Edge ion-to-electron temperature ratio in the Tore Supra tokamak

Both ion and electron temperatures in the scrape-off layer (SOL) of the Tore Supra tokamak were measured by a retarding field analyzer during an ohmic density scan. SOL Ti was found to be higher than Te by a factor of 4–7. The ion-to-electron temperature ratio τ decreases with increasing density. Core Ti and Te measurements in Tore Supra combined with a multi-machine database of τ measurements show that τ > 1 also in the edge of the confined plasma and increases with radius.