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An alternative harmonic model for representing power system nonlinear loads by a "crossed-frequency" admittance matrix is presented in the paper. This harmonic model is applicable to passive and stationary electrical loads assuming a constant fundamental frequency voltage. Results of the proposed harmonic model are reported and compared with experimental tests.

The results of the first year of operation of the experiment RFX are reported. Profiles of electron density, electron and ion temperature and impurity emission have been measured at plasma current I

The behavior of an electromagnetic control valve under a perturbative magnetic field is evaluated. The electromagnetic valve is numerically modeled by means of a nonlinear 2D field-element code. The electromagnetic force produced on the valve's plug is obtained using the Maxwell stress tensor approach, under both normal and perturbed conditions. The numerical results are compared with those of experimental tests, which have been carried out under the same conditions as the numerical analysis. >

The aim of this study is to demonstrate the feasibility of employing pulsed ultra wideband (UWB) communication schemes over a communal master antenna TV system (MATV). Models for both the UWB link and the TV signal spectrum are derived in order to study their behavior. The influence of the TV channels on UWB performance and the constraints imposed by the MATV specifications on the allowed emitted power spectral density are analyzed. Based on these results, the effect of the signal parameters on the throughput is determined

The “plasma system” of RFX includes the first wall, the vacuum vessel, the stabilizing shell, the vacuum and gas injection system, the remote handling system and the relevant auxiliary plants (cooling, baking, glow discharge cleaning, etc.). Since no limiters are provided, the full energy and particle flux from the plasma must be absorbed by the first wall. Taking into account the significant power losses from the plasma in nominal conditions, the high peaking factors due to “dynamo” effects, field errors and plasma shift, and possible sudden losses of configuration, the first wall was designed to be able to withstand high thermal loads. Also the need to use a low Z plasma-facing material led to the choice of pure, microcrystalline graphite. The wall is subdivided into 2016 tiles, individually clamped to the vacuum vessel by means of a special bayonet system suitable for remote handling. The remote handling system, which was designed to facilitate the replacement and inspection of all 2016 graphite tiles, comprises an arm with five degrees of freedom, two grippers for different tasks, two television cameras, and a control system for automatic or teleoperated motions. The vacuum vessel is a stiff sandwich structure with 72 solid poloidal rings bearing the first wall tile supports. It is cooled by CO2 flowing through the interspace; baking up to 350°C is also provided by means of heating cables attached to the outer surface. The vessel is closely surrounded by a shell, giving passive stabilization against magnetohydrodynamic modes; the shell is made of aluminium alloy, 65 mm thick, and, to allow fast field penetration, it is electrically subdivided into four sections, by means of epoxy-glass layers. The RFX vacuum system is a combination of 12 cryopumps and 12 turbomolecular pumps, giving a total pumping speed at the vessel of 4500 1 s−1 for nitrogen. Because of the short plasma pulse duration, the gas injection system must produce high gas throughputs (up to 700 Pa m3 s−1) with very short response times (some milliseconds). The glow discharge cleaning system utilizes four anodes toroidally equispaced and located at the centre of the vessel minor cross-section, is r.f. assisted and allows wall conditioning in hydrogen, helium or methane. In this paper we present the basic concepts underlying the main design choices and then, for the main components and plants, we describe the significant design features, as well as the methods and results of the structural, thermal and electromagnetic calculations. We also deal with preliminary tests on prototypes and with the most important manufacturing technologies, production cycles, and assembly procedures. Finally, the preliminary design of the control system for the plasma main electromagnetic parameters is presented.

The commissioning of the RFX power supplies and their integration with the machine windings were performed in steps of increasing complexity; the target was to start the experiments with plasma in the final configuration of all systems, tested up to the performances required for first operation. After a brief description of RFX circuits and operation, the final tests on the power supplies, their commissioning with the control, data acquisition and fast protection systems and the integration with the machine windings are presented. Indications on operation reliability following the first experimental phase are finally given.

The Reverse Field Pinch experiment RFX has been operating since the end of 1991. The paper, after a brief description of the load assembly, presents the most significant aspects of the assembly phase and discusses methods and results of the final tests, carried out before producing the first plasma. Finally, the machine behaviour during the first experimental phase is described.

The performance of a double-walled cylindrical shield for magnetostatic field has been optimized using a 3-D numerical code. The shielding factor of the double-walled screen has been evaluated by varying the geometrical parameters. The optimization of the screen and the design criteria are reported. The influence on the shielding factor of the presence of a hole perpendicular to the cylindrical shield has been evaluated by calculating the field penetration into the internal region of the screen. Finally, the FEM (finite-element method) results have been tested by means of measurements performed on a shield prototype. The comparison between the numerical and experimental data shows good agreement, especially in the region where the finite-element model has been refined with more elements. >

The paper, after a brief introduction covering the basic concepts underlying the design of the RFX first wall, describes the main features of the graphite tiles and presents their predicted operating conditions in the presence of applied heat fluxes and electrodynamic forces. On the basis of the results of experimental tests performed to measure the tile-vessel contact conductance, the thermal behaviour is analyzed by means of numerical models which simulate the real operating conditions of the first wall and vacuum vessel, with its forced gas cooling system and its thermal insulation. The safety margin, preventing tile rupture due to electrodynamic extraction forces during fast plasma current terminations, is then investigated by means of mechanical tests closely reproducing the real load distribution. Finally, the stresses due to machining allowances on the tiles and on their grooved seats are analyzed by means of a finite-element model, under the load produced by the bayonet keys which clamp the tiles to the vacuum vessel stiffening rings.

Several factors can jeopardize the desired field configuration in the plasma region of a toroidal machine, namely: - the wrong positioning of the coil conductors

The vacuum vessel of RFX has been designed to operate between room temperature and 350/spl deg/C during the experimental sessions and during first wall conditioning operations. The temperature control system of the vacuum vessel consists of the measurement and the heating system, connected to the RFX central control system, SIGMA. The data acquisition electronics supplies the temperature signals to the heating system and to SIGMA. The heating system provides uniform heating in both toroidal and poloidal directions. SIGMA allows different modes of operation and handles the alarm signal. After a description of the main components, the results of the first two years of operation are presented.

To minimize MHD instabilities in the external plasma region, reverse-field-pinch experiments should be equipped with a stabilizing shell, made of a high-conductivity material and fitted as near as possible to the plasma edge. The most significant technologies adopted for constructing the stabilizing shell of the RFX Project are described. The focus is particularly on the forming and machining processes used to produce the shell quarters and the technology adopted for the electrical insulation of the vertical gaps (which are characterized by high mechanical and dielectrical stresses). The details of these technologies and the main test results are reported. >