Reduced-order particle-in-cell simulations of a high-power magnetically shielded Hall thruster

High-power magnetically shielded Hall thrusters have recently emerged to meet the needs of the next-generation space missions. Even though a few such thrusters are currently undergoing their late-stage development campaigns, many unanswered questions yet exist concerning the behavior and evolution of the plasma in these large-size thrusters that feature an unconventional magnetic field topology. Noting the complex, multi-dimensional nature of plasma processes in Hall thrusters, high-fidelity particle-in-cell simulations are optimal tools to study the intricate plasma behavior. Nonetheless, the significant computational cost of traditional PIC schemes renders simulating high-power thrusters without any physics-altering speed-up factors unfeasible. Thus, in this article, we demonstrate the applicability of the novel reduced-order PIC scheme for a cost-efficient, self-consistent study of the high-power Hall thrusters by performing simulations of a 20 kW magnetically shielded Hall thruster along the axial-azimuthal and radial-azimuthal coordinates. The axial-azimuthal simulations are performed for three operating conditions in a rather simplified representation of the thruster's inherently 3D configuration. Nevertheless, we resolved self-consistently an unprecedented 650 us of the discharge evolution without any ad-hoc electron mobility model, capturing several breathing cycles and approximating the experimental performance parameters with an accuracy of 70 to 80 % across the operating conditions. The radial-azimuthal simulations casted further light on the evolution of the azimuthal instabilities and the resulting variations in the electrons' cross-field mobility and the plasma-wall interactions. Particularly, we observed the development of a long-wavelength, relatively low-frequency wave mode near the exit plane of the thruster's channel that induces a notable electron transport.Comment: 29 pages, 25 figure

The Polarised Valence Quark Distribution from semi-inclusive DIS

The semi-inclusive difference asymmetry A^{h^{+}-h^{-}} for hadrons of opposite charge has been measured by the COMPASS experiment at CERN. The data were collected in the years 2002-2004 using a 160 GeV polarised muon beam scattered off a large polarised ^6LiD target and cover the range 0.006 < x < 0.7 and 1 < Q^2 < 100 (GeV/c)^2. In leading order QCD (LO) the asymmetry A_d^{h^{+}-h^{-}} measures the valence quark polarisation and provides an evaluation of the first moment of Delta u_v + Delta d_v which is found to be equal to 0.40 +- 0.07 (stat.) +- 0.05 (syst.) over the measured range of x at Q^2 = 10 (GeV/c)^2. When combined with the first moment of g_1^d previously measured on the same data, this result favours a non-symmetric polarisation of light quarks Delta u-bar = - Delta d-bar at a confidence level of two standard deviations, in contrast to the often assumed symmetric scenario Delta u-bar = Delta d-bar = Delta s-bar = Delta s.Comment: 7 pages, 3 figures, COMPASS, revised: details added, author list update

Mars- plus Europa-INPPS Flagship Missions with High Power Electric Thrusters and Heavy Science Payload

2020/2021 orbit calculations (DLR Bremen + MAI Moscow): 3 Orbits for one non-human MARS/EUROPA-INPPS flagship 1. Orbit Earth (11 Oct 2026) => Mars (28 Jan 2028); 2. Orbit Mars (22 Sept 2028) => Earth (29 Jul 2029); 3. Orbit Earth (12 Oct 2031) => Jupiter / Europa (6 Dec 2035) 22 ETs (for the INPPS flagship CET): example - gridded CET plate with combined ET

Humans to Mars: by MARS- plus EUROPA-INPPS Flagship Mission

The first non-human INPPS (International Nuclear Power and Propulsion System) flagship flight with orbits Earth-Mars-Earth-Jupiter/Europa (after 2025) is the most maximal space qualification test of INPPS flagship to carry out the second INPPS flagship flight to Mars with humans (in the 2030th). This high power space transportation tug is realistic because of A) the successful finalization of the European-Russian DEMOCRITOS and MEGAHIT projects with their three concepts of space, ground and nuclear demonstrators for INPPS realization (reached in 2017), B) the successful ground based test of the Russian nuclear reactor with 1MWel plus important heat dissipation solution via droplet radiators (confirmed in 2018), C) the space qualification of the Russian reactor by 2025 and D) the perfect celestial constellation for a Earth-Mars/Phobos-Earth-Jupiter/Europa trajectory between 2026 and 2035. Therefore the talk sketches the preparation status of INPPS flagship with its subsystems. Critical performance will be studied by parallel realizations of the ground and nuclear demonstrators of DEMOCRITOS (until 2025). The space qualification of INPPS with all subsystems including the nuclear reactor in the middle of the 2020th plus the INPPS tests for about one to two years - first in high Earth orbit robotic assembly phase of INPPS and later extended in nearby Earth space environment flight - means a complete concepts driven approval for all applied INPPS space subsystem technologies. It is also important to consider wider aspects for the overall mission implementation phase. Component like the nuclear reactor as the power source for the propulsion system will have to agree with the 1992 UN principles relevant to the use of nuclear power sources (NPS) in outer space. Therefore this talk will look into the legal and policy issues of nuclear space systems related to the international realization of mission design, requirements of associated safety regulations (including AI applications in the subsystems) and new aspects for INPPS flagship commercialization and new media communication on board

Non-Human + Human Deep Space Exploration: By The NEP INPPS Flagship

INPPS Flagship Structure & Subsystems, Ground Based Tests, Pure NEP, International Electric Thrusters, Humans Internationally To Mar

Background Pressure Effects on the Performance of a 20 kW Magnetically Shielded Hall Thruster Operating in Various Configurations

The paper reports the characterization results of a 20 kW-class magnetically shielded Hall thruster in three different configurations and operating with a centrally mounted cathode. The characterization was carried out at two different pumping speeds in SITAEL’s IV10 vacuum chamber, resulting in two different background pressure levels for each tested operating point. A linear behavior of discharge current and thrust values versus the anode mass flow rate was noticed for both pumping speeds levels and for all the three configurations. In addition, the thrust and discharge current values were always found to be lower at lower background pressure levels. From the performance levels, a preliminary estimate of the ingested mass flow rates was performed, and the values were then compared to a recently developed background flow model. The results suggested that, for this thruster and in the tested operating regimes, the change in performance due to background pressure could be ascribed not only to the ingestion of external mass flow coming from the chamber but also to other physical processes caused by the flux of residual background neutrals

Development of a 20kW-class Hall effect thruster.

