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UNIVERSITE TOULOUSE III – PAUL SABATIER U.F.R…..

T H E S E en vue de l’obtention du

DOCTORAT DE L'UNIVERSITE DE TOULOUSE délivré par l’Université Toulouse III – Paul Sabatier

Discipline :... présentée et soutenue

par

Ella Marion SCIAMMA

le 27 novembre 2007

Titre :

Développement d’un Outil de Diagnostique par Spectroscopie des Plasmas Utilisant des Modèles Collisionel-Radiatifs

et son Application à Différentes Décharges Plasmas

pour la Détermination de la Température Electronique et de la Densité des Neutres Directeurs de thèse :

Leanne C. PITCHFORD (France)

Gary A. HALLOCK et Roger D. BENGTSON (USA) JURY

M. Gary A. HALLOCK, Président M. Roger D. BENGTSON Mme. Leanne C. PITCHFORD

M. Vincent PUECH M. Michael F. BECKER

M. Edward J. POWERS M. Richard FOURNIER

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 

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           

 

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iv

Acknowledgments

First I would like to deeply thank Roger Bengtson, my supervisor in the Physics Department who made me discover “the wonderful world of physics” and guided and supported me during the good and bad days of my PhD. His way of thinking, like a physicist and not like an engineer, has made me look at problems with a new eye.

I would also like to thank Gary Hallock, my supervisor in the Electrical and Computer Engineering Department who helped me enter the UT graduate school and introduced me to Roger Bengtson. For his continuous interest and support for the last five years I am grateful. My thanks go to Leanne Pitchford as well, my supervisor at the Université Paul Sabatier, for helping me start a cotutelle de thèse with France and keep me connected to the French scientific community; her interest and support have made a difference in the last years of my thesis.

I thank my reviewers Vincent Puech and Chris Sneden for their patience and their understanding and for accepting to read my dissertation in such a short time and give me feedback so quickly. I also thank Michael Becker, Edward Powers and Richard Fournier for accepting to be on my dissertation committee.

This research would not have been possible without the financial support of ASPL at NASA Johnson Space Center and Ad Astra Rocket company and especially without the passion of Franklin Chang-Diaz. From ASPL, I’d like to thank Franklin Chang-Diaz, Verlin Jacobson, Jacob Chancery, Greg McCaskill, Chris Deline, Andrew Ilin, and Jared Squire who helped me with the data acquisition and processing on the VASIMR

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experiments. I also thank Chris Dobson, Greg Chavers and Jonathan Jones from NASA Marshall Space Flight Center for their help with the interferometer data.

I would like to thank Boris Breizman and Alexey Arefiev for their insights on the theory of the helicon and ICRH operation and their suggestions. I am also grateful for the opportunity to work in Japan in Takashi Fujimoto’s group and in particular with Atsushi Iwamae. Many thanks go to Motoshi Goto, Keiji Sawada, Amy Keesee and Bill Rowan who provided me with the collisional-radiative models for helium neutrals, hydrogen neutrals, argon neutrals and argon ions used in this research. I would also like to thank Karl Umstadter who provided me with the Archimedes’ LabVIEW program to control my spectrometer.

There wouldn’t be a 12th floor lab without Keith Carter whom I thank for always being there when you need him and fixing things in seconds when you’ve been stuck on them for hours. I also want to thank Jack Clifford, from the machine shop, who spent endless hours working with me on yet another fiber holder. My thanks also go to Sharee Aery, Maria Aguirre and Teresa Garza for making me feel that I belonged in the Physics Department, and to Melanie Gulick for keeping me in the loop of the Electrical Engineering Department requirements.

Thanks to Kevin Lee and Ken Gentle who made it possible for me to take data on the Helimak experiment and include it in my research, and Charles Lee and Dan Berisford, my labmates, for their assistance with the Helicon experiment but also for their friendship during the five years I spent at UT. I also thank Hernan Quevedo, Jeremy Murphy, Kevin Casey, Guangye Chen, Harish Subbaraman, Daniela Kraft, Henry Wu,

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Rainer “sparky” Hoerlein, and Cindy Ginestra, the rest of Roger Bengtson’s crew for their discussions and friendship.

