Determination of neutral particle density and magnetic field direction from laser-induced Lyman-alpha fluorescence II - Two-photon excitation
Doppler-free two-photon excitation of Lyman-alpha fluorescence is investigated as a possible tool for measuring locally the neutral particle density and magnetic field direction in a tokamak. It is shown that if sufficient laser power is available, the desired information can, in a variety of cases, be inferred from the total intensity and from the polarisation of the fluorescence. Limitations arising from depolarising collisions are studied by generalising a previously developed theory for the collisional redistribution of light. An error analysis is performed to derive the expected experimental precision for various plasma conditions and laser energies. The conclusions of this analysis are similar to those of a previous study of one-photon excited fluorescence. They imply that with presently available laser energies the method would be restricted to the outer plasma regions, while application to the central regions would require further developments in laser technology. Various advantages and disadvantages of the two methods based on one-photon and two-photon excitation are discussed in detail.
Bibliographic Reference: Report: EUR-CEA-FC-1387 EN (1990) 75 pp.
Availability: Available from CEA, Département de Recherches sur la Fusion Contrôlée, Saint-Paul-lez-Durance (FR)
Record Number: 199011074 / Last updated on: 1994-12-01
Original language: en
Available languages: en