A feasibility study for a Doppler Reflectometer System in the JT-60SA tokamak

TL;DR

This study evaluates the feasibility of installing a Doppler Reflectometer (DR) on JT-60SA to validate turbulence and transport models in reactor-relevant regimes. It uses TRAVIS ray-tracing to optimize antenna geometry, demonstrating that a single-axis steering system can access core and edge turbulence across a wide $k_\perp$ range, with $k_\perp\rho_i$ spanning roughly $0.5$ to $15$. A two-channel concept (V-band edge with X- or O-mode and W/V-band core with O- or X-mode) is proposed, operable within a fraction of a horizontal port, along with a minimum viable design and baseline configurations to accommodate space constraints and future upgrades. The work provides a practical path toward GK-model validation for ITER/DEMO scenarios and enhances capability to study L-H transition, ETB physics, and rotation/NTV effects through direct turbulence measurements.

Abstract

In this work we present a study on the viability and practicality of installing a Doppler reflectometer (DR) system in the JT-60SA advanced tokamak. First, we discuss its scientific scope in the context of the JT-60SA research plan. We identify a number of fields in which a DR would be very relevant for the accomplishment of said plan and outline a scientific program for the diagnostic. Then, starting from a number of design hypothesis, we use a ray tracing code to carry out a feasibility study for a number of relevant scenarios and identify a geometric solution for the installation of a DR such that both core and edge can be probed in the prescribed wave number range, thus achieving the proposed scientific objectives. Finally, we perform a preliminary discussion on the different possibilities for a conceptual design (including a minimum viable system and a baseline system) and their requirements in terms of components and space. We conclude that a viable conceptual design could be carried out using a small fraction of a horizontal port, leaving room for additional diagnostic systems.

Figures (14)

• Figure 1: Overview of the P-18 Horizontal Port ref32d. Left, current status of the diagnostic flange, including the diagnostic port allocation. Right, 3D view of the port including an hypothetical reflectometer cabinet and waveguide system.
• Figure 2: Antenna position and launching angles represented on a poloidal section of JT-60SA along with the silhouette of the P18 port (dimensions are approximate). Image adapted from ref34).
• Figure 3: Plasma and magnetic field profiles of the three considered scenarios. DR accessible regions for k$_\perp \simeq 10$ cm$^{-1}$, as calculated in section \ref{['secondTravis']}, are represented on the left column using red/blue for V/W band and light/dark shade for O/X mode.
• Figure 4: Safety factor profile for each of the three configurations presented in Fig. \ref{['Figure_4']}.
• Figure 5: First scan of elevation and azimuth carried out with TRAVIS. Launching directions of the beam array are represented as golden cones emanating from the antenna position. For reference, purple and green surfaces represent a toroidal section of the $\rho = 1$ and $\rho = 0.1$ flux surfaces, respectively