M.L. Apicella

Current drive at plasma densities required for thermonuclear reactors

Progress in thermonuclear fusion energy research based on deuterium plasmas magnetically confined in toroidal tokamak devices requires the development of efficient current drive methods. Previous experiments have shown that plasma current can be driven effectively by externally launched radio frequency power coupled to lower hybrid plasma waves. However, at the high plasma densities required for fusion power plants, the coupled radio frequency power does not penetrate into the plasma core, possibly because of strong wave interactions with the plasma edge. Here we show experiments performed on FTU (Frascati Tokamak Upgrade) based on theoretical predictions that nonlinear interactions diminish when the peripheral plasma electron temperature is high, allowing significant wave penetration at high density. The results show that the coupled radio frequency power can penetrate into high-density plasmas due to weaker plasma edge effects, thus extending the effective range of lower hybrid current drive towards the domain relevant for fusion reactors.

High Plasma Density Lower-Hybrid Current Drive in the FTU Tokamak

s Vol. 19C (European Physical Society, Geneva, 1995), Part III, p. 361. [15] G. Tonon et al., Plasma Phys. Controlled Fusion 35, A105

Thermal load analysis and real time hot spots recognition in TOKAMAK using cellular nonlinear networks

A recent innovative technology in the field of plasma-wall interaction in nuclear fusion experiments is represented by the Liquid Lithium Limiter (LLL), a Limiter with a cooling system based on Liquid Lithium. Since its performance depends on the spatial temperature distribution, a thermal load analysis is important for long term developments. Furthermore, temperature is often not uniformly distributed leading to hot spots formation, that should be detected in real time to avoid any plasma disruptions. In this paper, an approach based on the definition of a suitable Cellular Nonlinear Network algorithm for the real-time image processing of thermal images taken during a plasma experiment is introduced. It allows both to map the LLL temperature and to detect hot spots over the limiter surface. Offline testing of the proposed procedure reveals the effectiveness of the approach paving the way to the modeling of the limiter surface temperature providing reliable information.

Temperature Model Identification of FTU Liquid Lithium Limiter

In this paper, the model identification of the temperature over the surface of the limiter adopted in the Frascati Tokamak Upgrade (FTU) is presented. Tokamaks are considered as the most interesting facilities to study self-sustained nuclear fusion reactions. Recently, a Liquid Lithium Limiter (LLL) has been introduced in the FTU with the aim of reducing impurities in the plasma. However, the performance of the LLL are maximized when temperature over its surface is uniformly distributed. In this paper, we face the problem of modeling the thermal behavior of the limiter surface following two different data-driven approaches: a linear autoregressive model, and a nonlinear autoregressive model. A comparison among the two models will be given, showing also which physical quantities are relevant to the specific modeling problem.

Temperature model identification on FTU liquid lithium limiter

In this brief, the thermal model identification of the limiter surface placed in nuclear fusion plants facilities is presented. Experimental data measured at the Frascati Tokamak Upgrade (FTU) have been considered in order to identify a nonlinear dynamical model of the temperature distribution over the cooled lithium limiter used in the FTU. Three data-driven approaches have been followed: 1) a linear autoregressive (ARX) model; 2) a nonlinear ARX model; and 3) a Hammerstein model. The selection procedure of the relevant physical quantities will be outlined and a comparison among the obtained models will be given.

Corrigendum: Current drive at plasma densities required for thermonuclear reactors

Nature Communications 1: Article number: 55 (2010); Published: 10 August 2010; Updated:19 September 2013. In Fig. 3 of this Article, the colours of the blue and green curves were accidentally interchanged while the manuscript was being revised. In addition, the x axis labels on Fig. 4 should have read ‘Frequency (MHz)’.

The Frascati Tokamak Upgrade machine: availability analysis, main results and future programme

The paper presents a general overview of the Frascati Tokamak Upgrade (FTU) machine operation in the last two years. About 3500 pulses were performed (mostly in D/sub 2/) with a toroidal field between 2.5 and 8 Tesla and a plasma current between 0.35-1.3 MA, according to the experimental programmes. An availability analysis of the FTU plant was performed, which pointed out the number of pulses per day and the causes of delay. The main research activities concentrated on plasma MHD studies with different heating scenarios: lower hybrid waves current drive (LHCD) and electron cyclotron resonance heating (ECRH) were used both alone and together to investigate synergetic effects. Strong effort was devoted to high density (1/spl times/10/sup 20/ m/sup -3/) current drive experiments and investigating the possibility of obtaining and sustaining shear reversal configurations. Near term scientific and technological programmes are also reported.