I would like to thank Zonta international for its financial support but also and most importantly the women of the Zonta Club of Austin for their friendship and moral support. Many thanks go to my karate club, my tango club and the Austin tango community as well without which I would not have stood the stress level of graduate school so well. I am also grateful for Lubo and Rachelle (and Milena), Irina and David, Georgia, Chuck, Kyungjoo and kt’s friendship and support.

Last but not least I am deeply thankful for my husband Dan O’Brien for his endless support and his patience during the long days of writing, for his family and for my parents and siblings for believing in me in the first place.

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Plasma Spectroscopic Diagnostic Tool Using Collisional-Radiative Models

and its Application to Different Plasma Discharges for

Electron Temperature and Neutral Density Determination

Publication No._____________________

Ella Marion Sciamma, Ph.D. 1The University of Texas at Austin, 2007

2Université Paul Sabatier, Toulouse, France (joint Ph.D.), 2007

Co-supervisor: Gary A. Hallock1 Co-supervisor: Roger D. Bengtson1 Co-supervisor: Leanne C. Pitchford2

A spectroscopic diagnostic tool has been developed to determine the electron temperature and the neutral density in helium, hydrogen and argon plasmas from absolutely calibrated spectroscopic measurements. For each gas, a method of analysis which uses models specific to each species present in the plasma (neutral atom or singly ionized atom) has been defined. The experimental electron density is used as an input parameter to the models, and the absolutely calibrated spectroscopic data are processed beforehand to obtain the populations of the upper excited levels corresponding to the observed spectral lines.

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For helium plasmas, the electron temperature is inferred from the experimental helium ion excited level p = 4 population using a corona model, and then the neutral density is determined from the experimental helium neutral excited level populations using a collisional-radiative model for helium neutrals. For hydrogen plasmas, combinations of the electron temperature and the neutral density are determined from the experimental hydrogen neutral excited level populations using a collisional-radiative model specific to hydrogen atoms. For argon plasmas, the electron temperature is inferred from the experimental argon ion excited level populations using a collisional-radiative model for argon ions, and then the neutral density is determined from the experimental argon neutral excited level populations using a collisional-radiative model for argon neutrals.

This diagnostic tool was applied to three experiments with different geometries and plasma conditions to test the validity of each data analysis method. The helium and hydrogen data analysis methods were tested and validated on helium and hydrogen plasmas produced in the VASIMR experiment, a plasma propulsion system concept. They gave electron temperatures and neutral densities that were consistent with other diagnostics and theory. The argon diagnostic tool was tested on argon plasmas produced in the VASIMR experiment, the Helimak experiment and the Helicon experiment. The electron temperature and neutral density obtained on both the Helimak and the Helicon experiments were consistent with other diagnostics and with theory, and validated the method of analysis. An impurity problem on the VASIMR experiment made it difficult for the data analysis to be validated.

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Développement d’un Outil de Diagnostique par Spectroscopie des Plasmas Utilisant des Modèles Collisionel-Radiatifs

et son Application à Différentes Décharges Plasma

pour la Détermination de la Température Electronique et de la Densité des Neutres

Cette thèse décrit les outils de spectroscopie utilisés et la méthode d’analyse développée pour obtenir la température des électrons et la densité des neutres à partir des spectres d’émission mesurés dans une décharge plasma. La spectroscopie est une méthode non intrusive et permettant des mesures à différentes positions axiales et radiales dans le plasma ; d’où son intérêt comparée à des sondes généralement fixes et qui, surtout, pénètrent et interagissent avec le plasma. A partir des raies d’émission d’une décharge plasma observée par spectroscopie, il est possible, après calibration absolue, de calculer la densité de population des états excités des différents éléments constituant le plasma (ions et neutres). Ces populations expérimentales sont alors comparées à leurs prédictions théoriques, calculées par des modèles mathématiques, afin d’estimer la température des électrons puis la densité des neutres par minimisation de la déviation entre expérience et théorie. Nous utilisons des modèles dits collisionel-radiatifs qui, pour un élément donné, prennent en compte les processus radiatifs mais aussi collisionels pour calculer la population des états excités de cet élément.

