-
Author(s):
M. Bacal, M. Nishiura, M. Sasao, M. Wada, M. Hamabe and H. Yamaoka
-
Title:
Effect of Argon Additive in Negative Hydrogen Ion Sources
Date of publication:
Aug. 2001
-
Key words:
Negative ions, H^-, vibrational excited molecules, argon additive, Werner system, Lyman system, VUV, Photo detachment
-
Abstract:
We investigated using the photodetachment technique the negative ion density in the extraction region of a magnetically filtered multicusp ion source (21cm in diameter and 27 cm long) when argon is added to hydrogen (up to 100%). A cylindrical probe was used to measure the plasma parameters (electron density and temperature, plasma and floating potential). We found that the negative ion density goes up at most by a factor 1.5 when argon is added to low base hydrogen pressure (0.05 or 0.1 Pa), but goes down when argon is added to higher initial hydrogen pressure (0.5 or 1 Pa). The optimum argon additive pressure is 40 to 60% of the base hydrogen pressure. The replacement of hydrogen by argon when the total pressure is kept constant does not change the electron temperature. We found that the negative ion temperature is lowered by the argon mixing to hydrogen. We also checked the hypothesis proposed by Curran et al [1], namely that the sequential energy transfer from the excited argon states through a photon to hydrogen singlet states would be the cause of enhanced highly excited vibrational population of hydrogen molecules. To do this we investigated whether the argon additive had any effect on the Werner and Lyman system lines in the VUV . No effect of argon on the mentioned hydrogen lines was found .
-
|
