During two last decades the ideas and methods of computerized tomography (CT) have found wide application in different fields of plasma physics1'2. Having in mind many other diagnostic tools and techniques applicable in studying of plasma processes one may conclude that the CT is especially efficient when the whole 2D image of the plasma cross—section (and sometimes even 3D image) can be derived from the set of projections measured simultaneously. Unique possibilities of that kind play the3 nost important role in the situations with magnetic reconnection . Magnetic reconnection in high-conductivity plasma is the fundamental physical process and the basis of various phenomena of plasma physics and astrophysics. Solar flares, magnetospheric , sub.storms, disruption processes in tokamaks, cardinal structural changes in the reversed-field pinches, plasma focus devices compact tori etc are the typical examples. As a result of reconnection the transfer of the excess magnetic energy into kinetic and thermal energies of plasma, into radiation and also into the energy of accelerated particles takes place. Physicists often distinguish two types of magnetic reconnection: spontaneous and forced. Laboratory plasmas and the natural processes in outer space are usually closer to a spontaneous reconnection. In that case a definite accumulation of magnetic energy precedes the reconnection and the process similar to tearing modes develops at that initial stage. The forced reconnection due to an external forces is more convenient for purposeful experimental observation of recon— ection phenomena, e.g. by creation of current sheets '8.It is also more suitable for theoretical description and numerical simulation. Some independent calculations and checks of the diagnostic CT results are possible in that case. We restrict the scope of this paper to the two examples of reconnection investigations by tomographic methods related firstly to spontaneous and secondly to forced reconnection. The Part I presents basic concepts and somewhat puzzling nowadays situation with the socalled saw tooth problem arising in tokamak devices. An advanced radial modulators CT algorithm of 2D image reconstruction from limited views chord—integrated plasma emission measurements is described. This algorithm can be recommended as an efficient diagnostic tool for the future study of magnetic reconnection in various laboratory plasmas.The novel version of Monte Carlo CT reconstruction suitable for spectrotomographic activity is also described. The Part II presents our own spectrotomographic experiment with the plane pinch current sheet in the nonlinear regime.

Date Published: 3 November 1992
PDF: 17 pages
Proc. SPIE 1843, Analytical Methods for Optical Tomography, (3 November 1992); doi: 10.1117/12.131872

Published in SPIE Proceedings Vol. 1843:
Analytical Methods for Optical Tomography
Gennady G. Levin, Editor(s)