Data Acquisition and Trigger system for CRDS diagnostic in Negative Ion source

Abstract ROBIN is single driver RF (100 kW, 1 MHz) based Negative Ion source being operated at IPR. In order to characterize ROBIN, multiple diagnostics are designed and interfaced. Cavity Ring Down Spectroscopy (CRDS) is one such diagnostic interfaced with ROBIN to determine the temporal negative Ion density. CRDS is a laser based absorption/scattering diagnostic used to quantify traces of a species in a particular volume upto ppb/ppt sensitivity. CRDS diagnostic system consists of pulsed laser firing photons in a high finesse optical cavity. The decay of the photon flux in time is recorded with the help of suitable detection mechanism and provides the information regarding species density. Successful integration of CRDS needs a reliable Electronic system. The Electronics needs to cater to two main requirements of the diagnostic. Precise laser triggering and acquiring high bandwidth signal are two top level requirements. The laser system need to be triggered at a particular frequency with microseconds resolution. The signal chain involves High voltage referenced systems and hence needs appropriate isolation. The decay signal needs high sampling rate of more than 40 MSPS. For meeting these challenges a Data Acquisition and Trigger system (DAqTS) is developed at ROBIN for signal detection and integration of CRDS. ROBIN control and data acquisition system is based on S7400 Siemens PLC and PXI which are suitable for up to 0.1 ms time resolution. Hence, a custom system is needed which can meet the requirements of CRDS for precise triggering and high-speed acquisition. The DAqTS trigger the laser unit in synchronization with the central PLC control system and acquires data at high sampling rate. The data is accessible to experimentalists via a LabVIEW based utility for facilitating quick data analysis. DAqTS is based on FPGA and high speed digitizer system. The present report covers the requirement, design, development and integration of DAqTS for CRDS diagnostic in ROBIN. The test results are also discussed.