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Featured researches published by E. de la Cal.


Plasma Physics and Controlled Fusion | 1999

First plasmas in the TJ-II flexible Heliac

C Alejaldre; J. Alonso; L Almoguera; E. Ascasíbar; A. Baciero; R Balbín; M Blaumoser; J. Botija; B. Brañas; E. de la Cal; A Cappa; R. Carrasco; F. Castejón; J R Cepero; C Cremy; J Doncel; C Dulya; T. Estrada; A. Fernández; M Francés; C. Fuentes; A. García; I. García-Cortés; J. Guasp; J Herranz; C. Hidalgo; J.A. Jiménez; I. Kirpitchev; V Krivenski; I Labrador

The first experimental campaign of the TJ-II stellarator has been conducted using electron cyclotron resonance heating (, ) with a pulse length of . The flexibility of the device has been used to study five different configurations varying plasma volume and rotational transform. In this paper, the main results of this campaign are presented and, in particular, the influence of plasma-wall interaction phenomena on TJ-II confinement is briefly discussed.


Journal of Nuclear Materials | 1997

Wall conditioning technique development in Tore Supra with permanent magnetic field by ICRF wave injection

E. Gauthier; E. de la Cal; B. Beaumont; A. Becoulet; C. Gil; C. Grisolia; A. Grosman; T. Hutter; H. Kuus; L. Ladurelle; J.L. Segui

Abstract Wall conditioning techniques tokamaks with a permanent magnetic field have been performed in Tore Supra by using an ion cyclotron range frequency (ICRF) facility. Plasmas have been produced by injection of ICRF power in the range from 40 kW to 350 kW either in helium or deuterium gas. Electron density in the range of 1 · 10 17 to 6 · 10 17 m −3 and electron temperatures from 1.5 to 8 eV have been measured depending on the gas pressure and injected power. Energetic neutral atoms of hydrogen and deuterium with energies up to 50 keV have been produced. High hydrogen removal rates have been obtained in helium discharges, either in a continuous or pulsed operation mode.


Plasma Physics and Controlled Fusion | 2006

Impact of different confinement regimes on the two-dimensional structure of edge turbulence

J. Alonso; S. J. Zweben; P.A. Carvalho; J.L. de Pablos; E. de la Cal; C. Hidalgo; T Klinger; B. Ph. van Milligen; R. J. Maqueda; M. A. Pedrosa; C. Silva; M Spolaore; H Thomsen

This paper reports the impact of different confinement regimes on the 2D structure of edge turbulence. An image analysis method based on two-dimensional continuous wavelet transformation is used to localize structures (blobs) in the images and to extract their geometrical characteristics (position, scale, orientation angle and aspect ratio). We study the impact of edge shear-layers on these geometrical aspects of blobs. Results show a reduction in the angular dispersion of blobs as the shear layer is established in the boundary, as well as an increase in the elongation of these structures. Similar behaviour is found in NSTX image sequences when going from L to H mode plasmas. During improved confinement regimes the number of detected blobs decreases. Some indications are found suggesting that the turbulence reduction could be scale-selective in the biasing-induced improved confinement regime of TJ-II stellarator. Perpendicular flow reversal is visualized with the cameras and the time scales for flow reversal are found to be less than 50 µs. Radially propagating structures are found in the SOL with velocities in the range ~1000 m/s and with a poloidally asymmetric spatial distribution.


