The procedure to estimate the average local temperature, density, and plasma potential by conditionally selecting points of the Langmuir probe characteristic curve is revised and applied to the study of intermittent bursts in the Texas Helimak and TCABR tokamak. The improvements made allow us to distinguish the burst temperature from the turbulent background and to study burst propagation. Thus, in Texas Helimak, we identify important differences with respect to the burst temperature measured in the top and the bottom regions of the machine. While in the bottom region the burst temperatures are almost equal to the background, the bursts in the top region are hotter than the background with the temperature peak clearly shifted with respect to the density one. On the other hand, in the TCABR tokamak, we found that there is a temperature peak simultaneously with the density one. Moreover, the radial profile of bursts in the top region of Helimak and in the edge and scrape-off layer regions of TCABR shows that in both machines, there are spatial regions where the relative difference between the burst and the background temperatures is significant: up to 25% in Texas Helimak and around 50% in TCABR. However, in Texas Helimak, there are also regions where these temperatures are almost the same.

Blob-like filamentary structures are omnipresent in magnetized plasmas. Their transport deteriorates the particle confinement and may damage plasma-facing components of future fusion devices. In local measurements of density, these turbulent structures are seen as high-amplitude bursts, and, since the last decade, a stochastic pulse train model (SPTM) has been developed to describe these locally measured signals. The SPTM, which is also known as a filtered Poisson process, models plasma fluctuations as a superposition of pulses plus a background with Gaussian noise. In the present article, a fitting method for this model is introduced, considering a mixture of dynamical and observational noise. The proposed method exploits the fact the model parameters can be fitted in steps, using first the signal characteristic function, then the conditionally averaged burst, and finally the frequency spectrum. By employing this fit, we compare predictions of the model for ion saturation current measurements made with a Langmuir probe mounted in the outboard mid-plane region of the TCABR tokamak. The model is able to highlight a series of differences between the plasma edge and scrape-off layer. Furthermore, radial profiles of the SPTM parameters reveal a relation between the signal kurtosis, the intermittency of the pulses, and background parameters. Also, a linear increase in the pulse duration was found with the position. Finally, by using recurrence quantification analysis, we show evidence that the mixture of dynamical and measurement noise may be more accurate than just one of the two to describe the dynamic behavior of density fluctuations in TCABR.

The effects of coherent structures in plasma edge turbulence are an important topic in the study of plasma cross-field transport in magnetically confined plasmas. To properly characterize these structures, their temperature must be measured, which is often done by using Langmuir probes. In this work, the techniques of Langmuir sweep and triple probe are used, considering the effect of plasma sheath expansion in both methods. It is shown that if the sheath expansion is ignored, the triple probe technique gives overestimated temperature values. In addition, the conditional analysis is applied to both techniques in order to evaluate the mean temperature time trace of the coherent structures. It is shown that these time traces can be distorted in the case of the triple probe technique, due to fact that coherent structures destroy the homogeneity condition on the pins array. Therefore, the sweep technique with a conditional selection of points is more suitable than the triple probe to study coherent structures related to bursts, as it performs a local measurement.