Reman, B. C. G. (2018) Interpreting observations of Ion Cyclotron Emission from energetic ion populations in large helical device plasmas. PhD thesis, University of Warwick.

Preview

PDF WRAP_Theses_Reman_2018.pdf - Submitted Version - Requires a PDF viewer. Download (112Mb) | Preview

Request Changes to record.

Abstract

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.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QC Physics T Technology > TK Electrical engineering. Electronics Nuclear engineering
Library of Congress Subject Headings (LCSH):	Ions, Tokamaks, Fusion reactors, Stellarators, Neutral beams
Official Date:	October 2018
Dates:	Date Event October 2018 Published
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Dendy, R. O.; Chapman, Sandra C.
Format of File:	pdf
Extent:	xxx, 240 pages: illustrations, charts
Language:	eng

Request changes or add full text files to a record

Repository staff actions (login required)

View Item

Downloads