Alternative solutions to caesium in negative-ion sources: a study of negative-ion surface production on diamond in H 2 /D 2 plasmas

TL;DR

This study investigates negative ion surface production on diamond in low pressure H2/D2 plasmas, exploring how material properties and experimental conditions affect negative ion yields, with implications for ion source development.

Contribution

It introduces experimental methods to analyze negative ion production on diamond surfaces and compares different diamond materials with graphite under various conditions.

Findings

Diamond's electronic properties favor negative-ion production.

Negative ion yield decreases with higher defect density.

Surface temperature and bias influence ion yield.

Abstract

This paper deals with a study of H-/D-negative ion surface production on diamond in low pressure H2/D2 plasmas. A sample placed in the plasma is negatively biased with respect to plasma potential. Upon positive ion impacts on the sample, some negative ions are formed and detected according to their mass and energy by a mass spectrometer placed in front of the sample. The experimental methods developed to study negative ion surface production and obtain negative ion energy and angle distribution functions are first presented. Different diamond materials ranging from nanocrystalline to single crystal layers, either doped with boron or intrinsic, are then investigated and compared with graphite. The negative ion yields obtained are presented as a function of different experimental parameters such as the exposure time, the sample bias which determines the positive ion impact energy and the sample surface temperature. It is concluded from these experiments that the electronic properties of diamond materials, among them the negative electron affinity, seem to be favourable for negative-ion surface production. However, the negative ion yield decreases with the plasma induced defect density.