A plasma channel is a conductive channel of plasma

Plasma (physics)

In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

. A plasma channel can be formed in these ways:-

• With a high-powered laser
  Laser
  A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
  
   that operates at a certain frequency that will provide enough energy for an atmospheric gas to break into its ion
  Ion
  An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
  
  s, or form a plasma, such as in a Laser-Induced Plasma Channel, for example in an electrolaser
  Electrolaser
  An electrolaser is a type of electroshock weapon which is also a directed-energy weapon. It uses lasers to form an electrically conductive laser-induced plasma channel...
  
  .
• With a voltage higher than the dielectric breakdown voltage applied across a dielectric
  Dielectric
  A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
  
  , and dielectric breakdown occurs.

A plasma channel has a low electrical resistance

Electrical resistance

The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...

 and, once formed, will permit continuous current flow if the energy source that heats the plasma can be maintained. Unlike a normal electrical conductor, the resistance (and voltage drop) across an unconfined plasma channel decreases with increasing current flow, a property called negative resistance

Negative resistance

Negative resistance is a property of some electric circuits where an increase in the current entering a port results in a decreased voltage across the same port. This is in contrast to a simple ohmic resistor, which exhibits an increase in voltage under the same conditions. Negative resistors are...

. As a result, an electric spark

Electric spark

An electric spark is a type of electrostatic discharge that occurs when an electric field creates an ionized electrically conductive channel in air producing a brief emission of light and sound. A spark is formed when the electric field strength exceeds the dielectric field strength of air...

 that initially required a very high voltage to initiate avalanche breakdown within the insulating gas will rapidly evolve into a hot low voltage electric arc

Electric arc

An electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. A synonym is arc discharge. An arc discharge is characterized by a lower voltage than a glow discharge, and relies on...

 if the electrical power source can continue to deliver sufficient power to the arc. Plasma channels tend to self constrict (see plasma pinch) due to magnetic

Magnetism

Magnetism is a property of materials that respond at an atomic or subatomic level to an applied magnetic field. Ferromagnetism is the strongest and most familiar type of magnetism. It is responsible for the behavior of permanent magnets, which produce their own persistent magnetic fields, as well...

forces stemming from the current flowing through the plasma.