Lower hybrid current drive accessibility study with reconstructed magnetic equilibria in PBX-M

Abstract

Ray tracing simulations based on experimental PBX-M equilibria show a limited range of the parallel wavenumber (n, = R,c/w) along a ray trajectory. The range of nl accessible to the excited wave is shown to have both a lower and an upper bound. The ray's phase volume is projected into (n,, R, Z) space to define a domain of wave accessibility for each toroidal mode number excited by the launcher. A comparison of circular and bean shaped plasmas with a high aspect ratio ( A -5.5) shows that the rays fill a substantially larger portion of the accessible domain in bean shaped plasmas. Furthermore, in the bean shaped case the accessible domain tends to extend to higher n N .

Analysis of the Chaotic Behavior of the Lower Hybrid Wave Propagation in Magnetised Plasma by Hamiltonian Theory

“…The authors of the paper in question examined the eventual effects of a resonance caused by the magnetic ripple, which we chose not to consider in our work. The comparison with previous works, in particular with [50][51][52], brings us to reconsider in part our results in terms of the existence of a resonance that causes an anomalous increase in n . This resonance, which comes directly from the LH dispersion relation, is not evident from the study of the system through the canonical perturbation theory.…”

“…In particular, in the density range between 9 × 10 13 cm −3 and 1.2 × 10 14 cm −3 , n reaches values higher than 10 2 , meaning that the oblique resonance mentioned above may be located somewhere in between. This picture has to be compared to the several plots shown in the papers quoted above, in particular with those from [50,51]. In Figure 8b, we show the trapping of the ray trajectories in the narrow region located at half-radius, where the phenomenon of wave number amplification occurs.…”

“…In the case of the LH dispersion relation, these resonances are not present to first order in the inverse aspect ratio , so that the chaotic behavior of the ray trajectories, which they observe in the θ − m plane, must be due to higher order perturbations. Paoletti et al [51] also perform both an analytical and a numerical study of the range of n during the ray propagation. By means of analytical calculations, they come to explicit lower and higher boundaries for the parallel wave numbers, where they show the explicit dependence of these boundaries on the plasma parameters, in particular on the electron plasma frequency and the ratio between the poloidal and the total magnetic field.…”

Experimental and Theoretical Investigation of Synergy between Ion Bernstein and Lower Hybrid Waves in PBX-M

“…One of the main goals of the LHCD experiment on PBX-M was to modify the current density profile in order to produce a more stable plasma discharge 13,14,15 .…”

Spreading of wave-driven currents in a tokamak

“…It has been shown [24] that this maximum tends to be reached in bean-shaped plasmas such as PBX-M after many reflections from the wall, whereas it may not be reached in similar circular plasmas.…”