Diagnostic strategy of the W7-X stellarator

Abstract

The Wendelstein 7-X experiment is a concept test for properties of reactor relevant plasmas in advanced stellarators. Prominent features include a modular superconducting coil assembly, a fivefold toroidal symmetry, and a helical magnetic axis. Due to the optimization process, W7-X is characterized by a vacuum magnetic field configuration with smooth magnetic surfaces, improved equilibrium properties with a weak dependence of rotational transform and shear on the plasma pressure β, good magneto-hydrodynamic stability properties due to magnetic well stabilization, reduced neoclassical transport losses and negligible bootstrap current in the long mean-free-path regime, good collisionless α-particle confinement in an equivalent reactor, and, as a technical aspect, good feasibility of the superconducting modular coils. W7-X will be heated by continuous electron cyclotron resonance heating and pulsed neutral beam injection and ion cyclotron resonance heating. The envisaged parameters are Te⩽10 keV, Ti⩽6 keV central densities ⩽3×1020 m−3 with an averaged 〈β〉⩽5%. Despite the complicated geometrical structure, all basic diagnostics are compatible with W7-X. Generally, diagnostic methods and applications in a stellarator are not different from those in tokamaks. However, special efforts are being made to equip the experiment with those diagnostics necessary to measure the quantities directly related with the optimization of the machine: the verification of the predicted magnetic topology and characterization of the configuration throughout the entire parameter range, the identification of equilibrium and stability, and the determination of the confinement properties. The article describes the strategy developed which assures that the detailed measurement needs of the W7-X experimental program can be met.

Bayesian Design of Diagnostics: Case Studies for Wendelstein 7-X

“…The set of "start-up" diagnostics for Wendelstein 7-X is oriented to resolve physical issues of stellarator optimization [1]. The diagnostics philosophy of W7-X aims at extendable setups which are to be supplemented along the operation of the device.…”

Bayesian design of plasma diagnostics

“…confinement studies. This philosophy is reflected by the choice of "start-up" diagnostics for Wendelstein 7-X which is oriented to resolve physical issues of stellarator optimization [2]. In assistance, the robustness of the results is assessed by any available additional information, e.g.…”

Design and Calibration of a Polychromator for the Thomson Scattering at Wendelstein 7-X

“…Thomson scattering (TS) is envisaged as a standard diagnostic for both electron temperature (T e ) and electron density (n e ) profile measurements on Wendelstein 7-X [1]. As an essential part of the diagnostic setup the spectral analysis of the scattered light is performed with polychromators for the so-called bulk Thomson scattering system which is expected to deliver full profiles of n e and T e .…”