# Electric Arc Current?

1. Feb 19, 2009

### mgibson

Hello,

I am trying to find an estimated value (or range) for the current of an electric arc. I imagine this may be a function of the voltage producing the arc, the distance between the electrodes, and other parameters. If this is true, then take the voltage to be around 80kV and the distance between electrodes to be about an inch. I am just trying to get an estimate for an average arc current (in Amperes) in order to use this current in a theoretical Lorentz force calculation.

Also, is the arc current affected by the supply from which the voltage comes from? For example, if a power supply is providing lets say 1kV of voltage at a low current(<1A), if this current arcs across a centimeter gap, will the arc current be effected by the low current source?

Any help, comments, or suggestions would be greatly appreciated. Thanks so much!

2. Feb 19, 2009

### mgb_phys

The voltage and the gap are related (the bigger the gap the more voltage you need to strike the arc). Once the arc has formed the ionised air provides a low resistance path and the current depends mostly on the supply.

You can strike an arc with 1Kv from a van-der-graff generator (or rubbing balloons on your shirt) with almost no current - or you can have 200A of current from an arc welder.

3. Feb 19, 2009

### mgibson

Thank you mgb_phys for your response. The power supply i am using is a 0 - 100kV tesla coil with a current around 1-2mA. I am using it for an application (mini arcjet thruster) were it will be arcing constantly across an inch gap or so, the arc current is used to induce a Lorentz force on the ionized gas thus accelerating it outwards. I am trying to figure out if this power source will be able to provide a high enough arc current to generate a fairly strong lorentz force. Thanks again for your help.

4. Feb 21, 2009

### m.s.j

Have you heard about classical Ayrton equation? You can refer to Protection Riddle No.29 from http://electrical-riddles.com for a short discussion.
Also for increasing of continuous arc current you should be increased rated power of circuit power supply.

5. Feb 22, 2009

### Phrak

A Tesla coil won't sustain current in one direction for very long. The primary arc sustains alternating current. The secondary tries to follow.

What Lorentz force?

6. Feb 22, 2009

### mgibson

Thank you for your response. I am realizing that I probably will not be able to generate a high enough current to use the Lorentz force to accelerate the plasma. I may try and use permanent magnets instead to generate the strong b-field. I plan to use a power supply (similar to a tesla-coil) to generate the arcing and hopefully a plasma. Then use permanent magnets to try and accelerate it. Just a simple proof of concept project.

Lorentz force is the force on a point charge due to electromagnetic fields. It is given by the following equation in terms of the electric and magnetic fields:

F=q(E+(VxB))

where
F is the force (in newtons)
E is the electric field (in volts per metre)
B is the magnetic field (in teslas)
q is the electric charge of the particle (in coulombs)
v is the instantaneous velocity of the particle (in metres per second)
× is the vector cross product
∇ and ∇ × are gradient and curl, respectively

or F=JxB where J is the total current and B the magnetic field