It has been estimated that plasma, the fourth state of matter, occupies approximately 99% of matter in the visible universe. As can be seen below the ionized gas that constitutes plasma has created unmatched beauty across the universe as well as here on earth. Solar prominences illustrate how plasma "tracks" magnetic field lines.
The aurora borealis, or northern lights, observed in the northernmost latitudes are also created by the flow of charged particles from the solar wind guided by earth's magnetic field in the Polar regions. In the southern hemisphere a similar display occurs, known as the aurora australis (or southern dawn). This flow of charged particles ionizes gases, such as oxygen, creating the swirling curtains of colored light.
The energy of our sun comes from fusion reactions between light elements. This converts mass to energy primarily in the form of radiation. Every second, the sun turns 600 million tons of hydrogen into helium, releasing an enormous amount of energy. The sun confines the hot plasma through gravitational forces. Fusion energy research has the goal of creating a star here on earth! Magnetic fields are used to confine the hot plasma within a toroidal vacuum vessel - see photographs of the START spherical torus and the ASDEX tokamak.
ITER represents the next major step in the search for a fusion energy source here on earth. The European Union, Japan, the People's Republic of China, India, the Republic of Korea, the Russian Federation and the USA have formed an international collaboration of scientists and engineers who will construct and operate the facility.
Plasma diagnostics systems will have important roles in machine safety, operational control, as well as in burning plasma physics understanding. ITER will be harsh environment with unprecedented fluxes of heat and radiation. Many diagnostic measurements will be extremely difficult - especially those involving visible radiation such as Thomson scattering, charge exchange recombination, motional Stark effect, etc. Millimeter wave diagnostics such as electron cyclotron emission and reflectometry are better suited to the harsh environment, but have their own set of challenges. The UCLA PDG recently performed an assessment of the planned low-field side reflectometer system. This system has the primary goal of measuring the electron density profile but will also contribute to the study of MHD/ fast-particle-driven modes, as well as plasma flow and microturbulence. Publications and presentations related to this work are provided below.
Advanced Interferometry (and Polarimetry) Techniques for Burning Plasmas: David L. Brower, Internation Conference on Burning Plasma Diagnostics - Varenna, Italy, September 24-28 2007
Conceptual Design for ITER Divertor Interferometer: D.L. Brower, 12th ITPA Topical Group Meeting on Plasma Diagnostics, Princeton Plasma Physics Laboratory, March 26-30, 2007
Evaluation of ITER Tangetial interferometer-Polarimeter (TIP) Conceptual Design: D.L. Brower, 12th ITPA Topical Group Meeting on Plasma Diagnostics, Princeton Plasma Physics Laboratory, March 26-30, 2007
Assessment of ITER LFS Reflectometer System: Tony Peebles,, 12th Meeting of ITPA Topical Group on Diagnostics PPPL, 3/26/2007
Divertor Interferometer Diagnostic for ITER: D.L. Brower, B.H. Deng and W.X. Ding, Review of Scientific Instruments 77, 10E911, 2006.
Relativistic effects on reconstruction of density profiles via reflectometry in ITER and potential for electron temperature measurements: L Zeng, W A Peebles, E J Doyle, T L Rhodes and G Wang , Plasma Phys. Control. Fusion 49 (2007) 1277-1287.
Reflectometry Applications to ITER: E.J. Doyle, K.W. Kim, J.H. Lee, W.A. Peebles, C.L. Rettig, T.L. Rhodes and R.T. Snider, Diagnostics for Experimental Thermonuclear Fusion Reactors, Plenum Press, pp 117-132, (1996).