Lawsoncriterion

The Lawson criterion is a fundamental concept in plasma physics used to determine the conditions necessary for a self-sustaining fusion reaction, often referred to as ignition. It was developed by John D. Lawson in 1955 and published in the journal Proceedings of the Physical Society. The criterion essentially balances the rate at which energy is lost from the plasma with the rate at which energy is generated by fusion reactions.

At its core, the Lawson criterion states that for a plasma to achieve ignition, the product of the plasma density and the energy confinement time must exceed a certain critical value. This value is dependent on the temperature of the plasma and the specific fusion fuel being used. Higher temperatures generally lead to a higher fusion reaction rate, which can relax the requirements on density and confinement time.

The energy confinement time, often denoted by the symbol τE, represents how long the plasma can hold onto its thermal energy before it is lost through processes like conduction, convection, and radiation. Plasma density, represented by n, is simply the number of particles per unit volume.

If the product nτE is too low, the energy lost from the plasma will exceed the energy produced by fusion, and the plasma will cool down, stopping the reaction. Conversely, if nτE is sufficiently high, the fusion reactions will generate enough energy to maintain the plasma temperature, leading to a self-sustaining burn. The Lawson criterion has been a guiding principle in the design and development of fusion energy research devices such as tokamaks and stellarators.