Electron density behaviour in the TPE-RX reversed field pinch experiment and comparison with the particle transport model of the RFX experiment

摘要

Measure of electron density along two chords is now available in TPE-RX, a large reversed field pinch (RFP) experiment (a = 0.45 m, R = 1.72 m), giving for the first time information on the shape of electron density profiles in this machine. The behaviour of density and of profiles in standard discharges in TPE-RX is analysed in this paper. Density grows almost linearly with plasma current whereas the profiles are highly peaked and flatten progressively as density increases. The presence of the locking of magnetic modes also influences the density behaviour and causes profiles to be less peaked. The behaviour of TPE-RX profiles is compared with the profiles measured at RFX, another RFP of similar size operating in a different current and density range, which exhibits flat or hollow profiles. The difference between the two machines can be explained with the different profile of the particle source, due to the different density range of operation. The comparison with RFX is extended to particle transport studies by verifying that TPE-RX results are compatible with the transport model developed at RFX after detailed analysis of the profiles measured by a 13-chords interferometer. In RFX, data showed that a magnetic transport, parametrized according to the Rechester and Rosembluth theory, can account for the particle transport in the plasma core, while an electrostatic diffusivity dominates at the plasma edge. The results presented in this work show that the same physical frame can also account for the behaviour of TPE-RX density profiles and give an indication that the transport model tailored to RFX could be considered characteristic of RFP plasmas.