Diamond-coated probe head for measurements in the deep SOL and beyond

We have tested two cylindrical graphite probe heads coated by a layer of electrically isolating UNCD (Ultra Nano-Crystalline Diamond) using a CVD (Chemical Vapour Deposition) method. The probe heads were mounted on the reciprocating probe manipulator of the Experimental Advanced Superconducting Tokamak (EAST) in Hefei, People's Republic of China.

Transport parameters, plasma density, temperature, potential, as well as toroidal rotation near the separatrix were determined up to a distance of 15 mm inside the LCFS in high confinement regimes. A very important result was that the UNCD coating could also prevent the sputtering of graphite from the probe head and the subsequent coating of the BN isolation between probe pins and probe head by a layer of conductive graphite almost completely.