Design and development of the ITER CTS diagnostic

S B Korsholm ,Jesper Rasmussen,Erik Nonbøl,Catarina Vidal,Thomas Jensen,Alberto Vale,Elsa Henriques,A Taormina ,M Salewski ,A Lopes ,A.w Larsen ,M Jessen ,F Leipold ,Laura Sánchez ,V Infante ,R Luís ,H.e Gutierrez ,E B Klinkby ,B Gonçalves ,M Stejner ,S K Nielsen ,R Morón Ballester ,V Naulin ,V S Udintsev

doi:10.1051/epjconf/201920303002

Abstract

The Collective Thomson Scattering (CTS) diagnostic will be a primary diagnostic for measuring the dynamics of the confined fusion born alpha particles in ITER and will be the only diagnostic for alphas below 1.7 MeV [1]. The probe beam of the CTS diagnostic comes from a 60 GHz 1 MW gyrotron operated in a ~100 Hz modulation sequence. In the plasma, the probing beam will be scattered off fluctuations primarily due to the dynamics of the ions. Seven fixed receiver mirrors will pick up scattered radiation (the CTS signal) from seven measurement volumes along the probe beam covering the cross section of the plasma. The diagnostic is planned to provide a temporal resolution of ~100 ms and a spatial resolution of ~a/4 in the core and ~a/20 near the plasma edge where a = 2.0 m is the nominal minor radius of ITER. The front-end quasi-optics will be installed in an equatorial port plug (EPP#12). A particular challenge will be to pass the probing beam through the fundamental electron cyclotron resonance, which is located in the port plug (R=10.3 m) for the nominal magnetic field Bt = 5.3 T. Hence, particular mitigation actions against arcing have to be applied. The status of the design and specific challenges will be discussed.

Highlights

The primary aim of the step fusion experiment ITER is to demonstrate – in an integrated system – the production of net power from fusing deuterium and tritium
A few ITER diagnostics can measure the confined fast alpha dynamics. One of these is the ITER Collective Thomson Scattering (CTS) diagnostic which has the primary role for the fast ion energy spectrum
The primary challenge of the ITER CTS diagnostic in the port plug is the transmission of the gyrotron probe beam through the fundamental electron cyclotron resonance, which is located inside the port plug for most of the proposed operating main magnetic fields of ITER

Summary

Introduction

The primary aim of the step fusion experiment ITER is to demonstrate – in an integrated system – the production of net power from fusing deuterium and tritium. The fusion born alpha particles (birth energy of 3.5 MeV) will have much higher relative densities than in present machines and will have a substantial effect on the overall dynamics of the ITER fusion plasma. A few ITER diagnostics can measure the confined fast alpha dynamics. One of these is the ITER Collective Thomson Scattering (CTS) diagnostic which has the primary role for the fast ion energy spectrum. Recent analysis shows that for alpha energies below 1.7 MeV, the CTS diagnostic will be the only diagnostic on ITER [1]. This article does not intend to give an overview of the present day CTS diagnostics and not the fast ion CTS principle and analysis. This paper intends to give a brief overview of the ITER CTS diagnostic, and more the development of the in-vessel front-end components

Overview of the ITER CTS Diagnostic

CTS front-end component design

Measurement capabilities

Findings

Conclusions