Experimental data are presented showing filamentation of the Rijnhuizentokamak project (RTP) plasma. These filaments are only resolved by thehigh-resolution double pulse Thomson scattering diagnostic, and appear asmultiple peaks in the Te profile with a typical width of 5-10 mm andan amplitude as high as 1 keV in a 2 keV ambient plasma. This paper shows theoccurrence of filaments under various plasma conditions. It shows thatfilaments are statistically significant plasma physical phenomena. A parameterstudy shows a weak dependence of their amplitude on qa, whereas astrong inverse dependence on plasma density has been found. It takes filamentsseveral milliseconds to develop after the switch-on of electron cyclotronheating; they are wiped out by a sawtooth crash and take only a few hundredmicroseconds to reappear after such a crash. They mainly occur in the centreof additionally heated plasmas by means of electron cyclotron heating, buthave also been observed in transiently heated plasmas and off-axis innon-centrally heated plasmas. Finally, two interpretations of filamenttopology are tested by means of three experiments. It turns out that theinterpretation of filaments as independent closed tube-like structures seemsto best fit the RTP data.
The importance of realistic plasma filament waveforms for the study of resonant wave-filament interactions in tokamak edge plasmas