Increasing the Space Charge Limit and Other Effects of Cesium Seeding in Hydrogen211 Negative Ion Sources

摘要

The role of cesium seeding in increasing the negative ion current in volume211u001esources is described. By a reduction in the local plasma potential the current of 211u001eextracted electrons is vastly reduced. As a result, cesium increases the fraction 211u001eof the transverse space charge limit available to the ions by as much as a factor 211u001eof three. In addition, cesium can increase the total space charge limit by 211u001einjection of Cs+ into the presheath-a newly recognized phenomenon consistent with 211u001eexperimental measurements and determined from application of a Double-Vlasov 211u001emodel for negative ion extraction.