Edge turbulence controlled by topologically self-optimized fluxes in fusion devices

Abstract

The integration of a theory regarding the dynamics of averaged magnetic moment in a turbulent setting with the concept of a self-optimized cascade loop of helical fluxes, either spontaneously or intentionally generated near the separatrix, enables the derivation of spectral laws for the floating potential and ion saturation current, which align with findings from various experiments conducted on tokamaks, stellarators, and RFX-mod reversed field pinches. The notion of distributed chaos enables a quantitative evaluation of the randomness levels of chaotic/turbulent states observed inside and outside the separatrix, linking them to self-optimized helical fluxes.

Figures (13)

• Figure 1: Power spectra of the floating potential time series measured at two different radial positions (with respect to the separatrix location at $r_{sep}$): $\Delta r = \pm 5$ mm, where $\Delta r = r-r_{sep}$, for the ISTTOK tokamak, The spectra are vertically shifted for clarity.
• Figure 2: A sketch of the HSX stellarator.
• Figure 3: Power spectra of the floating potential time series measured at different radial positions (with respect to the separatrix location at $r_{sep}$): $\Delta r = r-r_{sep}$, for HSX stellarator. The spectra are vertically shifted for clarity.
• Figure 4: As in Fig. 3 but for positive $\Delta r$.
• Figure 5: Power spectrum of the floating potential fluctuations for ASDEX Upgrade tokamak. The measurements were produced a few millimeters outside the separatrix ($\Delta r > 0$). The cut-off frequency of the anti-aliasing filters are shown by the vertical gray band.