Atomic, Nuclear and Plasma Physics

Space physics is the study of plasmas as they arise naturally in the Earth's upper atmosphere. It includes heliophysics which includes the solar physics of the Sun: the solar wind, planetary magnetospheres and ionospheres, cosmic rays. It is an essential part of the study of space weather and has important consequences not only to understand the universe, but also to practical everyday life, and also includes the process of communications and weather satellites. Space physics uses measurements from high altitude rockets and spacecraft.

Several members of the Astrophysics Group are part of the Space Plasma Climate Section. Relevant research in this group includes studies of the formation and evolution of dusty galaxies, studies of the formation of stars and planets, investigations into the habitability of planets forming around stars of varied types, the study of the Sun and Sun-like stars, quantification of the variability of the Sun for use in climate modelling, and the search for signs of biological activity within our own Solar System.

Atomic physics is the subfield of AMO that studies atoms as an isolated system of electrons and an atomic nucleus, while Molecular physics is the study of the physical properties of molecules

Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions. Everything we can see in the night time sky is made of nuclear matter. The nuclear physics deals with the nucleus as a system consisting of a nucleon i.e., protons and neutrons.

A dusty plasma is a plasma containing nanometer or micrometer-sized particles suspended in it. A grain plasma contains larger particles than dusty plasmas. Examples include comets, planetary rings, exposed dusty surfaces, and the zodiacal dust cloud.

Since plasmas are very good electric conductors, electric potentials play an important role. The potential as it exists on average in the space between charged particles, independent of the question of how it can be measured, is called the "plasma potential", or the "space potential". If an electrode is inserted into a plasma, its potential will generally lie considerably below the plasma potential due to what is termed a Debye sheath. The good electrical conductivity of plasmas makes their electric fields very small. This results in the important concept of "quasineutrality", which says the density of negative charges is approximately equal to the density of positive charges over large volumes of the plasma, but on the scale of the Debye length there can be charge imbalance. In the special case that double layers are formed, the charge separation can extend some tens of Debye lengths.

"Colloidal plasmas may "condense" under certain conditions into liquid and crystalline states, while retaining their essential plasma properties. This "plasma condensation" therefore leads to new states of matter: "liquid plasmas" and "plasma crystals." The experimental discovery was first reported in 1994".

Thermal plasmas have electrons and the heavy particles at the same temperature, i.e. they are in thermal equilibrium with each other.

Nonthermal plasmas on the other hand are non-equilibrium ionized gases, with two temperatures: ions and neutrals stay at a low temperature, whereas electrons are much hotter. A kind of common nonthermal plasma is the mercury vapor gas within a fluorescent lamp, where the "electrons gas" reaches a temperature of 10,000 kelvins while the rest of the gas stays barely above room temperature, so the bulb can even be touched with hands while operating.

Active plasma regions: These carry field-aligned currents which give them filamentary or sheet structure with thickness down to a few cyclotron radii (ionic or even electronic). They transmit energy from one region to another and produce electric double layers which accelerate particles to high energies. Active regions cannot be described by hydromagnetic theories. Boundary conditions are essential and may be introduced by circuit theory.

"Passive plasma regions, which can be described by classical hydrodynamic theory. They transmit waves and high energy charged particles but if the field-aligned currents exceed a certain value they are transferred into.

Plasma temperature is commonly measured in kelvins or electronvolts and is, informally, a measure of the thermal kinetic energy per particle. High temperatures are usually needed to sustain ionization, which is a defining feature of a plasma. The degree of plasma ionisation is determined by the electron temperature relative to the ionization energy (and more weakly by the density), in a relationship called the Saha equation. At low temperatures, ions and electrons tend to recombine into bound states—atoms—and the plasma will eventually become a gas.

Plasma with a magnetic field strong enough to influence the motion of the charged particles is said to be magnetized. A common quantitative criterion is that a particle on average completes at least one gyration around the magnetic field before making a collision is the "electron collision rate". It is often the case that the electrons are magnetized while the ions are not. Magnetized plasmas are anisotropic, meaning that their properties in the direction parallel to the magnetic field are different from those perpendicular to it.