Electric field spikes formed by electron beam{endash}plasma interaction in plasma density gradients
- Division of Plasma Physics, Alfven Laboratory, Royal Institute of Technology, SE-100 44 Stockholm (Sweden)
In the electron beam{endash}plasma interaction at an electric double layer the beam density is much higher than in the classical beam{endash}plasma experiments. The wave propagation takes place along the density gradient that is present at the high potential side of the double layer. Such a case is studied experimentally by injecting the electron beam from a plane cathode, without any grids suppressing the gradient, and by particle simulations. The high frequency field concentrates in a sharp {open_quotes}spike{close_quotes} with a half width of the order of one wavelength. The spike is found to be a standing wave surrounded by regions dominated by propagating waves. It forms at a position where its frequency is close to the local plasma frequency. The spike forms also when the electric field is well below the threshold for modulational instability, and long before a density cavity is formed in the simulations. Particle simulations reveal that, at the spike, there is a backward traveling wave that, when it is strongly damped, accelerates electrons back towards the cathode. In a simulation of a homogeneous plasma without the density gradient no spike is seen, and the wave is purely travelling instead of standing. {copyright} {ital 1997 American Institute of Physics.}
- OSTI ID:
- 526912
- Journal Information:
- Physics of Plasmas, Vol. 4, Issue 8; Other Information: PBD: Aug 1997
- Country of Publication:
- United States
- Language:
- English
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