Dans notre méthode d’analyse, pour des plasmas produits à partir de gaz d’hélium ou d’argon, la température électronique est estimée par comparaison des populations expérimentales des états excités des ions dans le plasma aux résultats d’un modèle spécifique à ces ions. La densité des neutres, elle, est estimée par comparaison des

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populations expérimentales des états excités des neutres aux résultats d’un modèle spécifique à ces atomes neutres. Pour des plasmas produits à partir de gaz d’hydrogène, la comparaison des populations expérimentales des états excités de l’atome d’hydrogène à leur prédictions théorique calculées par un modèle spécifique aux atomes d’hydrogène ne permet d’obtenir qu’un ensemble de combinaisons [température électronique/densité des neutres] possibles. Chaque modèle collisionel-radiatif étant spécifique à un élément chimique donné, il faut donc changer de modèle si l’on change le gaz utilisé pour produire le plasma. Nous avons par conséquent développé une méthode d’analyse qui utilise trois séries de modèles pour pouvoir l’appliquer à ces trois gaz : l’hélium, l’hydrogène et l’argon.

Nous avons appliqué notre outil de diagnostique à trois systèmes expérimentaux différents. Premièrement, des décharges plasma d’hélium, d’argon et d’hydrogène ont été étudiées sur l’expérience VASIMR, un prototype de système de propulsion électromagnétique. Deuxièmement, une décharge plasma toroidale d’argon a été étudiée sur l’expérience Helimak qui a pour but d’étudier les perturbations présentes dans les plasmas de type fusion magnetique. Enfin des décharges plasma d’argon ont été étudiées sur deux configurations différentes de l’expérience Hélicon, qui a pour but l’étude des modes de fonctionnement des antennes hélicon. Nous présentons l’analyse effectuée sur ces trois expériences et les résultats obtenus, dans la deuxième partie de cette thèse. Les températures électroniques et les densités des neutres obtenues par notre outil de diagnostique spectroscopique concordent avec les autres diagnostiques traditionnels utilisés sur ces expériences (sondes), et avec la théorie.

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Table of Contents

List of Tables ... xvi

List of Figures... xix

List of Equations ... xxii

1. INTRODUCTION ... 1

1.1. Motivation: the physics of the VASIMR experiment ...2

1.2. Objectives: development of a spectroscopic diagnostic tool ...5

1.3. Organization of the dissertation ...7

2. DIAGNOSTICS ... 9

2.1. Spectroscopy ...9

2.1.1. Observation system...9

2.1.2. Data acquisition system ...13

2.1.2.1. OOIBase32 software: used for Helimak and Helicon experiments...13

2.1.2.2. OOILVD software: used for VASIMR experiment ...14

2.1.3. Calibration...17

2.2. Other diagnostics used in the data analysis...24

2.2.1. VASIMR experiment ...24 2.2.1.1. VX-30 ...24 2.2.1.2. VX-50 ...24 2.2.1.3. VX-100 ...25 2.2.2. Helimak experiment...25 2.2.3. Helicon experiment...26

3. DATA ANALYSIS... 28

3.1. Experimental population calculation ...29

3.1.1. Principle ...29

3.1.2. MATLAB code ...31

3.2. Plasma equilibriums and modeling of populations...32

3.2.1. Partial Local Thermodynamic Equilibrium (LTE) ...33

3.2.2. Corona Equilibrium (CE)...35

3.2.3. Collisional-radiative (CR) model...37

3.2.3.1. Differential rate equations...37

3.2.3.2. Quasi-steady-state solution...38

3.2.4. Comparison between LTE, CE and CR and application to our analysis...39

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3.3.1. CE model for ionized helium to determine the electron

