Instrumentation for the joint European torus motional Stark effect diagnostic
- Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States)
- JET Joint Undertaking, Abingdon, Oxon OX14 3EA (United Kingdom)
A motional Stark effect magnetic field pitch angle diagnostic has been implemented on the joint European torus (JET) tokamak. The instrumentation designed following the study by Hawkes {ital et al.} (these proceedings) is described. D{sub {alpha}} emission from the Octant 4 neutral beams is collected by optics which transport the plasma image outside the vacuum vessel and through a pair of photoelastic modulators (PEMs) and a linear polarizer. The light is fiber-optically coupled to interference filter spectrometers, which incorporate a remotely controlled filter tilting mechanism. This allows the center wavelength of the filter bandpass to be tuned over a range sufficient for observation of the {sigma} and {pi} lines of the Stark spectrum emitted by the full- and half-energy components of the beam, providing flexibility to make measurements with a variety of beam configurations. The detectors are low-noise avalanche photodiode modules. Fast digital signal processing techniques are used to extract the Fourier components of the signal at the PEM first and second harmonic frequencies. Analysis of these signals will yield the magnetic field pitch angle, which will be used as a constraint on EFIT equilibrium reconstruction modeling to obtain the q(r) profile. The system has 25 spatial channels covering the outer-half of a JET plasma with spatial resolution of 0.03{endash}0.07 m per channel with {approximately}0.05 m channel-to-channel separation. Time resolution is expected to be 1{endash}10 ms. {copyright} {ital 1999 American Institute of Physics.}
- OSTI ID:
- 295664
- Report Number(s):
- CONF-980605-; ISSN 0034-6748; TRN: 99:001850
- Journal Information:
- Review of Scientific Instruments, Vol. 70, Issue 1; Conference: 12. topical conference on high-temperature plasma diagnostics, Princeton, NJ (United States), 7-11 Jun 1998; Other Information: PBD: Jan 1999
- Country of Publication:
- United States
- Language:
- English
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