Several experiments aimed at optimizing plasma pre-ionization using electron cyclotron (EC) waves have been carried out on many tokamaks in recent years as the basis of a multi-machine comparison study made to define the best operation scenarios for ITER, where the plasma breakdown will have to be achieved with a toroidal electric field of only 0.3 V m-1. The FTU (Frascati Tokamak Upgrade, R = 0.935 m, a = 0.3 m) contribution to this study is the main subject of this work. A reduction in electric field, as can be obtained with pre-ionization by ECH, can lower the transformer flux consumption in the start-up phase leading to a longer plasma current flat top. This point is of particular interest in the conceptual design of the steady-state scenario of the proposed FAST tokamak and has also been addressed. In the FTU experiment the scan in pre-filling pressure has evidenced the capability of EC power to increase, by a factor 4, the range of working pressure useful for plasma start-up. Varying the breakdown a minimum electric field of 0.41 V m -1 has been found with 0.8 MW of EC in perpendicular injection. A scan in magnetic field has evidenced that plasma start-up is likely insensitive to alignment between EC resonance and null position. A total transformer flux saving of 22% has been found acting on plasma resistivity (by increasing electron temperature) and on the plasma starting point (for an internal inductance reduction). © 2011 IAEA, Vienna.
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics
- Condensed Matter Physics
Granucci, G., Ramponi, G., Calabrò, G., Crisanti, F., Nowak, S., Ramogida, G., ... Romano, A. (2011). Plasma start-up results with electron cyclotron assisted breakdown on Frascati Tokamak Upgrade. Nuclear Fusion, 51(7), -. . https://doi.org/10.1088/0029-5515/51/7/073042