The need of large payloads in space plays a crucial role for future space exploration. This issue can be tackled using large chemical rockets if short transfer times are requested by the mission. The other promising option is electric propulsion, which enables significant propellant mass savings, resulting in larger payloads. The use of this technology has been limited in the past by the power avalilable on spacecrafts. Very high power electric propulsion has been typically associated with futuristic high power sources, such as nuclear reactors. However, recent developments in the field of solar arrays technology allowed to increase the available power on board modern spacecrafts. This trend is clearly expressed in last geostationary platforms, which reached and even exceeded the 20kW of produced power. Moreover, among different electric propulsion systems, Hall effect thrusters represent a versatile solution, due to their easy scalability and good performance in terms of thrust efficiency and specific impulse. In the present work, after a brief introduction on space propulsion, a short description of the working principles of Hall thrusters is provided. Then, an extensive review of very high power Hall thrusters (>10kW), developed and tested up to the present date is presented. In order to design a new 20kW-class thruster, the scaling method developed by SITAEL in the past years was used to describe high-power configurations. The method, which was first validated against the experimental data of a reviewed thruster, allowed the preliminary assessment of the thruster performance also for non-conventional designs. A thruster configuration, with reduced size compared to existing models of the same power, was then selected for manufacturing. Nominal conditions in terms of thrust and specific impulse, obtained from the scaling process, are taken as a reference to analyse different mission scenarios. In this ancillary part of the work, simple examples of near-term and long-term scenarios are provided. Finally, performance data of the new thruster are presented. The thruster performed well in terms of specific impulse and thrust efficiency, especially at high voltages. In addition, at the nominal discharge power of 20kW, it demonstrated thrust levels higher than 1N and a maximum thrust efficiency of approximately 63%. As a result, the new thruster represents a promising solution for deep space esploration, and, in near term scenarios, for Earth-Moon cargo missions

Characterization of the background pressure effects on high power Hall thrusters

Nowadays, the Hall Thruster technology has experienced an increased use for spacecrafts propulsion and attitude control. This opened the market to larger payloads in space and also to new kinds space exploration and trasportation missions. Indeed, the recent developments in solar panel technology together with power distribution allowed to increase the available power on board latest spacecrafts. As a consequence, the use of high power Hall thruster is increasingly expected for high-powered platforms. However, in order to develop and qualify such propulsion systems, large vacuum facilities, with satisfactory levels of vacuum, are needed. The aim of this thesis is to characterize the effect of the background pressure on the behaviour of high power Hall Thrusters and assess which physical parameters change due to pressure. In the present work, we start by introducing a simplified performance model that also consider the ingested mass flow rate coming from the residual neutrals inside chamber, after that, we performed a sensitivity analysis and isolated the terms that are affected by the change in the pumping speed of the chamber. It turns out that the change in performance can be due to a ingestion of the neutrals together with the change in the plasma proprieties. Moreover, the two most common characterization strategies for Hall thrusters have been formalized and presented, relating them to the background pressure problem. In parallel, a simple one dimensional model model, summarizing the neutral dynamics at steady state inside the vacuum chamber, has been introduced and commented. The model, coming from literature, has been reformulated and takes into account the pumps positions and the main dimensions of the vacuum chamber. It is then possible to estimate the neutrals particle density in the proximity of the thruster exit plane and to calculate the ingested mass flow rates levels. After the introduction of the test items and plasma diagnotics, we performed and exstensive experimental campaign on different 20 kW class Hall thruster models, all featuring the magnetic shielding of the ceramic channel. The results of the campaign showed that the measured performance levels were mainly related to a change of the physics of the plasma discharge, these aspects are better studied in the last part of the work. The conclusive part of the work consist of the analysis of the plasma discharge measurements on a 5 kW class Hall thruster operating at the same operating point in two different vacuum chambers. We first estimated the values of the electron mobility on the two cases and then we used the gathered data to calibrate a non-stationary one dimensional Hall thruster plasma discharge model. The results of this work highlight that, in order to have a predictive tool to estrapolate the performance in space, the future research effort should be focused on a better study and uderstanding of the change of the electron mobility as a function of the neutrals surrounding environment

Background Pressure Effects on the Performance of a 20 kW Magnetically Shielded Hall Thruster Operating in Various Configurations

The paper reports the characterization results of a 20 kW‐class magnetically shielded Hall thruster in three different configurations and operating with a centrally mounted cathode. The characterization was carried out at two different pumping speeds in SITAEL’s IV10 vacuum chamber, resulting in two different background pressure levels for each tested operating point. A linear behavior of discharge current and thrust values versus the anode mass flow rate was noticed for both pumping speeds levels and for all the three configurations. In addition, the thrust and discharge current values were always found to be lower at lower background pressure levels. From the performance levels, a preliminary estimate of the ingested mass flow rates was performed, and the values were then compared to a recently developed background flow model. The results suggested that, for this thruster and in the tested operating regimes, the change in performance due to background pressure could be ascribed not only to the ingestion of external mass flow coming from the chamber but also to other physical processes caused by the flux of residual background neutrals