Helicons and their Surface Mode

By Charles R. Legendy

Introduction

The "second solution" of the helicon equation, the surface mode, has attracted much attention in recent years, since it arguably holds the key to the operation of the helicon plasma source.

The properties of the surface mode have been described in detail in the original helicon papers, back in the mid-sixties. However, these descriptions have been overlooked in many of the subsequent helicon-related publications. This probably happened because at the time helicons were just a curiosity, and not all their details were of interest. Whatever the reason, the outcome is that by now these descriptions of the surface mode are buried in the old papers, and are apparently unknown to many current contributors to the helicon literature. In fact, some of the old results are now (unfortunately) re-invented and published as if they were new.

I am writing this brief note in order to call attention to the original helicon papers. Incidentally, one message from these papers is, as will be seen, that the most crucial properties of the surface mode do not require that the frequencies and magnetic fields be within the Trivelpiece-Gould (TG) range; in other words, the terms "surface mode" and "TG mode" cannot be used interchangeably.

More...

Rod Boswell's Thesis

As part of the effort to make the original helicon references visible to the world, we have placed the complete text of Roderick Boswell's doctoral thesis on this website. Written some 14 years before the papers which made the physics community aware of the discovery, Boswell's thesis, as you will see, contains a full description of Boswell's ground-breaking experimental series on helicon plasma production. The thesis also contains a discussion of Landau damping as a possible mechanism of the rapid ion production in helicon plasmas (in Chapter 4), and the conclusion that Landau damping cannot explain what is observed in the lab.

Cover, Statement, Acknowledgements

Preface to the Internet edition by Rod Boswell

Abstract

Chapter 1 - Introduction and Literature Survey

1.1 Introduction - page 1.1
1.2 Compressional Alfven Waves - page 1.11
1.3 Helicon Waves 1.12
1.4 Electron-Cyclotron Waves - page 1.13
1.5 Discussion --page 1.14

Chapter 2 - Alfven Wave Experiments

2.1 Introduction - page 2.1
2.2 Theory - page 2.2
2.3 Experimental Apparatus - page 2.5
2.4 Diagnostic Equipment - page 2.10
2.5 Experimental Conditions - page 2.11
2.6 Wave Velocity - page 2.15
2.7 Wave Attenuation - page 2.18
2.8 Conclusions - page 2.20

Chapter 3- Theory of Helicon wave propagation

3.1 Propagation of Waves in an Infinite Medium of Uniform Density - page 3.1
3.2 Propagation in a Uniform Cylindrical Plasma - page 3.3
3.3 Energy Distribution of a Helicon Wave in a Uniform Cylindrical Plasma - page 3.6
3.4 Dependence of Helicon Wave Radial Structure on Electron Inertia - page 3.10
3.5 Dispersion of a Standing Helicon Wave in a Non-Uniform Resistive Cylindrical Plasma, Including the Effects of Electron Inertia
(a) Conducting Boundaries - page 3.27
(b) Rigid Non-Conducting Cylindrical Boundaries - page 3.27
Appendix A - page 3.37

Chapter 4 - The Case of Low Resistivity plasmas

Introduction - page 4.1
4.2 Experimental Considerations - page 4.1
4.3 Collisionless Damping Mechanisms - page 4.14

Chapter 5 - Experimental Apparatus

5.1 Introduction - page 5.1
5.2 Large System - page 5.1
5.3 The Solenoid - page 5.7
5.4 Production of the R .F . Magnetic Field - page 5.11
5.5 Small System - page 5.18

Chapter6 - Diagnostic Procedure and Theory

6.1 Introduction - page 6.1
6.2 Magnetic Probes - page 6.1
6.3 Langmuir Floating Double Probes - page 6.6
6.4 8 mm Microwave Interferometer - page 6.11
6.5 Spectroscopic Measurements - page 6.19
6.6 Spectroscopic Discussion - page 6.24

Chapter7 - Results and Discussion

Introduction - page 7.1
7.2 Probe Measurements of Magnetic Field - page 7.2
7.3 Langmuir Probes - page 7.11
7.4 Microwave Interferometer - page 7.12
7.5 Interpretation of Spectroscopic Measurements - page 7.17
7.6 Discussion - page 7.23
7.7 Possible Studies Arising from this Work - page 7.34

References