Abstract
Electron energy probability functions (eepfs) have been measured along the axis of low pressure plasma expanding in a magnetic nozzle. The eepf at the maximum magnetic field of the nozzle shows a depleted tail commencing at an energy corresponding to the measured potential drop in the magnetic nozzle. The eepfs measured along the axis demonstrate that the potential and kinetic energies of the electrons are conserved and confirm the non-local collisionless kinetics of the electron dynamics.
Highlights
In low pressure partially-ionized plasmas the electron energy probability function is typically non-Maxwellian because electron-electron collisions are not frequent enough compared to other processes responsible for the eepf formation [1]
In low-pressure plasmas where the mean free path for electronneutral collisions is typically longer than the typical dimension of the system the wall losses can become important for the bulk eepf, since the electrons visit the boundaries more often than they collide with other electrons and their distribution in energy will reflect this
⎤ ⎦, kTe where the particles are assumed to be in an electric field (φ is the electric potential, k is the Boltzmann constant, e is the electronic charge and Te is the electron temperature)
Summary
In low pressure partially-ionized plasmas the electron energy probability function (eepf) is typically non-Maxwellian because electron-electron collisions are not frequent enough compared to other processes responsible for the eepf formation [1]. ⎤ ⎦, kTe where the particles are assumed to be in an electric field (φ is the electric potential, k is the Boltzmann constant, e is the electronic charge and Te is the electron temperature) This is the general form of the Maxwell distribution function. As the electric potential φ does not depend on velocity, it can be taken outside the integral and serves to change the absolute value of the integral, while the shape of the distribution remains invariant. This is a property of Gaussian distributions and is encountered in many situations, such as an ensemble of balls in the bottom of a hole, or gravitational well
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