*Here is another way of looking at the coil current.*

Every wave must start with a wave front, some kind of initial small step
increase in the voltage and current.

This initial increase in voltage and current must enter the coil by
charging the space around the wire to some voltage, which requires
current to complete. This requires power and effectively 'charges' some
length of coil wire to some energy level, identical to charging a
capacitor. The initial wave front is moving, so we can think of the
capacitor (wire) behind the wave front as being charged and the
capacitor in front of the wave front as being uncharged.

As the wave front enters the coil, a small initial length of the coil
will be charged, with the stored energy located at a radial distance
from the wire. Within close radial distance of a coiled wire, we have
the adjacent coils and the wire on the other side of the coil. Both are
within the radial energy field expansion from the small initial length
of coil freshly charged by the initial wave.

The layers of coils can be considered as a series of capacitors, each
spaced at a distance equal to the coil turn spacing. The initial field
charges this series of capacitors at a velocity of field propagation.
The length of time required to charge the series of capacitors is the
time it takes for a wave traveling at the speed of light to travel the
length of the coil, not the wire length contained within the coil. This
explains the short time required for the initial pulse to be detectable
across the coil.

Obviously, this series of capacitors is shorted together by a path much
longer than the distance between coil windings. The wave front
continues down and around this longer path, taking a period of time
equal to time of travel of light traveling the length of the wire as if
it were stretched straight. Again obviously, while part of the energy
of the wave front has been stored in the capacitors of the adjacent
coils resulting in a wave front with diminished power, the reduction
would be a division between the series capacitors and the forward path
along the wire.

We must consider the magnetic field in this analysis. The initial step
voltage that is picked will determine the current which flows as a
result of the wire size and the surrounding materials, just as it does
for a transmission line. The initial step current will be steady (DC)
once the wave front has passed any point on the coil. The increasing
magnetic field in the axis of the coil is a result of the increasing
distance traveled by the wave front along the coiled wire, leaving a
steady state current and voltage (and unchanging magnetic and electrical
field) in place at points on the wire passed by the wave front.

The establishment of the steady magnetic field must be accompanied by a
changing magnetic field at the wave front. This magnetic field passes
the wire on the opposite side of the coil and induces a back voltage
before the initial wave front can follow the wire around the coil
circumference to reach the far side. As a result, the wave front
encounters a back voltage and current after the initial front has passed
a very short distance into the curved coil wire.

Please notice that the wave front described is equivalent to a square
wave on the forward face of the wave. A complete sine wave would be
made of successive rectangular waves, each of the appropriate length and
magnitude needed to compose a smooth sine wave as a final construction.

Assuming that the wave front will be traveling on a straight wire before
it enters the curved wires of the coil, the impedance of the wire will
change at the junction of straight and bent where the wire comes close
to the adjoining coil. This will cause a small reflection. There will
be a second reflection when the wave front encounters the reverse
voltage generated by the magnetic field that has crossed the coil, which
acts to cause a change in the impedance of the wire. Once traveling in
a relatively steady state along the curved portion of the coil wire, the
impedance would continue to change slowly as the wire winds between
environments from one coil end to the other. (Remember, the impedance
of the wire is the ratio of voltage to current detectable on the wire.)

Eventually the wave front will reach the far end of the coil where it
will encounter a new environment. A reflection will occur or not,
depending upon the end conditions. The amount of power stored in the
coil when the wave front reaches the coil end is the steady state
voltage X current X time. The time term is the time required for the
wave front to travel the length of wire in the coil.

73, Roger, W7WKB