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Inter-machine plasma perturbation studies in EU-DEMO relevant scenarios: lessons…

A new scientific paper has been published by the UNITUS Nuclear Fusion Research team, concerning inter-machine plasma perturbation studies in EU-DEMO relevant scenarios.

The DEMO wall protection strategy is among one of the key issues to be solved to achieve commercial nuclear fusion reactors and fusion energy. Therefore, the development of comprehensive analyses is mandatory to assess how transient perturbations on plasma shape control and on vertical stability affect the tokamak performances with elongated plasmas. Moreover, the design of the limiter structures needs a deep understanding also of the effects induced by one of the most severe load conditions to occur in tokamaks, the Vertical Displacement Events (VDEs). Electromagnetic loads during VDEs are among the DEMO limiter’s design drivers because they provide specifications regarding their electromagnetic and mechanical performances. Therefore, predictive simulations of the final plasma position and of EM loads following a VDE are essential to understand the operational space of the future commercial nuclear fusion reactors. For this purpose, a multi-tokamak study has been carried out and an inter-machine database has been built and populated with experimental transient plasma perturbations and VDEs from JET and ASDEX Upgrade (AUG) tokamaks. Thanks to statistical analyses carried out on the data collected into the database, some transient plasma perturbations (namely, low-to-high confinement mode transitions, high-to-low confinement mode transitions and Edge Localized Modes) have been characterized. They have been chosen since they may lead to high control actions by the vertical stability system in terms of variations of the plasma’s internal parameters and vertical displacements. Then, experimental transient plasma perturbations have been properly scaled to DEMO reference geometries with different magnetic configurations. Finally, initial predictive electromagnetic loads on DEMO limiter structures are calculated in the case of VDEs following plasma perturbations, providing lessons to be learnt in view of DEMO.

Sias, S. Minucci, M. Lacquaniti, R. Lombroni et al., “Inter-machine plasma perturbation studies in EU-DEMO relevant scenarios: lessons learnt for EM forces prediction during VDEs”, accepted for publication on Nuclear Fusion.

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An equivalent-circuit model for saw resonators: from room down…

The concept of the surface acoustic wave (SAW) technology was first explored in 1885 by Lord Rayleigh, who studied the propagation of acoustic waves in piezoelectric materials. SAW devices today represent a hot research topic because of their widespread use in several fields. They are compact, easy to fabricate, and cost-effective. They represent a key technology in many fields, such as automotives, electronics, medical, aerospace, and defense. Moreover, SAW resonators are widely used in sensing applications because of their unique features that enable them to be used as detectors in battery-less systems with remote wireless interrogation.

The operating principle of a SAW resonator is relatively simple. An acoustic wave travels through the surface of a piezoelectric material. Any stimulus or perturbation on the device substrate (e.g., a temperature change) may affect the propagation of the acoustic wave, thus altering the characteristic resonant frequency.

The activity carried out at University of Messina by a research group head by Prof. Nicola Donato (Res4Net member), in collaboration with the University of Niš (Serbia), is focused on the electrical characterization of a commercial SAW resonator over the temperature range between 20 K and 373 K. An equivalent-circuit model is extracted and validated in the entire range of the investigated temperature and the major scientific results have been published in IEEE Sensors Journal and MDPI Micromachines Journal in March 2021 and in MDPI Sensors Journal in April 2022.

The developed study, based on coupling an extensive temperature-dependent experimental characterization with equivalent-circuit modeling, enable one to analyze in detail the SAW performance over the selected temperature range and to verify the accuracy and robustness of the modeling procedure, from low- to high-temperature conditions. In the latest contribution, the extraction procedure has been improved for a more accurate determination of the model parameters (i.e., the values of the equivalent-circuit elements). This improvement has been accomplished by using a complex Lorentzian function to fit both real and imaginary parts of the short-circuit input and output admittances (i.e., Y11 and Y22) of the SAW under test, thereby allowing an improvement in the determination of the resonant parameters, which are used for the extraction of the equivalent-circuit elements. The extraction software has been developed in Python and is described here.

