The first evidence of dust-impact ionization processes in the scrape-off layer of the Frascati tokamak upgrade (FTU) was reported inNucl. Fusion47L5 (2007). In this work an extended data analysis (both of electrostatic probe signals and probe surface analysis) is presented, using results of empirical studies of hypervelocity impacts. Within the accuracy and limits of application of such results to tokamak plasma environment, the data are shown to be consistent with occurrence of impacts by micrometre size iron particles at velocities of the order of 10 km s⁻¹.

The use of electrostatic probes as a diagnostic tool of the dust particles in the tokamak edge plasmas is investigated. Probe measurements of electrostatic fluctuations in the scrape-off layer of the Frascati Tokamak Upgrade revealed that some features of the signals can be explained only by a local non-propagating phenomenon. These signal features are shown to be both in qualitative and quantitative agreement with ionization, and consequent extra charge collected by the probes, due to the impact of micrometre-sized dust at a velocity of the order of 10 km s−1. Electron microscope analysis of the probe surface yielded direct support for such an interpretation.

The introduction of artificial pinning sites in ${\text{YBa}}_2{\text{Cu}}_3{\text{O}}_{7-\delta }$ (YBCO) epitaxial thin films has been obtained by pulsed laser deposition (PLD) technique from YBCO-${\text{BaZrO}}_3$ (BZO) composite targets with BZO concentration ranging from 2.5 to $7\text{mol}\mathrm{\%}$ . The typical critical temperature, $T_c$ , drop observed in YBCO-secondary phase films grown by PLD has been successfully recovered by increasing the deposition temperature. Transport properties analyses revealed improved pinning force values for YBCO-BZO films for BZO concentration above $5\text{mol}\mathrm{\%}$ . These films exhibited an anomalous dual peak structure which has been ascribed to the presence of two pinning contributions. The crossover field, $B_m$ , separating these two pinning regimes has been observed to be temperature independent suggesting the occurrence of the matching field effect. The measured value of $B_m$ agreed with the matching field value, $B_{\Phi }=K{n}_d{\Phi }_0$ , as evaluated from transmission electron microscopy investigations. The mark of this phenomenon is retained down to 10 K, making YBCO-BZO more performing than pristine YBCO films at applied magnetic fields below $B_m$ in all the temperature range inspected. On the contrary, in the high magnetic field range (above $B_m$ ), the effectiveness of correlated pinning is progressively reduced on lowering the temperature suggesting that at low temperatures the dominant pinning contribution arises from isotropic pinning centers.