text: The stability of these systems can be characterized by the ratio of two forms of pressure; that ratio is symbolized beta.
full_question: The stability of these systems can be characterized by the ratio of two forms of pressure; that ratio is symbolized beta. The product of Boltzmann's constant, temperature, and number density gives these systems' namesake pressure. When these systems are subject to a tension force proportional to "B dot grad B," they can be compressed into "pinches," according to ideal MHD. These substances are confined at very high temperatures and densities in a torus-shaped device called a tokamak to perform nuclear fusion. Natural examples of these substances include the aurora borealis, the ionosphere, and lightning. For 10 points, name these ionized gases usually considered the fourth state of matter.
first_sentence: The stability of these systems can be characterized by the ratio of two forms of pressure; that ratio is symbolized beta.