Particle control systems at the edge of RFP experiments

Abstract

Plasma performance in reversed field pinch (RFP) devices, as in the tokamak, is strongly affected by neutrals at the edge. So far only a few experiments have been dedicated to an active control of the neutral particle using conventional solutions of axisymmetric magnetic divertors or throat limiters. The alternative 'vented pump limiter' concept is more attractive for an RFP experiment due to the edge plasma and confinement properties of this magnetic configuration. In this paper, the application of a vented pump limiter to an RFP is discussed and the prototype module of the vented pump limiter designed for the RFX experiment is presented. Finally, the optimization of this concept for a next step RFP device is presented.

Experimental and simulated M-shell nickel spectra in the 14.4–18.0 nm region from magnetic fusion devices

“…For the limiter configuration with a LCFS radius of 1.2 m, no SOL was considered. In previous simulations of JET spectroscopic data, both in divertor [4,5,39] and in limiter configurations [40], it was necessary to include a transport barrier inside the LCFS for both intrinsic and injected impurities. This is obtained by shaping either both D(r ) and V (r ) or just one of them in such a way that a 'peripheral barrier' is created [40].…”

“…Diffusive barriers obtained by reducing D(r ) or convective ones produced by increasing V (r ) have been compared and several possible transport coefficients were found. In more recent simulations [4,5,39] we assumed mainly diffusive barriers: in the core plasma D(r ) was generally found to decrease towards the plasma axis, whereas V (r ) inward, i.e. positive at the periphery, and could become large in the centre (indicating impurity peaking); or it could become outward (i.e., negative toward the centre), indicating hollow impurity profiles.…”

“…positive at the periphery, and could become large in the centre (indicating impurity peaking); or it could become outward (i.e., negative toward the centre), indicating hollow impurity profiles. For the simulations done for the present paper (considering only peripheral ions) we took the D(r ) and V (r ) curves used in [4] and [39], changing, in different trials, only D(r ) in the last meshes.…”

“…Figure 6 shows, for the best simulation of the JET divertor spectrum (with λ T = 30 mm and λ n = 50 mm), peripheral radial profiles of (a) n e and T e ; (b) D and V (the same as in [39] They are all quite near to, but slightly larger than, the corresponding T e of maximum abundance that would be obtained in the simulation with D(r ) and V (r ) approaching zero. Still, in spite of the low ionization potential of the Ni ions considered, the influence of recombination is not negligible.…”

“…The lines which have not been simulated are not Ni lines (their identification can be found in [16]), with the exception of the feature around 14.7 nm, which is a Ni line presumably due to a lower ionization stage (in the tables of [25] a Ni IX line is given at 14.70 nm). Several other simulations were performed: (1) varying λ n between 40 and 60 mm, (2) varying λ T between 25 and 40 mm, (3) increasing D outside the LCFS from 0.13 to 0.2 m 2 s −1 , (4) taking the D(r ) and V (r ) curves used in [4] and (5) adding a neutral deuterium profile similar to the one used in [39] with a SOL density in the 10 15 m −3 range. Among these simulations, No 3 was generally the best.…”