The developed modeling procedure will be useful for the in-depth characterization and modeling of SAW gas sensors.

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Tokamak Energy Ltd chooses the UNITUS school of Engineering…

An important collaboration between the UNITUS school of engineering and Tokamak Energy Ltd (TE) was set. TE is a privately funded company based in the UK [1]. Founded in 2009, the company is developing compact fusion power plants based on two promising technologies: Spherical Tokamaks (STs) and High Temperature Superconductors (HTSs). As regards STs, they are a particular type of tokamak with a higher aspect ratio than that of conventional tokamaks. The ST concept demonstrates all the main features of more compact tokamaks having the real potential to significatively reduce costs and timescales on the path to Fusion power, at the same time. As for HTSs, this technology allows significant increase in the toroidal magnetic field, which it was found to improve the plasma confinement in STs. In addition, HTS magnets can operate at relative high temperatures (conventional superconductors are cooled to 4 K, while an HTS usually operates at 80 K), which is beneficial in the design of these components where space is very limited in the central zone of a ST device. The combination of the efficiency of STs and the benefits of the HTSs opens a route to lower-volume fusion reactors [1]. In summary, the mission of Tokamak Energy is to exploit this opportunity by pioneering the use of spherical tokamaks in conjunction with HTS magnets technology. Tokamak Energy Ltd is presently operating ST40 [1][2]. ST40 is a new generation high magnetic field ST and results as the highest magnetic field device of its kind (capable of reaching values above 2 Tesla). It aimes at demonstrating burning plasma condition parameters for a ST device. In the recent years, ST40 has been upgraded with the aim to reach higher plasma performances and to prepare the machine for the ongoing experimental campaign started in May 2021 [2].

In this context, a new record was recently achieved within a ST40 experiment of March 2022: Tokamak Energy has demonstrated a world-first with its privately funded ST40 spherical tokamak, achieving a plasma temperature of 100 million degrees Celsius, the threshold required for commercial fusion energy [1]. This is by far the highest temperature ever achieved in a ST and by any privately funded tokamak. In this video (Moving closer to commercial fusion-YouTube link), published by Tokamak Energy website, is presented the announcement of the record. The result was obtained also thanks to the analyses commissioned to the UNITUS team by TE as one of several studies to prepare ST40 for the experimental operations [2], in which this incredible performance has been reached.

As a matter of facts, within the ST40 upgrade, the necessity to analyse in detail the electromagnetic behaviour of the main device components under the loads coming from some plasma abnormal events, namely disruptions [3], has recently emerged in order to verify the ST40 design or drive further modifications. In this context, several studies to analyse the ElectroMagnetic (EM) response of ST40 components during a plasma non ordinary scenario have been carried out by UNITUS by means of a specific coupling tool procedure, following a recently developed methodology fully described in [3]. The main output of these studies is the evaluation of the EM force density evolution that affect ST40 components during a plasma disruption for subsequent mechanical assessments. In addition, the UNITUS team is engaging in the study of innovative materials, such as liquid metals or tungsten foams for the design of plasma facing components to be implemented in ST40. Finally, to support the ST40 Tokamak operations, causes and effects associated with disruptions are under investigation by the UNITUS team. In this regard, the focus is on the population of a disruptions database aimed at characterizing off-normal plasma scenarios and at providing lessons to be learnt for the next ST40 experimental campaign and for the design of future ST devices.

As for TE future steps, the ST40 device will now undergo a new upgrade and be used to develop technologies for future devices. The ST-HTS (or Intermediate Device), which will be the world’s first spherical tokamak to demonstrate the full potential of HTS magnets, is due to be commissioned in the mid-2020s. This device will demonstrate multiple advanced technologies required for fusion energy and inform the design of a world first fusion pilot plant, namely ST-E1, to be commissioned in the early 2030s [1]. Each of these future steps set out in the Tokamak Energy roadmap on its path to commercial fusion power will directly involve the UNITUS school of engineering thanks to the scientific collaboration signed between the two institutions.

