Using Laser-Induced Rydberg Spectroscopy diagnostic for direct measurements of the local electric field in the edge region of NSTX/NSTX-U: Modeling

We discuss a novel diagnostic allowing direct measurements of the local electric field in the edge region of NSTX/NSTX-U. This laser based diagnostic's principle consists of depleting the naturally populated n = 3 level to a Rydberg state-sensitive to electric fields-that will result in a suppression of part of the D-alpha emission. We refer to this approach as Laser-Induced Rydberg Spectroscopy. It is shown that the local electric field can be measured through the Stark induced resonances observed as dips in the D-alpha emission. Using forward-modeling of simulated absorption spectra, we show precisions reaching +/- 2 kV m(-1) in regions with a local electric field of 15 kV m(-1). Published by AIP Publishing

Modeling of a Laser-Induced Rydberg Spectroscopy diagnostic for Direct Measurement of the Local Electric Field in the Edge Region of NSTX/NSTX-U

We discuss a novel diagnostic allowing direct measurements of the local electric field in the edge region in NSTX/NSTX-U. This laser based diagnostic's principle consists of depleting the naturally populated $n=3$ level to a Rydberg state --sensitive to electric fields-- that will result in a suppression of part of the $D_{\alpha}$ emission. We refer to this approach as Laser-Induced Rydberg Spectroscopy (LIRyS). It is shown that the local electric field can be measured through the Stark induced resonances observed as dips in the $D_\alpha$ emission. Using forward-modeling of simulated absorption spectra, we show precisions reaching \SI{\pm 2}{\kilo\volt\per\meter} in regions with a local electric field of \SI{15}{\kilo\volt\per\meter}.readme, digital data file

Quantitative imaging of carbon dimer precursor for nanomaterial synthesis in the carbon arc

Delineating the dominant processes responsible for nanomaterial synthesis in a plasma environment requires measurements of the precursor species contributing to the growth of nanostructures. We performed comprehensive measurements of spatial and temporal profiles of carbon dimers in sub-atmospheric-pressure carbon arc by laser-induced fluorescence. Measured spatial profiles of carbon dimers coincide with the growth region of carbon nanotubes (Fang et al 2016 Carbon 107 273-80) and vary depending on the arc operation mode, which is determined by the discharge current and the ablation rate of the graphite anode. The carbon dimer density profile exhibits large spatial and time variations due to motion of the arc core. A comparison of the experimental data with the 2D simulation results of self-consistent arc modeling shows a good agreement. The model predicts well the main processes determining spatial profiles of carbon dimers.Read me and data files

Time-resolved investigation of nanosecond discharge in dense gas sustained by short and long high-voltage pulse

The results of experimental and numerical studies of the generation of runaway electrons (RAE) in a pressurized air-filled diode under the application of 20 ns, 5 ns and 1 ns duration high-voltage pulses with an amplitude up to 160 kV are presented. It is shown that with a 1 ns pulse, RAE with energy ⩾20 keV reach the anode prior to the formation of the plasma channel between the cathode and anode. Conversely, with 20 ns or 5 ns pulses, RAE with energy ⩾20 keV were obtained at the anode only after the formation of the plasma channel. In addition, the high- and low-impedance stages of the development of the discharge were found. Finally, a comparison between experimental and numerical simulation results is presented