Mesure de la température ionique dans le plasma périphérique du Tokamak Tore-Supra, Ion tempeture measurements in the scrape-off layer of the Tore Supra Tokamak

Martin Kocan

Description

Sous la direction de Gérard Bonhomme, James Paul Gunn
Thèse soutenue le 06 octobre 2009: Nancy 1
La thèse décrit les mesures de températures ioniques (Ti) dans la Scrape-Off-Layer (SOL) – un paramètre important cependant rarement mesuré – à l'aide d'une sonde Analyseur à Retard de Champ (RFA) installée sur le Tokamak Tore Supra. La thèse s'organise en 4 chapitres. Dans le premier sont brièvement rappelés les enjeux de la fusion nucléaire, la géométrie des limiteurs et la physique la SOL, le principe des sondes de Langmuir, etc. Sont aussi adressés les différents diagnostics dédiés aux mesures de Ti dans la SOL, utilisés dans le passé. Le second chapitre est consacré au RFA. Le principe de l'analyseur, les détails techniques et opérationnels sur Tore Supra ainsi que les effets instrumentaux sur les mesures y sont abordés. Il est conclut que l'influence instrumentale sur les mesures RFA de Ti sont relativement faibles. Dans le troisième chapitre, les mesures systématiques de Ti (ainsi que d'autres paramètres) dans la SOL de Tore Supra sont présentées. Il est montré que le rapport Ti / Te > 1 (Te étant la température électronique) dans la SOL, mais aussi dans le plasma confiné ; et que ce rapport augmente avec le rayon plasma. Un autre résultat important est que Ti dans la SOL change significativement, suivant étroitement les paramètres centraux, alors que Te dans la SOL n'évolue presque pas. Dans le dernier chapitre est présenté le statut actuel de trois projets en cours visant à valider indépendamment la mesure de Ti dans la SOL de Tore Supra : le développement d'une tête de sonde à tunnel segmenté permettant une mesure des fluctuations de Ti dans la SOL ; la mesure de Ti au bord des plasmas du Tokamak Joint European Torus (JET) ; et la comparaison des mesures de RFA avec les mesures de spectroscopie d'échange de charge et recombinaison (CXRS) sur Tore Supra.
-Températures ioniques
-Plasma du bord
-Scrape-Off-Layer
-Tokamak
-Tore Supra
The thesis describes measurements of the scrape-off layer (SOL) ion temperature Ti – an important but yet rarely measured parameter – with a retarding field analyzer (RFA) probe in the limiter tokamak Tore Supra. The thesis is organized in four chapters. In the first chapter, some well known facts about nuclear fusion, limiter SOL, Langmuir probes, etc. are briefly recalled. Various diagnostics for SOL Ti measurements developed in the past are addressed as well. The second chapter is dedicated to the RFA. The principle of the RFA, technical details and operation of the Tore Supra RFA, and the influence of instrumental effects on RFA measurements are addressed. It is concluded that the influence of instrumental effects on RFA Ti measurements is relatively small. In the third chapter, the systematic measurements of Ti (as well as other parameters) in the Tore Supra SOL are presented. It is shown that Ti / Te >1 (with Te being the electron temperature) in the SOL but also in the confined plasma, and increases with radius. Also important result is that while SOL Ti changes significantly, following the core properties rather closely, SOL Te hardly changes at all. In the final chapter the present status of three ongoing projects aimed at the independent validation of SOL Ti measurements in Tore Supra is presented: the development of the segmented tunnel probe for fast SOL Ti measurements, the measurement of edge ion temperature in Joint European Torus (JET) tokamak, and the comparison of RFA with charge exchange recombination spectroscopy in Tore Supra.
Source: http://www.theses.fr/2009NAN10116/document

Informations

• Publié par: Thesee
• Nombre de lectures: 70
• Langue: English
• Poids de l'ouvrage: 15 Mo

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Code de la Propriété Intellectuelle. articles L 122. 4
Code de la Propriété Intellectuelle. articles L 335.2- L 335.10
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U.F.R. Sciences & Techniques de la Matière et des Procédés
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Thèse
présentée pour l'obtention du titre de
Docteur de l'Université Henri Poincaré, Nancy-I
en Physique des plasmas
par Martin KOČAN

Ion temperature measurements in the scrape-off layer of
the Tore Supra tokamak


Soutenance publique prévue l’Octobre 6, 2009


Membres du jury :
Président : M. Michel VERGNAT Professeur, U.H.P., Nancy I
Rapporteurs : M. Jan STÖCKEL Chercheur (HDR) IPP, Prague
M. Volker ROHDE Chercheur (HDR) IPP, Garching
Examinateurs : M. Gerard BONHOMME Professeur, U.H.P., Nancy I
(Directeur de thèse)
M. James Paul GUNN Chercheur CEA, Cadarache
(Directeur de thèse CEA)
M. André GROSMAN Chercheur CEA, Cadarache
M. Guido Van OOST Professeur, Gent University
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Laboratoire de Physique des Milieux Ionisés et Applications
Faculté des Sciences & Techniques - 54500 Vandoeuvre-lès-Nancy Abstract

