[en] Experimental stUdy Was made on various mechanisms, responsible for impurity generation plasma at the inner surface of a gas-discharge tokamak chamber. Consideration is given to basic characteristics of impurity formation processes resulting from th.ermal evaporation and sputtering of surface atom as well as erosion caused by homopolar arc burning. Data are presented on generation mechanism of impurities which could be used for erosion identification during discharge and for evaluation of impurity inflow into a plasma. It is concluded that an arc can be formed and the limiter surface can melt in discharges with limiters, therefore different mechanisms of impurity generation could exist at different discharge phases. A decrease in the ion-and electron temperatures at the end of a discharge reduces the effect of such mechanisms of impurity formation as arc origination, evaporation and ionic sputtering. In this case sputtering due to atom recharging can become dominating mechanism