High field properties of NbN conductors on practical substrates

A new UHV, oil free, two gun magnetron sputtering system has been developed to allow continuous production of NbN conductors. A scaling rule relating film properties to preparation conditions was successfully used to predict the preparation conditions necessary to achieve the best NbN film properties in the two gun system. Comparison of high field J
c
results between the new two gun system and a diffusion pumped one gun system show similar results for NbN on sapphire substrates, suggesting no effect from oil backstreaming. Short sections of double side coated Ti tapes 25 μm thick with
\approx5 \mu
m of NbN have J
c
=1×10
⁴
A/cm
²
at 18 T with H
c2
(4.2K) of 22.5 - 23 T. Ta wires made under the same conditions with
\approx2.7 \mu
m of NbN had J
c
(18 T) a factor of two lower. An 11 turn coil with a 2.5 cm bending radius has been made by coating one side of a moving tape 1.3 m long with
\approx3 \mu
m of NbN. The best section had a J
c
=1 ×10
⁴
A/cm
²
at 18 T and J
c
=4×10
³
A/cm
²
at 20 T.