Victor Tribaldos

Victor Tribaldos
University Carlos III de Madrid | UC3M · Department of Physics

PhD

About

138
Publications
7,960
Reads
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2,124
Citations
Citations since 2016
10 Research Items
731 Citations
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
Additional affiliations
August 2009 - present
University Carlos III de Madrid
Position
  • Professor (Associate)
January 1988 - July 2009
Ciemat-Centro Investigaciones Energéticas, Medioambientales Y Tecnológicas
Position
  • Researcher

Publications

Publications (138)
Article
An adequate confinement of α-particles is fundamental for the operation of future fusion powered reactors. An even more critical situation arises for stellarator devices, whose complex magnetic geometry can substantially increase α-particle losses. A traditional approach to transport evaluation is based on a diffusive paradigm; however, a growing b...
Article
The confinement of alpha-particles is vital for any future fusion reactor. Unfortunately, the inevitable appearance of inhomogeneities in the magnetic field activates the non-collisional transport by virtue of ripple trapping and ripple induced stochastization. While a large and growing body of literature is devoted to the mitigation of these chann...
Article
A new method is proposed to solve Ampere's equation in an arbitrary toroidal domain in which all currents are known, given proper boundary conditions for the magnetic vector potential. The novelty of the approach lies in the application of singular value decomposition (SVD) techniques to tackle the difficulties caused by the kernel associated by th...
Article
The existence of a population of ions, with energies well above the corresponding thermal values, in plasmas heated by neutral beam injection (NBI) in the stellarator TJ‐II and in other magnetically confined plasmas devices is well known. Moreover, during the NBI phase of the TJ‐II, edge‐localized mode‐like (ELM‐like) instabilities often appear. Th...
Article
The recently developed free-plasma-boundary version of the SIESTA MHD equilibrium code [1, 2] is used for the first time to study scenarios with considerable bootstrap currents for the Wendelstein 7-X (W7-X) stellarator. Bootstrap currents in the range of tens of kAs can lead to the formation of unwanted magnetic island chains or stochastic regions...
Article
Numerous observation exist of a population of high energetic ions with energies well above the corresponding thermal values in plasmas generated by electron cyclotron resonance (ECR) heating in TJ-II stellarator and in other magnetically confined plasmas devices. In this work we study the impact of ECR heating different conditions (positions and po...
Article
SIESTA [Hirshman et al., Phys. Plasmas 18, 062504 (2011)] is a recently developed MHD equilibrium code designed to perform fast and accurate calculations of ideal MHD equilibria for three-dimensional magnetic configurations. Since SIESTA does not assume closed magnetic surfaces, the solution can exhibit magnetic islands and stochastic regions. In i...
Article
A systematic study of scintillation materials was undertaken to improve the time resolution of the fast ion diagnostic currently installed at TJ-II stellarator. It was found that YAP:Ce (formula YAlO3:Ce, Yttrium Aluminum Perovskite doped with Cerium) ionoluminescence offers better sensitivity and time response compared to the standard detector mat...
Article
Quasi-symmetric configurations have a better neoclassical confinement compared to that of standard stellarators. The reduction of the neoclassical viscosity along the direction of quasi-symmetry should facilitate the self-generation of zonal flows and, consequently, the mitigation of turbulent fluctuations and the ensuing radial transport. Therefor...
Poster
Full-text available
In order to better understand the dynamics of fusion plasmas it is of utmost importance to have a reliable knowledge of the magnetohydrodynamics of the given device. SIESTA is a code that allows the self-consistent calculation of the MHD equilibrium of any three-dimensional machine. Although the code is still in development, it is already being suc...
Article
Full-text available
The goal of this work is to study the empirical behaviour of suprathermal ions in the electron cyclotron resonance heating (ECRH) and neutral-beam injection (NBI) phases of the TJ-II stellarator. Our approach combines passive emission spectroscopy, which detects confined suprathermal ions with energies up to hundreds of electronvolts, and a lumines...
Article
Microwave reflectometry technique has experienced significant advances in the last two decades becoming a very attractive diagnostic presently used in almost all fusion devices. This technique allows measuring electron density profiles, plasma instabilities, turbulence and radial electric fields with excellent spatial and temporal resolution. Altho...
Article
Full-text available
This work extends previous Monte Carlo estimations of neoclassical transport for the TJ-II stellarator [V. Tribaldos, Phys. Plasmas 8, 1229 (2001)] to include, for the first time, the bootstrap current in low collisionality electron cyclotron resonance heated (ECRH) plasmas. The calculations are based on the mono-energetic coefficients calculated w...
Article
Full-text available
Numerical results for the three mono-energetic transport coefficients required for a complete neoclassical description of stellarator plasmas have been benchmarked within an international collaboration. These transport coefficients are flux-surface-averaged moments of solutions to the linearized drift kinetic equation which have been determined usi...
Article
Full-text available
The benchmarking of the thermal neoclassical transport coefficients is described using examples of the Large Helical Device (LHD) and TJ-II stellarators. The thermal coefficients are evaluated by energy convolution of the monoenergetic coefficients obtained by direct interpolation or neural network techniques from the databases precalculated by dif...
Article
Full-text available
