Dispersion relations for electrostatic surface waves in a homogeneous plasma-layer \vhich interacts with a n external electric pumping field parallel to the boundaries are derived in the framework of the kinetic theory. The parametrically excited and purely growing instabilities are investigated. Electric threshold fields and growth rates for the instable surface modes are given. It can be shown that the minimum threshold for parametric excitation occurs for those modes which are symmetric about the midplane of the layer.

Pnrainetric resonance phenomena are investigated in a plasma layer with thickness d and thin iiilioiiiogeneous boiindnry regions. The modulated UHF electric field is parallel to the plasma layer.\Vc consider both strong and low modulation of the field amplitude and suppose, that the carrier frcqucncy wo of the prinip wave is much larger than the LANCYUIR frequency wLc. \Ve find the region for the iiiocliilution frequency R, in which the parametric growing of the asymmetric and symmetric siirfiice wavcs occurs. The mnximiim growth rates of these waves, the direction of their propagation iintl tlic threshold valiie of the inodiilution depth a of the UHF pump field are calc.itlntion. EinlcitungDie bei der Wechselwirkung eines starken nionochroniatischen elektrischen l'utnpfeldes E, sin mot mit eineui houiogenen und unbegrenzten Plasma auft retcnden paraiiietrischen Instabilitaten, die zii einer experimentell nachgewiesenen nichtohnischen -4ufheizung des Ylasnias und dessen schnellen Zerfalls fiihren, wurden theoretisch zuerst von SILIN