Plasma surface waves are excited by a high frequency field in a semi-infinite plasma with a plane boundary when omega 0- omega p approximately=+or-( omega p/ square root 2) and omega 0- omega p approximately=+or-( omega p square root 2)- omega 0 ( omega 0 being the frequency of the high frequency field and omega p the plasma frequency). The instabilities, in effect, take place at (nc/n0)=3, 8.5*10-2, 0.72 and 2*10-2, where nc and n0 are the critical and the particle densities respectively. Threshold conditions are derived for plasmas with and without a low density electron beam. In the absence of the beam the thresholds are more than the relativistic limit while its presence reduces the thresholds considerably under certain conditions.
半无限等离子体中，平面边界处由高频场激发的表面等离子体激元，在ω₀-ωₚ≈±(ωₚ/√2)和ω₀-ωₚ≈±(ωₚ√2)-ω₀时发生不稳定性（其中ω₀为高频场频率，ωₚ为等离子体频率）。实际上，不稳定性发生在(n_c/n₀)=3、8.5×10⁻²、0.72和2×10⁻⁴处，其中n_c和n₀分别为临界密度和粒子密度。推导了有无低密度电子束时等离子体的阈值条件。无电子束时，阈值超过相对论极限；而在一定条件下，电子束的存在会显著降低阈值。