Current to Flux to current

[J4e8a16n]

Hi,

About the toroid as a coil.

In a Joule Thief, when the current comes in from 0V,  the coil résist the current by storing it in the flux (and magnetic field). When the voltage induced is equal to the Vcc, the flux is full and let the current pass like a wire.  The flux is still there.
When the incoming source current stop or slow down for any reason, the flux will be transform again in a current flowing trying to maintain the flow of a current.

[DmitryL]

I think that Maxwell, Heaviside and co. explained it slightly better.
https://en.wikipedia.org/wiki/Maxwell%27s_equations

[J4e8a16n]

the flux is full and let the current pass like a wire.

It  is a simple question. The flux is still there?  It wait around the coil?

JP