Search

The present paper describes and analyzes the recent experimental results obtained at the High Voltage Padova Test Facility (HVPTF), the laboratory aimed at supporting the development of the prototype for the ITER Neutral Beam Injector. Evidences of Electron Stimulated Desorption of gas released from anodic surfaces have been observed during the onset of high voltage Direct Current vacuum discharges between stainless steel electrodes, separated by vacuum gaps of a few millimeters and with voltages of about 200 kV. The count of x-ray photons, produced by the accelerated electrons impinging the anode surface and observed as breakdown precursor in the 40% of the cases, was analyzed together with the images taken by an ultra-high speed camera during the onset of breakdown events. Electron stimulated desorption of neutral gas from the anodic surface appears to be a candidate for the voltage breakdown. The dynamic of the observed phenomena has been compared with the results obtained by a numerical model. The latter assumes a Townsend like discharge which develops following the emission of gas from the anode surface. The comparison shows good agreement between the experimental data and numerical simulations.

In the context of magnetic confinement fusion, the Megavolt ITER Injector and Concept Advancement (MITICA) project is supported by another experiment called High-Voltage Padova Test Facility (HVPTF): a device designed to improve the knowledge of high voltage holding in a vacuum. HVPTF includes a vacuum chamber containing two electrodes separated by an insulator or a vacuum gap, across which electrical discharges can develop. The electrodes are powered by two independent Cockcroft–Walton power supplies, allowing for a total voltage difference up to 800 kV. The current, voltage, and pressure inside the chamber are monitored at a sampling rate of 100 Hz. Studying the physics behind electrical discharges is fundamental to prevent their development in MITICA, where they can lead to structural damage to the experimental components. For this reason, in April 2022, a gas electron multiplier (GEM) detector was installed at HVPTF, allowing to perform X-ray measurements resolved in time, space, and energy at high rates ( ) without incurring severe pile-up problems. This work describes the analysis of data coming from current, voltage, and pressure sensors, and the X-ray GEM (XR-GEM) detector at HVPTF during two 2022 experimental campaigns. Correlations between sensor signals with the X-ray measurements have been highlighted. Experimental results indicate the presence of characteristic X-ray emissions from anode atoms during electrical discharge events in the needle–plane electrode configuration. An algorithm was developed for generating synthetic detector data based on user-defined X-ray emissions within the vacuum chamber and performing tomographic reconstructions using actual or synthetic detector data. Preliminary results indicate possible gas emissions from the anode’s surface during electrical discharge events. IEEE

The MITICA experiment, under construction at Consorzio RFX (Padova, Italy), is the full-scale prototype for the Neutral Beam Injector (NBI) of the ITER tokamak. One of the critical aspects for the ion beam accelerator is high voltage holding over long vacuum gaps (up to 1 MV from the ion source to the enclosing vessel), with the main issue being the occurrence of discharge events, which could severely damage the machine. To study this phenomenology, with the aim of prevention of discharges, the High Voltage Padova Test Facility (HVPTF) experiment is in operation. The setup of HVPTF consists in a cylindrical vacuum vessel, with stable pressure control, in which two replaceable electrodes are mounted with an adjustable gap width. The electrodes are powered by independent power supplies, allowing for a total voltage difference up to 800kV. Current and voltage of the power supplies, as well as the pressure and the gas composition inside the chamber are monitored at a sampling rate of 100 Hz. Additionally, the bremsstrahlung X-ray emission produced by the accelerated electrons during discharges is monitored by means of scintillators at higher rates (up to 1 MHz). Data from past experimental campaigns have been analyzed and correlations between the current/voltage signals and the X-ray emission have been highlighted. Recently, a new detector, based on the Gas Electron Multiplier (GEM) and optimized for X-ray detection, has been installed at HVPTF. The detector acts as a very fast single photon counting system (with rates up to about 125 MHz), allowing for real-time measurement of the X-ray emission rate, which could be used as basis for the development of a feedback control system for the prevention of discharges. The aim of this work is to illustrate the development of a new data analysis software, tailored on the data read by the GEM detector, displaying some of the first results obtained from the recent experimental campaigns. Future perspectives will also be drawn, fo

