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ENEA - Fusion division

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Plasma Theory Group

Contact: Fulvio Zonca
e-mail: fulvio.zonca@frascati.enea.it
tel.    : 0039 06 9400 5621
fax.   : 0039 06 9400 5735

At Frascati, the physics theory research programme as applied to the analysis of thermonuclear plasmas is characterised by diverse activities, ranging from those directly concerned with currently urgent problems related to the next experiments on burning plasmas (ITER and IGNITOR projects) to those addressing longer term research.

Most of the theory studies are carried out under consolidated international collaborations with national laboratories and universities. Two examples of primary importance are the collaborations with the Plasma Physics Laboratory of the University of Princeton and with the Department of Physics and Astronomy of the University of California at Irvine.

Research on the generation of non-inductive currents is directly relevant to experiments concerning present and future reactors. Detailed analyses of parallel and anti-parallel lower hybrid current drive (LHCD) have shown us how form and sustain the halo-current profiles required for reversed shear operation in FTU. The same studies have also shown that it is possible to obtain the same improved confinement properties, associated with reversed shear operation, in the IGNITOR plasmas. Non-inductive current generation at the electron cyclotron resonance frequency (ECRF) is fundamental for controlling and/or suppressing instabilities in magnetohydrodynamic (MHD) plasmas in reactor-relevant regimes.

By analysing the propagation and absorption of radiofrequency (RF) waves in toroidal plasmas, we can look for the optimum conditions needed to heat the plasma and to reach improved confinement regimes. Studies of ion Bernstein waves (IBWs) have given us the basic theory to explain some of the improved confinement regimes in FTU. Similarly, the work on ECRF is necessary for interpreting the strong peaking at the centre of the electron temperature profile in FTU. The experimental results are then compared by means of predictive and interpretative modelling of transport.

The studies on the dynamic properties of fusion products in ignited plasmas and on the energetic ions produced by radiofrequency and neutral beam injection follow two main lines. The first, with direct relevance to ITER, consists in using a hybrid MHD gyrokinetic code (HMGC) to numerically simulate the interaction of energetic particles with Alfvèn waves. These numerical studies are based on particle-in-cell (PIC) simulation codes and have demonstrated that the threshold for linear excitation of energetic particle modes (EPMs) and for the non-linear behaviour (transport) of energetic ions is largely the same. The second line of research, carried out in collaboration with the University of California at Irvine, addresses the fundamental processes associated with Alfvèn-wave propagation in ignited plasmas. A recently developed theory is that low-frequency Alfvèn waves play a significant role in the transport of both the energetic and the heat components of a reactor plasma.

Most of the analyses in burning-plasma physics are possible only with the use of extremely advanced, massively parallel numerical codes (e.g., the HMGC developed at Frascati) as well as appropriate techniques for representing or depicting the numerical results.
The work involved is extremely complex – as only to be expected in the field of high-performance calculations – but very “appetising” because of its potential application in neighbouring research fields, for example, accelerator physics. However, we can expect applications even in seemingly unconnected sectors, such as the simulation of automobile traffic.

 

(More details on the Plasma Theory Group external website »)