Can you be a bit more specific? You can make a plasma with a DC discharge or an AC source...just put half a grape in the microwave. What are you specifically wanting to do/answer?

http://www.youtube.com/watch?v=vCNNqgKqnaQ

i want a better reason why we are using dc High voltage source for plasma generation .

simply because you can - why would'nt you use it?

It was the first discharge principle to be developed, it is easy to build and for some scientific/technical problems it is the best way to go (for example for examination of lightning in your lab - here the reason is that lightning in nature is also a DC phenomenon).

Johannes is right. DC was easy, so people like Edison lobbied for this system to power things, because it is very straight forward. In the end AC is way better for long distance power transfer, and Tesla was smart enough to understand the utility, a bit of a visionary, while Edison only wanted to promote his own ideas (that he could follow is my guess). AC is not intuitive, nor as easy to harness. Lyden jars (ca. 1750) had been used for over half a century to "catch and store" electricity, so it was natural to experiment with DC as these could be stacked in enormous quantities to produce high current - high voltage discharges, and basically do plasma physics (though they didn't know it was a plasma). Before the advent of an Electro-Magnetism description of electricity people had used electrostatic generators (invented in 1660s by Otto von Guericke), which were very easily used to charge Lyden jars (basically a capacitor) and then in 1800 they could use the Voltic Pile (invented by Alessandro Volta, what we would call a battery), and now they could use a steady stream of DC electricity instead of a Lyden jar discharge. In the early 1800s William Nicholson and Anthony Carlisle used a Voltic Pile to turn water into Hydrogen and Oxygen! Then came the most important invention, the battery powered Arc Lamp by Humphry Davy in 1810, which was basically lightening in a bottle, and is still used in some movie projectors today, and to pump most lasers, like the NIF! (Diodes are slowly taking over, one day your toaster will use efficient diodes to toast the bread, and not a filament :-) ) Hope that helps.

I would also add that not only AC or DC are your options. My experience has been that most people use DC for it's simplicity and wide availability. However, the field of AC discharges is quite significant, particularly in the microwave frequency regime.

In addition to this, there are many people who would like to do unipolar pulsed discharges. When the pulse widths are on the order of a few nanoseconds, it is possible to drive a discharge with really extreme E/N before an arc can establish. This allows for a huge increase in efficiency, and in some cases a lot more power input while maintaining stability. However the technology to develop these pulses is limited and remains a challenge to researchers.

You can generate high power microwaves discharging capacitors on low inductance coils at a high efficiency. It could be increased using graphene. It is a pity that graphene not reached the marked yet.

As long as the time it takes to apply voltage is long enough to achieve enough amount of ionization ablation via electron collision to the neutral atoms (basic principle of the generation of the discharge plasma), you can choose either AC or DC. I'm just wondered RF has comparable average power to DC. I think RF is used to generate plasma for long period while DC is for usually pulsed or single mode operation. Practically high voltage DC can't sustain more than ms, I think.

DC can last for hours - we run our experiments for over a week if needed.

 I used a DC high voltage (12 KV) power supply to generate plasma , how can i determine whether the generated plasma was pulsed type plasma or not? 

the similary is they both could make plasma by high electrical field. the difference is the materials used for processing. Dc can not be used for insulator but AC does

Hello Jacob Coty Stephens, I'm wondering what E/N means in your comments? I want to know this as it looks relating to power transfer efficiency to the plasma from discharge circuit.

Hi all. I'm trying to generate a plasma (DBD plasma actuator for wind tunnel testing). We could generate a 'small and nonhomogenous' plasma by using a 6kv AC pulse generator. I would like to ask for some advice;

1. the homogenousity of a plasma - what is the main influencing factor?

2. tried using high voltage DC, but did not work. I thought DC is not suitable but from the literature, I know it can. Can you give some advice on either AC or DC or both is best for a plasma generation?

Thank you.

Using DC/AC may only be possible in jet configuration, i.e. applying gas flow around a sharp HV electrode. In this case you would have a glass tube containing the gas flow and a ground electrode is a ring sitting around the tube. This yields a non-homogeneous plasma jet with diameter of 2-3 mm and length of several mm. 

The way to produce homogeneous DBD discharge is to apply nanosecond pulses. Amplitude of several KV, the more the better, FWHM in ns timescale ( the shorter the better) . HV electrode can be pin, knife edge  or multiple knife edges for large scale plasma. 

Look up literature for DBD discharges, u can start from this review: 

Kogelschatz U. Dielectric-barrier discharges: their

history, discharge physics, and industrial

applications[J]. Plasma chemistry and plasma

processing, 2003, 23(1): 1-46.

Hi

What about cathodes?

which cathodes are best choice for ionization?

For example:

The Gas is Neon and Electrodes Al

I mean which cathodes would be a best choice like Al, metal or etc

I need it to understand about cathodes.

Thank you

I think it is also about how to generate a "high power" pulses. In DC, one can deposit a high energy in very short time, yield a high power, which is not easily generated in AC.

Synchronous generators in power plants produce sine-form AC that is conditioned by rotating of rotor and its magnetic field. In the case of plasma generator we get just DC because of rectilinear motion of charged plasma in magnetic field.

In fact discharge can be generated using either DC or AC voltage. However in the case of DC one can deposit lot of energy in short time by discharging a capacitor. Deposited energy will depend on both the DC voltage as well as on Capacitor value.The rate of energy deposition will be dependent on the RC value of the electrical circuit of discharge.

In our project we confine high speed plasma and use ac magnetic field to accelerate it to allow compress 550keV plasma. It is not possible in old fashion tokamaks.