M. A. Ochando
A5023436557- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Fusion materials and technologies
- Laser-Plasma Interactions and Diagnostics
- Superconducting Materials and Applications
- Solar and Space Plasma Dynamics
- Particle accelerators and beam dynamics
- Atomic and Subatomic Physics Research
- Laser-induced spectroscopy and plasma
- Plasma Diagnostics and Applications
- Nuclear Physics and Applications
- Radiation Detection and Scintillator Technologies
- Nuclear reactor physics and engineering
- Magnesium Oxide Properties and Applications
- High-pressure geophysics and materials
- Time Series Analysis and Forecasting
- Nuclear Materials and Properties
- Muon and positron interactions and applications
- nanoparticles nucleation surface interactions
- Solidification and crystal growth phenomena
- Magnetic Field Sensors Techniques
- Electronic and Structural Properties of Oxides
- High-Energy Particle Collisions Research
- Surface and Thin Film Phenomena
- Electron and X-Ray Spectroscopy Techniques
Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas
2014-2024
Hospital Universitario de Gran Canaria Doctor Negrín
2024
Universidad Complutense de Madrid
2009-2022
Hospital Universitario Virgen del Rocío
2022
Max Planck Society
1991-2016
Max Planck Institute for Plasma Physics
1989-2016
Fusion for Energy
2004-2010
Oak Ridge National Laboratory
1991-1992
The first plasma experiments on the W7AS advanced stellarator were conducted in October 1988, after magnetic surface mapping. characteristics of device are described. During phase operation, 70 GHz ECF was used to generate and heat a 'currentless' which maintained quasi-steady state for typically 0.5 s. Effects configuration confinement measures deal with observed current (bootstrap ECF-driven current) investigated. Preliminary results transport analysis presented compared predictions models.
Sheared flows have been experimentally studied in TJ-II plasmas. In low-density ECH plasmas, sheared can be easily controlled by changing the plasma density, thereby allowing radial origin and evolution of edge velocity shear layer to studied. high density NBI heated plasmas a negative electric field is observed that dominated diamagnetic component. The increases at L–H transition an amount depends on magnetic configuration heating power. Magnetic configurations with without low order...
The first experimental campaign of the TJ-II stellarator has been conducted using electron cyclotron resonance heating (, ) with a pulse length . flexibility device used to study five different configurations varying plasma volume and rotational transform. In this paper, main results are presented and, in particular, influence plasma-wall interaction phenomena on confinement is briefly discussed.
This paper presents the latest results on confinement studies in TJ-II stellarator. The inherently strong plasma–wall interaction of 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 this element, thus giving special relevance to investigation its properties. Li-coating led important changes plasma performance. Particularly, effective density limit NBI plasmas extended...
This paper describes a series of experiments performed in TJ-II stellarator with the aim studying influence magnetic configuration on stability and transport properties plasmas. Plasma potential profiles have been measured several configurations up to plasma core heavy ion beam probe diagnostic. Low-order rational surfaces positioned at different radii observing effect features. edge turbulent has studied that are marginally stable due decreased well. Results show dynamical coupling between...
In the last campaign, TJ-II heliac has been operated under lithium-coated walls, representing first stellarator ever working these boundary conditions. Enhanced density control and discharge reproducibility, leading to drastic enlargement of operational window, have obtained. A strong decrease in recycling together with changes shot by fuelling characteristics wall particle inventory recorded. These changes, associated new scenario, had led a long-lasting good control. The conditions were...
Alfvén eigenmode (AE) activity driven by NBI-produced fast ions is observed in TJ-II plasmas. A two-step response of the measured AEs to electron cyclotron heating (ECH) power seen. In a first step, continuous character unstable changes chirping marginally when moderate values ECH are applied NBI-only-heated plasma. second significant reduction AE amplitude doubled. This stabilizing effect has been experimentally confirmed both on shot-by-shot basis and along single discharge means...
Excitation of modes in the Alfvénic frequency range, 30 kHz < fAE 300 kHz, was observed hydrogen plasma heated by neutral beam injection (NBI) TJ-II heliac. Co-field and counter-field NBI were injected, components poloidal magnetic field varied one combinations, order to investigate beam-driven over an extended range rotational transform values, . Taking advantage unique capabilities, a dynamic configuration experiment with variation during discharges has shown strong effects on mode via...
Density and temperature fluctuations have been measured in the plasma bulk side of velocity-shear location TJ-I tokamak using a fast swept Langmuir probe technique. Evidence has found that substantial phase difference close to \ensuremath{\psi} with respect corresponding density fluctuations. This result suggests possible role radiation determining edge fluctuation levels calls into question determination potential from current floating
The heavy ion beam probe diagnostic is used in the TJ-II stellarator to study directly plasma electric potential with good spatial (up 1 cm) and temporal 2 μs) resolution. Singly charged ions, Cs+, energies of up 125 keV are column from edge core. Both electron cyclotron resonance heating (ECRH) neutral injection (NBI)-heated plasmas (PECRH = 200 400 kW, PNBI ENBI 28 keV) have been studied.Low-density ECRH [[over bar]n (0.5 1.1) × 1019 m-3] characterized by positive on order 1000 V. A...
The magnitude of radial transport in magnetic confinement devices for controlled nuclear fusion suffers spontaneous bifurcations when specific system parameter values are exceeded. Here we show, the first time, that correlation length plasma potential becomes order machine size during edge bifurcation itself, quite unlike density fluctuations. mechanism governing development this bifurcation, leading to establishment an barrier, is still one main scientific conundrums facing community after...