[1] https://www.tokamakenergy.co.uk

[2] “M. Romanelli et al. “Preparing for first diverted plasma operation in the ST40 high-field spherical tokamak.”, 47th EPS Conference on Plasma Physics (June 2021), P3.1058.”

[3] R. Lombroni, F. Giorgetti, G. Calabrò, P. Fanelli, and G. Ramogida, “Using MAXFEA code in combination with ANSYS APDL for the simulation of plasma disruption events on EU DEMO.”, Fusion Eng. Des., no. March, p. 112697, 2021.

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An Adaptive Measurement System for the Simultaneous Evaluation of…

In-liquid measurements with quartz-based sensors are used in many different application fields, among which are chemical sensing, biosensing and viscosity measurements [1,2,3,4].

Sensing systems based on quartzes exploit their electromechanical resonant behavior: their piezoelectric properties provide a transduction of mechanical quantities into electrical quantities, whereas the pure elastic behavior of the quartz, which is an almost ideal resonator, is extremely sensitive to the changes of mechanical properties (mass, stiffness and damping). These particular properties have been exploited to obtain many different sensors: the most traditional ones are Quartz Crystal Microbalances (QCM), operating as mass sensors with resolutions down to a few nanograms [5,6,7,8], although, if used in liquid environments, it is possible to employ resonant measurement systems to characterize liquid viscosity and density. In this contest, the use of resonant structures is widely diffused and spread in different applications. Just to mention a couple, García-Arribas et al. developed a magnetoelastic sensor to sensitively measure the viscosity of fluids, aimed at developing an online and real-time monitoring of the lubricant oil degradation in machinery [9], and Zang et al. used a self-oscillating tuning fork device to perform fast measurements of viscosity and density, with the aim of characterizing different phases of liquids in a multiphase flow [10]. Moreover, in several applications, the research interest is focused on the realization of distributed sensor networks using sensor fusion techniques [11,12,13].

The basic structure of a quartz-based chemical or biosensor is the QCM, which is usually an AT-cut quartz disk operating in the MHz range provided by two electrodes on the two opposite surfaces. When the quartz vibrates in air, it is possible to assume no damping, and the modal frequencies of the device are set by the disk thickness [14]. In particular, it can be written [15]:

where

f_{s}_{N}

represents the N-th modal frequency,

N \in ℵ

and N odd and t is the thickness of the quartz, whereas

ρ_{Q}

and

μ_{Q}

are the quartz density and shear modulus.

A mass sensor is obtained by functionalizing one of the quartz surfaces with a material providing the selective adsorption of a target species. If, due to functionalization and to adsorption, a small additional mass (

Δ m

) is deposited on one of the quartz surfaces, by assuming that the mechanical properties of the added layer are the same as those of the quartz, then the effect changes the resonator thickness and, accordingly, shifts the modal frequencies of a quantity (

Δ f_{s N}

) related to the added mass:

where

m_{Q}

is the quartz mass, and the linear relation stems from the assumption of small thickness variations. Notice that Equation (2), written in a different form, is also known as the Sauerbrey equation [16].

By means of the piezoelectric effect, the mechanical vibrations are converted into an electrical charge or voltage signal. Therefore, a QCM is, in principle, a linear mass sensor providing the frequency as an output quantity. A typical 10-MHz AT-cut QCM provides, theoretically, a response of

Δ f_{s 1} (H z) = - 0.8 Δ m

(ng) [17].

A complete sensing system can be obtained by inserting the quartz into an electronic circuit providing the frequency metering [1].

