Juan A Jiménez

Juan A Jiménez
Instituto Español de Oceanografia | IEO · Centro Oceanográfico de Baleares

PhD

About

106
Publications
6,699
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
1,197
Citations

Publications

Publications (106)
Article
Full-text available
Seamounts constitute an obstacle to the ocean circulation, modifying it. As a result, a variety of hydrodynamical processes and phenomena may take place over seamounts, among others, flow intensification, current deflection, upwelling, Taylor caps, and internal waves. These oceanographic effects may turn seamounts into very productive ecosystems wi...
Conference Paper
Full-text available
En el proyecto RADMED hemos medido el oxígeno disuelto (µmol/kg) en toda columna de agua, 4 veces al año, desde el año 2007 hasta el año 2016, en aproximadamente 80 estaciones de muestreo en el Mediterráneo Occidental. La zona del mínimo de oxígeno (OMZ) se encuentra alrededor de los 400 metros de profundidad identificada por su valor de oxígeno di...
Poster
Full-text available
Since 2007, Spanish Institute of Oceanography (IEO) is supporting a Mediterranean monitoring programme (RADMED) that is the result of merging four previous projects:, some of them starting in 1992, and the inclusion of new transects not sampled before. Four times per year several sections are sampled routinely, from Cabo Pino (close to Straits of G...
Conference Paper
Full-text available
Since 2007, the Spanish Institute of Oceanography (IEO) is supporting a Mediterranean monitoring program (RADMED) that is the result of merging four previous monitoring projects, some of them starting in 1992, and the inclusion of new transects never sampled before. Four times per year several sections are sampled routinely, from Cabo Pino (close t...
Technical Report
The MEDWAVES (MEDiterranean out flow WAter and Vulnerable EcosystemS) cruise targeted areas under the potential influence of the MOW within the Mediterranean and Atlantic realms. These include seamounts where Cold-water corals (CWCs) have been reported but that are still poorly known, and which may act as essential “stepping stones” connecting faun...
Poster
Full-text available
Poster presented in Seminarios Ibéricos de Química Marina en Alicante (2016)
Article
Beam-driven Alfvén eigenmodes (AEs) have been studied in the TJ-II low-magnetic-shear flexible heliac (B 0 = 0.95 T, R = 1.5 m, a = 0.22 m), in L-mode hydrogen plasmas with hydrogen NBI and ECR heating (P NBI 1.0 MW, E NBI = 32 keV, P ECRH 0.6 MW). In low-density plasmas in the range = (0.3-1.5) ×10¹⁹ m⁻³, a large variety of AEs have been observed...
Conference Paper
Full-text available
Temporal evolution of the Western Mediterranean Transition (WMT) was analysed using θ-S data from two deep stations seasonally sampled in the NE of Minorca and off Cape Palos since 2003 and 2007 respectively. Increasing trends in S and θ of the order of 10-3 year-1 and 5·10-3 ºC year-1 were shown, higher than values previously reported for the 1900...
Article
The main TJ-II results since 2012 are presented in this overview. Impurity confinement is studied showing an isotopic dependence of impurity confinement time, asymmetries in parallel impurity flows in TJ-II ion-root plasmas and impurity density asymmetries within a flux surface. In addition, first observations of electrostatic potential variations...
Article
Full-text available
Excitation of modes in the Alfvénic frequency range, 30 kHz f AE f AE, based on the local Alfvén eigenmode (AE) dispersion relation, was proposed to characterize the observation. It was shown that all the observations, including vacuum iota and plasma current variations, may be fitted by the model, so the linear mode frequency dependence on &$\unic...
Article
Full-text available
This work deals with the results on flow dynamics in TJ-II plasmas under Li-coated wall conditions, which produces low recycling and facilitates the density control and access to improved confinement transitions. The low-density transition, characterized by the emergence of the shear flow layer, is described from first principles and within the fra...
Article
Full-text available
A new algorithm based on metaheuristics has been developed to perform stellarator optimization. This algorithm, which is inspired by the behaviour of bees and is called distributed asynchronous bees, has been used for the optimization under three criteria: minimization of B × grad(B) drift, Mercier and ballooning stability. This algorithm is tested...
Article
Full-text available
This paper presents an overview of experimental results and progress made in investigating density control using Li-coating, transport and L–H transitions in TJ-II. The Li-coating changes drastically the plasma–wall interaction, decreasing the recycling, and enlarges substantially the operational range of the device delaying the appearance of radia...
Article
Full-text available
Calculations of the bootstrap current for the TJ-II stellarator are presented. DKES and NEO-MC codes are employed; the latter has allowed, for the first time, the precise computation of the bootstrap transport coefficient in the long mean free path regime of this device. The low error bars allow a precise convolution of the monoenergetic coefficien...
Article
