Plasma parameters define various characteristics of a
plasma, an electrically conductive collection of
charged and neutral
particles of various species (
electrons and
ions) that responds collectively to
electromagnetic forces.[1] Such particle systems can be studied
statistically, i.e., their behaviour can be described based on a limited number of global parameters instead of tracking each particle separately.[2]
Fundamental
The fundamental plasma parameters in a
steady state are
the
number density of each particle species present in the plasma,
classical distance of closest approach, also known as "Landau length" the closest that two particles with the elementary charge come to each other if they approach head-on and each has a velocity typical of the temperature, ignoring quantum-mechanical effects:
electron gyroradius, the radius of the circular motion of an electron in the plane perpendicular to the magnetic field:
ion gyroradius, the radius of the circular motion of an ion in the plane perpendicular to the magnetic field:
plasma
skin depth (also called the electron
inertial length), the depth in a plasma to which electromagnetic radiation can penetrate:
Debye length, the scale over which electric fields are screened out by a redistribution of the electrons:
ion inertial length, the scale at which ions decouple from electrons and the magnetic field becomes frozen into the electron fluid rather than the bulk plasma:
mean free path, the average distance between two subsequent collisions of the electron (ion) with plasma components:
where is an average velocity of the electron (ion) and is the electron or ion collision rate.
Temperature is a statistical quantity whose formal definition is
or the change in internal energy with respect to
entropy, holding volume and particle number constant. A practical definition comes from the fact that the atoms, molecules, or whatever particles in a system have an average kinetic energy. The average means to average over the kinetic energy of all the particles in a system.
If the
velocities of a group of
electrons, e.g., in a
plasma, follow a
Maxwell–Boltzmann distribution, then the electron temperature is defined as the
temperature of that distribution. For other distributions, not assumed to be in equilibrium or have a temperature, two-thirds of the average energy is often referred to as the temperature, since for a Maxwell–Boltzmann distribution with three
degrees of freedom, .
The
SI unit of temperature is the
kelvin (K), but using the above relation the electron temperature is often expressed in terms of the energy unit
electronvolt (eV). Each kelvin (1 K) corresponds to 8.617333262...×10−5 eV; this factor is the ratio of the
Boltzmann constant to the
elementary charge.[6] Each eV is equivalent to 11,605
kelvins, which can be calculated by the relation .
The electron temperature of a plasma can be several orders of magnitude higher than the temperature of the neutral species or of the
ions. This is a result of two facts. Firstly, many
plasma sources heat the electrons more strongly than the ions. Secondly, atoms and ions are much heavier than electrons, and energy transfer in a two-body
collision is much more efficient if the masses are similar. Therefore, equilibration of the temperature happens very slowly, and is not achieved during the time range of the observation.
^Wenzel, K and Sigmar, D.. Nucl. Fusion 30, 1117 (1990)
^
Mohr, Peter J.; Newell, David B.; Taylor, Barry N.; Tiesenga, E. (20 May 2019).
"CODATA Energy conversion factor: Factor x for relating K to eV". The NIST Reference on Constants, Units, and Uncertainty. National Institute of Standards and Technology. Retrieved 11 November 2019.
Plasma parameters define various characteristics of a
plasma, an electrically conductive collection of
charged and neutral
particles of various species (
electrons and
ions) that responds collectively to
electromagnetic forces.[1] Such particle systems can be studied
statistically, i.e., their behaviour can be described based on a limited number of global parameters instead of tracking each particle separately.[2]
Fundamental
The fundamental plasma parameters in a
steady state are
the
number density of each particle species present in the plasma,
classical distance of closest approach, also known as "Landau length" the closest that two particles with the elementary charge come to each other if they approach head-on and each has a velocity typical of the temperature, ignoring quantum-mechanical effects:
electron gyroradius, the radius of the circular motion of an electron in the plane perpendicular to the magnetic field:
ion gyroradius, the radius of the circular motion of an ion in the plane perpendicular to the magnetic field:
plasma
skin depth (also called the electron
inertial length), the depth in a plasma to which electromagnetic radiation can penetrate:
Debye length, the scale over which electric fields are screened out by a redistribution of the electrons:
ion inertial length, the scale at which ions decouple from electrons and the magnetic field becomes frozen into the electron fluid rather than the bulk plasma:
mean free path, the average distance between two subsequent collisions of the electron (ion) with plasma components:
where is an average velocity of the electron (ion) and is the electron or ion collision rate.
Temperature is a statistical quantity whose formal definition is
or the change in internal energy with respect to
entropy, holding volume and particle number constant. A practical definition comes from the fact that the atoms, molecules, or whatever particles in a system have an average kinetic energy. The average means to average over the kinetic energy of all the particles in a system.
If the
velocities of a group of
electrons, e.g., in a
plasma, follow a
Maxwell–Boltzmann distribution, then the electron temperature is defined as the
temperature of that distribution. For other distributions, not assumed to be in equilibrium or have a temperature, two-thirds of the average energy is often referred to as the temperature, since for a Maxwell–Boltzmann distribution with three
degrees of freedom, .
The
SI unit of temperature is the
kelvin (K), but using the above relation the electron temperature is often expressed in terms of the energy unit
electronvolt (eV). Each kelvin (1 K) corresponds to 8.617333262...×10−5 eV; this factor is the ratio of the
Boltzmann constant to the
elementary charge.[6] Each eV is equivalent to 11,605
kelvins, which can be calculated by the relation .
The electron temperature of a plasma can be several orders of magnitude higher than the temperature of the neutral species or of the
ions. This is a result of two facts. Firstly, many
plasma sources heat the electrons more strongly than the ions. Secondly, atoms and ions are much heavier than electrons, and energy transfer in a two-body
collision is much more efficient if the masses are similar. Therefore, equilibration of the temperature happens very slowly, and is not achieved during the time range of the observation.
^Wenzel, K and Sigmar, D.. Nucl. Fusion 30, 1117 (1990)
^
Mohr, Peter J.; Newell, David B.; Taylor, Barry N.; Tiesenga, E. (20 May 2019).
"CODATA Energy conversion factor: Factor x for relating K to eV". The NIST Reference on Constants, Units, and Uncertainty. National Institute of Standards and Technology. Retrieved 11 November 2019.