Review of Scientific Instruments | 2012

A protection system for the JET ITER-like wall based on imaging diagnostics

G. Arnoux; S. Devaux; D. Alves; I. Balboa; C. Balorin; N. Balshaw; M. Beldishevski; P.A. Carvalho; M. Clever; S. Cramp; J.L. de Pablos; E. de la Cal; D. Falie; P. Garcia-Sanchez; R. Felton; V. Gervaise; A. Goodyear; A. Horton; S. Jachmich; A. Huber; M. Jouve; D. Kinna; U. Kruezi; A. Manzanares; Vincent Martin; P. McCullen; V. Moncada; K. Obrejan; K. Patel; P. Lomas

The new JET ITER-like wall (made of beryllium and tungsten) is more fragile than the former carbon fiber composite wall and requires active protection to prevent excessive heat loads on the plasma facing components (PFC). Analog CCD cameras operating in the near infrared wavelength are used to measure surface temperature of the PFCs. Region of interest (ROI) analysis is performed in real time and the maximum temperature measured in each ROI is sent to the vessel thermal map. The protection of the ITER-like wall system started in October 2011 and has already successfully led to a safe landing of the plasma when hot spots were observed on the Be main chamber PFCs. Divertor protection is more of a challenge due to dust deposits that often generate false hot spots. In this contribution we describe the camera, data capture and real time processing systems. We discuss the calibration strategy for the temperature measurements with cross validation with thermal IR cameras and bi-color pyrometers. Most importantly, we demonstrate that a protection system based on CCD cameras can work and show examples of hot spot detections that stop the plasma pulse. The limits of such a design and the associated constraints on the operations are also presented.


Plasma Physics and Controlled Fusion | 2005

Review of radio frequency conditioning discharges with magnetic fields in superconducting fusion reactors

E. de la Cal; E. Gauthier

Wall conditioning techniques based on radio frequency (RF) discharges in fusion devices with permanent magnetic field were developed a few years ago. The first experiments of RF plasma discharges in the ion cyclotron frequency range called ion cyclotron conditioning were performed in Tore Supra and Textor and later also in HT-7 and W7-AS. A high conditioning efficiency in terms of hydrogen removal and surface cleaning has been demonstrated. The other alternative, RF conditioning discharges in the electron cyclotron range of frequencies and called electron cyclotron conditioning, has also been studied in the recent past. Besides surface hydrogen removal and surface cleaning, RF discharges have also been applied to thin film deposition. We report in this paper the main results obtained with several fusion devices on RF conditioning discharges and present conclusions for future devices such as ITER.


Nuclear Fusion | 2008

Spatially resolved Hα-emission simulation with EIRENE in TJ-II to study hydrogen atomic and molecular physics in low density, high temperature fusion edge plasmas

E. de la Cal; J. Guasp; A. Salas; D. Reiter; P. Börner; Javier A. Alonso; R. Balbin; D. Carralero; C. Hidalgo; J.L. de Pablos; F.L. Tabarés

This paper is a continuation of previous studies (de la Cal et al 2007 J. Nucl. Mater. 363–365 764, de la Cal et al 2007 Proc. 34th EPS Conf. (Poland, Warsaw) P 2.029), where hydrogen recycling under ionizing plasma conditions was analysed by spatially resolved Hα-emission spectroscopy with a tangentially viewing camera looking at a poloidal limiter of the TJ-II stellarator operated with a low density, high temperature plasma edge (ne = (1–10) × 1012 cm−3 and Te = 40–400 eV). In this study, the first objective is to validate for hydrogen the recently implemented EIRENE code* by comparing simulated Hα-emission chords with that obtained experimentally. The second objective is to analyse the atom and molecular neutral distributions in front of the limiter and at other plasma and chamber locations. The third one is to study the atomic and molecular reactions involved in the dissociation, ionization and excitation reactions, as calculated from the EIRENE code, in order to study hydrogen atomic and molecular physics in a low density, high temperature fusion plasma edge, with special focus on interpretation of Hα-emission. The contribution of the different reactions to the emission is analysed as a function of plasma radius. A relevant result obtained from EIRENE under this item is that the main precursor of the molecular Hα-emission is not H2 as proposed in many previous studies, but .


