Instability in low energy beams extracted from BF3 plasma

Ion beam instabilities on a wide ribbon beam which cross-section is 150 cm × 10 cm are discussed. At low energy conditions, we detected two kinds of instabilities on the ion beam extracted from BF₃ plasmas. One kind of the instabilities is that onset of the instability is dependent on the extraction current from the ion source. This instability occurred when the extraction current exceeded 300 - 350 mA at the energy of 15keV. Another is that the onset is dependent on the BF₂⁺ beam current. The BF₂⁺ beam current became unstable when it exceeded about 20 μA/cm² at 15keV. Energy dependence of these instabilities is also discussed.