On the Measurement of the Threshold Electric Field for Runaway Electron Generation in FTU - Esposito ., B; Martin Solis, Jose Ramon; Panaccione, Luigi; Podda, Salvatore; Ramogida, Giuseppe; Riva, Marco; Romano, Afra; Tudisco, Onofrio; Popovic, Zana; Artaserse, Giovanni; Belli, Francesco; Botrugno, Antonio; et al. (25th IAEA Fusion Energy Conference, 2014)