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Description

Master thesis project by Suzanne Zamany Andersen.
Thesis abstract:
The work in this thesis is based on a recently introduced 3D surface-prole technique,
i.e. the two-level undercut-prole substrate (2LUPS) concept [1]-[2], used for production of
multi-lamentary high-temperature coated conductor (CC) tapes. Reducing the superconductor
lament width linearly reduces the alternating current hysteretic energy losses [3], and it enables
manufacturing of stable high-temperature superconducting magnets [4]. A new process of tape
masking and Ni-based electroplating on a Ni-W metal alloy substrate to form similar 3D surfacepro
les as those achieved by the 2LUPS concept [5], which is based on two levels of plateaus
connected via an undercut-prole, is investigated. The undercut-prole should be large enough
to enable a shading eect during subsequent physical vapor deposition (PVD) of layers, thereby
creating self-formed and physically separated superconductor laments on the two plateaus, while
still utilizing the full width of the CC. This will theoretically increase the engineering current
density compared to current lament techniques utilizing e.g. laser striation or mechanical
scribing.
Inspection of the metal substrate cross-section using focused ion beam milling and scanning
electron microscopy (FIBSEM) reveals that an undercut-prole is achieved by using kapton tape
as a mask while electroplating nickel to create the upper plateaus. The arithmetic surface
roughness of the electroplated nickel layer is determined via atomic force microscopy (AFM)
to be suitable for CC fabrication. To verify if the undercut-prole is sucient, an electrically
insulating layer of SiO, simulating the buer layers in CCs, followed by an electrically conductive
layer of Ag, simulating the superconducting layer, is deposited using PVD, and four-point probe
measurements to create I/V characteristics are used to measure resistance across plateaus. The
plateaus are deemed electrically insulated from each other, as the resistances from each insulating
layer adds up to the total resistance through both plateaus. Accordingly, it is expected that
these new electroplated 3D surface-proles will also enable lamentization of superconductors
produced by PVD processes. A small caveat to these ndings, is the lack of a suitable prole
for the use in CC fabrication being manufactured in this project. The adhesive in the masking
tape creates bulges or protrusions in the prole, so a further study on thinner adhesive layers or
a dierent masking material altogether is needed.
The possibility of texture transfer from the Ni-W metal substrates to the plated Ni layer
is also investigated, for the use in the cheaper rolling assisted bi-axially textured substrate (RABiTS)
fabrication process. The electrodeposited Ni would during annealing at low temperatures
experience an abnormal grain growth stage, thereby rendering it incapable of attaining the texture
needed for RABiTS fabrication. Furthermore, the thermal grooving during annealing of the
pure Ni could also become a problem for the ion beam assisted deposition (IBAD) process, as a
surface roughness of
StatusFinished
Effective start/end date22/08/201612/02/2017
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