Plasma

Temperature, Time and Density
For fusion to work there are three essential elements for two attractive particles to become fused: temperature, time, and density. Without the appropriate ratio among these three elements fusion can not occur. Examples of particles that have been attracted to each other, but lack the density needed to create fusion, are lightning, neon signs, the aurora, and space nebulas. A basic idea between the relationship of temperature and density can be understood through an example of a steaming pot of hot water. The density of the hot water in the pot is much greater than the steam coming from the water. As a result of this the steam carries less heat than the water, so a person could put their hand in the steam with much more confidence than in the water (Newman). In a fusion reaction the example of this process lies in the plasma.
Provided by: The Pervasive Plasma State

Plasma
Plasma is considered the fourth state of matter, the first three being liquid, solid, and gas. For matter to reach this state it first has to be in a gas form, which is then stimulated in some way that causes the electrons to detach from the atom, leaving the atom ionized. "Without ionization it would be impossible to obtain plasma" (Kamenetskii 35). Ionization of a gas can form in three ways: heat, radiation, and electrical discharge. An example of ionization by electrical discharge is lightning. When the lightning strikes it separates the electrons from the air molecules which create plasma for a short period of time. Heat ionization is created in the sun. This occurs when a particle is heated to the point that it is close to the energy of the weakest bound electron. When the electron bond energy is equal to the heat of the atom the electron is no longer attracted to the atom and is pushed away, creating an ionized particle. Ionization in a fusion reaction is important because with the electrons detached from the atoms the plasma has an electrical charge, leaving them highly reactive to magnetic stimulation.
Provided by: www.seds.org/hst/M16WF2.html