Negative Hydrogen Ion Density Measurement in a Permanent Magnet based Helicon Ion Source (HELEN-I) using Cavity Ring-Down Spectroscopic Technique

In this paper, negative hydrogen ion (IT ion) density is measured ma permanent magnet based helicon ion source (IIELEN-I) plasma by using cavity ring down spectroscopic (CRDS) technique, a non-invasive diagnostic system. The present optical cavity is of having 1.2 m length, with two mirrors at the end having reflectivity similar to 99.99% (company specified). The radius of curvature of the mirrors arc 6m each and they form a stable cavity.The cavity alignment and mirror reflectivity status is of utmost importance for this spectroscopy. It is observed that similar to 10(17)m(-3) negative ion density is obtained m this helicon device, even without any Caesium (Cs) seeding.