temperature Te...42

3.3.1.1. Development of the method...42

3.3.1.2. Final method applicable to singly ionized helium in helium plasmas...45

3.3.2. CR model for neutral helium to determine the neutral density nz-1(1)...46

3.3.2.1. Development of the method...46

3.3.2.2. Final method applicable to neutral helium in helium plasmas...50

3.4. Method of data analysis for hydrogen plasmas...51

3.4.1. CR model for neutral hydrogen to determine [Te / nz-1(1)] ...51

3.4.1.1. Development of the method...51

3.4.1.2. Final method applicable to neutral hydrogen in hydrogen plasmas ...55

3.5. Method of data analysis for argon plasmas...56

3.5.1. ADAS CR model for ionized argon to determine Te...56

3.5.1.1. Development of the method...56

3.5.1.2. Final method applicable to singly ionized argon in argon plasmas...65

3.5.2. CR model for neutral argon to determine nz-1(1) ...66

3.5.2.1. Development of the method...66

3.5.2.2. Final method applicable to neutral argon in argon plasmas ...74

3.6. Applications of the data analysis methods...76

4. APPLICATION TO VASIMR EXPERIMENTS... 77

4.1. VASIMR experiment: VX ...77

4.2. VX-30 with helium ...80

4.2.1. Experimental setup...80

4.2.2. Experimental data ...82

4.2.3. Data analysis and results...84

4.2.3.1. Experimental upper excited level populations calculation...84

4.2.3.2. Electron temperature determination using the He II CE model ...86

4.2.3.3. Helium neutral density determination using the He I CR model ...87

4.2.4. Discussion ...89

4.3. VX-50 with hydrogen ...92

4.3.1. Experimental setup...92

4.3.2. Experimental data ...94

4.3.3. Data analysis and results...97

4.3.3.1. Experimental upper excited level populations calculation...97

4.3.3.2. First estimate of Te from population ratios using LTE ...98

4.3.3.3. Determination of [Te , n0] combinations using the H I CR model ....99

4.3.4. Discussion ...101

4.4. VX-100 with argon ...103

4.4.1. Experimental setup...103

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4.4.3. Data analysis and results...108

4.4.3.1. Experimental upper excited level populations calculation...108

4.4.3.2. Electron temperature determination using the Ar II ADAS CR model...109

4.4.3.3. Argon neutral density determination using the Ar I CR model ...117

4.4.4. Discussion ...119

5. APPLICATION TO HELIMAK EXPERIMENT ... 121

5.1. Experimental setup...122

5.2. Experimental data ...124

5.3. Data analysis and results...127

5.3.1. Experimental upper excited level populations calculation ...127

5.3.2. Electron temperature determination using the Ar II ADAS CR model ...129

5.3.3. Argon neutral density determination using the Ar I CR model ...133

5.4. Discussion ...135

6. APPLICATION TO HELICON EXPERIMENT ... 137

6.1. Experimental setup...138

6.2. Initial configuration of the helicon experiment ...139

6.2.1. Experimental setup specific to the initial configuration ...139

6.2.2. Experimental data ...141

6.2.3. Data analysis and results...144

6.2.3.1. Experimental upper excited level populations calculation...144

6.2.3.2. Electron temperature determination using the Ar II ADAS CR model...146

6.2.3.3. Argon neutral density determination using the Ar I CR model ...149

6.2.4. Discussion ...152

6.3. New configuration of the helicon experiment ...153

6.3.1. Experimental setup specific to the new configuration...153

6.3.2. Experimental data ...155

6.3.3. Data analysis and results...160

6.3.3.1. Experimental upper state populations calculation ...160

6.3.3.2. Electron temperature determination using the Ar II ADAS CR model...164

6.3.3.3. Argon neutral density determination using the Ar I CR model ...168

6.3.4. Discussion ...171

7. SUMMARY... 173

APPENDIX A:

MATLAB subroutines to preprocess the spectral lines

... 180

processdata_He_new.m ...180

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xiv processdata_ArII_new.m ...186 processdata_ArI_new.m...194 find_peak_new.m...199 lines_process_new.m ...200 baseline_new.m...201 calibline_new.m ...204 cleanlines_new.m...205 fit_absint_new...206 He_gaussiandef_new.m ...210 H_gaussiandef_new.m ...212 ArII_gaussiandef_new.m ...214 ArI_gaussiandef_new.m ...218 AbsInt_new.m...221 pop_new.m...222 sumpop_new.m ...224 averagepop_new.m ...226 ADAS_Ne_new.m ...227 ADAS_expne_new.m ...228 ADAS_Te_new.m...229 Te_series_new.m ...230

