Joint Individual-Group Modeling for Tracking

We present a novel probabilistic framework that jointly models individuals and groups for tracking. Managing groups is challenging, primarily because of their nonlinear dynamics and complex layout which lead to repeated splitting and merging events. The proposed approach assumes a tight relation of mutual support between the modeling of individuals and groups, promoting the idea that groups are better modeled if individuals are considered and vice versa. This concept is translated in a mathematical model using a decentralized particle filtering framework which deals with a joint individual-group state space. The model factorizes the joint space into two dependent subspaces, where individuals and groups share the knowledge of the joint individual-group distribution. The assignment of people to the different groups (and thus group initialization, split and merge) is implemented by two alternative strategies: using classifiers trained beforehand on statistics of group configurations, and through online learning of a Dirichlet process mixture model, assuming that no training data is available before tracking. These strategies lead to two different methods that can be used on top of any person detector (simulated using the ground truth in our experiments). We provide convincing results on two recent challenging tracking benchmarks

A strategy to identify breakdown location in MITICA test facility: results of high voltage test campaign

The Acceleration Grid Power Supply of the MITICA test facility in Padova (Italy) is currently under commissioning. The power conversion system, the DC generator, and the High Voltage equipment have been individually commissioned, whereas the integration tests are ongoing. It is a challenging process due to the unconventional application, to the variety of different electrical technologies involved and to the complexity of the interfaces. During the integrated tests of the power supplies the achievement of 700kV stable operation has been demonstrated for the first time in a Neutral Beam Injector, but an unexpected event occurred, most likely a breakdown in the HV part, which resulted in a fault of the DC generator. A subsequent test using an auxiliary power supply was performed to check the voltage withstanding capability of the HV plant, but another breakdown occurred at around 1MV. This paper describes the activity performed to identify the location of the breakdowns affecting the integrated tests. A test campaign has been devised with increased diagnostic capabilities and specific strategy conceived to trigger intentional breakdowns in specific locations and collect measurement patterns for different cases. The results of the campaign will be presented and the current understanding of the issue will be described, with a view on future tests and further improvements of diagnostics

Partial Discharges detection in 1 MV power supplies in MITICA experiment, the ITER Heating Neutral Beam Injector prototype

MITICA (Megavolt ITER Injector & Concept Advancement), the full scale prototype of ITER Heating Neutral Beam, is under realization at the Neutral Beam Test Facility (Padova, Italy). It is designed to deliver 16.5 MW to ITER plasma, obtained by accelerating negative Deuterium ions up to 1 MeV for a total ion current of 40 A and then neutralized. MITICA Acceleration Power Supply is composed of several non-standard equipment, beyond industrial standard for insulation voltage level (-1 MVdc) and dimensions. Voltage withstand tests (up to 1.265 MVdc) have been performed in five subsequent steps (from 2018 to 2019), according to the installation progress, after connecting equipment belonging to different procurements. During integrated commissioning, started in 2021, two breakdowns occurred in a position of the HV plant not still identified, so they could be occurred either in air or in SF6. To identify the locations of possible weak insulation points, the existing diagnostics for partial discharge detection (the precursor of breakdowns) as a first step have been improved on air-insulated parts by consisting in a set of instrumentation, like capacitive probes and off-the-shelf instruments for AC application (acoustic and electromagnetic sensors). The paper deals with the instruments qualification to assess their suitability for DC usage and then with the investigation performed in MITICA, in particular: 1) sensitivity assessment campaign, with artificially produced corona effect to identify the minimum threshold of each diagnostics 2) voltage application to MITICA plant, moving the instrumentation around equipment and increasing progressively the voltage looking for corona phenomena to identify possible weak insulation points.Comment: Nine pages, twelve figures, accepted manuscript of a paper published in Fusion Engineering and Desig

Overview on electrical issues faced during the SPIDER experimental campaigns

SPIDER is the full-scale prototype of the ion source of the ITER Heating Neutral Beam Injector, where negative ions of Hydrogen or Deuterium are produced by a RF generated plasma and accelerated with a set of grids up to ~100 keV. The Power Supply System is composed of high voltage dc power supplies capable of handling frequent grid breakdowns, high current dc generators for the magnetic filter field and RF generators for the plasma generation. During the first 3 years of SPIDER operation different electrical issues were discovered, understood and addressed thanks to deep analyses of the experimental results supported by modelling activities. The paper gives an overview on the observed phenomena and relevant analyses to understand them, on the effectiveness of the short-term modifications provided to SPIDER to face the encountered issues and on the design principle of long-term solutions to be introduced during the currently ongoing long shutdown.Comment: 8 pages, 12 figures. Presented at SOFT 202

Online Bayesian Non-parametrics for Social Group Detection

Group detection represents an emerging Computer Vision research topic, motivated by the increasing interest in the modelling of the social behaviour of people. This paper presents an unsupervised method for group detection which is based on an on-line inference process over Dirichlet Process Mixture Models. Formally, groups are modelled as components of an infinite mixture and individuals are seen as observations generated from them. A sequential variational framework allows to perform the inference in real-time, while social psychology constraints of proxemics ensure the production of proper group hypotheses, consistent with the human perception. The results obtained on different compare favorably with state-of-the-art approaches, setting the best performance in some of them

The DTT device: Power supplies and electrical distribution system

Abstract This paper presents the design criteria and the preliminary characteristics of the power supply and electrical systems of the Divertor Tokamak Test (DTT) facility. The power supply system has to feed: 6 superconducting modules of the central solenoid, 6 poloidal field superconducting coils, 18 toroidal field superconducting coils designed for a current up to 50 kA, some coils for plasma fast control and vertical stabilization, the electron (ECRH) and ion (ICRH) cyclotron additional heating systems designed to deliver about 25 MW to the plasma, further 20 MW to the plasma generated by a neutral beam injector (NBI) and all the auxiliary systems and services. The analysis was carried out on a reference scenario with a plasma current of 6 MA, mainly to estimate the electrical power needed to operate the facility, but also to identify some design choices and component ratings

Improvements in the SPIDER RF system

In SPIDER the negative ions are extracted from a plasma generated with RadioFrequency drivers, each fed with a power up to 100 kW at the frequency of 1 MHz. One of its distinguishing characteristics is the source fully installed within a vacuum vessel and operated in the residual gas pressure, including the matching networks for the driver impedance installed on the source backside. These features lead to more challenging design and integration also of the RF system, and in fact during the experimentation some issues arose: the operation of the RF generators is affected by the magnetic coupling among the RF circuits on board the source; breakdowns are observed on the source backside while powering the RF circuit and common mode RF currents ow through the diagnostics and dc power circuits. An overall system design review was launched with the aim to identify the root cause of these issues, feasible solutions and a plan for their x, which are presented and discussed in this pape