Giuseppe Maffia

Commissioning of the plasma central column for the PROTO-SPHERA spherical tokamak

PROTO-SPHERA is the first plasma project with a simply connected configuration, namely not requiring other objects inside the plasma. This is obtained by a hydrogen plasma arc, shaped as a screw pinch, acting as the central column of a spherical torus with minimal aspect ratio. The reduced size and complexity of the configuration can lead to several physical and engineering advantages, providing relevant contributions to the magnetic plasma confinement methods. Moreover, due to the limited costs and requirements, the set-up is attractive for replication and developments also on an industrial scale with many potential applications. This paper describes the initial activities of the PROTO-SPHERA project, with emphasis on the electrical tests and commissioning performed to implement the plasma central column. In particular, an intermediated experiment classified as MULTI-PINCH was designed to investigate the breakdown conditions and the pinch stability.

A new generation of pulsed power supplies for experimental physics based on supercapacitors

Big physics experiments often require high power peaks for a short duration with low duty cycle. Even though the effective energy may be relatively small, the power supplies of these experiments can be critical from the technical, economic, and environmental points of view. This paper shows that the supercapacitor technology can simplify many power supply systems and can extend the scenarios explored by the experiments. Supercapacitors were already proposed and introduced for many applications, but their use is particularly advantageous in big physics experiments, especially when the current is high and the voltage is relatively low. This statement will be supported by some models and case studies based on real experimental devices (operating or that are going to be commissioned) with currents up to 60 kA. The presented designs based on supercapacitors simplify the existing apparatus, reduce the costs, increase the local power availability, and even extend the possible experimental activities. The reported analyses and results are mainly focused on nuclear fusion researches, but can be easily applied to many other fields.

A novel digital controller for 12-pulse back-to-back AC/DC converters in nuclear fusion experiments

This paper presents a novel digital controller purposely developed for nuclear fusion power supply systems and a MATLAB/Simulink model to simulate its behavior. Nuclear fusion experiments, as ITER, JT-60SA, FAST and DTT, require high current AC/DC converters, typically implemented in 4-quadrant 12-pulse back-to-back configurations, able to follow a desired current profile (scenario). With respect to a classic PID controller, the new digital controller features: a simple and robust feedback loop control of current by using two digital PID-based current controllers, an adapted and flexible direct control of the circulating current, good accuracy and stability during the current circulation to avoid dangerous oscillations, faster dynamic response, sequential control, variable firing angle limits, lower reactive power and reduced harmonic distortion. The controller and the developed simulation models were used to design and analyze the power supply systems for JT-60SA, an international fusion research project that is under construction with the joint contribution of Japanese and European researchers. The JT-60SA converters are designed to supply a DC current up to ±20 kA with an accuracy of ±1%.

ETHICAL: A modular supercapacitor-based power amplifier for high-current arbitrary generation

ETHICAL (Efficient Time to High-I Converter with Affordable Load) project aims to develop modular systems based on supercapacitors able to “amplify” at their output the power and the current adsorbed at their input. The project is named after the principle to take into account the social, environmental and economic impacts of the power supplies. Using the ETHICAL approach, high currents and high powers with arbitrary waveforms can be obtained from low voltage and low power sources, even in places without invasive structures and high or medium voltage grids. The input power features also a good quality, as the reactive power and harmonic content are negligible. The design of a prototype rated 120 V and 2 kA is presented, but these values can be increased by parallel connection or by part replacing. The extreme modularity and flexibility improve the general reliability and simplify the maintenance, fault detection and replacement activities. Therefore, the ETHICAL approach could be introduced in many fields of engineering.

A novel conceptual design for gyrotron's high voltage power supplies

The scope of this paper is a detailed description for an innovative conceptual design of high voltage power supplies for 110/138 GHz gyrotrons, including both the High Voltage Main Power Supply (HVMPS), that feeds in parallel the two gyrotron cathodes, both the Body Power Supplies (BPS), that establishes a voltage between Body and Collector and regulating the voltage between Body and Cathode; and both the Anode Power Supplies (APS) that controls the voltage between Anode and Cathode in order to keep the beam current and the electron pitch factor of gyrotrons. This conceptual design consists in a complete set of simulations that points out how the dynamic behavior of all ECPSs is compliant technical requirements. It is the result of a collaboration between the National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) and POSEICO SPA. expert in power electronic converters. The advantages include a small amount of power modules and a high level of reliability and redundancy.