During heating, by neutral beam injection, of magnetically confined plasmas in the TJ-II stellarator broad spectral structures, that straddle intense emission lines from multiply ionized oxygen ions, are observed by a normal-incidence spectrometer viewing a plasma region well separated from the neutral beam/plasma interaction volume. These features...
Article
Full-text available
The TJ-II is a 4-period heliac-type stellarator with a major radius of 1.5 m, a bean shaped plasma cross-section, with an average minor radius of !0.22 m, and magnetic field B(0) !1 T. It is designed to explore a wide rotational transform range (0.9 ! !(0)/2" ! 2.2) in low, negative shear configurations (#!/! <6%) [1]. Plasmas, created with hydroge...
Article
Full-text available
This paper presents the latest results on confinement studies in the TJ-II stellarator. The inherently strong plasma--wall interaction of TJ-II has been successfully reduced after lithium coating by vacuum evaporation. Besides H retention and low Z , Li was chosen because there exists a reactor-oriented interest in this element, thus giving special...
Book
Full-text available
The development of nuclear fusion is rapidly becoming a vital necessity in view of the continuing rise of the world’s energy demand. Nuclear fusion offers a virtually endless source of energy that is both environmentally friendly and capable of meeting any foreseeable energy demand. The progress of fusion constitutes one of the greatest technologic...
Book
The project outlined in this report describes the construction of a singular scientific and technological facility (the National Centre for Fusion Technologies TechnoFusión) in the Madrid region, to create the infrastructure required to develop the technologies needed in future commercial fusion reactors, and to assure the participation of Spanish...
Article
Full-text available
A Doppler reflectometer system has recently been installed in the stellarator TJ-II. The system is optimized for the Q-band (33-50 GHz) and the high-curvature plasmas produced in TJ-II. The launch angle of the microwave beam can be controlled by a steerable mirror to obtain angles between +/-20 degrees enabling the measurement of perpendicular wave...
Article
The characterization of ECH plasma confinement in Heliotron J was studied with special regard to its magnetic configuration effects. Recent experiments on 70-GHz ECH revealed that the energy confinement characteristics in the normal confinement mode (T e < 1.5 keV, T i CX < 0.2 keV, n e = (0.2 -3.0)x10 19 m -3 , W p diam < 3 kJ, and B 0 < 1.5 T) sh...
Article
Full-text available
This paper presents the latest results on confinement studies in the TJ-II stellarator. The inherently strong plasma--wall interaction of TJ-II has been successfully reduced after lithium coating by vacuum evaporation. Besides H retention and low Z , Li was chosen because there exists a reactor-oriented interest in this element, thus giving special...
Article
Full-text available
This paper presents the latest results on confinement studies in the TJ-II stellarator. The inherently strong plasma--wall interaction of TJ-II has been successfully reduced after lithium coating by vacuum evaporation. Besides H retention and low Z , Li was chosen because there exists a reactor-oriented interest in this element, thus giving special...
Article
First impurity ion temperature profiles obtained using an active diagnostic system, recently installed on the TJ-II stellarator, are presented. This diagnostic consists of a multichannel spectrometer and a compact diagnostic neutral beam injector system optimized for performing charge-exchange recombination spectroscopy. Here, after summarizing the...
Conference Paper
Full-text available
The International Collaboration on Neoclassical Transport in Stellarators (ICNTS) is one of several activities initiated by the stellarator community to develop the tools and know-how necessary to describe and predict the behavior of non-axisymmetric plasmas during high-performance discharges. This contribution presents an overview of benchmarking...
Article
A set of powerful tools has been developed in the last years for the design of new stellarator devices. These codes, usually working in magnetic co-ordinates, comprise minimization of neoclassical transport, maximizing equilibrium and stability properties, etc. However, for certain conditions the stellarator magnetic field can be originally obtaine...
Article
Full-text available
Profile stiffness is quantified using a simple technique. The approach is tested on a paradigmatic numerical stiff transport model for one field (particles). The stiffness is found to exhibit radial structure and to depend on collisionality, which might help explaining the observed lack of stiffness in stellarators, as compared to tokamaks. The ext...
Article
Full-text available
This work surveys the main results concerning the effects of the rotational transform, its low order rational values and its shear on the confining properties of low shear devices. It is meant to promote further studies aimed at clarifying their role in future, reactor grade, devices. 1-D transport studies are encouraged as the effects of rotationa...
Article
Full-text available
A concise systematic study of impurity parameter profiles (impurity ion temperatures and poloidal velocities) measured under different plasma conditions has been carried out in the TJ-II stellarator using an active spectroscopic diagnostic system covering a large section of the central plasma minor radius, from r/a = 0.3 to 0.85, with high spatial...
Article
Full-text available
This paper presents an overview of experimental results and progress made in investigating the link between magnetic topology, electric fields and transport in the TJ-II stellarator. The smooth change from positive to negative electric field observed in the core region as the density is raised is correlated with global and local transport data. A s...
Article
Full-text available
The International Stellarator Confinement Database (ISCDB) is a joint effort of the helical device community. It is publicly available at http://www.ipp.mpg.de/ISS and http://iscdb.nifs.ac.jp. The validity of physics models is investigated employing ISCDB data. Bayesian model comparison shows differences in the confinement scaling of data subgroups...