APPENDIX B:

Cross section and rate coefficient calculation for the He II excited level corona model

... 231

APPENDIX C:

ArII ADAS CR model population rate tables

... 238

APPENDIX D:

Ar I CR model MATLAB subroutines

... 241

ArICR.m...241 arcrmodel_new.m...244 calcul_EEDF.m...253 Sione.m ...254 Srec1e.m...255 Srec2e.m...256 Sexce.m...257 Sdeexe.m...259 Sionth.m...259 Sreci.m ...260 Siona.m ...261 Sexcth.m...262 Sdeexth.m...263 d_erf.m ...264 gammp.m ...264 gser.m...265

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xv gammln.m ...266 gamcf.m ...267

REFERENCES ... 268

VITA ... 273

CV ... 274

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List of Tables

Table 3.1 Comparison of the gases, species and methods of data analysis used on the three experiments under investigation in this dissertation...41 Table 3.2 Ar I ADAS CR model population table for level parent 13. Te is in [eV]

and ne is in [cm-3] ...59

Table 3.3 Index, electron configurations and total angular momentums of the Ar I ADAS CR model level parents of interest in our analysis...61 Table 3.4 Formulas to calculate the total experimental Ar II ADAS CR model level

parents populations. ...64 Table 3.5 Indexes, designations, and excitation energies of the 65 effective energy

levels considered in the Ar I CR model ...68 Table 3.6 Formulas to calculate the total experimental Ar I CR model level parents

populations...72 Table 4.1 VX-30, VX-50 and VX-100 operation parameters and characteristics ...79 Table 4.2 Absolute radiances of the helium neutral and ion lines of interest

in VX-30 ...85 Table 4.3 Upper excited level populations of the helium neutral and ion lines of

interest in VX-30...85 Table 4.4 Absolute radiances and upper excited level populations of the Dδ, Dε and

Dζ Balmer lines during the recombining phase of VX-50 ...97 Table 4.5 Different [n0 , Te] solutions for the CR best fit of the experimental upper

excited level populations...100 Table 4.6 Averaged total experimental population, neutral density, and

corresponding degree of ionization obtained for each Ar I level parent of interest, in VX-100’s argon helicon discharge ...118 Table 5.1 Absolute radiances and upper excited level populations of the Ar II lines of interest in the Helimak argon plasma discharge ...128 Table 5.2 Absolute radiances and upper excited level populations of the Ar I lines of

interest in the Helimak argon plasma discharge ...129 Table 5.3 Averaged Ar II populations and total experimental level parent populations for the three Ar II ADAS CR model level parents of interest in the Helimak argon discharge ...130 Table 5.4 Ar II ADAS CR population columns for the measured Helimak electron

density ...131 Table 5.5 Level parent electron temperatures and averaged Helimak plasma electron

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Table 5.6 Averaged Ar I populations and total experimental level parent populations for the four Ar I CR model level parents of interest in the Helimak argon discharge ...133 Table 5.7 Neutral density for each Ar I level parent of interest and averaged plasma

neutral density in the Helimak experiment ...134 Table 6.1 Operating parameters for the initial configuration of the helicon

experiment...140 Table 6.2 Absolute radiances and upper excited level populations of the Ar II lines

of interest in the initial helicon experiment argon plasma

discharge ...145 Table 6.3 Absolute radiances and upper excited level populations of the Ar I lines

of interest in the initial Helicon experiment argon plasma

discharge ...146 Table 6.4 Averaged Ar II populations and total experimental level parent populations for the three Ar II ADAS CR model level parents of interest in the initial Helicon experiment argon discharge ...147 Table 6.5 Ar II ADAS population columns for the measured electron density in the

initial Helicon experiment argon plasma discharge, under the helicon antenna ...148 Table 6.6 Level parent electron temperatures and averaged plasma electron