An integrated data analysis system based on Bayesian inference has been developed for the TJ-II stellarator. It reconstructs the electron density profile at a single time point, using data from interferometry, reflectometry, Thomson scattering, and the Helium beam, while providing a detailed error analysis. In this work, we present a novel analysis...
Article
Full-text available
High frequency modes (150-300 kHz) are found in several magnetic configurations of TJ-II plasmas heated by neutral beam injection (NBI). The clear dependence of mode frequency on plasma density and mass species suggests them to be Alfvén eigenmodes. The appearance of these modes is linked to the presence of low order rational surfaces close to the...
Article
This paper presents an overview of experimental results and progress made in investigating density control using Li-coating, transport and L–H transitions in TJ-II. The Li-coating changes drastically the plasma–wall interaction, decreasing the recycling, and enlarges substantially the operational range of the device delaying the appearance of radia...
Article
This paper presents an overview of experimental results and progress made in investigating density control using Li-coating, transport and L–H transitions in TJ-II. The Li-coating changes drastically the plasma–wall interaction, decreasing the recycling, and enlarges substantially the operational range of the device delaying the appearance of radia...
Article
Full-text available
This paper presents an overview of experimental results and progress made in investigating density control using Li-coating, transport and L–H transitions in TJ-II. The Li-coating changes drastically the plasma–wall interaction, decreasing the recycling, and enlarges substantially the operational range of the device delaying the appearance of radia...
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
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
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
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
Magnetic fluctuations have been studied in the TJ-II stellarator. MHD events have been analysed for ECRH heated pressure driven modes and NBI Alfvén Eigenmodes.
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
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
Edge localized mode (ELM) events are typically observed in a broad variety of tokamaks and stellarators. In the TJ-II Heliac, ELM-like events have been observed in experiments at low plasma parameters (Te ~ Ti ~ 100 eV, n ~ 6 × 1012 cm−3, where Ti, Te and n are the ion and the electron temperatures and the plasma density, respectively) away from th...
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...
Article
Full-text available
TJ-II plasmas respond in a very controllable way to the external induction of a loop voltage in electron cyclotron resonance heating conditions. First experiments showed that the confinement improves (degrades) when a negative (positive) electric field is induced. Combining loop voltage induction with electron cyclotron current drive, the cause is...
Conference Paper
The influence of plasma density and edge gradients in the development of perpendicular sheared flows and radial electric fields, has been investigated in the plasma edge region of the TJ-II stellarator. Experimental results show that the development of the "naturally occurring" velocity shear layer requires a minimum plasma density (or gradient). N...
Article
The influence of limiter biasing on plasma confinement, turbulence and plasma flows is investigated in the TJ-II stellarator. Experimental results show that it is possible to modify global confinement and edge plasma parameters with both positive and negative biasing. Significant and minor modifications in the structure of plasma fluctuations have...
Conference Paper
Full-text available
On April 17<sup>th</sup> 2002, Spanish Government formally offered the Vandellos site as a possible European ITER site. In this work main technical site specific characteristics of the site are compared with generic requirements. It is shown that Vandellos site offers a number of technical advantages over the reference design mainly in relation wit...
Article
The studies carried out to evaluate and select a candidate site for International Thermonuclear Experimental Reactor (ITER) construction in Spain are presented in this paper. The ITER design, completed in July 2001, considered a number of technical requirements that must be fulfilled by the selected site. Several assumptions concerning the ITER sit...
Conference Paper
Full-text available
In the past, it was universally recognized that magnetohydrodynamic (MHD) theory explains (and predicts) experimental results. However, it is impossi- ble to explain several modern experimental results within the frame of standard MHD theory. For example, experiments performed at TJ-II (Spain) showed that electromag- netic oscillations appear in th...
Article
Neutral Particle Analyzer diagnostic has been operated remotely from Universitat Politecnica de Catalunya in Barcelona, separated by more than 600 km from Laboratorion Nacional de Fusion in Madrid. Remote participation tools are used to control the diagnostic, to visualize the experimental TJ-II data, and to participate in scientific meetings on TJ...
Article
