Niobium Superconducting Cavity for Radio Frequency: A Review (original) (raw)
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Use of Niobium for Fabricating Superconducting Radio Frequency Cavities
Since the pioneer work done by the High-Energy Physics Lab at Stanford University in 1965, superconducting radio frequency (SRF) technology has been developing steadily up to now. Demanding on niobium (Nb) has been increasing constantly, since more and more particle accelerators select Nb based SRF technology as a key part of their accelerator constructions. For example, the proposed International Linear Collider (ILC) that will probe new physics using TeV collisions of electron and positron beams will need approximately 17,000 1-meter-long Nb SRF cavities. Others such as x-ray free electron laser (XFEL) at DESY in Germany, energy recovery linac (ERL) at Cornell University in USA, the new Spiral 2 facility in France, the isotope separation and acceleration (ISAC) II in Canada, and the 12 GeV upgrade of CEBAF at Jefferson Lab in USA will all require Nb. This popularity in Nb can be, at least partially, attributable to the unique physical and mechanical properties that Nb possesses ---the highest superconducting transition temperature of 9.25 K and the highest superheating field of 0.23 T among all available pure metals with excellent ductility that enables machining to be done relatively easily. In this chapter, the use of Nb for fabricating SRF cavities is reviewed, giving particular attention to some examples of important new developments in the past decade on reducing the production costs and increasing the throughput of high quality Nb SRF cavities. Some R&D examples on the study of the requirements in the physical, chemical, metallurgical, and mechanical properties of Nb for the applications in particle accelerators based on Nb SRF technology are updated and reviewed. This chapter also includes some unpublished experimental results from my own research. Hopefully this review can be served as a useful reference for new researchers who want to use Nb for their various R&D projects in particle accelerators and for Nb suppliers and manufacturers who want to provide the best and the most economic products to be used in particle accelerators.
Superconducting RF materials other than bulk niobium: a review
Superconductor Science and Technology
For the past five decades, bulk niobium (Nb) has been the material of choice for Superconducting RF (SRF) cavity applications. Alternatives such as Nb thin films and other higher-T c materials, mainly Nb compounds and A15 compounds, have been investigated with moderate effort in the past. In recent years, RF cavity performance has approached the theoretical limit for bulk Nb. For further improvement of RF cavity performance for future accelerator projects, research interest is renewed towards alternatives to bulk Nb. Institutions around the world are now investing renewed efforts in the investigation of Nb thin films and superconductors with higher transition temperature T c for application to SRF cavities. This paper gives an overview of the results obtained so far and challenges encountered for Nb films as well as other materials, such as Nb compounds, A15 compounds, MgB 2 , and oxypnictides, for SRF cavity applications. An interesting alternative using a Superconductor-Insulator-Superconductor multilayer approach has been recently proposed to delay the vortex penetration in Nb surfaces. This could potentially lead to further improvement in RF cavities performance using the benefit of the higher critical field H c of higher-T c superconductors without being limited with their lower H c1 .
Superconducting Radio-Frequency Cavities
Annual Review of Nuclear and Particle Science, 2014
Superconducting cavities have been operating routinely in a variety of accelerators with a range of demanding applications. With the success of completed projects, niobium cavities have become an enabling technology, offering upgrade paths for existing facilities and pushing frontier accelerators for nuclear physics, high-energy physics, materials science, and the life sciences. With continued progress in basic understanding of radio-frequency superconductivity, the performance of cavities has steadily improved to approach theoretical capabilities.
Superconducting Radio-Frequency Fundamentals for Particle Accelerators
Reviews of Accelerator Science and Technology, 2012
An overview of fundamentals of superconductors under radio-frequency electromagnetic fields in particle accelerators is given, with emphasis on intrinsic physics and materials mechanisms which limit the performance of the superconducting radio-frequency (SRF) resonator cavities. Multiscale mechanisms which control the surface resistance and the quality factor of the SRF cavities at low and high rf fields are discussed. We also discuss possible ways of pushing the limit of the SRF performance by materials impurities and multilayer nanostructuring which may open up opportunities of using materials other than Nb to significantly increase the maximum accelerating fields and improve the performance of the SRF cavities operating at 4.2 K.
Thin superconducting niobium-coatings for RF accelerator cavities
2005
The paper describes efforts of four institutions which are engaged in the realization of the Work Package 4 (Thin Film Cavity Production) of the Joint Research Activity (JRA-1) within a frame of the Coordinated Accelerator Research in Europe (CARE) program. JRA-1 is aimed at developing superconducting RF technology, mainly methods for producing superconducting Nb coated copper cavities which might ensure higher accelerating fields, lower RF losses and considerable reduction of costs, as compared with the present state of art. WP4 is thus focused on the development of a new method to produce thin Nb-coatings by means of arc discharges performed under ultra-high vacuum (UHV) conditions.
RF CHARACTERIZATION OF NIOBIUM FILMS FOR SUPERCONDUCTING CAVITIES *
The surface resistance R S of superconductors shows a complex dependence on the external parameters such as temperature, frequency or radio-frequency (RF) field. The excited modes of 400, 800 and 1200 MHz allow measure-ments at actual operating frequencies of superconducting cavities. Niobium films on copper substrates have several advantages over bulk niobium cavities. HIPIMS (High-power impulse magnetron sputtering) is a promising tech-nique to increase the quality and therefore the performance of niobium films. This contribution will introduce CERNs recently developed HIPIMS coating apparatus. Moreover, first results of niobium coated copper samples will be pre-sented, revealing the dominant loss mechanisms.
2010
A 1.3 GHz test cavity has been designed to test wafer samples of superconducting materials. The surface magnetic field on the sample wafer is 3.75 times greater than anywhere else on the cavity surface. The cavity also facilitates measurement of the rf surface resistance corresponding to a Q of 10 10 . The cavity is operated in a TE 01 mode. A high purity sapphire hemisphere is used to enhance the circulating field on the sample and suppress the fields on the remainder of the cavity surface. The sapphire purity must be tested for its loss tangent and dielectric constant. To test these properties a smaller sapphire rod of the same quality will be inserted into a CEBAF cavity operating in a TE 01 mode. This will allow us to measure the temperature of the sapphire as a function of input energy and time, and the dielectric constant through its effect on the resonant frequency.
2011
Significant performance degradation of superconducting RF (radio frequency) niobium cavities in high RF field is strongly associated with the breakdown of superconductivity on localized multi-scale surface defects lying within the 40 nm penetration depth. These defects may be on the nanometer scale, like grain boundaries and dislocations or even at the much larger scale of surface roughness and welding pits. By combining multiple superconducting characterization techniques including magneto-optical (MO) imaging and direct transport measurement with non-contact characterization of the surface topology using scanning confocal microscopy, we were able to show clear evidence of suppression of surface superconductivity at chemically treated RF-quality niobium. We found that pinning of vortices along GBs is weaker than pinning of vortices in the grains, which may indicate suppressed superfluid density on GBs. We also directly measured the local magnetic characteristics of BCP-treated Nb sample surface using a micro-Hall sensor in order to further understanding of the effect of surface topological features on the breakdown of superconducting state in RF mode.