BLANC - Blanc

Etude spectroscopique et contrôle des plasmas magnétisés – PHOTONITER

Submission summary

1. Laboratory and astrophysical plasmas are frequently affected by hydrodynamic turbulence, i.e. fluctuations of the velocity, density and temperature fields. The deleterious effect of these fluctuations on the confinement of magnetic fusion plasmas is now well known. Successful operation of the ITER tokamak, which will be build in the coming years at Cadarache, partly relies on a better understanding of turbulent transport. The influence of turbulence on the radiative processes in plasmas has not been investigated in details in the past. A deeper knowledge of radiative properties of these turbulent plasmas would on one the hand be a progress for fundamental research, and on the other hand allow to develop new optical plasma turbulence diagnostics. Laboratory magnetized plasmas, such as those developed either at the PIIM laboratory in Marseilles (Mistral, Pierre et al; Phys. Rev. Lett. 2004, and Mistor) or at the LPMIA in Nancy (Mirabelle), are very useful devices to validate our approach in well controlled conditions. In fact, turbulent regimes obtained in these machines are strikingly similar to those existing in Tokamak edge plasmas (Magni et al, Phys. Rev. E, 2005). The first aim of this project is to model accurately the spectroscopic signature of turbulence, both on line shapes and line intensities. The second aim is to perform simultaneous measurements of spectra (emission spectroscopy), velocity distribution functions of atoms and ions (LIF, Laser Induced Fluorescence, N. Claire et al., Nonlinear Sci. and Num. Simul., 3-4, 8 (2003)), and to develop ultra fast imaging in radiative turbulent plasmas. Moreover, ultra-fast imaging signals will be used to attempt real-time feedback control on turbulence, an approach which has been introduced in plasma physics by several co-authors of this project. 2. Our approach will simultaneously yield time (line intensities) and space (imaging) resolved information on turbulent fluctuations, thus providing a way to check which statistical properties can in practice be retrieved from time averaged data, such as spectral line shapes. We have indeed developed at the PIIM laboratory a formalism allowing to express the spectral line profile measured in a turbulent plasma, where hydrodynamic fields fluctuate (Y. Marandet et al., Europhys. Lett. 69, 531 (2005))). Comparison with FIL measurements, which provide time resolved velocity distributions (i.e the Doppler profile of spectral lines), will be especially interesting. Time resolved information can also be obtained from the intensities of various lines. These intensities are related to the populations of energy levels of the emitter, which can be calculated using a collisionnal-radiative model. The strength of the correlations between light intensity and plasma parameter fluctuations at the turbulent time scale is still an open issue. The self-consistent model currently developed in Marseilles for out of equilibrium H/He mixtures retains all relevant effects, in particular the coupling of different species by charge exchange, effects of diffusion and anomalous transport [F.B. Rosmej et al., Europhysics Letters 73, 342 (2006)], as well as radiative transport and supra-thermal electrons [Escarguel et al., PPCF 49, 85 (2006)]. Comparisons between experimental data measured on European Tokamaks (JET, Tore Supra and TEXTOR) and on laboratory plasmas will be carried out. First results obtained on the NAGDIS divertor simulator in Nagoya are very encouraging. Finally, line intensity and/or ultra fast imaging signals will be used to perform turbulence feedback control, an approach which relies on modern Digital Signal Processing (DSP) techniques. 3. The main outcome of the project will be a complementary set of optical diagnostics of turbulence in magnetized plasmas. The simultaneous use of this set of techniques allows to cross-check the results in well controlled laboratory plasmas. The continuation of this project would consist in diagnosing tokamak plasmas. The passive approach used here, that is no beam injection or probes required, does not perturb the plasma and is sufficiently robust to be operated in the harsh conditions characterizing burning fusion plasmas in ITER. Furthermore, time resolved signals will be used to investigate turbulence feedback control, a technique which could ultimately help to alleviate turbulent transport in Tokamaks.

Project coordination

Roland STAMM (Université)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Help of the ANR 440,000 euros
Beginning and duration of the scientific project: - 48 Months

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