Indeed, the measurement problem is far more complex [1,18]. First of all, the electromechanical vibrations can shift frequency not only due to the added mass (desired effect) but, also, due to the unwanted mechanical damping caused by the added layer, which has usually different and worse mechanical properties with respect to the quartz, especially in biosensors, where it consists of a lossy viscoelastic functionalization film and of the adsorbed target species (biological targets). Moreover, and more importantly, differently from AT-cut quartz oscillating in the air, where the surrounding medium can be well-described as an ideal fluid, and the standing elastic wave causing the vibration is confined in the solid disk, for in-liquid sensors, the surrounding medium is better described by a Newtonian fluid. In this case, part of the shear vibration can be transferred to the liquid and part of the elastic energy dissipated. The interaction with the fluid is, in this case, a non-negligible mechanical load (with both dissipative and conservative characteristics) that causes very large frequency shifts (up to hundreds of ppms). Due to this fact, some sensing systems exploit the dependency of the modal frequency of the quartz on the characteristics of the surrounding fluid to obtain viscosity measurements [14,19,20].

As a consequence, QCM-based measurement systems operating in liquid often couple the modal frequency shift assessment with the evaluation of the viscoelastic characteristics of the added layer through the monitoring of other dynamic parameters, such as the dissipation coefficient δ or, equivalently, the Q-factor [21,22]. This could unravel the inertial and dissipative behaviour of the ad-layer and enable distinguishing between the added mass and the surrounding liquid effects.

To continue with the issues related to the QCM-based measurements, it must be underlined that the way in which the vibrations are generated and measured can influence their frequency, which can be different from the searched modal frequency: for instance, the front-end circuit loads and influences the electromechanical resonance [1].

In a typical QCM system, the quartz is embedded in the feedback network of an oscillator circuit, and its output frequency is measured by, e.g., a digital frequency meter. QCM systems with dissipation monitoring (D-QCM) also provide a measurement of the dissipation factor δ (equivalent to the Q-factor) by inducing transients, e.g., disconnecting the feedback loop [23] and evaluating the transient decay duration. This allows for assessing the damping coefficient of the resonant electromechanical system.

In this paper, the problems related to measurements based on QCM in in-liquid applications are summarized, and a novel system based on a Meacham oscillator embedding an amplifier with adjustable gain is proposed. An automatic strategy is described that allows for gain tuning and maintaining the oscillator frequency close to the modal resonance of the quartz. From the adjusted gain value, an estimation of the series electromechanical resistance can be obtained, providing also the monitoring of the dissipative behavior of the electromechanical system through a robust estimation technique.

This paper is organized as follows: in Section 2, the operation of quartzes in liquid is presented, and the main measurement problems are discussed. In Section 3, the proposed oscillator topology, the series resistance estimation technique and the gain adjustment strategy are described. In Section 4, a prototype system, used to verify the proposed solution, is described, whereas Section 5 shows and discusses the experimental results. The conclusions are drawn in Section 6.

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Extended Reality and Human Computer Interaction for Medicine, Cultural…

The research activity in medicine and surgery is focused on the use of Virtual and Augmented Reality technologies to support surgeons in the diagnosis, the preoperative planning and the intraoperative phase in minimally invasive surgery. In addition, the use of touchless interaction is being investigated to enable a simple and intuitive fruition of specific patient’s data in those environments, such as the operative theatre, where any contact with the devices should be avoided to provide aseptic interactions between computer systems and medical staff.
Another line of research concerns the use of virtual, augmented and mixed reality for the treatment of children with ADHD through game-oriented activities (serious games).
Software applications are being designed, also based on mixed reality environments and serious games, for monitoring and rehabilitating patients with motor problems using touchless devices for detecting postures and arm and hand movements.
The research activity in Cultural Heritage is investigating the use of Virtual and Augmented Reality technologies to recreate historic sites for educational purposes and showcase features at visitor centres. In particular, Virtual Reality allows opening up real places normally not accessible to people by providing a realistic computer-generated navigation and sense of presence.
Spatial augmented reality, also known as video mapping, turns a building into a display surface for video projection: it uses audio-visual language to tell the story of a building and its surroundings through animations and sounds.

