Modeling of parasitic plasma under the divertor roof baffle

Ammonia formation and W coatings interaction with deuterium/nitrogen plasmas in the linear device GyM

“…The GyM plasma parameters used in the experiment were n e = 1.6 Á 10 16 m À3 , T e = 3.3 eV (on the axis, in correspondence of the sample, as measured by Langmuir probes) and corresponding to an ion flux of 1.22 Á 10 20 m À2 s À1 . These values are comparable to those predicted for divertor of ITER [6]. The sample has been exposed to GyM plasma integrating several discharges in order to reach the required fluence ($10 24 m À2 ); the plasma composition was monitored by OES spectra, acquired with a spectral resolution of 0.06 nm, with a line of sight transversal to plasma at 35 cm a part from the sample (see Fig.…”

Introduction of a new experimental device for simulating parasitic plasmas such as those expected under the divertor dome

“…This was already observed in ASDEX-Upgrade, and also predicted for ITER [1,2]. In these shadowed areas, due to lower pressure and density, parasitic discharges may indeed be ignited because of a combination of photo-ionisation of neutral gas in volume and electron-impact ionisation by photo-electrons emitted from the surface.…”

“…Below the divertor of ASDEX-Upgrade, the neutral temperature in the high-recycling regime was estimated around 0.1 eV ($1160 K) [1]. In order to check if the gas temperature in the CASI-MIR reactor matches this requirement, OES measurements were performed in pure H 2 or D 2 discharges to estimate temperature of the excited hydrogen species.…”

“…In these shadowed areas, due to lower pressure and density, parasitic discharges may indeed be ignited because of a combination of photo-ionisation of neutral gas in volume and electron-impact ionisation by photo-electrons emitted from the surface. Simulation results showed that plasma with electron density n e $ 10 10 cm À3 and electron temperature T e $ 1.7 eV may be created in the system [1]. These characteristics are (at least partly) similar to low temperature plasmas encountered in plasma processing devices [3].…”

Interaction of metal dust adhered on castellated substrates with the ELMy H-mode plasmas of ASDEX-Upgrade

“…In spite of the limited statistics and the poor surface quality, the observation of few post-exposure modifications is consistent with such a restricted interaction with the plasma. (ii) The bottom spots can only interact with parasitic plasmas generated from the neutrals present inside the gap by direct photo-ionization and/or electron impact ioniz ation by surface photo-electrons [63,64]. These cold tenuous plasmas are unable to cause any modifications to the adhered dust, as demonstrated by the results of the post-exposure SEM analysis.…”