temperature in the initial Helicon experiment argon discharge ...149 Table 6.7 Averaged Ar I populations and total experimental level parent populations

for the three Ar I CR model level parents of interest in the initial Helicon experiment argon discharge ...150 Table 6.8 Neutral density for each Ar I level parent of interest and averaged plasma

neutral density in the initial Helicon experiment argon plasma discharge, under the helicon antenna ...151 Table 6.9 Operating parameters for the new configuration of the Helicon

experiment...154 Table 6.10 Absolute radiances and upper excited level populations of the Ar II lines of interest in the new Helicon experiment argon plasma discharge, at the first view port location ...162 Table 6.11 Absolute radiances and upper excited level populations of the Ar I lines of

interest in the new Helicon experiment argon plasma discharge, at the first view port location ...162 Table 6.12 Absolute radiances and upper excited level populations of the Ar II lines of interest in the new Helicon experiment argon plasma discharge, at the second view port location ...163 Table 6.13 Absolute radiances and upper excited level populations of the Ar I lines of

interest in the new Helicon experiment argon plasma discharge, at the second view port location ...163

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Table 6.14 Averaged Ar II populations and total experimental level parent populations for the three Ar II ADAS CR model level parents of interest in the new Helicon experiment argon discharge, at the first view port location...165 Table 6.15 Averaged Ar II populations and total experimental level parent populations for the three Ar II ADAS CR model level parents of interest in the new Helicon experiment argon discharge, at the second view port location...165 Table 6.16 Ar II ADAS population columns for the measured electron density in the

new Helicon experiment argon plasma discharge, at the first view port location ...166 Table 6.17 Ar II ADAS population columns for the measured electron density in the

new Helicon experiment argon plasma discharge, at the second view port location ...166 Table 6.18 Level parent electron temperatures and averaged plasma electron

temperature in the new Helicon experiment argon discharge, at the first view port location ...167 Table 6.19 Level parent electron temperatures and averaged plasma electron

temperature in the new Helicon experiment argon discharge, at the second view port location ...167 Table 6.20 Averaged Ar I populations and total experimental level parent populations

for the four Ar I CR model level parents of interest in the new Helicon experiment argon discharge, at

the first view port location ...169 Table 6.21 Averaged Ar I populations and total experimental level parent populations

for the four Ar I CR model level parents of interest in the new Helicon experiment argon discharge, at the second view port location...169 Table 6.22 Neutral density for each Ar I level parent of interest and averaged plasma

neutral density in the new Helicon experiment argon plasma

discharge, at the first view port location...170 Table 6.23 Neutral density for each Ar I level parent of interest and averaged plasma

neutral density in the new Helicon experiment argon plasma

discharge, at the second view port location ...170 Table B1 Transition probabilities from He II excited level p = 4 and other parameters

used for their calculation...237 Table C1 Ar II ADAS CR model population rate table for level parent 13 ...238 Table C2 Ar II ADAS CR model population rate table for level parent 14 ...239 Table C3 Ar II ADAS CR model population rate table for level parent 15 ...240

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xix

List of Figures

Fig. 2.1 HR2000 optical bench components...11 Fig. 2.2 Spectral lines from a Helium discharge lamp showing the spherical

aberrations of the spectrometer...12 Fig. 2.3 Spectral radiance of the Optronics Laboratory calibration sphere source

model OL 450-2...18 Fig. 2.4 Optical setup for calibrating the spectrometer...19 Fig. 2.5a Sphere source emission spectra for different integration times

in [counts] ...20 Fig. 2.5b Sphere source emission spectra for different integration times

in [counts s-1]...21 Fig. 2.6 Unique sphere source radiation spectrum...22 Fig. 2.7 Calibration factors as a function of wavelength for our HR2000

spectrometer...22 Fig. 2.8 Optical setup for the three experiments studied ...23 Fig. 2.9 Plasma radiating volume observed ...23 Fig. 2.10 Radial view of the helicon experiment and the axial Langmuir probe inside

the chamber...26 Fig. 2.11 Axial view of the helicon experiment and the axial Langmuir probe inside