The High Voltage Padova Test Facility (HVPTF) is an experimental device for investigating High Voltage Direct Current insulation in vacuum, in support of the realization of MITICA, the prototype of a neutral beam injector for ITER. Inside a high vacuum chamber, two stainless steel electrodes, separated by a few centimetres gap, can achieve a voltage difference up to 800 kV. During the conditioning process of the electrodes, current micro-discharges (MD) and associated X-rays are observed, along with a global increase of gas emission (H2 and CO2 are detected by the Residual Gas Analyser). During the last five years, different X-rays detectors have been installed on HVPTF, with the aim to investigate the physical processes behind the conditioning.In this contribution, the fine dynamics of the micro-discharge phenomenon is studied with the purpose to sketch a possible physical interpretation of this mechanism. In particular, the time evolution, during the electrode conditioning, of the MD fine dynamics seems to be related with the increasing asymmetry between the MD current peak values collected by the positive and the negative electrodes. The possible (increasing) contribution of the vacuum chamber, operating as a third electrode, is investigated, by means of a toy model: the different current contributions collected by the two electrodes are evaluated, in particular those generated by secondary electron emission. The rate between anode and cathode currents evaluated by the toy model is in good agreement with the experimental one.

Objectives: This study aimed to (1) explore the changes in conspiracy mentality across the four waves of the COVID-19 pandemic; (2) assess the relationship between conspirative mentality and psychological/behavioural variables; (3) identify the predictors of conspirative mentality; and (4) explore the effect of conspirative mentality on COVID-19 protective behaviour. Study design: This was a multiwave survey. Methods: A total of 10,013 Italian individuals, aged 18–70 years, were assessed across the four waves (from January to May 2021) through online survey. We collected information about the sociodemographic characteristics of participants, personal experiences of COVID-19 infection, trust, COVID-19 protective behaviours, COVID-19 risk perception, arousal, auto-efficacy, resilience and well-being. Conspiracy mentality was assessed with the Conspiracy Mentality Questionnaire. The statistical analyses included exploratory factorial analyses, Pearson correlations and multiple linear regressions. Results: The conspiracy mentality score during the COVID-19 pandemic was medium–high (mean 59.0 on a 0–100 scale) and slightly increased from 58.2 to 59.9 across months, in parallel with a slight decrease in trust in health institutions and scientific informational sources. Individuals aged >35 years, poorly educated and particularly scared about their financial situation were at risk of showing higher levels of conspirative mentality. Higher levels of conspirative mentality were risk factors for low levels of COVID-19 protective behaviours. Conclusions: Clear and effective communication may improve trust in health institutions and informational sources, decrease conspirative theories and increase compliance with protective behaviour.

Despite the actual availability of COVID-19 vaccines to combat the pandemic, many people are still vacillating in their decision to vaccinate. In this study, we considered the effect of two relevant contextual issues on vaccination intention: the number of people infected with COVID-19 is increasing, and the pace of vaccination is gaining speed. Specifically, we hypothesized that having already contracted SARS-CoV-2 (post-positive reluctance) could lead people to underestimate the importance of vaccination. Moreover, as the number of vaccinated people increases, more hesitant people could fall into the free-riding intention category, benefitting from the immunity provided by others' vaccinations. Vaccine hesitancy becomes more critical as the vaccination campaign proceeds: at one point, it will be inevitable to deal with hesitant people. This study is part of a WHO Regional Office for Europe project and involved a representative sample of 5006 Italians interviewed in January–February 2021. In case of post-positive reluctance, both young age and female gender increase vaccine hesitancy, while a high level of education reduces free-riding intention. Considering post-positive reluctance and free riding, a protective effect on hesitancy is associated with negative affective states, adherence to protective behaviors, trust in health information sources, and resilience. In contrast, increased vaccine hesitancy is associated with a high level of conspiracy-mindedness and trust in media information sources. Recognizing and studying the post-positive reluctance and the phenomenon of free-riding people can help us to become more efficient in combatting the virus.

BackgroundThe hesitancy in taking the COVID-19 vaccine is a global challenge. The need to identify predictors of COVID-19 vaccine reluctance is critical. Our objectives were to evaluate sociodemographic, psychological, and behavioral factors, as well as attitudes and beliefs that influence COVID-19 vaccination hesitancy in the general population of Italy. MethodsA total of 2,015 people were assessed in two waves (March, April and May, 2021). Participants were divided into three groups: (1) individuals who accepted the vaccination ("accepters"); (2) individuals who refused the vaccination ("rejecters"); and (3) individuals who were uncertain about their attitudes toward the vaccination ("fence sitters"). Group comparisons were performed using ANOVA, the Kruskal-Wallis test and chi-square tests. The strength of the association between the groups and the participants' characteristics was analyzed using a series of multinomial logistic regression models with bootstrap internal validation (one for each factor). ResultsThe "fence sitters" group, when compared to the others, included individuals of younger age, lower educational level, and worsening economic situation in the previous 3 months. After controlling for sociodemographic factors, the following features emerged as the main risk factors for being "fence sitters" (compared with vaccine "accepters"): reporting lower levels of protective behaviors, trust in institutions and informational sources, frequency of use of informational sources, agreement with restrictions and higher conspirative mentality. Higher levels of COVID-19 perceived risk, trust in institutions and informational sources, frequency of use of informational sources, agreement with restrictions and protective behaviors were associated with a higher likelihood of becoming "fence sitters" rather than vaccine "rejecters." ConclusionsThe "fence sitters" profile revealed by this study is intriguing and should be the focus of public programmes aimed at impro

