I used to deposite titanium oxide by DC magnetron sputtering method and I have to control vacuum hight enough for getting plasma existence. Similar for RF sputtering also need vacuum. Certainly you need use some gas for making plasma. The distance depending on your potential you apply.

yes, you can make plasma if you reduce pressure and apply high Dc voltage. Colour of plasma will depend upon low pressure gas in chamber.

@ harpreet sir..as we evacuated the whole chamber ? what is mean by low pressure gas.

I would try a 4 mm gap distance. If you increase the distance between the electrodes, you will need to apply a larger input voltage to achieve the same breakdown voltage. Also depending on your application, the make-up gas in the chamber also matters. We generally use argon. If you are trying to decide what discharge parameters to do in gas phase only, I'd try looking Pashen curves for various gases. They are plotted as a function of pressure and gap distance.

The creation of plasma is possible @low pressure and high pressure.

As said Kevin Hsieh the Pashen Laws give an idea of what is possible for plasma ignition vs pressure. But in reality it depends on multiple parameters.

In theoretical vacuum it is impossible to create plasma cos' plasma is an ionized gas.

So you need gas to create it. The best is to control the pressure. Most of the time, a "medium" pressure to ignite the plasma then you can decrease the pressure and be able to maintain the plasma

By saying "vacuum" one usually means "much lower pressure than atmospheric".  So the term "vacuum" is relative.   One does not create a perfect vacuum in a chamber.  The pressure gauge on a vacuum chamber will read some value, unless it is the wrong gauge to be using for the pressure you are achieving.  So as long as there are molecules and free electrons floating about inside your chamber (and there always are), there is the chance of collision between an electron and a molecule, resulting in excitation or even ionization of the molecule.  The electric field needed to break down a gas ("ignite" a plasma) is pressure dependent, with the optimum pressure for lowest required electric field usually being sub-atmospheric.  For DC electric field you can check out Paschen's law to see the inter-relationship between pressure, electrode separation and breakdown voltage.  The pressure that results in the lowest breakdown electric field if frequency dependent.  My experience is in microwave, where the pressure that has the lowest breakdown voltage is roughly linear in frequency.  This rule might extend into the AC frequency range that you are wondering about.  As an example, for nitrogen gas in a field with 1 GHz frequency and a gap of about 2 mm, I will get breakdown at the lowest applied electric field of about 300 V/cm with a pressure around 2 Torr (2.6 mbar).   Also, for very small gaps, say

Yes  it  is possible. It depends on electrical parameters, pressure, gas characteristics and volume enclosed between the electrode gap.

I am agree with all above answers. Exactly in theoretical vacuum you cant create plasma . With low pressure you need comparative less high voltage. 

Yes, you can. That's how the vacuum diodes. The effect of explosive emission. Material for plasma taken from the cathode. Requires a high value of the electric field.

yes, by using discharge capillary you can make plasma or using gasjet and interaction with a laser pulse also you can make plasma. these mechanisms is used in laser plasma acceleration. 

Plasmas can be created in vacuum (i.e. without any feed of gas or static pressure of any atom/molecule inside a chamber). There are usually referred to as "vacuum arcs" where the ionized gas is formed by sputtering of the cathode inside the vacuum chamber. The plasma density and gas pressure will then strongly depends of the erosion of the cathode with various non-linearities. I do not think that such plasma can be described at all in terms of some modified Paschen's curves. For a start, this review paper about vacuum arcs might be of interest: http://iopscience.iop.org/0022-3727/22/8/001

sustained In order to form a plasma from an electric field is necessary to have several conditions. The main are:

- to have a vacuum level, for example in the range of 0.01 ro 100 mbar, with sufficient ionization to have a self-sustained gas discharge.

- to have an electric field capable of transferring enough energy to free electrons to ionize the atoms and molecules

- the electrodes must be spaced at a distance great enough to ensure that between them there is ionization. If the mean free path length of the free electrons (distance between two collisions) is greater than that distance, then plasma does not light (please, check Paschen's law).

The absolute vacuum have nothing in it. But just as the answers above, when we treat extreme low pressure as vacuum, certainly you can.

I do agree with the opinion that vacuum means there is no matter. So there is no question to create plasma as plasma is on of the state of matter. However, In general, vacuum is consider as low pressure region and it is possible to create plasma. There are several method to do so.

