First plasmas have been successfully achieved in the TJ-II stellarator using electron cyclotron resonance heating (f = 53.2 GHz, P ECRH = 250 kW). Initial experiments have explored the TJ-II flexibility in a wide range of plasma volumes, different rotational transform and magnetic well values. In this paper, the main results of this campaign are presented and, in particular, the influence of plasma wall interaction phenomena on TJ-II operation is discussed briefly.

The first study of the interaction of metallic dust (tungsten, aluminum) adhered on tungsten substrates with transient plasma heat loads is presented. Experiments were carried out in the Pilot-PSI linear device with transient heat fluxes up to 550 MW m−2 and in the DIII-D divertor tokamak. The central role of the dust-substrate contact area in heat conduction is highlighted and confirmed by heat transfer simulations. The experiments provide evidence of the occurrence of wetting-induced coagulation, a novel growth mechanism where cluster melting accompanied by droplet wetting leads to the formation of larger grains. The physical processes behind this mechanism are elucidated. The remobilization activity of the newly formed dust and the survivability of tungsten dust on hot surfaces are documented and discussed in the light of implications for ITER.

Non-equilibrium plasmas for plasma-assisted combustion, pollutant remediation, fuel reforming, and catalysis rely on the production of energetic electrons that ionize, dissociate, and excite the fuel and oxidizer molecules. Experimental characterization of the electron temperature, electron density, and vibrational temperature are necessary to validate and improve plasma kinetic models. An experimental apparatus capable of Thomson scattering and vibrational Raman scattering measurements in the same discharge with molecular admixtures was developed. Both diagnostics are necessary to study the induced vibrational non-equilibrium from electron impact. Thomson scattering spectra were resolved by placing a physical mask at the output of a single grating spectrometer. The electron temperature and density and the impact of hydrocarbon addition was measured for a 60 Torr CH 4 /He nanosecond pulsed plane-to-plane dielectric barrier discharge with 0%-2% CH 4 addition. Electron densities as low as 1 × 10 12 cm −3 and electron temperatures ranging from 0.5 eV to 9 eV were observed. A decrease in the electron temperature and density was observed even with 1% CH 4 addition. Moreover, the addition of N 2 to the discharge enabled vibrational Raman scattering and quantification of the first level vibrational temperature starting from 75 ns after the voltage pulse. The electron temperature and density were also measured in this CH 4 /N 2 /He mixture by Thomson scattering. Addition of N 2 led to a faster electron temperature decay than in the original CH 4 /He mixture. The advantages and disadvantages of this detection scheme for Thomson scattering over the triple grating spectrometer and the volume Bragg grating notch filter is discussed.

No abstract

We measured the electron density and temperature using laser Thomson scattering and metastable state (2 3 S) of He atoms using laser absorption spectroscopy in the detached recombining plasmas in the divertor simulator NAGDIS-II. Using the measured electron density and temperature combined with the particle trajectory trace simulation, we discussed the behavior of the metastable state He atoms based on comparisons with the experimental results. It is shown that the metastable states atoms are mainly produced at the peripheral region of the plasma column, where the temperature is lower than the central part, and diffused in the vacuum vessel. It was shown that the 0D model is not valid and the transport of the metastable states is to be taken into account for the population distribution of He atoms valid in the detached plasmas.