Continuous YBCO - Tape Coating by Thermal Evaporation
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Continuous YBCO – Tape Coating by Thermal Evaporation
Ralf Nemetschek, Werner Prusseit THEVA GmbH, Eching-Dietersheim, Germany B. Holzapfel, J. Eickemeyer, B. deBoer IFW Dresden, Germany U. Miller, Plansee AG, Reutte, Austria E. Maher Oxford Superconductivity plc, UK
ABSTRACT
Currently, due to simultaneous large area coating thermal evaporation (TE) allows the highest YBa2Cu3O7 (YBCO) volume deposition rates among various coating techniques. The simultaneous large area deposition translates into long length when the deposition area is closely filled up with metal tape. On short RABiTS samples thermal evaporation has already established critical current densities in excess of 1 MA/cm² at 77K. Recently, the deposition technique has been scaled up using a multi-turn tape winder for a simultaneously coatable length of 4 meters of 1 cm wide tape. The reel to reel tape deposition system is designed for long term operation based on a vapor composition control by atomic absorption spectroscopy and in situ refillable evaporation sources. In the initial setup phase the system has been able to reproduce the above results on small samples. The first results on continuously moving tape substrate coating up to a length of several meters will be reported.
INTRODUCTION Since the discovery of high temperature superconductivity (HTS) there were several attempts to fabricate wire or tape of these materials especially for power applications. As the cost for such a superconducting tape plays a key role for commercial use, there are attempts to replace the established, but expensive powder in tube – process (OPIT, based on a silver E9.2.1
sheathed Bi2Sr2CaCu2O8-compound) by a cheaper alternative. One of the most promising approaches is the coating of a textured metal substrate with a thin film of YBa2Cu3O7 (coated conductors). The texturing of the tape can be generated by depositing an aligned buffer layer on a non-textured metal tape by either IBAD (Ion Beam Assisted Deposition) or ISD (Inclined Substrate Deposition). Both techniques yield good results but are very time consuming and the availability of long lengths of buffered tape is still limited. Another route is the texturing of the tape itself by a simple rolling process with subsequent annealing (Rolling Assisted Biaxially Textured Substrate, RABiTS [1-2]), which is already established on an industrial scale up to lengths of hundreds of meters. The deposition of the superconductor is another essential cost factor, strongly depending on the technique used. Among the so called in situ techniques thermal evaporation is one of the most established and reliable methods to coat various substrates with thin HTS films [3-4]. The comparably low substrate temperatures allow a very simple and therefore economic buffer layer architecture to prevent interdiffusion of metal atoms in the superconductor. In this paper we present the latest progress on our way to the fabrication of long length coated conductors.
EXPERIMENTAL
Substrates The RABiTS tape was supplied either by the Institut f
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