Structure of electric potential near the extraction region in a negative ion source is investigated analytically with the effect of strong surface H(-) production. The potential profile is analyzed one dimensional by solving the plasma-sheath equation, which gives the electric potential in the plasma region and the sheath region near the wall self-consistently. The potential profile depends on the production rate and the temperature of negative ions. As the production rate becomes large and the negative ion energy becomes small, the potential near the extraction region decreases. The negative potential peak is formed near the plasma grid (PG) surface for the case of large amount and low energy surface production. As a result, negative ions are reflected by this negative potential peak near the PG and returned to the PG surface. This reflection mechanism by the negative potential peak possibly affects the negative ion extraction.
[1]
Keishi Sakamoto,et al.
Improvement of beam uniformity by magnetic filter optimization in a Cs-seeded large negative-ion source
,
2006
.
[2]
D. Riz,et al.
Modeling of negative ion transport in a plasma source (invited)
,
1998
.
[3]
J. N. Davidson,et al.
Electric sheath and presheath in a collisionless, finite ion temperature plasma
,
1980
.
[4]
J. H. Whealton,et al.
Calculations involving ion beam source
,
1978
.
[5]
J. C. Whitson,et al.
Optics of ion beams of arbitrary perveance extracted from a plasma
,
1978
.