arXiv subjects

D. Mancini

Publications and source records attributed to D. Mancini.

12 recordsLinked to original sources

arXiv2025

Comparison of filament properties in real-size GBS simulations and experiments of TCV-X21

A direct quantitative comparison of Scrape-Off Layer (SOL) filament properties from fluid turbulence simulations using the GBS code and from experiments on the TCV tokamak is performed within the TCV-X21 validation case. This comparison is made possible by extending the open TCV-X21 dataset with 2D turbulence measurements obtained with Gas Puff Imaging (GPI), providing critical information on the size, velocity, and other key characteristics of turbulent filaments at the outboard midplane and in the divertor region. For the comparison, GBS simulations of TCV-X21 are analyzed using a dedicated synthetic GPI diagnostic that models the neutral helium-plasma interaction and emission processes and accounts for line-integration effects. Poloidal and radial filament velocities are found to be in good agreement between simulations and experiments, while the simulations overestimate the filament radial and poloidal sizes and underestimate the relative fluctuation levels. The simulations further indicate that filaments in the SOL are predominantly represented by density perturbations rather than temperature perturbations, consistent with previous assumptions in experimental analyses of cross-field turbulent transport from GPI data. The poloidal velocity direction of the filaments agrees with the time-averaged $\boldsymbol{E}\times\boldsymbol{B}$ direction at the outboard midplane and X-point region, but not in the divertor leg. Possible explanations are proposed and discussed, highlighting the influence of the instantaneous $\boldsymbol{E}\times\boldsymbol{B}$ velocity components in both poloidal and radial directions. This study provides new insights into turbulent filament behavior and contributes to guiding future efforts to improve first-principles simulations of the boundary plasma.

physics.plasm-ph↗

arXiv2023

Self-consistent multi-component simulation of plasma turbulence and neutrals in detached conditions

Simulations of high-density deuterium plasmas in a lower single-null magnetic configuration based on a TCV discharge are presented. We evolve the dynamics of three charged species (electrons, D$^{+}$ and D$_{2}^{+}$), interacting with two neutrals species (D and D$_2$) through ionization, charge-exchange, recombination and molecular dissociation processes. The plasma is modelled by using the drift-reduced fluid Braginskii equations, while the neutral dynamics is described by a kinetic model. To control the divertor conditions, a D$_2$ puffing is used and the effect of increasing the puffing strength is investigated. The increase in fuelling leads to an increase of density in the scrape-off layer and a decrease of the plasma temperature. At the same time, the particle and heat fluxes to the divertor target decrease and the detachment of the inner target is observed. The analysis of particle and transport balance in the divertor volume shows that the decrease of the particle flux is caused by a decrease of the local neutral ionization together with a decrease of the parallel velocity, both caused by the lower plasma temperature. The relative importance of the different collision terms is assessed, showing the crucial role of molecular interactions, as they are responsible for increasing the atomic neutral density and temperature, since most of the D neutrals are produced by molecular activated recombination and D$_2$ dissociation. The presence of strong electric fields in high-density plasmas is also shown, revealing the role of the $E \times B$ drift in setting the asymmetry between the divertor targets. Simulation results are in agreement with experimental observations of increased density decay length, attributed to a decrease of parallel transport, together with an increase of plasma blob size and radial velocity.

physics.plasm-ph↗

arXiv2023

The commissioning phase

In May 1997 a consistent part of the services and structures committed to the industry had already been released to the commissioning group. The telescope itself was, with the exception of the Nasmyth derotators, motors and all the optics groups, basically ready in its mechanical parts to accept the integration of all services and control equipment. Also the verification of the cabling (interlocks, data-nets, power and controls) already mounted was started in the same period. Starting from June 1998 (telescope first-light date) the telescope went gradually in use, several nights per week, in order to test and tune the tracking and pointing system, the optics and the first derotator system (Nasmyth A station). At the end of the commissioning period and with the first scientific instruments mounted (April 1999) also the first routinely observations started. In this moment the telescope is doing astronomy 80% of time and the complete first-light instrumentation is mounted.

