Research Needs for Magnetic Fusion Energy Sciences - US Burning ...

front layers of the field magnets closest to the plasma, insulation must also be able to withstand
neutron and gamma irradiation. The ability to withstand this radiation is frequently the magnet
limit that determines the thickness of the neutron shield, and typically dictates the operating life
of the magnet systems.
a good insulation system should exhibit four main characteristics:
1) higher specific dielectric performance in the insulation.
2) compatibility with heat treatment and other magnet fabrication processes.
3) ease of application, e.g., impregnation temperature, pot life, etc.
4) Radiation resistance over the design life.
Required research includes the development of inorganic insulating systems and ceramic insulators,
and would likely need the coordinated efforts of universities, national labs, and industry. in
addition, better means of applying the insulation are required. The insulating step in conventional
superconducting winding is tedious. it needs to be carried out with a high level of inspection
because of the potential for damaging the superconductor or the insulation itself being damaged
during coil assembly and handling. alternative approaches to the insulation materials, such as
new nanodielectric materials and means of integrating the insulation process with the coil manufacturing,
should be explored.
joints
Joints between very large, multi-strand cables of the type required for fusion applications are difficult
to make. They must simultaneously achieve the conflicting goals of low resistance, low-ac
loss, and high stability. a joint is “superior” if it concurrently improves the goodness factors for
volume, dc loss, and ac loss.
although the fusion magnet community has significant experience producing high-current joints
with large cables made from round wires (lts), there is no equivalent experience in joining large
cables or conductors made from many thin, flat hts tapes.
The fabrication of high-current hts samples should be developed in the laboratory, with a
structured program for understanding joining methods, dc resistance and interface resistances,
current transfer, ac losses, and stability. The joint samples should be tested as hairpins
and insert coils to establish overall properties. simple resistance tests can be performed
relatively easily with existing equipment. Full-scale prototype joint samples can be tested in
the Pulse test Facility after undergoing some modification to change the test environment
from forced-flow supercritical helium to either liquid nitrogen coolant or intermediate temperatures
by cooled helium gas.
The greatest programmatic impact will derive from developing a method of joining entire coil
cross-sections as a unit while having the ability to be connected, disconnected, and reconnect-
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