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Computer screen photo-assisted technique: a low-cost interface for colorimetric…

Chemical sensors with an optical response play a key role in industrial, environmental, and clinical fields due to their low-cost, miniaturization capability, and great flexibility. Among the various typologies of optical sensors, colorimetric sensors are desirable because they can identify target substances by associating the concentration with a color change, thereby ensuring an easily measurable analytical response. Colorimetric sensors are devices whose fluorescence emission or absorption properties in the visible spectrum change upon interaction with specific targets. The operating principle of these sensors is relatively simple: they are used in combination with a light source, with a set wavelength, and a detector. The light source illuminates the sensor, and the changes in the spectral properties of the reflected/transmitted radiation or the fluorescence emission are evaluated by using the detector.

The Computer Screen Photo-assisted Technique (CSPT) can be employed for a proper evaluation of the response of this kind of sensors. It is a characterization technique based on a simple but effective idea: it exploits the possibility of using parts of a computer screen as a programmable light source and a camera to record and analyze changes in the spectrum produced by the sample. In such context, the information on the wavelength of the light source (i.e., the color of the employed irradiation) is substitute with an RGB value (i.e., Red, Green and Blue values of a computer screen). This technique aims to create a device capable of evaluating the response of colorimetric sensors by using mainly commercially available devices. Usually, an LCD acts as a light source, and a conventional camera (e.g., a webcam) plays the role of a detector. The light from the LCD is reflected (or transmitted) by the chemical sensor, and the camera detects it.

The a group from the University of Messina, headed by Prof. Nicola Donato (Res4Net member), in collaboration with the ICAR-CNR of Palermo (Italy), developed a compact and low-cost measurement system based on CSPT, able to evaluate spectral information of both reflected and transmitted light from colorimetric sensors. The proposed system uses low-cost components, broadly available on the market and it includes a single-board computer, with a 7-inch touch screen display. The resulted system is powerful, versatile, and compact: able to be employed in on-field applications. A block diagram and a picture of the developed device are shown in the figure.

The developed device supports multiple colorimetric sensors and can be used for in-field applications such as low-cost detection of contaminants (Fe-ions and others, especially highly toxic heavy metals) present in wastewater and used as tracers of chemical contamination.

A more detailed description of the developed prototype can be found here

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Low power sensor networks and embedded sensing systems

Development of novel sensors, sensor networks and embedded sensing systems improving the condition monitoring system capabilities especially through the monitoring of gas composition.
Development of novel sensors and sensing strategies design for the enhancement of the condition monitoring system robustness, exploiting also the virtualization of redundancy through modeling.
Development of Minimum invasive sensing systems, exploiting low power technologies, low power wireless data transmission, energy harvesting.

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Wearable brain–computer interface instrument for augmented reality-based inspection in…

The proposed wearable monitoring system for inspection in the framework of Industry 4.0 is based on Brain-Computer Interface (BCI) and Augmented Reality (AR) integration. AR offers a new communication channel, capable of enhancing human-machine interactions. BCI can be particularly effective to interact with an AR headset, essentially working as a “thinking mouse” and allowing hands-free control of the system, so that the operator can simultaneously carry out other tasks.

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A virtual platform for real-time performance analysis of EM…

Background: Electromagnetic Tracking Systems (EMTSs) are widely used in surgical navigation, allowing to improve the outcome of diagnosis and surgical interventions, by providing the surgeon with intraoperative real-time position of surgical instruments during medical procedures. In particular, a very small magnetic sensor, which measures the magnetic field produced by a known field generator (FG), is inserted into the surgical instrument (e.g., a flexible instrument such as an endoscope or a needle), and the position of the sensor is estimated by means of a suitable algorithm.

Objectives: The main limitation of EM technology is the short tracking distance, which is generally no longer than 0.5 m from the FG in current commercial systems, due to the reduced amplitude of the magnetic field with distance, and the high sensitivity to EM interferences and magnetic field distortions, thus limiting tracking accuracy far from the FG. Many aspects affect system performance, and engineers and manufacturers should consider all of them, since also a small accuracy or distance increase is a valuable achievement in this field.