A variety of core transport phenomena have been observed in low-density plasmas in TJ-II stellarator with electron cyclotron resonance heating (ECRH). Experimental evidence of the linkage between the appearance of these phenomena and the magnetic structure is discussed. These experimental findings point out the crucial role played by the low-order...
Article
TJ‐II flexibility is exploited to perform an investigation on the transport properties of this device. Rotational transform can be varied in a wide range, which allows one to introduce low order rationals and to study their effect on transport. On the other hand, confinement properties can be studied at very different rotational transform values an...
Article
Full-text available
This paper describes a series of experiments performed in TJ-II stellarator with the aim of studying the influence of magnetic configuration on stability and transport properties of TJ-II plasmas. Plasma potential profiles have been measured in several configurations up to the plasma core with the heavy ion beam probe diagnostic. Low-order rational...
Article
A study of the stability limits for ideal ballooning modes in helical axis stellarators (heliac type stellarators) has been performed. Specific configurations similar to those of the TJ-II heliac have been taken, having a deep magnetic well and almost zero shear, which is characteristic for a heliac. The stability limits are those imposed by the de...
Article
Measurements are reported of the average plasma beta of ECRH plasmas in the TJ-IU torsatron using external flux loops. The method is based on measurements of the magnetic flux produced by the Pfirsch-Schluter current due to the plasma pressure. The most important advantages of using this method over the conventional diamagnetic method are much high...
Article
Full-text available
The influence of the magnetic topology, and rational surfaces in particular, on core transport has been an area of increasing interest in the recent years. In tokamak plasmas, a correlation between the appearance of low-order rational surfaces (as the q profile evolves) and the formation of the ITBs has been seen on several devices (1-3). Local tra...
Article
The probability density function (PDF) of turbulent transport has been investigated in the plasma edge region of tokamak (JET) and stellarator (TJ-II) fusion devices. PDFs can be re-scaled using a functional form, PDF(ΓE×B) = L−1g(ΓE×B/L), where L is directly related with the level of fluctuations in the turbulent flux. This kind of re-scaling hold...
Article
A transient behaviour is observed in the plasma core of TJ-II stellarator with fast drops in the electron temperature. Changes in the line-averaged density are observed synchronized with temperature drops. This phenomenon appears in plasmas created and heated using 300 kW of electron cyclotron heating with high power density. The transient behaviou...
Article
TJ‐II flexibility is exploited to perform an investigation on the transport properties of this device. Rotational transform can be varied in a wide range, which allows one to introduce low order rationals and to study their effect on transport. On the other hand, confinement properties can be studied at very different rotational transform values an...
Article
Introduction - The radial propagation of perturbations is an important tool for probing transport properties in a fusion plasma. Indeed, the propagation of cold pulses, induced by either deliberate or spontaneous edge cooling, has been studied in many devices (e.g. JET (1, 2, 3), TFTR (4), TEXT (5), RTP (6, 7), ASDEX (8) and W7-AS (9)). The analysi...
Article
Full-text available
Perturbative transport experiments have been performed at the stellarator TJ-II. Both the inward propagation of edge cooling pulses induced by the injection of nitrogen, and the outward propagation of heat pulses due to spontaneous spikes of the central temperature have been analysed. It has been found that the observed propagation is incompatible...
Article
The operation protocols for the TJ-II require that all diagnostics be controlled remotely during machine operation. For this reason, most diagnostics have control systems that permit remote actions to be performed on their various subsystems. An Internet browser, which connects to a server where the human machine interfaces (HMIs) for all diagnosti...
Article
Full-text available
Kinetic corrections to a previous ideal MHD ballooning stability study of the TJ-II heliac standard configuration are numerically calculated using a criterion derived from the gyrokinetic Maxwell equations for modes with perpendicular wavelengths on the scale of the ion gyroradius in a general magnetic geometry. In this criterion, finite ion gyrora...
Article
Full-text available
ELM-like activity has been recently observed in TJ-II, in plasmas with stored energy above 1 kJ. The plasma is observed to develop bursts of magnetic activity (seen in Mirnov coil signals) which are followed by a large and distinct spike in the Hα signal. An increase in electrostatic and magnetic fluctuations at the plasma edge and a cold pulse tow...
Article
Full-text available
TJ-II is a four period, low magnetic shear stellarator (R = 1.5 m, a < 0.22 m, B0 ≤ 1.2 T) which was designed to have a high degree of magnetic configuration flexibility. In the most recent experimental campaign, coupling of the full ECRH power (PECRH ≤ 600 kW) to the plasma has been possible using two ECRH transmission lines which have differen...