1,721,072 research outputs found
Development of a power electrode for plasma biasing on RFX
No full textA movable power electrode has been developed on the RFX experiment to modify the radial electric field at the edge of the plasma configuration. The electrode insertion head is a mushroom shaped limiter made of a carbon-carbon composite, and boron nitride is used as insulating material to be exposed to the plasma. The power electrode is designed to carry a 10 kA impulsive current and is insulated for 10 kV dc. The current into the electrode is driven by a power supply based on capacitor banks, and protective actions to cope with fault conditions have been implemented. The design of the electrode supporting structure has been done by using 3D finite element analyses, performed to evaluate the dynamic response of the system subjected to impulsive electromagnetic loads. The system has been used on the RFX experiment, showing the expected capability and flexibility. The current and voltage electrode waveforms are reported and discussed as far as the experimental results are concerned. Displacements of the electrode stiffening structure under electromagnetic load have been measured and compared to the numerical results
Model of the RFX-mod poloidal field circuit
No full textAiming at predictive simulation of the plasma magnetic parameters during the RFX-mod discharges, a model was designed to simulate the poloidal field power supply system, detailing each individual switching unit and the single ac-dc converter with its local control circuit, together with the magnet system and the complete multi-variable feedback system devoted to the plasma shape and position control. The model was realized by coupling a linear model of the axi-symmetric evolution of the plasma with a detailed implementation of the RFX-mod circuit developed by means of the SimPowerSystem Toolbox in the framework of the Matlab-SimulinkTM package. In order to evolve the plasma current, a Bessel Function Model (BFM) is adopted to implement the energy transfer from the toroidal to the poloidal field. The axi-symmetric controller is implemented to close the loop and is the same running on the VME nodes of the real control system. The model was successfully tested against experimental data, showing good agreement between measured and calculated waveforms
Harmonic Impedance Measurement and Calculation in the EHV Transmission Network
No full textThe results of a measurement campaign regarding the driving point harmonic impedance of one node of the 400 kV Italian transmission network are presented and discussed, using a method suitable for high order harmonics (up to 50th). A model of the network has been then set up and the relevant results compared with the measurement, showing the crucial effect of the equivalent impedance simulating the external network
Analysis of the transient voltage distribution due to the energy transfer units on the RFX poloidal windings
No full textParametric analysis of current extinction in counterpulse systems
No full textThe results of the parametric analysis of current extinction in counterpulse systems without saturable reactor are presented in this paper. The current dcrivative di/dt has been assumed as a free parameter to iiwestigate ils effect on the design of the counterpulse capacitor bank and tuning induetor. General design criteria of the counterpulse systems are presented and compared with the solutions employing saturable reactors
Effect of magnetic field on voltage holding in the MITICA electrostatic accelerator
No full textMITICA is the complete full-scale prototype of a 17 MW Heating Neutral Beam Injector for ITER. This experimental device, presently under construction in Padova, includes a negative Ion Source (H- or D-), and an electrostatic Accelerator (1 MV, 40 A, 3600 s).
Voltage holding is recognized to be one of the most critical issues for the 1 MV accelerator operations, not only due to the complex multi-stage electrostatic accelerator structure, but also for the presence of magnetic field, which is necessary for deflecting the co-extracted and secondary electrons as early as possible, before they are accelerated. The required magnetic field is produced by a combination of several sources, such as permanent magnets and current-carrying conductors.
In order to avoid breakdowns, the design of the accelerator shall guarantee that electrostatic configuration and the pressure distribution correspond to an operating point located on the left branch of the Paschen curve, i.e. where the H2 gas pressure multiplied by the largest electrode distance (p.d) is always below a certain limit, which is 0.1-0.3 Pa.m. Actually, the presence of the magnetic field might reduce this limit, moving the left branch of the Paschen curve towards the operating point thus affecting voltage holding even during the conditioning phase.
In order to support the design of MITICA at low gas pressure and in the presence of magnetic field, an experimental campaign has been carried out at the High Voltage Padova Test Facility
Thyristor Making Switch System for Plasma Startup Control in RFX
No full textThe necessity of better plasma current control during the startup phase asks for a toroidal loop voltage modulation obtained with the multi step reduction of the transfer energy resistor in the OH circuit. The paper begins by discussing the characteristics of such a modulation and then describes the modifications realized and tested on the power supply and magnet systems to prove the feasibility of such an operation; finally, on the basis of the results obtained, we describe the design of the making switch system, based on a 100 mm thyristor valv
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