Plasma Physics and Controlled Fusion | 1997

First-wall cleaning and isotope control studies by ICRF conditioning in Tore Supra with a permanent magnetic field

E. de la Cal; E. Gauthier

The use of a permanent magnetic field in superconducting magnetic fusion devices impedes conditioning by glow discharges as actually applied in most pulsed machines. An alternative has been studied in Tore Supra for this purpose with a 3.8 T permanent field: a discharge produced by ion cyclotron range of frequency wave injection (ICRF). Helium ICRF discharge conditioning (ICRF-DC) has already been shown to desaturate the deuterium-loaded carbon first wall efficiently. In this paper, we describe how ICRF-DC can be applied to clean the wall or change its hydrogen isotopic ratio. This is achieved by pumping wall-desorbed molecules induced by particle bombardment from the ICRF plasma. The conditioning efficiency is optimized as a function of two input parameters: the gas pressure and the applied power. A plasma characterization is also given as a function of these parameters and a global model has been used to compare the experimental results and to interpret the main processes to which the neutral and charged species are subjected. The key to optimizing ICRF-DC is the wave ion heating to produce energetic particle bombardment of the first wall, while still achieving a low electron density, low-temperature plasma , to avoid reionization and redeposition of wall-desorbed neutrals before they can be evacuated by the torus pumping system.


Journal of Applied Physics | 1993

Characterization of He/CH4 dc glow discharge plasmas by optical emission spectroscopy, mass spectrometry, and actinometry

E. de la Cal; D. Tafalla; F.L. Tabarés

The gas‐phase kinetics responsible for the formation of some electronically excited radicals (CH) and atoms (H, He, Ar) in glow discharge plasmas of He‐methane admixtures has been investigated under several conditions of gas composition and discharge current at a total initial pressure of 0.01 Torr. Actinometry has been used to characterize the microscopic plasma parameters and, in combination with mass spectrometry and optical emission spectroscopy, to establish the formation mechanism of excited species. A very good correlation between CH emission intensity and carbon deposition rate has been found under all conditions. The effective cracking kinetic constant for methane molecules depends on plasma conditions, its value ranging from ≊1 to 5×10−10 cm3 s−1 as plasma current is increased, in good agreement with the expected value according to the actinometric results. A simplified kinetic model, accounting for all the observations reported in this work, is proposed.


34th European Physical Society Conference on Plasma Physics 2007, EPS 2007 | 2008

Fast visible camera installation and operation in JET

A. Alonso; P. Andrew; A. Neto; J.L. de Pablos; E. de la Cal; H. Fernandes; J. Gafert; P. Heesterman; C. Hidalgo; G. Kocsis; A. Manzanares; A. Murari; G. Petravich; L. Rios; C. Silva; P. D. Thomas

This article is a summary of the measurements of the recently installed wide‐view fast visible camera in the Joint European Tokamak JET. Here we limit ourselves to a description of the different phenomena and leave for forthcoming articles a more extensive analysis of every phenomenon.


Nuclear Fusion | 2001

Review of confinement and transport studies in the TJ-II flexible heliac

C Alejaldre; L Almoguera; J. Alonso; E. Ascasíbar; A. Baciero; R Balbín; M Blaumoser; J. Botija; B. Brañas; E. de la Cal; A Cappa; R. Carrasco; F. Castejón; J. Castellano; J R Cepero; C Cremy; J Doncel; S. Eguilior; T. Estrada; A. Fernández; C. Fuentes; A. García; I. García-Cortés; J. Guasp; J. Herranz; C. Hidalgo; J.A. Jiménez; I. Kirpitchev; V. Krivenski; I Labrador

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 different power densities. Both helium and hydrogen fuelled plasmas have been investigated. The article reviews the latest physics results in particle control, configuration effects, and transport and fluctuation studies.

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J.L. de Pablos

Complutense University of Madrid

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F.L. Tabarés

European Atomic Energy Community

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C. Hidalgo

European Atomic Energy Community

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V. Philipps

Forschungszentrum Jülich

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A. Lyssoivan

European Atomic Energy Community

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A. Manzanares

Complutense University of Madrid

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B. Brañas

Complutense University of Madrid

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