Infrared (IR) absorption spectroscopy and mass spectrometry have been simultaneously applied to dusty radiofrequency (RF) plasmas in methane, acetylene and ethylene. The combination of IR absorption spectroscopy and mass spectrometry allows the chemical composition and structure of the most relevant plasma-produced neutral species, the ionic plasma composition and the chemical composition of the nanometer-sized particles to be precisely identified. The production of acetylenic compounds (C2Hx) seems to be a key mechanism for the powder formation in all the investigated hydrocarbon plasmas. Electron attachment to acetylenic compounds and the following ion-neutral reactions might lead to the high-mass carbon anions, which are trapped in the plasma and finally end in powder formation. The hydrogenation of the monomer strongly influences the composition of the ions. Finally the composition of the plasma-produced particles is mainly sp3 bonded carbon and the infrared spectra show similarities to that of polyethylene.

The gas phase species produced in rf plasmas of hexamethyldisiloxane (HMDSO), Si2O(CH3)6, diluted with oxygen, have been investigated. The complementarity of Fourier transform infrared absorption spectroscopy and mass spectrometry allows the determination of the most abundant neutral components present in the discharge. The measurements reveal that methyl groups (CH3), abundantly formed by the dissociation of the HMDSO molecule, are the precursor for the most abundant species which stem from two kinds of reaction. The first kind of reaction is combustion of CH3 by oxygen-producing formaldehyde (COH2), formic acid (CO2H2), carbon monoxide (CO), carbon dioxide (CO2) and water. It is shown that high mass carbonated radicals, such as SixOyCzHt, first diffuse to the surface and then the carbon is removed by oxygen etching to form CO2. The second is hydrocarbon chemistry promoted by CH3, producing mainly hydrogen (H2), methane (CH4) and acetylene (C2H2).

The fluid flow in a radio-frequency induction thermal plasma (RF-ITP) system for the synthesis of nanoparticles has been characterized using three-and two-dimensional modelling supported by enthalpy probe and calorimetric measurements in order to provide insights for the improvement of the process. The RF-ITP system is composed of a commercial inductively coupled plasma torch mounted on a reaction chamber that is equipped with viewports for diagnostics. The three-dimensional model predicted an almost axisymmetric temperature field in the reaction chamber in agreement with enthalpy probe measurements performed along two perpendicular scan axes, whereas recirculating flow patterns resulted in being strongly non-axisymmetric. Temperature profiles at two distances (60 mm and 100 mm) from the torch outlet have been calculated using two-dimensional modelling and compared with enthalpy probe measurements for different operating conditions with the aim of validating the predictive ability of the modelling tool. Calorimetric measurements have been performed in order to estimate the power coupled to the torch, which is usually an arbitrary input parameter for the models. Poor agreement was obtained between energy balances from modelling and from calorimetric measurements and, starting from this, a discussion on the uncertainties in the calculation of the radiative losses has been proposed. Finally, new insights for the improvement of the process of nanoparticle synthesis in the RF-ITP system are suggested.

The TCV tokamak (B T < 1.5 T, R ≈ 0.88 m, a < 0.25 m) has produced a wide variety of plasma configurations, both diverted and limited, with elongations κ a ranging from 0.9 to 2.58, triangularities δ a from −0.7 to 1 as well as discharges with nearly rectangular cross sections. Plasma currents of 1 MA have been obtained in elongated discharges (κ a ≈ 2.3). Ohmic discharges with δ a < 0 have smaller sawteeth and higher levels of MHD mode activity than plasmas with δ a > 0. The main change in MHD behaviour when elongation is increased beyond two is an increase in the relative importance of modes with m, n < 1 and a reduction of sawtooth amplitudes. Confinement is strongly dependent on plasma shape. In ohmic limiter L-modes energy confinement times improve typically by a factor of two as the plasma triangularity is reduced from 0.5 to 0 at constant q a . There is also an improvement of confinement as the elongation is increased. In most discharges the changes in confinement are explained by a combination of geometrical effects and power degradation. A global factor of merit H s (shape enhancement factor) has been introduced to quantify the effect of flux surface geometry. The introduction of H s into well known confinement scaling expressions such as Neo-Alcator and Rebut-Lallia-Watkins scaling leads to improved descriptions of the effect of shape for a given confinement mode. In some cases with κ a 1.7 limited ohmic L-modes undergo a slow transition to a confinement regime with an energy confinement improved by a factor of up to 1.5 and higher particle confinement. First experiments to study the effect of shape in ECRH at a frequency of 83 GHz (second harmonic) have been undertaken with 500 kW of additional power.

The unique flexibility of TCV for the creation of a wide variety of plasma shapes has been exploited to address some aspects of tokamak physics for which the shape may play an important role. The electron energy confinement time in limited ohmic L-mode plasmas whose elongation and triangularity have been varied (K = 1.3 -1.9, 6 = 0.1 -0.7) has been observed to improve with elongation as but to degrade with triangularity as (1 -0.8 S), for fixed safety factor. Ohmic H-modes have, been obtained in several diverted and limited configurations, with some of the diverted discharges featuring large ELMs whose effects on the global Confinement have been quantified. These effects depend on the configuration: in double null @N) equilibria, a single ELM expels on average 2%, 6% and 2.5% of the particle, impurity and thermal energy content respectively, whilst in single null (SN) configurations, the corresponding numbers are 3.5% 7% and 9%, indicative of larger ELM effects. The presence or absence of large ELMs in DN discharges has been actively controlled in a single discharge by alternately forcing one or other of the two X-points to lie on the separatrix, permitting stationary density and impurity content (Zeff = 1.6) in long H-modes (1.5 s).