This paper presents an overview of experimental results and progress made in investigating density control using Li-coating, transport L–H transitions TJ-II. The Li-coating changes drastically the plasma–wall interaction, decreasing recycling, enlarges substantially operational range device delaying appearance radiative collapse that happens for higher densities, which permits confinement properties much denser plasmas to be studied. Moreover, mode transition has only been achieved after...
The first experiments of exposure a LiSn alloy (Li/Sn atomic ratio = 20/80) to hydrogen plasma in TJ-II are here presented. Solid and liquid samples have been inserted at the edge evidence sample melting solid during has observed. A negligible perturbation recorded, even when stellarator plasmas particularly sensitive high Z elements due tendency central impurity accumulation. Melting by thermal load did not lead any deleterious effect on performance. Strong lithium emission was detected but...
Perturbative transport experiments have been performed at the stellarator TJ-II. Both inward propagation of edge cooling pulses induced by injection nitrogen, and outward heat due to spontaneous spikes central temperature analysed. It has found that observed is incompatible with diffusive models. Simultaneous eliminates an explanation in terms a pinch. A numerical simulation resistive interchange turbulence model suggests related successive destabilizations pressure gradient driven modes...
Abstract Achieving impurity and helium ash control is a crucial issue in the path towards fusion-grade magnetic confinement devices, this particularly case of helical reactors, whose low-collisionality ion-root operation scenarios usually display negative radial electric field which expected to cause inwards pinch. In work we discuss, based on experimental measurements standard predictions neoclassical theory, how plasmas very low ion collisionality, similar those observed hole large device...
Abstract The effect of electron cyclotron heating (ECH) and current drive (ECCD) on energetic-particle (EP)-driven magnetohydrodynamic (MHD) modes is studied in the helical devices LHD, TJ-II Heliotron J. We demonstrate that EP-driven MHD modes, including Alfvén eigenmodes (AEs) energetic particle (EPMs), can be controlled by ECH/ECCD. In LHD device, which has a moderate rotational transform high magnetic shear, co-ECCD enhances toroidal AEs (TAEs) global (GAEs), while counter-ECCD...
Abstract In this paper, we analyze the impact of electron cyclotron resonance heating and current drive on Alfvénic instabilities driven by neutral beam injection observed in TJ-II stellarator. An MHD stability analysis Alfvén eigenmodes compatible with experimental plasma parameters is carried out order to compare data provided magnetic coils, radiation monitors, heavy ion probes. To end, vacuum configuration modified different levels current, thermal fast pressure profiles generated...
Abstract 2D plasma potential ϕ distribution was measured in the electron cyclotron resonance heating (ECRH) and neutral beam injection (NBI) plasmas of TJ-II stellarator with heavy ion probe for whole radial range wide area poloidal angle, supported by Langmuir data at edge. The operation domain on-axis ECRH explored ( <?CDATA ${\bar n_{\text{e}}}$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mover> <mml:mi>n</mml:mi>...
The influence of limiter biasing on plasma confinement, turbulence and flows is investigated in the TJ-II stellarator. Experimental results show that it possible to modify global confinement edge parameters with both positive negative biasing. Significant minor modifications structure fluctuations have been observed during transition improved regimes induced by These evidence electric field via multiple mechanisms. investigation relaxation potential fields shows two different characteristic...
This paper presents an overview of experimental results and progress made in investigating the role magnetic configuration on stability transport TJ-II stellarator. Global confinement studies have revealed a positive dependence energy rotational transform plasma density, together with different parametric dependences for metallic boronized wall conditions. Spontaneous biasing-induced improved transitions, some characteristics that resemble those previously reported H-mode regimes other...
The effect of edge biasing on plasma potential was investigated in the TJ-II stellarator and T-10 tokamak. Heavy Ion Beam Probe (HIBP) diagnostic, a unique tool for studying core directly, used both machines. Experiments show that it is possible to modify global confinement parameters with limiter biasing, illustrating direct impact radial electric fields properties. For first time shown column can be charged as whole hot, near-reactor-relevant plasma. evolve two different characteristic...
Abstract TJ-II stellarator results on modelling and validation of plasma flow asymmetries due to on-surface potential variations, fuelling physics, Alfvén eigenmodes (AEs) control stability, the interplay between turbulence neoclassical (NC) mechanisms liquid metals are reported. Regarding neoclassically predicted asymmetries, its impact radial electric field along flux surface has been successfully validated against Doppler reflectometry measurements. Research physics core with pellets...
A new type of instability mode, related to suprathermal electrons, was found in extremely low-density plasmas, (ne = (0.2-0.5) × 1019 m−3) with electron cyclotron resonance heating and current drive (ECRH/ECCD) the TJ-II heliac. The quasi-monochromatic density plasma potential oscillations frequency range 20-120 kHz tend have several "branches" constant shift between them. typical amplitude mode induced estimated be ΔφEM ∼ 20 V. branches an individual finite radial extent, odd low poloidal...
The dependence of impurity confinement time on the charge and mass ions injected from various samples (LiF, BN, W) by laser blow-off method is reported for electron cyclotron heated discharges TJ-II heliac. Distinct confinements are distinguished clearly these in plasma core as revealed soft x-ray analysis tomographic reconstruction bolometer array signals. A with seems to be most probable explanation, confirmed spectrally resolved data vacuum–ultraviolet range. This discussed terms...