Dottorato in ENERGIA E AMBIENTE

Titolo della tesi: Plasma thruster design for space transportation

The project "plasma thruster design for sustainable space transportation" is a research project that is born from the collaboration between the School of Aerospace Engineering of Sapienza University of Rome (SIA) and the ENEA Research Center of Frascati. The project of innovative plasma thruster arises from the PROTO-SPHERA experiment of the ENEA Research Center of Frascati, a new experiment of plasma magnetic confinement, with the aim of generating a spherical simply connected plasma that has no central metallic conductor, that inspired the study and the conceptualization of fusion plasma thrusters. The PROTO-SPHERA experiment constitutes a new frontiers for machines that confine magnetically a plasma and potentially can sustain nuclear fusion reactions, because it can generate a closed magnetic configuration for confining a plasma starting from an axial plasma discharge (this magnetic configuration is also called simply connected because there are not voids or holes in the produced magnetic configuration). In comparison with the tokamak machine it has a lighter structure that needs less maintenance, it is easier to access for plasma feeding and experimental measurements, because it has not metallic structure of the central solenoid, of the toroidal solenoid (that is the most critical and expensive component of a tokamak) and of the lateral surfaces that surround the tokamak, it is therefore for plasma diagnostics and it has the highest β among the tokamaks, being a spherical magnetic configuration, and therefore it can confine the plasma for the same plasma pressure with a lower magnetic field and therefore with lower energy consumption. This type of magnetic configuration of the PROTO-SPHERA experiment is of interest for the study of magnetic reconnections, astrophysical space plasmas and for its potential in being transformed in a nuclear fusion reactor. The features of lightness, energy, constructive simplicity and the low enviromental impact lead to the investigation of PROTO-SPHERA as a plasma thruster and a fusion plasma thruster. From the good experimental results that the machine provided in the plasma production and in the generation of spherical plasmas it was decided to evaluate the performance that could provide a fusion nuclear thruster in a scaled configuration of the present machine. From this idea of transforming the PROTO-SPHERA experiment in a plasma thruster this PhD project was born and it was structured in a first part for the study of plasmas and the magnetic confinement machines (in particular of PROTO-SPHERA and its experimental results), a second part of study and experimentation on innovative electric plasma thrusters (electric thrusters and helicon thrusters) with an experimental activity made in the laboratory of plasma propulsion at the University of Stuttgart, and a third part of conceptualization and modellization of an innovative nuclear fusion thruster based on the PROTO-SPHERA experiment. In particular are made two studies on plasma propulsion in the PhD project: the helicon plasma thruster and the nuclear fusion thruster based on the PROTO-SPHERA experiment. This category of low thrust thruster is used for space flight beyond the terrestrial atmosphere when the space vehicles are already in orbit or in a interplanetary flight and their study and design open the possibility to experiment in laboratory this type of technology and to space missions that can be performed with this type of rocket engine. In an international scenario in which the access to space become always more needed, with hundreds of satellites launched in orbit every year and the need of removing the decommissioned satellites, the study and the design of innovative propulsion systems that allow a safe orbital transfer with high efficiency become a priority. A plasma nuclear fusion thruster for example is a space transportation system with very high specific impulse that can provide moderate thrusts (from few Newton to thousands of Newton) and that can be used for interplanetary space missions with heavy load, therefore its application in this PhD project was conceived for an interplanetary transfer inside the solar system. The helicon thruster instead is in the category of low thrust thrusters and high specific impulse, but lower than the one of the nuclear fusion thrusters, and it is suitable for orbital transfer inside the Earth sphere of influence. They are both new technologies for the space flight and therefore they are both technologies that for now are at laboratory level and that must be tested more, increasing their TRL (Technology Readiness Level), before to be used. This PhD study has the objective to model the main components of these two types of plasma thrusters, starting from their working principle and from the physics of their components, proposing a first sizing and an estimation of their performance.