Distinct stages of radio frequency emission at the onset of pedestal collapse in KSTAR H-mode plasmas
Using a high-speed and broadband radio frequency (RF) (0.1–1 GHz) spectrum analyzer developed on the KSTAR tokamak, it is found that several distinct stages of RF emission appear at the pedestal collapse in high confinement discharges. Comparison with 2D electron cyclotron emission (ECE) images has revealed that each stage is related to the instantaneous condition at the outboard mid-plane edge. First, high-harmonic ion cyclotron emissions (ICE) are intensified with the appearance of a non-modal filamentary perturbation in the edge within several tens of microseconds before the collapse. Then, the RF emission becomes broad toward high-frequency range (<500 MHz) at the burst onset of the non-modal filament. During the pedestal collapse initiated by the filament burst, rapid chirping (1–3 μs) appear with additional filament bursts. The strong correlation between the RF spectra and the perturbation structure provides important clues on the stability of edge-localized modes and on the ion dynamics in the plasma boundary.
Interpreting observations of Ion Cyclotron Emission from energetic ion populations in large helical device plasmas
Ion cyclotron emission (ICE) has been reported from most magnetic confinement fusion devices (MCF), both large tokamaks and stellarators. The ICE phenomenology is rich as it results from fusion products and from neutral beam injection (NBI) energetic ions. These can drive ICE on confined trajectories or during MHD instabilities as they are expelled from the plasma. In either scenario, an inversion in velocity space perpendicular to the local magnetic field is thought to take place. In particular ICE was observed during DT experiments in both JET and TFTR, driven by the 3.5MeV a particle. Self-consistent hybrid [19] and full [20] particle-in-cell (PIC) simulations of the magnetoacoustic cyclotron instability (MCI) [21] captured ICE features related to JET ICE. The linear scaling of the ICE intensity with the _ particle density, used as a proxy for the measured neutron flux, was reported in Ref. [22]. Ion cyclotron emission has been proposed as a non invasive diagnostic in ITER [23]. 
 
In this thesis, we study ICE detected in the Large Helical Device (LHD) heliotron stellarator with hybrid PIC simulations. Unlike full PIC, hybrid PIC treats the electron as a neutralising fluid while the ion species are still fully kinetic. We focus on NBI-driven ICE in hydrogen plasmas and explore the sub- and super-Alfvenic regime where NBI proton speeds vNBI are either lower or higher than the Alfven speed which is determined at the emission location. Our simulations show that relaxation of these protons drive the MCI, at perpendicular and oblique propagation angles, and spectral peaks at proton cyclotron harmonics are obtained. 
 
Deuterium was introduced for the first time during the 2017 LHD campaign [24] and brought ICE measurements with it. The spectral features of NBI-driven ICE are reported to qualitatively and quantitatively vary across LHD plasma discharges. We interpret the observations to be the result of the different edge plasma density which controls the ratio vNBI=VA and affects the ICE power spectra as suggested by hybrid PIC simulations. Doppler-shifted ICE is detected during MHD instabilities [25]. Fusion-born protons could be driving the ICE and account for the large Doppler shifts as explored via hybrid simulations. We perform cepstra analysis on the measured spectra to identify which cyclotron harmonics are present. 
 
The hybrid kinetic dispersion relation with inertial electrons is derived, generalazing the massless case [26]. Solutions are obtained in the case of background Maxwellians and energetic ring beams and compared against the full- and neutralkinetic dispersion relations.
The crystal structure of stilpnomelane. Part II. The full cell
Summary The structural formula of stilpnomelane averaged from 37 representative literature analyses and based on the determined structure is (Ca,Na,K)4(Ti0·1Al2·3Fe35·5Mn0·8Mg9·3)[Si63Al9](O,OH)216·nH2O. Ferrostilpnomelanes have up to 12 R 3+ cations in the octahedral sheet, ferristilpnomelanes commonly have between 24 and 30 R 3+ cations, rarely up to 37. The two groups can be distinguished by accurate X-ray powder diffraction, ferrostilpnomelanes having d 001 less and a greater than have ferristilpnomelanes. The unit cell is triclinic, a = b∼21·8 Å, γ = 120°, d 001∼12·2 Å, P . Hexagonal groups or ‘islands’ of 24 silicon-oxygen tetrahedra co-ordinate to the octahedral sheet, the centres of the ‘islands’ are displaced by 5a/12, 8b/12 on either side of the octahedral sheet as a result of warping of this sheet to permit articulation with the smaller tetrahedral sheet. The 24-tetrahedra ‘islands’ are linked laterally by 6-member rings of inverted tetrahedra, which in turn link at their apices to like rings connecting the next sheet of ‘islands’. Thus a single tetrahedral layer is 4 tetrahedra thick and has symmetry 6/m. The 6-member rings of tetrahedra act as hinges permitting up to 0·5 Å extension or contraction of the tetrahedral sheet to accommodate variations in the octahedral sheet dimensions with varying R 2+/R 3+ ratio.