Methods: In this research, we propose a virtual platform for assessing the performance of EMTSs for surgical navigation, showing in real time how the various sources of error affect the accuracy of tracking distance estimation. The virtual platform is designed to be used in combination with a robot to move the sensor and provide accurate position references. The platform is composed of six main sections, and its functioning is illustrated in Fig. 1. The model of the EMTS if defined in an external file and imported into the platform, and the user defines the trajectory for sensor movement. Two different modalities can be performed: i) in the experimental mode, the platform connects to the DAQ device and the induced signal in the magnetic sensor is acquired as it is moved by the robot along the defined trajectory, ii) in the simulation mode, the signal of the magnetic sensor is simulated by employing a model of the magnetic field; in both cases, noise can be added to the signal. Finally, the position of the sensor is estimated by means of a suitable reconstruction algorithm, providing real-time 3D representation and error statistics.

Results: Simulations and experimental tests are performed to validate the proposed virtual platform in practical cases, showing its usefulness in assisting engineers during EMTS design and characterization, and by employing it to assess the performance of a real EMTS prototype (shown in Fig. 2), obtaining a mean Euclidean position error of about 2 mm at a distance of 600 mm from the FG, which is comparable with the ones obtained by simulations and suitable for many surgical procedures.

Conclusions: The platform provides a useful real-time tool to analyse EMTS components and field generator configurations, for a deeper understanding of EMTS technology, thus supporting engineers during system design and characterization.

References:[1] Ragolia, M. A., Attivissimo, F., Di Nisio, A., Lanzolla, A. M. L., & Scarpetta, M. (2021). “A virtual platform for real-time performance analysis of electromagnetic tracking systems for surgical navigation”. Acta IMEKO, 10(4), 103-110. doi:10.21014/acta_imeko.v10i4.1191.

[2] M. A. Ragolia, F. Attivissimo, A. Di Nisio, A. Maria Lucia Lanzolla and M. Scarpetta, “Reducing effect of magnetic field noise on sensor position estimation in surgical EM tracking,” 2021 IEEE International Symposium on Medical Measurements and Applications (MeMeA), Neuchâtel, Switzerland, 2021, pp. 1-6, doi: 10.1109/MeMeA52024.2021.9478723.

[3] M. A. Ragolia et al., “EM tracking system for surgical navigation”, research project; https://www.researchgate.net/project/EM-tracking-system-for-surgical-navigation

Experimental setup for system characterization. The developed prototype is composed of three main components: a Field Generator (FG), a Magnetic Sensor (MS) and a Control Unit (CU). The FG is composed of five transmitting coils, whose arrangement minimizes mutual inductances. Each coil is powered with a sinusoidal current at different frequencies (approximately from 1 to 5 kHz), thus generating an AC magnetic field. The whole magnetic flux generates an induced voltage on the MS, which is acquired, digitalized, and filtered by means of five band-pass filters thus obtaining five RMS voltage components, related to the different excitation frequencies. These components are used to estimate sensor position by means of a suitable reconstruction algorithm. The control software is developed in LabVIEW®, and the sensor is moved by means of an industrial robot (by Mitsubishi), which provides accurate position reference.

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Important updates on the IEEE MetroXRAINE2022 conference

Save the dates!

Abstract Submission Deadline

March 18, 2022

Authors should prepare an Abstract (1 – 2 pages) that clearly indicates the originality of the contribution and the relevance of the work. The Abstract should include the title of the paper, names and affiliations of the authors, an abstract, keywords, an introduction describing the nature of the problem, a description of the contribution, the results achieved and their applicability.

Abstract Acceptance Notification

March 30, 2022

When the first review process has been completed, authors receive a notification of either acceptance or rejection of the submission. If the abstract has been accepted, the authors can prepare a full paper.

Full Paper Submission Deadline

May 10, 2022

The format for the full paper is identical to the format for the abstract except for the number of pages: the full paper has a required minimum length of five (5) pages and a maximum of six (6) pages.

Full Paper Acceptance Notification

June 10, 2022

Full Papers will be reviewed by the Technical Program Committee.

Final Paper Submission Deadline

July 30, 2022

Authors of accepted full papers must submit the final paper version according to the deadline, register for the workshop, and attend to present their papers. The maximum length for final papers is 6 pages.