF cavity operation. This thermal optimization will include both static and dynamic heat load considerations as well as design and assembly techniques.

Energen has patented KelvinAll™, the first material, to exhibit magnetostrictive properties from elevated temperatures to near absolute zero, opening up a new range of applications for magnetostrictive devices. Magnetostrictive materials change their shape in the presence of a magnetic field. This elongation is precise, predictable, reversible and repeatable thereby enabling practical electromechanical devices. KelvinAll has magnetostriction comparable to Terfenol‐D at room temperature and its magnetostriction increases at cryogenic temperatures. Energen has developed and prototyped practical electromechanical devices using KelvinAll. These devices include tuners for superconducting radio frequency (SRF) cavities, components for magnetic refrigerators, flow control valves and precision translation stages some of which will be discussed in greater detail. Energen’s KelvinAll products enhance performance, increase reliability and reduce development costs.

When complete, the Spallation Neutron Source (SNS) will provide a 1 GeV, 2 MW beam for experiments. One portion of the machine’s linac consists of over 80 Superconducting Radio Frequency (SRF) 805 MHz cavities housed in a minimum of 23 cryomodules operating at a saturation temperature of 2.1 K. Minimization of the total heat load is critical to machine performance and for efficient operation of the system. The total heat load of the cryomodules consists of the fixed static load and the dynamic load, which is proportional to the cavity performance. The helium refrigerator supports mainly the cryomodule loads and to a lesser extent the distribution system loads. The estimated heat loads and calculated thermal performance are discussed along with two unique features of this design: the helium heat exchanger housed in the cryomodule return end can and the helium gas cooled fundamental power coupler.