Laser and electron beam processing of superconductors

Scanning irradiations using high power density beams of CW-CO2lasers and electrons have been applied for the fabrication of superconducting Nb3Ga, Nb3Al and Nb3(Al,Ge) conductors. The materials to be irradiated were prepared in tape form and the scanning was carried out by moving the material in a stationary beam with the intension of future development to industrial applications. For the formation of Nb3Ga, a tape composed of NbGa3compound layer on the Nb substrate was prepared by a continuous dipping process. The laser irradiation successfully produced a new layer containing A15 Nb3Ga by alloying the NbGa3layer and a portion of the underlying Nb substrate. The highest Tcattained by the irradiatioh is 15.9K (midpoint), and is increased to 18.2K by the following low temperature annealing at 700°C. Nb3Al and Nb3(Al,Ge) tape conductors were also fabricated by laser and electron beam scanning irradiations onto Nb-Al and Nb-Al-Ge composite tapes prepared by the conventional powder metallurgy method. The laser irradiation directly onto the Nb-Al composite produced a molten and then rapidly resolidified zone composed of α-Nb dendrite and A15 Nb3Al. The Tcvalues are well over 16K, which can be increased by 1-2K by the subsequent annealing. A maximum Jcfor reacted zone of 4.8 × 10⁴A/cm²was obtained at 23T and 4.2K. In order to minimize the loss of Al, the irradiation onto Nb-sheathed Nb-Al and Nb-Al-Ge composites was also carried out using both laser and electron beams. The Jcincreases with increasing power density until the melting including Nb-sheath occurs, and then rapidly decreases at higher power densities due to the decrease of A15 volume fraction. The Nb3Al and Nb3(Al,Ge) tapes processed under proper conditions show excellent high field properties, the Jcexceeding well over 10⁴A/cm²in magnetic fields up to 23T. Compared with the electron beam irradiation, the laser beam irradiation has a disadvantage that the absorption coefficient of energy into the material is sensitive to surfa- ce conditions neccesitating special care in handling the material surface. However, in the case of laser irradiation, operation in the pressurized atmosphere is possible, which is very effective to minimize the loss of volatile elements such as Al,Ga. In order to study the feasibility to large scale production, new continuous irradiation systems have been installed for both CW-CO2laser and electron, and the examinations to fabricate longer tapes of 10-100m are now in progress.