Abstract
The utilization of the Motional Stark Effect (MSE) experienced by the neutral hydrogen or deuterium injected into magnetically confined high temperature plasmas is a well established technique to infer the internal magnetic field distribution of fusion experiments. In their rest frame, the neutral atoms experience a Lorentz electric field, EL = v × B, which results in a characteristic line splitting and polarized line emission. The different properties of the Stark multiplet allow inferring, both the magnetic field strength and the orientation of the magnetic field vector. Besides recording the full MSE spectrum, several types of polarimeters have been developed to measure the polarization direction of the Stark line emission. To test physics models of the magnetic field distribution and dynamics, the accuracy requirements are quite demanding. In view of these requirements, the capabilities and issues of the different techniques are discussed, including the influence of the Zeeman Effect and the sensitivity to radial electric fields. A newly developed Imaging MSE system, which has been tested on the ASDEX Upgrade tokamak, is presented. The sensitivity allows to resolve sawtooth oscillations.A shorter version of this contribution is due to be published in PoS at: 1st EPS conference on Plasma Diagnostics
Highlights
Understanding magnetic confinement of high temperature fusion plasma, i.e. plasma transport and stability, requires the detailed knowledge of the magnetic field inside the plasma
The poloidal magnetic field generated by the toroidal plasma current distribution forms an essential part of the confining magnetic field
Many magnetic confinement fusion experiments which are equipped with a neutral beam injection system employ a multi-channel Motional Stark Effect (MSE) diagnostic to measure the radial profile of the magnetic field
Summary
Understanding magnetic confinement of high temperature fusion plasma, i.e. plasma transport and stability, requires the detailed knowledge of the magnetic field inside the plasma. Many magnetic confinement fusion experiments which are equipped with a neutral beam injection system employ a multi-channel MSE diagnostic to measure the radial profile of the magnetic field. Most such systems focus on the polarization measurement for the determination of the toroidal current density profile. In view of the increasing accuracy with which the spectral and polarization information can be measured, many inconsistencies or inaccuracies in the previous analysis become apparent These include atomic physics effects such as the correct treatment of the population densities of the atomic levels, which determine the line intensities[13,14,15], or the admixture of the Zeeman Effect to the Stark Effect[4,15]. Before concluding the paper, the so-called Imaging MSE diagnostic, which is a special form of polarization measurement, will be presented
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