Beam instability in the vicinity of beam extraction region of negative ion source

Abstract

Beam instability in the presheath region of negative ion beam extraction is investigated in theoretically and experimentally. The linear stability analysis shows that the beam instability is unstable due to coupling between positive ion flow and negative ion flow. On the other hand, no clear activity can be seen in the experiment in the frequency range predicted by the theory. The beam instability in the presheath region of negative ion beam extraction may not cause the degradation of the beam focusing because of collisional damping and/or Landau damping.

Simple 3D PIC Analysis for Beam Phase Space Oscillation in RF Driven Negative Hydrogen Ion Source

“…The beam current measurement via Faraday-Cup with a slit shows that the beam components in 2 and 4 MHz appear in different positions [5]. A key mechanism is indicated by the fast beamlet monitor measurements in NIFS that the beam instability is governed by the coupling between positive and negative ion flow in the extraction region [6]. However, the direct relation between the RF plasma oscillations and the observed beam has not been clarified yet.…”