Thermal effects and space-charge limited transition in crossed-field devices

Abstract

Articles you may be interested inRelativistic solutions for one-and two-dimensional space-charge limited current in coaxial diode Phys. Plasmas 20, 053103 (2013) A fully kinetic model for the electron flow in a crossed field device is derived and used to determine the system stationary states. It is found that for low injection temperatures, there is a simultaneous presence of distinct stationary solutions and an abrupt transition between accelerating and space-charge limited regimes. On the other hand, for high injection temperatures, there is only a single stationary solution branch and the change between the regimes becomes continuous. For intermediate temperatures, it is then identified a critical point that separates the abrupt and continuous behaviors. It is also investigated how intrinsic space-charge oscillations may drive stationary states unstable in certain parameter regimes. The results are verified with N-particle self-consistent simulations. V C 2014 AIP Publishing LLC. [http://dx

Stationary to nonstationary transition in crossed-field devices

“…This particularly affects the low energy particles-those injected with p y % 0-because if they loose energy they may fail to return to the cathode, becoming trapped in the gap region. [4][5][6] This causes a continuous increase in the charge accumulated inside the gap. At this point, the incompressibility in the evolution of the Vlasov equation becomes crucial because it sets a limit on the maximum density of particles found in the phase space which has to be always equal or smaller (in a coarse grained sense 13 ) than the density at the injection, namely, n 0 =p 0 .…”

“…Hence, the charge keeps increasing in the system up to the point where the available phase space is completely filled by the particles. 6 The available phase space corresponds to the region where the energy does not exceed H max . The stationary distribution function is then given by…”

“…What happens is that these particles may loose energy while transiting in the cathode-anode gap and fail to return to the cathode at the end of their cycloidal trajectory. [4][5][6] They then become trapped in the gap region leading to an increasing charge build up in the system. At high currents, the self-fields may also be responsible for the onset of a space-charge limited regime, where the accelerating field is completely shielded at the cathode by the electron distribution present in the gap region.…”

“…3 More recently, however, it has been found that thermal effects may play a major role in the electron dynamics in a crossed field gap. 6 In particular, it has been detected the occurrence of stationary solutions for currents well beyond the space-charge limiting threshold.…”

Single electron dynamics in a Hall thruster electromagnetic field profile

“…Simplistically, in a Hall thruster, electrons are accelerated and confined by crossed electric and magnetic fields 11,12 in an acceleration channel. There, they collide with atoms of a propellant gas, generating ions.…”