astro-ph.IM↗

arXiv2021

The GBS code for the self-consistent simulation of plasma turbulence and kinetic neutral dynamics in the tokamak boundary

A new version of GBS (Ricci et al. Plasma Phys. Control. Fusion 54, 124047, 2012; Halpern et al. J. Comput. Phys. 315, 388-408, 2016; Paruta et al. Phys. Plasmas 25, 112301, 2018) is described. GBS is a three-dimensional, flux-driven, global, two-fluid turbulence code developed for the self-consistent simulation of plasma turbulence and kinetic neutral dynamics in the tokamak boundary. In the new version presented here, the simulation domain is extended to encompass the whole plasma volume, avoiding an artificial boundary with the core, hence retaining the core-edge-SOL interplay. A new toroidal coordinate system is introduced to increase the code flexibility, allowing for the simulation of arbitrary magnetic configurations (e.g. single-null, double-null and snowflake configurations), which can also be the result of the equilibrium reconstruction of an experimental discharge. The implementation of a new iterative solver for the Poisson and Ampère equations is presented, leading to a remarkable speed-up of the code with respect to the use of direct solvers, therefore allowing for efficient electromagnetic simulations that avoid the use of the Boussinesq approximation. The self-consistent kinetic neutral model, initially developed for limited configurations, is ported to the magnetic configurations considered by the present version of GBS and carefully optimized. A new MPI parallelisation is implemented to evolve the plasma and neutral models in parallel, thus improving the code scalability. The numerical implementation of the plasma and neutral models is verified by means of the method of manufactured solutions. As an example of the simulation capabilities of the new version of GBS, a simulation of a TCV tokamak discharge is presented.

physics.plasm-ph↗

arXiv2005

VST - VLT Survey Telescope Integration Status

The VLT Survey Telescope (VST) is a 2.6m aperture, wide field, UV to I facility, to be installed at the European Southern Observatory (ESO) on the Cerro Paranal Chile. VST was primarily intended to complement the observing capabilities of VLT with wide-angle imaging for detecting and pre-characterising sources for further observations with the VLT.

astro-ph↗

arXiv2001

The VST telescope control software in the ESO VLT environment

The VST (VLT Survey Telescope) is a 2.6 m Alt-Az telescope to be installed at Mount Paranal in Chile, in the European Southern Observatory (ESO) site. The VST is a wide-field imaging facility planned to supply databases for the ESO Very Large Telescope (VLT) science and carry out stand-alone observations in the UV to I spectral range. This paper will focus mainly on control software aspects, describing the VST software architecture in the context of the whole ESO VLT control concept. The general architecture and the main components of the control software will be described.

astro-ph↗

arXiv2001

Active optics control of the VST telescope with the CAN field-bus

The VST (VLT Survey Telescope) is a 2.6 m class Alt-Az telescope to be installed at Mount Paranal in the Atacama desert, Chile, in the European Southern Observatory (ESO) site. The VST is a wide-field imaging facility planned to supply databases for the ESO Very Large Telescope (VLT) science and carry out stand-alone observations in the UV to I spectral range. This paper will focus on the distributed control system of active optics based on CAN bus and PIC microcontrollers. Both axial and radial pads of the primary mirror will be equipped by astatic lever supports controlled by microcontroller units. The same CAN bus + microcontroller boards approach will be used for the temperature acquisition modules.

astro-ph↗

arXiv2001

Integration of the VIMOS control system

The VIRMOS consortium of French and Italian Institutes (PI: O. Le Fevre, co-PI: G. Vettolani) is manufacturing two wide field imaging multi-object spectrographs for the European Southern Observatory Very Large Telescope (VLT), with emphasis on the ability to carry over spectroscopic surveys of large numbers of sources: the VIsible Multi-Object Spectrograph, VIMOS, and the Near InfraRed Multi-Object Spectrograph, NIRMOS. There are 52 motors to be controlled in parallel in the spectrograph, making VIMOS a complex machine to be handled. This paper will focus on the description of the control system, designed in the ESO VLT standard control concepts, and on some integration issues and problem solving strategies.

