No abstract

A new regime of runaway discharges has been found in TCABR (Tokamak Chauffage Alfvén Brésilien). This regime is obtained by initiating the discharge with low filling pressure and, after the initial current rise, maintaining a large filling rate. The line density reaches a maximum value around 2 × 10 19 m −3 , during the current ramp-up phase, and then drops by a factor of around four in the quasi-stationary phase of the discharge, when a new regime is achieved. The most distinctive features of this regime, as compared to 'conventional' runaway discharges reported in the literature, are (i) maintenance of the runaway discharge, with the plasma current almost entirely provided by the runaway beam, in a cold background plasma and with strong neutral gas injection; (ii) enhancement of the relaxation instability with strong spikes in the Hα emission and loop voltage correlated with sawtooth relaxation of the line density; and (iii) plasma detachment from the limiter. A simple phenomenological model, based upon straightforward particle and energy balance calculations, is proposed to explain the experimental observations. According to this model, the plasma is rather cold and the short pulses of gas ionization and the related density spikes are due to sudden plasma heating caused by the relaxation instability. Furthermore, it seems that the runaway generation for the conditions of the experiments can be explained only if the secondary generation process is invoked.

Application of microwave reflectometry to study Alfvén wave resonances in the TCABR tokamak is described. A microwave reflectometer was used to register plasma density oscillations driven by the excited Alfvén waves, under the condition of the spectrum scanned by a controlled plasma density rise. It is shown that when the position of the local Alfvén resonance r A , which is defined by the relation ϭk ʈ (r A )C A (r A ), is close to the plasma zone where the microwave signal is reflected, the high-frequency modulation of the output signal of the reflectometer at the rf generator frequency increases. This method can give information about the localization of the rf power deposition zone in Alfvén wave plasma heating and current drive experiments. It also allows finding the plasma current profile in the region of the rf power deposition.

No abstract

No abstract

The increasing processing power of today's HW/SW platforms leads to the integration of more and more functions in a single device. Additional design challenges arise when these functions share computing resources and belong to different criticality levels. The paper presents the CONTREX European project and its preliminary results. CONTREX complements current activities in the area of predictable computing platforms and segregation mechanisms with techniques to consider the extra-functional properties, i.e., timing constraints, power, and temperature. CONTREX enables energy efficient and cost aware design through analysis and optimization of these properties with regard to application demands at different criticality levels

This paper presents the COMPLEX UML/MARTE modeling methodology and its related framework for automatic generation of executable performance models. The modeling methodology supports Model-Driven Development (MDD), required by industrial flows, and a novel set of modeling features specifically suitable for Design Space Exploration (DSE), a crucial design activity. The COMPLEX framework has other advantages for DSE. The COMPLEX tooling enables the automatic generation of an executable and configurable model for fast performance analysis without requiring engineering effort. The COMPLEX tooling automates the production of an easily portable text-based representation of the UML/MARTE model. This representation is read by the underlying simulation infrastructure, which automatically builds a fast performance model supporting the evaluation of different configurations of the system. An important aspect of this performance analysis framework is that it supports a system-level text-based front-end, which is produced from the COMPLEX UML/MARTE model, and which avoids the development of SW implementations, HW refinements, or the implementation of HW/SW interfaces. Moreover, neither code regeneration, nor recompilation is required for any DSE iterations, and thus, the time taken in the exploration is mostly due to model simulation.

Plasma immersion ion implantation (PIII) of stainless steels with nitrogen has been successfully used for surface hardening purposes. This process has been carried out inside a toroidal discharge chamber in a DC/RF plasma. The RF plasma was created by one antenna located inside the chamber, diametrically opposite to the DC electrode. The latter is polarized with 1 kV and then the discharge is controlled by varying the gas pressure before the RF signal is applied. The main plasma parameters were established by means of double electric probes yielding electron temperature values within 0.5-1.5 eV and density values within 1.5×1015 to 4×10 15 m −3 for the DC case while 1.5-3.0 eV and 7×10 14 to 3×10 15 m −3 were reached with RF assisted DC. We present in this work the experimental results obtained from a PIII process applied to AISI 304 stainless steel plates. The outcome shows that the Vickers hardness has been incremented according to the gas pressure within the 1×10 −1 to 1×10 −3 mbar range. The treated plates were analyzed by scanning electron microscopy (SEM) and the results point to an increased percentage of nitrogen, around 20%. By means of x-ray diffractometry (XRD) the gamma expanded phase and compounds such as Fe3NiN, Ni4N, FeNiN and Fe3N were determined.