Multichannel Tangential FIR Laser
Interferometer/Polarimeter for NSTX (FIReTIP)
Computer Simulations Made
Prior to FIReTIP Operation
■ Test density profiles and
toroidal field of NSTX, as well as the beam displacement due to refraction in
the plasma are shown in the following figures. NSTX is likely to have a broad
density profile, so that refraction is minimum (<0.5 mm) at 119 mm.
■ Shown in the figures below are the interferometer phase shifts and Faraday rotation angles calculated for the test profiles shown above left. Minimum detectable signals of < 1/32 Fringe for density measurements and 0.02 degree for Faraday rotation measurements are expected.
■ Shown in the figures below are the base density and Faraday rotation angle profiles (in red), and the reconstructed profiles (blue) from the data of the seven sampling channels. It is seen that the agreement is quite good for a seven-channel system.
■ For a target plasma with b ~35 %, and a Shafranov Shift of about 20 cm, TRANSP code
calculates that the toroidal field modified by diamagnetic effect is ~100 Gauss
near the core, as shown below left.
Also shown below (right) is the difference in Faraday rotation angles due to
the change in magnetic field profile, calculated for different density
profiles. It is seen that the difference is large enough for detection.
■ Further information is available:
· Introduction to
the FIR Tangential Interferometer/Polarimeter (FIReTIP)
· Principles
of Interferometry/Polarimetry
· The CO2/FIR
Lasers for the FIReTIP System
· Optical
Layouts of the FIReTIP System
· Phase
Detection Electronics for the FIReTIP System
· Recent
Progress and Physics Results
Send comments to: cwdomier@ucdavis.edu.
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