Robust line density measurements at W7-AS using a Cotton-Mouton polarimeter
Magnetized plasma is birefringent. The wave which is propagating in the plasma can be regarded as superposition of two characteristic waves which propagate with different phase velocities, giving rise to a phase shift between them. The refractive indices depend on the probing beam frequency, f, the direction and absolute value of the magnetic field B(-->) and the electron density n(e). For an arbitrary angle between the magnetic field B(-->) and the wave vector k(-->), the characteristic waves are elliptically polarised. For the special cases B(-->) || k(-->) and B(-->) - k(-->) the Faraday- and the Cotton-Mouton effect ca be observed, respectively. For the Cotton-Mouton effect, the characteristic waves are linear polarised, the o-mode (E(-->) || B(-->)) and the x-mode (E(-->) - B(-->). A wave composed of an o- and an x-mode changes its ellipticity when passing the plasma. By measuring this change, the line integrated electron density p(e) can be determined. An unambiguous measurement of the line density is especially important for future long pulse machines. In this context a Cotton-Mouton polarimeter was proposed for ITER and for W7-X. A proof of principle experiment was performed successfully at W7-AS.
Bibliographic Reference: An article published in "Advanced Diagnostics for Magnetic and Inertial Fusion", edited by Stott et al. Kluwer Academic/Plenum Publishers, New York, 2002
Availability: Available from Max-Planck-Institut für Plasmaphysik, Teilinstitut Greifswald, Wendelsteinstrasse 1, D-17491 Greifswald Tel: (+49) (3834) 881211 Fax: (+49) (3934) 881219 E-mail: email@example.com
Record Number: 200316116 / Last updated on: 2003-03-26
Original language: en
Available languages: en