The thesis describes measurements of the scrape-off layer (SOL) ion temperature
T with a retarding field analyzer (RFA) in the limiter tokamak Tore Supra. In the first i
chapter, some well known facts about nuclear fusion, limiter SOL, Langmuir probes, etc.
are briefly recalled. Various diagnostics for SOL T measurements developed in the past i
are addressed as well. The second chapter is dedicated to the RFA. The principle of the
RFA, technical details and operation of the Tore Supra RFA, and the influence of
instrumental effects on RFA measurements are addressed. In the third chapter, the
experimental results are presented in the form of papers published (or submitted for
publication) during the thesis. Three ongoing projects to validate RFA T measurements i
in Tore Supra are summarized in the last chapter.
Considerable emphasis is placed on study of the instrumental effects of RFAs and
their influence on T measurements. In general, the influence of instrumental effects on T i i
measurements is found to be relatively small. Selective ion transmission through the RFA
slit is found to be responsible for an overestimation of T by less than 14% even for i
relatively thick slit plates. The effect of positive space charge inside the analyzer, the
influence of the electron repelling grid, the misalignment of the probe head with respect
to the magnetic field, and the attenuation of the incident ion current by some of the probe
components on T measurements is negligible. i
The instrumental study is followed by systematic measurements of T (as well as i
other parameters) in the Tore Supra SOL. This includes the scaling of SOL temperatures
and electron density with the main plasma parameters (such as the plasma density,
toroidal magnetic field, working gas, and the radiated power fraction). Except at very
high densities or in detached plasmas, SOL T is found to be higher than T by up to a i e
factor of 7. While SOL T is found to vary by almost two orders of magnitude, following i
the variation of the core temperatures, SOL T changes only little and seems to be e
decoupled from the core plasma. The first continuous T / T profile from the edge of the i e
confined plasma into the SOL is constructed using data from different tokamaks. It is
shown that T /T > 1 in the SOL but also in the confined plasma, and increases with i e
radius. Measurements of edge T /T in JET L-mode are analyzed. i e
The first evidence of poloidal asymmetry of the radial ion and electron energy
transport in the SOL is reported. Implications for ITER start-up phase are discussed.
Correlation of the asymmetries of SOL T and T measured from both directions along the i e
magnetic field lines with changes of the parallel Mach number is studied.
SOL T was measured for the first time in Tore Supra by charge exchange i
recombination spectroscopy (CXRS) and compared to RFA data. A factor of 4 higher T i
measured by CXRS is a subject of further analysis.
The segmented tunnel probe (STP) for fast measurements of SOL T and T has i e
been designed, built, calibrated by particle simulations, and used for the first time in a
large tokamak. Preliminary results from the STP measurements in Tore Supra are
presented. The disagreement between the currents to the probe electrodes predicted by
simulations and the measurements is addressed. Large floating potentials measured by the
side of the probe connected to the ICRH antenna are reported.
2Acknowledgement

I owe my thanks to many people who made this thesis possible. Foremost I thank my
thesis supervisor Jamie Gunn. His foresight and physical intuition has been a constant
guide throughout this entire work. Although my name appears alone on this thesis, he
certainly deserves to be a co-author.

I also thank my wife Hana for being so tolerant the past few months and my daughter
Judita for relatively calm nights.

Thanks are also due to Professor Gerard Bonhomme for his support as a thesis director.

I am greatly indebted to Jean Yves Pascal for his excellent technical expertise.

I thank the members of the jury for reading this thesis and for constructive comments.

I also record my appreciation for enlightening discussions with Vincent Basiuk, Sophie
Carpentier, Frederic Clairet, Yann Corre, Nicolas Fedorczak, Christel Fenzi, Xavier
Garbet, Thomas Gerbaud, Remy Guirlet, Philippe Ghendrih, Tuong Hoang, Frederic
Imbeaux, Philippe Lotte, Yannick Marandet, Philippe Moreau, Pascale Monier-Garbet,
Bernard Pegourie, Jean-Luc Segui, Jean-Claude Vallet and other members of the IRFM.

I would like to thank Michael Komm for running SPICE simulations, Patrick Tamain for
helping me with a simple edge power balance model and Richard Pitts for useful
comments.

I thank IRFM for supporting this work as well as my participations at the conferences,
workshops, summer schools and stays on MAST and JET. The leaders of the Tore Supra
task-force AP3 (Patrick Maget, Remy Guirlet and Pascale Hannequin) are gratefully
acknowledged for the experimental time offered for the measurements reported in this
thesis. I also thank CEA for financing my thesis.

I thank Yasmin Andrew for her help and many useful discussions during my stay on JET.

Finally, I would like to thank the members of the IPP Prague mechanical workshop for
the high quality work with which they manufactured the segmented tunnel probe for Tore
Supra.



3Contents

Chapter 1 – Introduction 6
Basic principle of magnetic confinement fusion 6
Why fusion 6
The principle of the nuclear fusion 8
Ignition 9
Magnetic confinement fusion 11
Tokamak 12
Progress in the tokamak research 14
ITER 15
Fusion power plant 17
Plasma boundary in tokamaks 18
Impurities 19
Limiter SOL 20
Radial drop of density and temperature in the SOL 21
The Debye sheath 22 he heat flux density and the heat transmission coefficient 23
Parallel density and potential gradients in the pre-sheath 24
Langmuir probes 25
Mach probe 27
Disturbance of the plasma by probe insertion 28
Tore Supra 30
Ion temperature measurements in the tokamak plasma boundary 33
The importance of SOL T measurements 33 iechniques for SOL T measurements 36 i
Ratynskaia probe 37
Katsumata probe 38
Rotating double probe 38
E×B probe 39
Plasma ion mass spectrometer (PIMS) 39
Langmuir probe with a thermocouple 40
Thermal desorption probe 40
Carbon resistance probe 40
Surface collection probe 41
Charge exchange recombination spectroscopy 42
Chapter 2 – Retarding field analyzer 43
RFA in the tokamak plasma boundary 43
RFA principle 45
Tor