COVID-19 pandemic had a negative impact on the mental health and well-being (WB) of citizens. This cross-sectional study included 4 waves of data collection aimed at identifying profiles of individuals with different levels of WB. The study included a representative stratified sample of 10,013 respondents in Italy. The WHO 5-item well-being scale (WHO-5) was used for the assessment of WB. Different supervised machine learning approaches (multinomial logistic regression, partial least-square discriminant analysis—PLS-DA—, classification tree—CT—) were applied to identify individual characteristics with different WB scores, first in waves 1–2 and, subsequently, in waves 3 and 4. Forty-one percent of participants reported “Good WB”, 30% “Poor WB”, and 28% “Depression”. Findings carried out using multinomial logistic regression show that Resilience was the most important variable able for discriminating the WB across all waves. Through the PLS-DA, Increased Unhealthy Behaviours proved to be the more important feature in the first two waves, while Financial Situation gained most relevance in the last two. COVID-19 Perceived Risk was relevant, but less than the other variables, across all waves. Interestingly, using the CT we were able to establish a cut-off for Resilience (equal to 4.5) that discriminated good WB with a probability of 65% in wave 4. Concluding, we found that COVID-19 had negative implications for WB. Governments should support evidence-based strategies considering factors that influence WB (i.e., Resilience, Perceived Risk, Healthy Behaviours, and Financial Situation).

The high voltage Padova test facility (HVPTF) is an experimental device for the study of HV insulation in vacuum, in support of the realization of the prototype of a neutral beam injector for International Thermonuclear Experimental Reactor (ITER), named megavolt ITER injector and concept advancement (MITICA). The facility investigates the physical phenomena underlying voltage holding in vacuum, in particular the mechanisms causing breakdowns and the electrode conditioning process. At HVPTF, inside a high vacuum chamber, two stainless steel electrodes, separated by a few centimeters gap, can achieve HV values for a maximum potential difference of 800 kV. During the voltage conditioning of the electrodes, current MicroDischarges (MDs) and high-energy X-rays are observed and analyzed. In this work, we present a characterization of the MD dynamics occurring during the conditioning process, with the aim to gain information on the reason of the growing difference between the current contributions measured by the two electrodes. The analysis will be performed due to two new X-rays detectors recently installed: an lutetium yttrium orthosilicate (LYSO) and a LaBr3(Ce) scintillating crystal. The new diagnostics indeed provide the fine dynamics of a single MD, recording energy and time of each single detected X-ray. In particular, we compare the MD dynamics at the beginning and at the end of the conditioning process and try to give a preliminary interpretation of the observations.

The development of MITICA, the prototype for a neutral beam injector for ITER, drives the interest in investigating high HV insulation in vacuum. The High Voltage Padova Test Facility (HVPTF) is an experimental device with the aim of studying the fundamental processes leading to discharges, offering a framework to develop new diagnostics, models, and mode of operations for MITICA. For this purpose, HVPTF features a vacuum chamber containing two electrodes which can achieve an HV difference up to 800 kV. X-ray bremsstrahlung radiation produced by free charges accelerated by the HV was proven to be a promising monitoring mechanism in the past; as such, two scintillating crystals, a LYSO and a LaBr3, coupled with fast electronics were used to conduct hard X-ray spectroscopy. This work describes a newly custom-developed software tool to analyze the spectroscopy from scintillators and integrate it with the HVPTF analog data. The tool was employed to study two experimental sessions, reaching promising results in the characterization of microdischarges, especially in terms of time resolution. Detection limits imposed by pile-up and other processes were identified and addressed, finding the best range of operation of the two scintillators. The performed study opens the way for the analysis of data obtained in all 2020 and 2021 experimental campaigns, thus giving the possibility to implement future improvements in HVPTF X-ray spectroscopy.

