National Academies Press: OpenBook
« Previous: Quasilinear Effects and Single-Wave Stochasticity.
Suggested Citation:"Plasma Sources." National Research Council. 1995. Plasma Science: From Fundamental Research to Technological Applications. Washington, DC: The National Academies Press. doi: 10.17226/4936.
×
Page 139
Suggested Citation:"Plasma Sources." National Research Council. 1995. Plasma Science: From Fundamental Research to Technological Applications. Washington, DC: The National Academies Press. doi: 10.17226/4936.
×
Page 140

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

BASIC PLASMA EXPERIMENTS 139 Collisionless Heat Transport. Laboratory experiments have now explored the important question of how heat is transported in collisionless plasmas. These measurements involve the application of high-power microwave beams to generate hot electron tails in a nonuniform plasma. The qualitative features of this effect and the important scaling properties have been identified. They have helped to clarify the relevant theoretical issues in this area. Strong Langmuir Turbulence. One of the significant advances in the understanding of nonlinear plasma behavior has been the development of the concept of plasma-wave collapse and the associated spiky turbulence that frequently accompanies it. Several laboratory experiments, aimed at uncovering the microscopic dynamics of Langmuir-wave collapse, have used both electromagnetic driving and electron beams to trigger the collapse, of extended wave packets, which in turn produces strongly localized fields and density depletions or cavitons. More recently, the ionosphere has been used to demonstrate the ubiquitous nature of these phenomena and the important role they play when a plasma is driven by large- amplitude perturbations. Experimental Techniques and Capabilities Opportunities for advances in experimental physics are often linked to the development of new technologies. The effect of these technologies is twofold. First, they enable the creation of experimental conditions that permit the demonstration and isolation of important physical effects. In plasma science, this frequently involves both new means of plasma production and new means of plasma confinement. In addition, new technologies frequently lead to new diagnostic techniques and new means of processing data, which not only result in improved accuracy and precision but often result in new perspectives on the underlying physics. Plasma Sources Over the past 20 years, there has been substantial progress in the development of improved, quiescent plasma sources. Some of the first, "high- quality" plasmas used in basic research were created in Q machines (Q stands for "quies

BASIC PLASMA EXPERIMENTS 140 FIGURE 8.2 Experimental study of the penetration of a pulsed current into a magnetized plasma. Shown are the characteristic field lines, sheets, and tubes of the current density, J(r), at different times after a 100-ns (FWHM) current pulse is applied to a disk electrode (shown). These data are extracted from a dataset of 10,000 point measurements at each time step. Typical experiments involve studying 1000 such time steps. At 80 ns, the current penetrates a short distance from the positive electrode into the plasma, before turning back to the negative electrode located at the back endwall of the vacuum chamber. Little helicity is observed in this fountain-like current flow. As the current propagates (120 ns) two distinct current systems are observable: a closed azimuthal Hall current in regions where Jz 0 and field-aligned solenoidal plasma currents between the positive and negative electrodes. At 150 ns a current tube starts off-axis, where Jz ` 0 and JB ` 0, and exhibits strong helicity; i.e., it twists and knots in the right-hand direction. After the end of the applied current pulse, at 200 ns, the current lines detach and propagate away from the electrodes, and shown is a closed, singly-knotted, twisted current tube. Experiments like this, which illustrate the fully three-dimensional nature of the dynamics of the plasma response resulting from such a current pulse, have recently been made possible by the advent of fast, relatively inexpensive laboratory computers with large data handling capabilities. (Courtesy of R. Stenzel and M. Urrutia, University of California, Los Angeles.)

Next: Mechanical Probes »
Plasma Science: From Fundamental Research to Technological Applications Get This Book
×
Buy Paperback | $65.00 Buy Ebook | $54.99
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

Plasma science is the study of ionized states of matter. This book discusses the field's potential contributions to society and recommends actions that would optimize those contributions. It includes an assessment of the field's scientific and technological status as well as a discussion of broad themes such as fundamental plasma experiments, theoretical and computational plasma research, and plasma science education.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!