Design of experiment to explore inside the LANSCE H− ion source with laser absorption techniques

The Los Alamos Neutron Science Center (LANSCE) H− ion source (LHIS) has provided stable output for decades of LANL mission needs. While several in-house improvements have been made to its stability and lifetime, its maximum beam output has remained the same at ~14 mA. While operationally well understood, the internal relationship between the LHIS plasma, cesium distribution (the catalyst for producing H− ions), and produced H− beam remains a mystery, only explored indirectly with models. We will develop fast, accurate, and non-invasive diagnostics techniques to measure the Cs and H− densities inside LHIS. These diagnostics are based on optical absorption spectroscopy that have been developed in the last decade for fusion based H- ion sources that can readily be applied to the accelerator based LHIS. A refined form of optical absorption spectroscopy, the laser absorption technique (LAT), utilizes lasers tuned to a given atomic species to measure its density. In this case a laser tuned to the D2 line of cesium will be used to determine its density inside LHIS. Similarly, a refined version of LAT called the cavity ring-ring down spectroscopy (CRDS) technique utilizes a laser tuned to H− photo-detachment to measure the H− densities at inside LHIS. With successful development of these diagnostic techniques, any hidden or dormant capabilities in LHIS will be found and capitalized upon, both in its modelling and operation. Also, its potential benefit to LANSCE and LANL future needs will be realized. More generally, this will be the first use of these plasma diagnostic techniques on an accelerator based H− ion sources. We will present on the preliminary status of the diagnostic setup.