starship-design: Steel Ring Flywheel, Tabletop Scale

[Johnny Thunderbird <jthunderbird@nternet.com>]

And now, for something completely different.

Down home in the lab, fetch a fine steel ring, and encase it in
a toroidal tube of glass. Wind the glass torus with a helical
wrap of superconductor. Feed in a little juice, and the steel
ring levitates, to try to center itself in the field. The ring
of steel contains the magnetic field, but with a constant field
it will not rotate. Now if there is a periodic modulation imposed
on the field, resonance conditions produce standing waves around
the coil, and these will correspond to regions of varying magnetic
saturation in the steel. A phase shift in the modulation will
induce torque within the ring, giving motor action. Too rapid a
modulation will make the superconductor lossy, and too intense a
confining field will produce ferromagnetic saturation in the
ring. Within these limits, motor and generator action may be
achieved with this flywheel device.

The use of a superconductor modulating coil may be most applicable
to the larger groundside units, for the larger the coil, the lower the
frequency may be used to produce an integral number of standing
waves around it. This reduces loss, which is heat produced in the
coil. To use a separate normal mode conductor as a stator winding,
for the motor generator functions, is an acceptable technique for making
ring flywheels in smaller sizes, for normal mode conductors lack
the frequency limitations of superconductors. But to use normal mode
conductors to establish the main ring field may be impractical,
for very massive windings would be needed to produce a strong
enough field to reinforce the metal microstructure. The energy
stored within the field itself, available from the windings, may
be quite large.

I don't know how to affect the velocity of the ring any further,
after the main ring current is ramped up to the saturation
magnetism for the ring material. No further features can be
induced in the magnetic structure of the material. Combined
materials are discouraged, for the desired strength may be found
only in pure material. Mechanical possibilities for further
acceleration seem iffy, at such high rotational speeds, and the
geometry is not encouraging for mechanical movers. For the
present, we may consider the act of clamping the steel into
saturation as setting the speed of the ring constant, for it is
no longer available for either motor or generator action until
the main coil current is reduced back down below the saturation
level.

Note that the saturation level does not have to limit the total
strength of the magnetic field, which can also build up in the
space surrounding the steel. After the steel ring has been
accelerated to its maximum safe speed, further energy can be
stored in the magnetic field. As noted, this excess magnetism
must be withdrawn before the rotational energy of the ring
can be tapped.

The condition of ferromagnetic saturation sets the limit for
the degree of strength enhancement in the metal. Grain shape
and size largely determine yield characteristics for a metal
under pure tension. The centrifugal force on the rotating
ring translates completely to tension. Material selection is
obviously critical to the operation of this device. Like any
other flywheel, there is only one failure mode worth worrying
about. Like in other high performance flywheels, rupture is an
explosion, confined to one plane. Much effort should be exerted
to avoid this eventuality, including getting really picky about
the steel used, and the process by which it is produced.

Even in terrestrial applications, I prefer use of a flywheel
counterrotating couple, rather than isolated units. Particularly
in vehicles, the gyroscopic effect can cause undesirable
motions, which when compensated results in steadiness. Motors
are now used with unbalanced rotation, but the gyroscopic
effect of these flywheels is much more extreme.

The saturation effect, by limiting the total amount of
reinforcement steel can receive from a magnetic field, evidently
prevents the truly gigantic rings I had at first envisioned.
However, because this is a very general form of the electric
engine, rotors will work ( in various modes ) even if they are
paramagnetic or diamagnetic in their bulk properties. To see
why, take the example of free space, good old high vacuum.

Will the field be established? Sure. Will it be induced to
rotate as the phase of the modulation is changed? Hard to say
no; this is almost a definition from antenna theory. But will
the fabric of space itself, its inertial coordinate system,
be dragged around the circle? That question is perfectly moot,
and depends entirely on your point of view. Well, vacuum wasn't
such a good example after all. But any material which can be
structured by a magnetic field, solid, liquid, or gas, will be
induced to rotate, by the magnetic handles stuck into its bulk
by the modulation field. Plasmas work particularly nicely: this
is the tokamak, with a spin. For my really, really big models,
it looks like I will need to go back to the storage ring concept,
with the nifty spiral orbit sheath of electrons, serving as my
windings.

Johnny Thunderbird
In Druid Woods http://www.nternet.com/~jthunderbird