astro-ph↗

arXiv2001

VST telescope dynamic analisys and position control algorithms

The VST (VLT Survey Telescope) is a 2.6 m class Alt-Az telescope to be installed on Cerro Paranal in the Atacama desert, Northern Chile, in the European Southern Observatory (ESO) site. The VST is a wide-field imaging facility planned to supply databases for the ESO Very Large Telescope (VLT) science and carry out stand-alone observations in the UV to I spectral range. So far no telescope has been dedicated entirely to surveys; the VST will be the first survey telescope to start the operation, as a powerful survey facility for the VLT observatory. This paper will focus on the axes motion control system. The dynamic model of the telescope will be analyzed, as well as the effect of the wind disturbance on the telescope performance. Some algorithms for the telescope position control will be briefly discussed.

astro-ph↗

arXiv2001

The VLT-VIRMOS Mask Manufacturing Unit

The VIRMOS Consortium has the task to design and manufacture two spectrographs for ESO VLT, VIMOS (Visible Multi-Object Spectrograph) and NIRMOS (Near Infrared Multi-Object Spectrograph). This paper describes how the Mask Manufacturing Unit (MMU), which cuts the slit masks to be used with both instruments, meets the scientific requirements and manages the storage and the insertion of the masks into the instrument. The components and the software of the two main parts of the MMU, the Mask Manufacturing Machine and the Mask Handling System, are illustrated together with the mask material and with the slit properties. Slit positioning is accurate within 15 micron, equivalent to 0.03 arcsec on the sky, while the slit edge roughness has an rms on the order of 0.03 pixels on scales of a slit 5 arcsec long and of 0.01 pixels on the pixel scale (0.205 arcsec). The MMU has been successfully installed during July/August 2000 at the Paranal Observatory and is now operational for spectroscopic mask cutting, compliant with the requested specifications.

astro-ph↗

arXiv2001

The VIRMOS-VLT Deep Survey

The aim of the VIRMOS VLT Deep Survey (VVDS) is to study of the evolution of galaxies, large scale structures and AGNs from a sample of more than 150,000 galaxies with measured redshifts in the range 0<z<5+. The VVDS will rely on the VIMOS and NIRMOS wide field multi-object spectrographs, which the VIRMOS consortium is delivering to ESO. Together, they offer unprecedented multiplex capability in the wavelength range 0.37-1.8microns, allowing for large surveys to be carried out. The VVDS has several main aspects: (1) a deep multi-color imaging survey over 18deg^2 of more than one million galaxies, (2) a "wide" spectroscopic survey with more than 130,000 redshifts measured for objects brighter than IAB=22.5 over 18deg^2, (3) a "deep" survey with 50,000 redshifts measured to IAB=24, (4) ultra-deep" surveys with several thousand redshifts measured to IAB=25, (5) multi-wavelength observations with the VLA and XMM.

astro-ph↗

arXiv1997

GOHSS: a Fibre-fed Multiobject NIR Spectrograph for the Italian Galileo Telescope

We present the concept and preliminary design of the Galileo OH Subtracted Spectrograph [GOHSS], a multifibre NIR spectrograph for faint objects. The instrument represents a collaboration between the Institute of Astronomy, Cambridge and the Observatories of Naples and Rome and will be a second-light instrument for the 3.6m Galileo telescope located on La Palma. The NIR spectrograph accomplishes OH night-sky suppression in a different way from the hardware solution used by both OHS (Maihara etal) and COHSI (Piche' et al). GOHSS provides a multiechelle design with software subtraction capable of yielding ~28 spectra in J+H bands at a spectral resolution R~3000. Such a resolution is the minimum necessary to reduce the impact of atmospheric OH lines.

astro-ph↗