About induced electromotive force
By Hidefumi KUBOTA
I explain about the question whether induced electromotive force is generated based on the law of electromagnetic induction by ripple current that flows intermittently and the force causes trouble in the function of superconductive electromagnetic engine.
When the strength of the ripple current is constant, the induced electromotive force cannot become a problem. Because, if forming the relation, "length of one round of loop = wavelength of the ripple current ", the magnetic flux of the ripple current to go through the loop is always one mountain of the wavelength. That is, the amount of the magnetic flux to go through the loop is constant and doesn't have a change. Therefore, induced electromotive force isn't generated.
However, when the strength of the ripple current changes and reversing its direction, the amount of the magnetic flux to go through the normal-conductive loop changes. In this case, the induced electromotive force is caused, and it becomes a problem whether the force causes trouble in the function of superconductive electromagnetic engine. Let's see the strength of the induced electromotive force in this case. The induced electromotive force V is shown by the following expression.
V=－⊿I/⊿t
Constant of proportion L is an amount in which the size of the self-inducement is shown and called "self inductance".
L = K×μ×π×a×a×N×N/l
In this expression
K = Nagaoka coefficient
μ= magnetic permeability
a = radius of the coil (m)
N = number of rolling of the coil
l = length of the coil (m) ※"l " is the length of the coil as the object and not the length of the lead.
Since the normal-conductive loop of the superconductive electromagnetic engine is taking a round, it becomes N =1. The Nagaoka coefficient is near 1 and the radius and the length of the coil is near 1, too. So they are ignored. Then, it is the magnetic permeability that becomes a problem. Since the wick of the normal-conductive loop of the superconductive electromagnetic engine is empty, the magnetic permeability of the vacuum can be approximately used. The magnetic permeability of the vacuum is 4π×10-7. Therefore, the self inductance of the normal-conductive loop becomes about μH (micro Henry). Since micro is 10-6, even if ⊿I is tens of thousands of amperes, when ⊿t takes time from 1 second to several seconds, the induced electromotive force becomes small to the extent that cannot become a problem.
Therefore, if as follows is done, the problem is not caused. When changing the strength of the ripple current, you make the time of the change long sufficiently. When the direction of the ripple current is reversed, it is done after making the strength of the ripple current small sufficiently.
Well, will the problem be caused to the superconductive loop of the superconductive magnet when the strength of the ripple current changes and reversing its direction? The induced electromotive force is a problem with Lorentz force to act on the direction which the eternal electric current flows through. The momentum order in the direction of the electromagnetic force was mainly described so far, but it is the problem of the momentum order in the direction of the electric current as the natural presupposition. What was described about the direction of the electromagnetic force applies to the direction of the electric current, too. Because, there is no change in that Lorentz force is caused by the size proportional to the strength of the magnetic field. Therefore, the strength of the eternal electric current is invariable and keeps flowing permanently in this case, too.