Electrostatic turbulence in the edge of TPE-RX and driving mechanisms

Abstract

In order to understand the driving mechanisms that underlie the turbulence in the plasma edge of fusion devices, contemporary measurements of light emission fluctuations with the gas puff imaging diagnostic and of the electrostatic potential with Langmuir probes are carried out in the TPE-RX plasma device. The analysis made with the conditional average technique demonstrates a clear link between the two types of structures, with a phase shift of π/2. This relation suggests that the curvature driven modes are a possible source of free energy for edge turbulence in this machine, as similarly found in other plasma devices.

Convective transport by intermittent blob-filaments: Comparison of theory and experiment

“…136 A good correlation was observed between blobs measured by optical imaging and Langmuir probes on MAST, 163 CSDX, 222 and TPE-RX. 197 A close connection between the radial speed inferred from E Â B and blob tracking measurements was obtained in VTF 131 and QUEST. 179 The range of electron density and temperature seen in Thomson scattering measurements of the SOL in DIII-D 18 and NSTX 134 was also consistent with the presence of large positive structures, i.e., blobs.…”

“…197 Both positive and negative blob potentials have been observed, corresponding to positive and negative vortices, along with both monopolar and dipolar potential structures. Two dimensional spatial maps of the vortexlike potential structure of blobs have been made in W7-AS, 119 ADITYA, 172 SINP, 174 TORPEX, 132,204 TJ-K, 184 the Riso Q machine, 226 and THORELLO.…”

“…V E). Experimentally, the existence of coherent propagating objects with a dipole potential structure has been verified using probe arrays in a wide variety of plasma devices including linear machines, 130 stellarators, 119 tokamaks, 138,167 reversed-field pinches 197 and other small toroidal machines. 131 An example of another kind of measurement of the blob density and potential structure on C-Mod 138 is shown in Fig.…”

“…The existence of large skewness for fluctuations in the far SOL is observed in simulations, 53,59,61,93,100 experiments on tokamaks 93,100,126,129,144,169 and experiments on a variety of other machines. 182,197,201,202,229 An example of an experimental measurement of the radial skewness and kurtosis profiles is shown in Fig. 18.…”

Comparison of edge turbulence imaging at two different poloidal locations in the scrape-off layer of Alcator C-Mod

“…We also assume that the He neutral density is not fluctuating on the space-time scale of the turbulence, although there could be some shadowing effect due to the turbulence itself [45]. On the other hand, there is good evidence that the GPI turbulence signals in the SOL correlate well with Langmuir probe turbulence signals when measured on the same field line, for example in C-Mod [19] and NSTX [53], and TPE-RX [54].…”