A Spectrally Resolved Motional Stark Effect Diagnostic for the TJ‐II Stellarator |
| |
| Authors: | K. J. McCarthy N. Panadero A. López‐Fraguas J. Hernández B. van Milligen |
| |
| Affiliation: | 1. Laboratorio Nacional de Fusión, Av. Complutense 40, 28040 Madrid, Spain;2. Facultad de Ciencias, Univ. Autónoma de Madrid, 28049 Cantoblanco, Madrid, Spain |
| |
| Abstract: | A spectrally resolved motional stark effect (MSE) diagnostic has been implemented for the TJ‐II stellarator to quantify the magnitude and pitch of components of the magnetic field created in this magnetic confinement device. The system includes a compact diagnostic neutral beam injector (DNBI) that provides a short pulse of accelerated neutral hydrogen atoms with an e–1 beam radius of 2.1 cm to stimulate the Doppler‐displaced Balmer Hαs emissions, which are the basis for this diagnostic. Measurement of the wavelength separation of the Stark splitting of the Hα spectrum, as well as of the relative line intensities of its components, allow the local magnitude and direction of the internal magnetic field components to be measured at 10 positions across the plasma. The use of a DNBI extends such measurements to the electron cyclotron resonance (ECR) heated phases of plasmas while also overcoming the need for the complicated inversion techniques that are required when such measurements are performed with a heating neutral beam injector (NBI). Moreover, the use of the shot‐to‐shot technique with reproducible discharges further simplifies fits to the MSE spectra as nearby impurity spectral emission lines can be eliminated or significantly reduced. After outlining the principles of this technique and the diagnostic set‐up, magnetic field measurements made during ECR or NBI heating phases are reported for a range of magnetic configurations and are compared with vacuum magnetic field estimates in order to evaluate the capabilities and limitations of this diagnostic for the TJ‐II. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) |
| |
| Keywords: | Stellarator plasma diagnostic magnetic field TJ‐II |
|
|
