Filamentation in the RTP tokamak plasma

Abstract

Experimental data are presented showing filamentation of the Rijnhuizen tokamak project (RTP) plasma. These filaments are only resolved by the highresolution double pulse Thomson scattering diagnostic, and appear as multiple peaks in the T e profile with a typical width of 5-10 mm and an amplitude as high as 1 keV in a 2 keV ambient plasma. This paper shows the occurrence of filaments under various plasma conditions. It shows that filaments are statistically significant plasma physical phenomena. A parameter study shows a weak dependence of their amplitude on q a , whereas a strong inverse dependence on plasma density has been found. It takes filaments several milliseconds to develop after the switch-on of electron cyclotron heating; they are wiped out by a sawtooth crash and take only a few hundred microseconds to reappear after such a crash. They mainly occur in the centre of additionally heated plasmas by means of electron cyclotron heating, but have also been observed in transiently heated plasmas and off-axis in non-centrally heated plasmas. Finally, two interpretations of filament topology are tested by means of three experiments. It turns out that the interpretation of filaments as independent closed tube-like structures seems to best fit the RTP data.

Experimental studies of electron transport

“…The TCV profiles illustrate the effect of counter-ECCD leading to very high temperatures. (Courtesy of Beurskens [13] for RTP and Angioni for TCV [19].) profile (figure 1) has also been confirmed by modulation experiments with ECH in RTP [11].…”

Three-Dimensional Observation of an Helical Hot Structure during a Sawtooth Crash in the WT-3 Tokamak

“…Although this is puzzling and not well understood from the present information on the SX images and ECE signals only, a possible process is speculated as follows. First, note that space resolution of the present SXCT is not good enough to detect fine hot structures such as the fine hot filaments observed in the Rijnhuizen tokamak project [15]. If many fine hot structures are broadly distributed on a relatively cold area in the plasma cross section, the area would look to be a broad warm region on the SX image.…”

Internal transport barriers in tokamak plasmas*

“…As a radial variation of the heat diffusion is not involved, one would not necessarily speak of a transport barrier in this case. However, it is still a matter of controversy which of the two models better suits the experimental results (Beurskens et al 2001).…”