Superconductive Solenoid
Design
A literature review on the current state of design is presented to
define the proposed design and material limits to be assessed.
In 1911, the Dutch physicist H. Kamerlingh Onnes discovered the
phenomenon of superconductivity, the vanishing of electrical resistance
in some metals at very low (<10 K) temperatures. The discovery
inspired Kamerlingh Onnes to propose a 100,000 Gauss (10 T) solenoid two
years later based on a superconducting coil cooled with liquid helium,
yet it took more than 50 years to realize this design in practice
[61]. In 1989 Motokawa et al at Tohoku University built the first of
a series of a new class of resistive magnet that were referred to as
repeating pulsed magnet [43] which provided pulsed fields of a few
millisecond duration as high as 25 T once every 2 second [8]. These
repetitively pulsed magnets were first built in a solenoid configuration
[44, 8, 21] Today, pioneering research is being conducted by several
high magnetic field centres [13, 19] around the world which are
achieving >100T strength fields and long pulse lengths.
Particle accelerators have used superconductive components for many
years to achieve the required energy densities in size constrained
tunnels underground [1, 31]. The superconductors allow current
densities orders of magnitude greater than regular resistance conductive
materials like copper [51]. Initially, small accelerators used
strings of permanently active electromagnets to create a controlled
turning path for particle beams but with developments in high energy
pulsed electromagnetics across the past two decades this has changed
[31, 51]. Development of high energy pulsed solenoids (HEPS) has
allowed a series of timely pulses to turn the particle beams direction,
reducing accelerator energy costs and rapidly advancing electromagnetic
design and research [27, 31, 50, 51]. The progress in pulsed high
magnetic field research in the last two decades was driven by the
transition to multicoil superconductive solenoid designs [22] and
capacitor power systems [18, 21, 24].
The addition of multiple concentric coils each pulsing as the successive
outer coils are energised is the key [23] to reaching 100T fields
and beyond [54]. The design improvements and high energy density
components required to achieve such a field enables high quality, high
power solenoids scaled to a small satellites capacitor system power
output. A field of >100T is likely not required in the
proposed contex. Magnet designers frequently trial improvements on 0.5m
to 2m test coils [14, 41, 62] and a review of papers on small bore
coils [13, 40] shows that high field pulses are achievable in a
satellite deployable package. [8, 12] By using the highest current
densities achievable, the solenoids pulsewave induces the strongest
current in the object above and the induced field repulsion force is
maximised as shown in Section IV.
As research has optimised NbTi cables almost to their material limits,
Nb3Sn has seen increased development as the next generation substitute
due to its higher temperature, field strength & current density
capabilities [27]. Nb3Sn is superconductive below 18.1K with a
maximum critical field strength of 25T, if the material exceeds either
of these limits then a quench occurs where superconductivity is lost and
the pulsed power must be diverted. Later research has refined the
thermodynamic field strength surface that bounds the material’s
superconductive state and the field penetration depth as the effect is
lost in a quench. The critical surface of Nb3Sn is shown in Figure 2
with a reference density of 3000 A/mm2 across the SC
area selected [27, 53].