Langmuir-probe measurement through the plasma grid aperture of hydrogen negative ion source

Abstract

The extraction physics of negative-ion sources is still unknown because of the complication of the plasma-beam boundary (meniscus), which includes electronegative plasma, the magnetic field, and a surface production of negative ions. This paper shows results from Langmuir probe measurements inside of the extraction aperture (EA) and the criteria for locating the meniscus. The criteria are defined by the appearance and disappearance of Maxwellian feature of plasma. The result gives direct information on the location and shape of the plasma-beam boundary.