Article
Full-text available
The improvement of core electron heat confinement has been realized in a wide range of helical devices such as CHS, LHD, TJ-II and W7-AS. Strongly peaked electron temperature profiles and large positive radial electric field, Er, in the core region are common features for this improved confinement. Such observations are consistent with a transition...
Article
Ion temperatures have been measured in the TJ-II stellarator using passive emission spectroscopy in parallel and perpendicular directions. A high-energy component was observed from the tails of the Hα line emission in both directions, suggesting a non-negligible population of suprathermal ions. The role of this fast ion energy component, which has...
Article
We explore whether the energy confinement and planned heating in the National Compact Stellarator Experiment (NCSX) are sufficient to test magnetohydrodynamic (MHD) stability limits, and whether the configuration is sufficiently quasi-axisymmetric to reduce the neoclassical ripple transport to low levels, thereby allowing tokamak-like transport. A...
Article
Full-text available
This paper presents an overview of experimental results and progress made in investigating the link between magnetic topology, electric fields and transport in the TJ-II stellarator. The smooth change from positive to negative electric field observed in the core region as the density is raised is correlated with global and local transport data. A s...
Conference Paper
Full-text available
This papers studies the effect of rotational transform and magnetic shear on the confinement of low shear stellarators.
Article
This paper presents an overview of experimental results and progress made in investigating the link between magnetic topology, electric fields and transport in the TJ-II stellarator. The smooth change from positive to negative electric field observed in the core region as the density is raised is correlated with global and local transport data. A s...
Article
Full-text available
This paper presents an overview of experimental results and progress made in investigating the link between magnetic topology, electric fields and transport in the TJ-II stellarator. The smooth change from positive to negative electric field observed in the core region as the density is raised is correlated with global and local transport data. A s...
Article
Full-text available
Further exploration of confinement trends in the evolving International Stellarator Confinement Database is reported. The impact of configurations on confinement is confirmed, and the performance close to operational limits is discussed. Model comparison techniques allow for tests of physical models against data. Correlations of configuration-descr...
Article
Plasma breakdown using second-harmonic electron cyclotron (EC) waves has been studied experimentally in three helical devices, Heliotron J, TJ-II and CHS. Recent technological progress on electron cyclotron heating (ECH) systems enables us to determine what the important factors for second-harmonic plasma breakdown are. Comparison of the experiment...
Article
Full-text available
The poloidal rotation of C V ions has been deduced, in the TJ-II stellarator, from spectral line shifts measured using a high-spectral-resolution spectrometer and a nine-fiber-channel system. Analysis of the data obtained has shown that a change of sign of the poloidal rotation direction occurs that depends abruptly on plasma density but is indepen...
Article
The characteristics of core electron-root confinement (CERC) in helical devices are illustrated using results from four different experiments: the Compact Helical System, Large Helical Device, TJ-II, and Wendelstein 7-AS, Common features include strongly peaked electron temperature profiles and large positive radial electric fields Er in the core r...
Article
Reflectometry with wavelengths in the centimetre to millimetre-wave range will be used in ITER to measure the density profile in the main plasma and divertor regions and to measure the plasma position and shape in order to provide a reference for the magnetic diagnostics in long pulses. In addition, it is expected to provide key information for the...
Article
A local model capable of simulating the cordintegrated emission of spectral lines in the TJ-II stellarator has been developed for inferring local parameters. The procedure was implemented on a numerical code, which starting from given analytical profiles of local emissivity, ion temperature, and toroidal rotation calculates the cord-integrated emis...
Article
Full-text available
A novel method for measuring absolutely calibrated rotation velocities in fusion plasmas by means of passive spectroscopy, using a single plasma view, is presented. The method consists of simultaneously recording the emission lines from the plasma and from a calibration lamp by means of a double fiber-fiber guide. A software simultaneously analyzes...
Article
International collaboration on development of a stellarator confinement database has progressed. More than 3000 data points from nine major stellarator experiments have been compiled. Robust dependences of the energy confinement time on the density and the heating power have been confirmed. Dependences on other operational parameters, i.e. the majo...
Article
Full-text available
The roadmap to a feasible fusion reactor based on the tokamak line is already established. However, options for further improvement are very desirable in order to be ready to meet the future requirements of the energy market. In this respect, stellarators have a significant role to play as candidates for steady state operation reactors.Like tokamak...
Article
Full-text available
This paper presents an overview of experimental results and progress made in investigating the role of magnetic configuration on stability and transport in the TJ-II stellarator. Global confinement studies have revealed a positive dependence of energy confinement on the rotational transform and plasma density, together with different parametric dep...