Phase Ramping and Modulation of Reflectometer Signals
The phase and amplitude signals of JET heterodyne reflectometers show varying levels of high frequency turbulence superimposed on a slow changing mean. The phase signal also shows multi-radian variations with two quite different time scales. In both cases the mean reflected power, together turbulent phase and amplitude fluctuation levels, are modulated synchronously with the phase fringes. The slow fringes appear to result from radial movement of the cutoff layer with the amplitude modulation possibly due to multiple reflection between plasma and wall. The fast fringes occur in intermittent bursts appear to be phase runaway resulting from the antenna misalignment. Using a 2D physical optics simulation code it is possible to replicate the fast bursts of phase runaway from steady-state turbulence and misaligned antennas. This offers a possible alternative explanation for some of the observations of bursting turbulence seen in reflectometer signals.
Bibliographic Reference: Article: JET-P(99)14 (1999), 9pp.
Record Number: 199911277 / Last updated on: 1999-08-27
Original language: en
Available languages: en