PhD Code: 2016-DC-18:
- Host institute 1: FP7-Instituto Superior Técnico (Home University)
- Host institute 2: FP2-Université de Lorraine (Host University)
- F6. Diagnostics, plasma control and data analysis
- Prof. Horacio Fernandes (promotor) - Dr. Carlos Silva (mentor)
- Prof. Stéphane Heuraux (co-promotor)
Background: Microwave reflectometry is a technique used to diagnose fusion plasmas to obtain information on the electronic density such as the density radial profile or information on coherent plasma events such as MHD activities and/or relaxation and turbulent phenomena. Simulations of a full reflectometer system should consider: (i) wave propagation in fluctuating plasmas; (ii) proper antenna setup and signal injection technique; (iii) signal detection and signal processing techniques; (iv) geometry of the problem and if possible (v) real size of the system. Simulation of wide band frequency modulated reflectometry (frequency modulated continuous wave – FMCW) where the frequency is continuously swept adds further requirements since a good behavior throughout the wide frequency band is required, including the numeric scheme used, absorbing boundary conditions, and signal injection (source). Signal injection poses particular challenges in the case where a decoupling between the injected signal (continuous) and the received one. Five O-mode plasma position reflectometers (PPR) are previewed for ITER and some of them are facing unfavorable conditions of operation, namely an electronic density poloidal divergence and curvature, adverse to the measurement of density profiles. Adding to that, severe effects of multi-reflection in the walls are expected, and the impact on the measurements of such together with fluctuating plasmas has also to be considered. It is of major importance to understand the impact of such topologies and plasma conditions in the measurements. To such propose numerical simulations of aforesaid systems is required and to have synthetic reflectometers able to perform such studies.
Objective: The objective proposed consists, using the O-mode fullwave FDTD code developed at IPFN (REFMUL) to set up a synthetic reflectometer and use it to simulate ITER Plasma Position Reflectometer (PPR) to develop methods able to provide reliable and accurate density profiles and plasma positioning in real time. Thus it is important to consider the geometric aspects of the reflectometer full-size setup: use of oversized waveguides, open waveguide as emission/reception antenna, existence of a surrounding blanket structure forming a cavity around the mouth of the waveguides, the expected plasma scenarios and the different lines of view faced by the reflectometers. Through simulations, the response of the PPRs and their dynamic range of the different reflectometers will be accessed and an evaluation of the effects of vertical displacement of the plasma, blanket and restriction imposed by the antennas/ blanket design can be obtained. Also essential, is to understand the impact of probing the plasma away from the midplane, where the isodensity lines exhibit significant density poloidal divergence and curvature. An evaluation of the error committed in these conditions when the traditional model is used is necessary together with research of eventual new procedures, to calculate density profiles when severe poloidal divergence and curvature is present. The role of the density fluctuations has to be also taken into account to establish the loose of accuracy in different cases: turbulence, MHD activities including eventually ELMs. The synthetic reflectometer setup obtained will be used not only at the specification and design phase of the PPR but will continue to be a useful tool as a platform for simulation of updated scenarios.
Time line and mobility scheme (research need to be performed for at least six month in two different countries): First year: Instituto Superior Técnico, Lisbon, Portugal Second year: Instituto Superior Técnico, Lisbon, Portugal (six months) Institut Jean Lamour, Univ. de Lorraine, Nancy, France (six months) Third year: Instituto Superior Técnico, Lisbon, Portugal
Original document: 2016-DC-18