Plasma Science: From Fundamental Research to Technological Applications (1995)
Chapter: Optical Diagnostics
New Experimental Capabilities
In any experimental science, and particularly in physics, advances in diagnostics consistently have led to new discoveries and frequently have opened up entirely new areas of research. Several new tools for plasma research are now becoming available. Some of these techniques have not been developed with plasma diagnostics in mind, but they can be expected to have significant impact on experimental plasma science. In many cases, progress is likely to require the collaboration of plasma physicists, solid-state physicists, and engineers. Much of this work will have important applications in other fields.
Use of Nanotechnology
Advances in nanotechnology are likely to have a profound impact on experimental plasma physics. Typical devices are miniature valves and mass analyzers. Techniques widely used in the semiconductor industry will enable the production of particle detectors, mass-sensitive energy analyzers, and magnetic and electric field probes with overall scale sizes smaller than 1 mm and active sensor areas less than 10 mm in diameter. These detectors will be capable of providing spatially resolved measurements on the scale of the Debye length and electron cyclotron radius in research plasmas with densities of the order of 1012 cm-3, electron temperatures of tens of electron volts and magnetic fields of 0.1 T. Such probes would produce a minimal perturbation of the plasma if their connections and supports were also microscopic (&2248;0.2 mm). It is likely to be possible to position many (e.g., 104 to 106) of these detectors on a lattice that could be moved within the plasma.
Optical Diagnostics
The recent discovery of giant Faraday rotation in magnetoactive crystals now enables the construction of magnetic field probes as small as 10 µm in diameter and less than 1 mm long. As a light beam traverses one of these small crystals, the plane of polarization of the light is rotated. Preliminary tests have demonstrated sensitivities of 1 G per degree of angular rotation and response times faster than 10-9 s. Such probes are immune to electrical pickup and are nonmetallic. Another important capability has been created by the discovery of the quantum-well effect in crystals. Quantum-well devices can now be fabricated into microscopic probes to measure the local amplitude of the electric field. Arrays of these optical probes could be used to diagnose the space-time behavior of the electric fields associated with plasma waves and currents.
