Calibration and operational experience with the JET motional Stark effect diagnostic
- Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon OX14 3DB (United Kingdom)
Motional Stark effect measurements of the magnetic field pitch angle on JET present several difficulties most serious of which is that the injection systems consist of more than one source, each with a different motional stark effect (MSE) angle. Attempts to describe the net polarization angle, within the EFIT equilibrium code, using the weighted sum of Stokes vectors, have proved inaccurate. Instead we rely on spectrally isolating the emission of a single source. Beam power modulation is helpful in differentiating background polarized light, but this technique fails in the presence of strong edge localized mode (ELMs). Calibration is difficult because of the presence of a mirror in the optical system. The mirror introduces a large optical phase shift which means that the polarimeter has to resolve circular as well as linear polarized components. Basic calibration is carried out off the tokamak using a motorized rotary encoder stage and a six-parameter physical model of the optical and electronic systems. This is readjusted using plasma emission, for mirror operation at 300 deg. C. Some of the operating experience obtained with the JET MSE diagnostic will be relevant to ITER, although the lack of independent power or voltage control of the ITER injectors is seen as the chief challenge facing the ITER MSE design.
- OSTI ID:
- 20861216
- Journal Information:
- Review of Scientific Instruments, Vol. 77, Issue 10; Other Information: DOI: 10.1063/1.2221915; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0034-6748
- Country of Publication:
- United States
- Language:
- English
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