Quiet-Time Statistics of Electrostatic Turbulent Fluxes from the JET Tokamak and the W7-AS and TJ-II Stellarators

The statistics of the quiet times between successive turbulent flux bursts measured at the edge of the JET tokamak and the W7-AS and TJ-II stellarators are analyzed in search for evidence of self-organized critical behavior. The results obtained are consistent with what would be expected in the situation where the underlying plasma is indeed in a near critical state.

Figure 1

(a) Detail of raw W7-AS flux signal; (b) same signal averaged with $m=32$; (c) absolute value of averaged signal together with a sketch of relevant definitions.

Figure 2

Examples of quiet-time survival functions for W7-AS shot No. 35427.

Figure 3

Above: burst-duration survival function for W7-AS data. Below: decades of extension of power-law behavior vs duration threshold $d$. Situation of $d$ relative to self-similar duration range shown by means of dashed vertical lines.

Figure 4

Quiet-time survival functions for JET shot No. 54278.

Figure 5

Idem as Fig. 3 but for JET data.