# Energy requirements of sustaining plasma vs first ionizing it.

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1. Jun 12, 2013

### Krejuski

Hello all,

I was wondering if it takes less energy to sustain an already ionized gas with an electric arc than it does when you are first trying to ionize the gas. I would think it would be, but im not sure.

Thanks.

2. Jun 12, 2013

### Staff: Mentor

The energy needed to sustain a plasma depends on the time. A better quantity is the power required to sustain it.

To get a plasma, you have to provide at least the same power, as this power corresponds to the energy loss to the environment.
The energy required to get a plasma is a completely different question.

3. Jun 18, 2013

### Deotheophilus

yes, in a uniform environment you are correct, the power needed to generate a plasma is less than the energy needed to sustain that same plasma... for this reason two major phenomenon are seen: first over time your plasma will increase in size, and second you will be able to sustain the plasma over a greater distance than required to generate that same plasma. (this is one reason a Jacobs ladder functions...) finally the reason for this, when first the plasma is generated it has to pass through cool, slow moving gas which is not in and of itself energized, then (as described by both thermodynamics and entropy) as the plasma forms it will release heat into the environment (its hot) which will ionize the gas creating an area in which the plasma can more easily exist, it will be under lower pressure, have more energy available from the environment, and be directly interacting with fewer particles... thus "it takes less energy to sustain an already ionized gas with an electric arc than it does when you are first trying to ionize the gas"...

4. Jun 18, 2013

### Deotheophilus

Plasma can be sustained for less

yes, in a uniform environment you are correct, the power needed to generate a plasma is less than the energy needed to sustain that same plasma... for this reason two major phenomenon are seen: first over time your plasma will increase in size, and second you will be able to sustain the plasma over a greater distance than required to generate that same plasma. (this is one reason a Jacobs ladder functions...) finally the reason for this, when first the plasma is generated it has to pass through cool, slow moving gas which is not in and of itself energized, then (as described by both thermodynamics and entropy) as the plasma forms it will release heat into the environment (its hot) which will ionize the gas creating an area in which the plasma can more easily exist, it will be under lower pressure, have more energy available from the environment, and be directly interacting with fewer particles... thus "it takes less energy to sustain an already ionized gas with an electric arc than it does when you are first trying to ionize the gas"...