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Simple equations for coilgun

1. Assessment of current.

We often need to suggest a value of current in a coil of gauss-gun i, given deposited energy is E. This can be performed by following simple equation. Other parameters are coil length l, projectile velocity v and capacitor voltage U. Then:

i ≈ (E·v)/(U·l)

The formula is precise when its components are constant. Thus, it works best for middle and last coils of multistage accelerator fed by common capacitor, where velocity and voltage change negligbly.


2. Point of maximum current.

It is sometimes necessary to determine a moment of time when curent in a coil achieves its maximal value. This moment is described by the next complicated equation (as it is shown here):


is capacitive constant of the circiut,

                                                                                           inductive constant,

damping factor,

R, C, L - resistance, capacitance and inductance, respectively,

arth - hyperbolic arctangent ( arth (x) = ½ln {(1+x)/(1-x)} ).

Fortunately, this formula can be substantially simplified  for strongly overdamped systems, where k<<1. This case realizes in high-capacity circuits (e.g. multistage coilguns driven by common capacitor) or in single stage gauss guns with thin coils (i.e. large length-to-diameter and length-to-thickness ratio).

Alas, decomposing the equation above to Taylor series and neglecting the second-order terms, we have



Category: Coilgun calculations | Added by: Eugen (21.06.2017)
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