High voltage (HV) insulation across a single gap in vacuum and low-pressure gas is a critical issue in relation to the development and realization of the electrostatic accelerator for the ITER neutral beam injector (NBI) (Toigo et al 2017 New J. Phys. 19 085004). The present paper describes and analyzes the recent experimental results obtained at the High Voltage Padova Test Facility (HVPTF), the laboratory aimed at supporting the development of the prototype for the ITER NBI (De Lorenzi et al 2011 Fusion Eng. Des. 86 742-5). A voltage up to 800kV(DC) was achieved in the HVPTF during the experimental campaigns with a sphere-plane configurations having variable gap length (from 30 to 150 mm) and pressure ranging from high vacuum (10(-7) mbar) to 10(-3) mbar in argon. Such an experimental campaign represents one of the few examples where voltages higher than 500-550 kV DC are sustained by a single vacuum gap between electrodes (Rohrbach 1971 CERN Report 71-5) and therefore constitutes additional experience to improve the knowledge of voltage holding across large vacuum gaps. The results in high vacuum indicate that at the beginning of voltage conditioning the breakdown events occur at the same cathodic electric field irrespective of the electrode geometry. However, after sufficient conditioning time, the breakdown voltage distribution seems to depend also on the electric field at the anode and on the total voltage between electrodes. A benchmark between a numerical tool previously developed to predict the voltage holding in high vacuum (voltage holding prediction model, VHPM (Pilan et al 2011 Fusion Eng. Des. 86 742-5)) and the experimental results is also reported and discussed.

The High Voltage Padova Test Facility (HVPTF) is an experimental device for investigating HV insulation in vacuum, in support of the realization of MITICA, the prototype of a neutral beam injector for ITER. The facility investigates the physical phenomena underlying voltage holding in vacuum, such as the mechanisms causing breakdowns and the electrode conditioning process, along with testing technical solutions to increase the breakdown threshold. Inside a high vacuum chamber, two stainless steel electrodes, separated by a few centimetres gap, can achieve HV values for a maximum of 800 kV potential difference. The conditioning process consists of the gradual increase of the breakdown voltage in time, until the system achieves a saturation value. Between two consecutive breakdown events, current micro-discharges involving the electrodes are observed; high energy X-rays (up to hundreds of keV) and a global increase of gas emission (in particular H2 and CO2 are detected by the Residual Gas Analyser) are measured in correspondence to the current events. Two new X-rays detectors have been recently installed: a small LYSO and a LaBr3(Ce) scintillating crystals, coupled to photomultipliers. They all are small sized scintillators, with very fast pulses (40-100 ns) in order to minimize pileup effects during the high intensity discharges. However, the high Z and densities guarantee a full energy absorption of the X-rays (they can measure up to 500 keV), with a significant probability, in spite of the small sizes. In this contribution we present a characterization of the micro-discharge dynamics occurring during the conditioning phase, focusing on the new details uncovered via the new diagnostics.

The High Voltage Padova Test Facilities (HVPTF) is a R&D project focused on understanding the physical processes behind breakdown and micro-discharges in high-voltage insulation, as well as developing new diagnostics, models, and operational modes to address these challenges and aid in the stable operation of MITICA. The X-rays produced during breakdown have a spectrum that extends from low energy (keV) up to several hundreds of keV and a flux that can reach 106 photons/cm2s. This paper shows the development and preliminary results of a newly designed X-Ray diagnostic based on Gas Electron Multiplier (SXR-GEM). This detector is able to stand very high rate (> MHz) in single photon counting mode and can cover the energy range from 3-50 keV. The XR-GEM detector is equipped with anodic pads (256 pads 6x6 mm2) readout with a new data acquisition system called GEMINI, which gives the possibility to obtain a counting rate of several MHz and sub-ms time resolution together with mm spatial resolution. Preliminary measurement shows that this kind of diagnostic is able to reconstruct the time evolution of the discharge at very high rates and to provide X-rays imaging.

The High Voltage Padova Test Facility is an experimental device realized to investigate the high voltage insulation in vacuum in support of the negative neutral beam injector prototype for ITER, MITICA. Moreover, the experiment aims to give a contribution on the understanding of the voltage holding in vacuum, as a physical phenomenon. Two stainless steel electrodes, with few cm of gap in a high vacuum chamber, achieve a saturation breakdown value (up to 400 kV) after about ten hours. A highly time resolved X-ray diagnostic has been recently installed in the device, measuring the X events (single events are detected) produced during the high voltage conditioning: high energy fluxes are observed in correspondence to the current peaks collected by the electrodes. This contribution presents a characterization of the current and X-ray emission events in terms of frequency, amplitude and their occurrence with respect to the voltage between the electrodes.