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{{unordered list
| '''electron gyrofrequency''', the angular frequency of the circular motion of an electron in the plane perpendicular to the magnetic field:
| '''ion gyrofrequency''', the angular frequency of the circular motion of an ion in the plane perpendicular to the magnetic field:
| '''electron plasma frequency''', the frequency with which electrons oscillate ([[plasma oscillation]]):
| '''ion plasma frequency''':
| '''electron trapping rate''':
| '''ion trapping rate''':
| '''electron collision rate in completely ionized plasmas''':
| '''ion collision rate in completely ionized plasmas''':
}}
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{{unordered list
| '''[[Thermal de Broglie wavelength|electron thermal de Broglie wavelength]]''', approximate average [[de Broglie wavelength]] of electrons in a 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 <math>\overline{v_{e,i}}</math> is an average velocity of the electron (ion) and <math>\nu_{e,i}</math> is the electron or ion '''collision rate'''.
}}
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{{unordered list
| '''electron thermal velocity''', typical velocity of an electron in a [[Maxwell–Boltzmann distribution]]:
| '''ion thermal velocity''', typical velocity of an ion in a [[Maxwell–Boltzmann distribution]]:
| '''ion speed of sound''', the speed of the longitudinal waves resulting from the mass of the ions and the pressure of the electrons:
where <math>\gamma</math> is the [[adiabatic index]]
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=== Dimensionless ===
[[Image:fusor running.jpg|thumb|right|300px|A 'sun in a test tube'. The [[Farnsworth-Hirsch Fusor]] during operation in so called "star mode" characterized by "rays" of glowing plasma which appear to emanate from the gaps in the inner grid.]]
* number of particles in a Debye sphere <math display="block">\left(\frac{4\pi}{3}\right)n\lambda_D^3 \approx 1.72 \times 10^9\,\left(\frac{T^3}{n}\right)^\frac{1}{2}</math>
*
*
*
*
*
▲*: <math>\frac{\omega_{pi}}{\omega_{ci}} \approx 0.137\,\frac{\left(\mu n_i\right)^\frac{1}{2}}{B}</math>
▲*: <math>\beta = \frac{8\pi nkT}{B^2} \approx 4.03 \times 10^{-11}\,\frac{nT}{B^2}</math>
==Collisionality==
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The [[Plasma (physics)|plasma]] collisionality <math>\nu^*</math> is defined as<ref>Nucl. Fusion, Vol. 39, No. 12 (1999)</ref><ref>Wenzel, K and Sigmar, D.. Nucl. Fusion 30, 1117 (1990)</ref>
<math display="block">
\nu^* = \nu_\mathrm{ei}\,\sqrt{\frac{m_\mathrm{e}}{k_\mathrm{B} T_\mathrm{e}}}\,\frac{1}{\epsilon^\frac{3}{2}} \, qR,▼
▲\nu^* = \nu_\mathrm{ei}\,\sqrt{\frac{m_\mathrm{e}}{k_\mathrm{B} T_\mathrm{e}}}\,\frac{1}{\epsilon^\frac{3}{2}}\,qR,
</math>
where <math>\nu_\mathrm{ei}</math> denotes the electron-ion [[collision frequency]], <math>R</math> is the major radius of the plasma, <math>\epsilon</math> is the inverse [[aspect-ratio]], and <math>q</math> is the [[safety factor]]. The [[Plasma (physics)|plasma]] parameters <math>m_\mathrm{i}</math> and <math>T_\mathrm{i}</math> denote, respectively, the [[mass]] and [[temperature]] of the [[ions]], and <math>k_\mathrm{B}</math> is the [[Boltzmann constant]].
==Electron temperature==
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 [[velocity|velocities]] of a group of [[electron]]s, e.g., in a [[plasma (physics)|plasma]], follow a [[Maxwell–Boltzmann distribution#Distribution of the velocity vector|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 (physics and chemistry)|degrees of freedom]], <math display="inline">\langle E \rangle =
The [[International System of Units|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 {{val|8.
{{cite web
|url=https://physics.nist.gov/cgi-bin/cuu/Convert?exp=0&num=1&From=k&To=ev&Action=Only+show+factor
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