the chamber...27 Fig. 3.1 Illustration of the three steps to obtain the absolute radiance of a line ...29 Fig. 3.2 Schematic of the dominant population and depopulation processes in corona

equilibrium...35 Fig. 3.3 Neutral helium energy level diagram used in the He I CR model...47 Fig. 3.4 Argon energy level diagram and lower-lying effective levels considered in

the Ar I CR model...69 Fig. 4.1 Principle of the VASIMR experiment ...78 Fig. 4.2 Magnetic field profile in VX-30 and VX-50 ...79 Fig. 4.3 VX-30 experiment magnetic cells configuration and diagnostics location...81 Fig. 4.4 Spectra of the helium helicon discharge radiation in VX-30 after 1000 ms,

for 3 ms (top) and 200 ms (bottom) integration...82 Fig. 4.5 Averaged spectrum of the helium helicon discharge in VX-30, 1000 ms after

the start of the helicon pulse ...83 Fig. 4.6 Averaged electron density ne from the line integrated 70, 90, and 110 GHZ

interferometer measurements...84 Fig. 4.7 Comparison between CR model populations and experimental populations

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Fig. 4.8 Best fit between the experimental and CR calculated 1S and 1D series upper excited level populations...88 Fig. 4.9 Influence of the metastable populations in the CR model excited level

populations calculation ...90 Fig. 4.10 VX-50 experiment magnetic cells configuration and diagnostics location...93 Fig. 4.11 Time sequence of the power applied to the helicon and ICRH antennas

in VX-50 ...93 Fig. 4.12 Time evolution of the electron density during the different stages of

the VX-50...95 Fig. 4.13 Representative spectra of the deuterium plasma produced in the VX-50 for

the three observed plasma phases ...96 Fig. 4.14 a) Balmer lines Dδ, Dε, Dζ observed during the recombining plasma phase,

b) upper excited level population to statistical weight ratios for the Dδ, Dε, Dζ Balmer lines ...98 Fig. 4.15 Comparison between CR model populations and experimental population to

statistical weight ratios for Te = 1.2 eV and various neutral

densities...100 Fig. 4.16 Time evolution of the pressure at the gas injection plate during VX-50’s

different stages ...102 Fig. 4.17 Picture of the VX-100 chamber and location of the diagnostics...103 Fig. 4.18 Time sequence of the power applied to the helicon and ICRH antennas in

VX-100 ...104 Fig. 4.19 Spectrum of the helicon + ICRH discharge in VX-100...106 Fig. 4.20 Time resolved spectra of the VX-100 discharge during the different stages of

its operation...106 Fig. 4.21 Electron density ne at the spectrometer location, extrapolated from the

32 GHz interferometer measurements for shot 0705310077...108 Fig. 4.22 Time evolution of the calibrated radiances of the hydrogen Balmer line at

486 nm and the argon ion line at 480 nm...111 Fig. 4.23 Time evolution of the electron density ne and the averaged electron

temperature Te in the VX-100 argon plasma discharge ...113

Fig. 5.1 The Helimak chamber ...123 Fig. 5.2 Cross section of the Helimak vessel ...123 Fig. 5.3 Averaged helimak argon plasma spectrum...125 Fig. 5.4a Averaged electron density radial profile in the Helimak discharge...126 Fig. 5.4b Averaged electron temperature radial profile in the Helimak discharge...126 Fig. 6.1 Schematic diagram of the Helicon experiment...138 Fig. 6.2 Picture of the plasma discharge in the initial helicon experiment...141 Fig. 6.3 Averaged argon plasma spectrum in the initial helicon experiment ...142 Fig. 6.4 a) Electron temperature radial profile and b) Electron density radial profile in the initial helicon experiment...143 Fig. 6.5 Picture of the plasma discharge in the new Helicon experiment...154

