Effect of total emitted electron velocity distribution function on the plasma sheath near a floating wall

Electrons emitted from a solid surface can noticeably affect characteristics of plasmasheath surrounding that surface by modifying current balance at wall, charge separation insheath region and Bohm criterion at sheath edge. We establish a static sheath model withkinetic electrons and cold ions to emphasize the effect of different total emittedelectron velocity distribution functions (EEVDFs) on classic sheath solution and itsstructure transition. Four total EEVDFs with same average energy are consideredseparately. It is found that total EEVDFs influence the sheath solution and the thresholdof total electron emission coefficient (EEC) for classic sheath dramatically, and cancause no solution for critical space-charge limited (SCL) sheath. These results indicatethat, as EEC increases from zero gradually, the sheath will not transit from classicsheath to SCL sheath structure for some special total EEVDFs