New Method to Evaluate Negative-Ion Density Using Conventional Langmuir Probe

Abstract

A new experimental method using a Langmuir probe to measure negative-ion density is introduced in an area that cannot use lasers, such as the extraction hole. An electron reduction Langmuir probe model is established to distinguish negative ions from electron density. A comparison between density measured by the Langmuir probe with the electron reduction model and a photo-detachment Langmuir probe is performed to verify the use of the newly developed model. c

Evaluation of H-/D- Density Using Langmuir Probe Measurement in a Cs Seeded Negative Ion Source

“…The electron reduction method [11] is reintroduced in this paper to perform negative ion evaluation of Deuterium and Hydrogen plasma in NIFS-RNIS. The eq.…”

“…Where ‫ܣ‬ is a probe geometry area, ‫ݍ‬ is a charge value, ‫ܫ݀‬ ା ଶ /ܸ݀ is a slope from negative saturation current-square, ‫ܫ݀‬ ି ଶ /ܸ݀ is a slope from positive saturation current-square. The β, by definition, is a ratio of square root of mass different between ion and electron where, ݉ is an ion mass, and ݉ is an electron mass and different between probe absorption area of electron and ion where ‫ܣ‬ is a probe electron absorption area, and ‫ܣ‬ is a probe geometry area [11]. Empirically, when considering electron-positive ion plasma, we can derive β from the Orbital Motion Limit theory (OML), which is defined by a ratio of the square root of negative saturation current-square and positive saturation current-square as written in eq.…”

“…Therefore, the saturate tendency of β versus the arc power indicates that β mainly depends on the ion's mass and magnetic field strength. Although the saturation is obtained, we use the saturation function (see [11]) to estimate the β value for the correction of electron thermal velocity.…”

“…Injecting the laser pulse near the PG hole is difficult because the grid-supporting structure scrapes off the pulse before reaching the extraction hole. For this reason, we developed a new method to evaluate negativeion density using a conventional Langmuir probe measurement [11].…”