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Fig. 6.6 Radial profiles of a) the 480 nm Ar II spectral line, and b) the 738 nm Ar I spectral line observed at the first view port ...156 Fig. 6.7 Radial profiles of a) the 480 nm Ar II spectral line, and b) the 727 nm Ar I

spectral line observed at the second view port...157 Fig. 6.8 Averaged argon plasma spectrum at the central radial position of the first

view port ...158 Fig. 6.9 Averaged argon plasma spectrum at the central radial position of the second

view port ...159 Fig. 6.10 Electron density profiles in the new Helicon experiment at the first (in blue)

and second (in pink) view ports ...159 Fig. B1 Cross section and rate coefficient for the electron impact excitation from the

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List of Equations

Eq. 3.1 Radiant flux of a line ...30 Eq. 3.2 Absolute radiance of a line ...30 Eq. 3.3 Upper excited level population from the line radiance ...30 Eq. 3.4 Boltzmann distribution ...33 Eq. 3.5 Saha-Boltzmann distribution ...34 Eq. 3.6 Saha-Boltzmann distribution (alternate expression) ...34 Eq. 3.7 Upper excited level population in corona equilibrium ...36 Eq. 3.8 (a and b) Excitation rate coefficient calculation...36 Eq. 3.9 Temporal development of the population in Collisional-Radiative regime ...37 Eq. 3.10 Quasi-steady-state approximation ...38 Eq. 3.11 Quasi-steady-state solution of a CR set of differential equations ...38 Eq. 3.12 Time derivative of the ground state and ion densities in CR ...39 Eq. 3.13 Collisional-radiative ionization rate coefficient ...39 Eq. 3.14 Collisional-radiate recombination rate coefficient ...39 Eq. 3.15 Electron impact excitation of the 4p state from the 1s ground state ...43 Eq. 3.16 Electron impact excitation cross section calculation for (1s_4p)...43 Eq. 3.17 Helium ion upper excited level population in corona equilibrium...44 Eq. 3.18 He I CR model first formulation for the population...48 Eq. 3.19 (a, b) Reduced recombination and ionization population coefficients ...49 Eq. 3.20 H I CR model quasi-steady-state solution of the differential equations...52 Eq. 3.21 Ar II CR model quasi-steady-state solution of the differential equations ...58 Eq. 3.22 Simplified Ar II CR model quasi-steady-state solution ...58 Eq. 3.23 (a, b, c) Interpolation of the Ar II CR model population rate tables ...59, 60 Eq. 3.24 Population calculation from the population rates...61 Eq. 3.25 Interpolation of the electron temperature from the Ar II CR model tables ....63 Eq. 3.26 Degree of ionization calculation...73 Eq. 3.27 Neutral density extrapolation from the Ar I CR model populations ...73 Eq. 4.1 Electron temperature calculation using a Boltzmann plot...98 Eq. 4.2 Electron density extrapolation from the 32GHz interferometer measurements

assuming a frozen flow ...107 Eq. 4.3 Definition of the electron density in terms of the argon ion density and the

proton density in VX-100 ...110 Eq. 4.4 Flux conservation ...114 Eq. 4.5 ICRH to helicon electron density ratio assuming flux conservation...115 Eq. 4.6 ICRH to helicon electron density ratio if all ions in VX-100 are Ar II...115 Eq. 4.7 Experimental ICRH to helicon electron density ratio ...116 Eq. 4.8 Calculation of the Ar II fraction in the electron density...116

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Eq. B1 He II excited level p = 4 population in corona equilibrium...231 Eq. B2 He II electron impact excitation cross section calculation for (1s_4p)...232 Eq. B3 He II electron impact excitation rate coefficient calculation...232 Eq. B4 Relative collision velocity and electron velocity for an electron impact

excitation of the He II ground state...233 Eq. B5 Simplified formula for the He II electron impact excitation rate coefficient

calculation ...234 Eq. B6 Transition probabilities calculation from oscillator strengths ...236 Eq. B7 Statistical weight calculation ...237 Eq. B8 Transition wavelength calculation ...237

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 

 

                                                                                                                                      

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                                                                                                                                            

 

 

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                                                                                                                          

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                                                                                                                                          

(37)

     

 

                                                                                                         

(38)

                                                                                

 

                                                 

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                                                                                                        

 

                                                     

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