Hi 

In order to create particles you need to have an energy density  E^2 in a compton wave length volume (\lambda^3)  greater than the  2 mc^2.  This is the Schwinger mechanism for particle production from the vacuum.  See

Physical Review D 40 (2), 456 (1989)

Physical Review D 45 (12), 4659 (1992)

There is a "Vacuum discharge" - vacuum breakdown, vacuum spark, and vacuum arc.

The plasma is created from the electrode material (cathode) by a trigger application (igniting high-voltage pulse, laser or plasma pulse action onto cathode, micro-particle impact, etc.).

See, e.g.

Mesyats G. A. 2013 IEEE Trans Plasma Science 41(4), 676-694

Anders A. 2014 Surface and Coatings Technology, 257, 308-325

or classical books

Mesyats G A, Proskurovsky D I Pulsed Electrical Discharge in Vacuum (Berlin: Springer-Verlag, 1989)

Anders A. 2008. Cathodic arcs: from fractal spots to energetic condensation, Springer

Trying to put some order in the answers.

The answer depends on the value of the "vacuum" yo do consider.

- Poor vacuum = a small fraction of the atmospheric pressure. The applied voltage creates a real plasma made out of ions from the residual gas and electrons.

- UHV - Ultra High Vacuum = the value of vacuum in space, ~1 atom/m3. A plasma can be created from matter ripped off from the electrodes.

- The third answer is about the creation of particles in vacuum from vacuum. Ultra-high electric fields can create particles in vacuum but this takes place at the ultra-high energy levels one finds in stellar reactions. Sumit Mishra, this part is related to the high energies generated with ultra-short light pulses I wrote about in the answer to one of your other questions.

@Nash Chu. Vacuum is not equivalent to void. In the present state of the quantum mechanics theory, vacuum is full of "half-photons" that are a consequence of the quantification of the electromagnetic fields. These "half-photons" do have real physical effects like the Casimir force for example.

Dear prof. Hirlimann, your answer is very precise. May I ask if you are aware of the existence of electrostatic/electromagnetic effects taking place inside interstellar vacuum, or if you expect that the third mechanism you named could give rise to some ascertainable effects there, such as plasma creation?

@Sara Liyuba Vesely. The effect of an electric field on vacuum is discussed in "Landau & Lifchitz" "Quantum mechanics" book. From my understanding, the conditions for this interaction to take place could be only found in stars.  I do not think this kind of effect can take place in-between stars. But I am not an astrophysicist and I might be missing something.

Yes it is possible to create a plasma in a vacuum. There is only a peak in the preassure in the moment when you start creating a plasma.

This depends on the level of vacuum you create. In low vacuum, the plasma may be used in surface treatment of a sample. this can be carried out for textile, polymer films and paper. 

@Charles Hirlimann. Thank you for your correction to consider the quantum mechanic effect of vacuum.  I was wondering if there were some results in high energy experiments to prove that we can create plasma from absolute vacuum.  

Hello,

While it may seem counter-intuitive, the separation between the electrodes and their shapes is more important than the surrounding air pressure or lack thereof.  Robert Francis Earhart showed this in 1901 when he used an interferometer to investigate electrical breakdown in air at small distances between electrodes.  He observed that there were two distinct regions of breakdown depending on the electrode separation: region 1 (>3 to 5 wavelengths of Na light), where  Paschen's law holds, and region 2 (

In my opinion, if you apply pure DC across two electrodes in vacuum, a fixed pattern of plasma with very very low current discharge would appear because of very very high capacitive reactance at zero frequency (case of pure DC) with showing glow discharge rule that form Faraday space, negative glow, anode glow and dark space in the region. However, if you want a higher density plasma discharge then either go for pulsed DC or medium frequency supply. Pulsed DC will provide you a dv/dt to increase the capacitive current through discharge. 

I just want to add to all these good answers that, the plasma can be created in vacuum or in a gaseous atmosphere. Plasma is a mixture of ions, electrons, photons and neutral atoms which is conductive in nature. Now to make any vacuum or gaseous environment conductive, you need either free electrons or ions. The free electrons or ions can be created in a vacuum by applying high electric potential greater than breakdown voltage across the cathode and anode. Free electrons will get released from cathode. One more way to get free electrons from cathode is by heating it at high temperature that will allow thermionic process to occur.

This is what my understanding is about how to create plasma.