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MOSS Spectroscopy Applications in Plasma Physics

MOSS Spectroscopy Applications in Plasma Physics. John Howard. Plasma Research Laboratory Australian National University. Outline. MOSS spectrometer Principle Doppler measurements on H-1 Polarization Spectroscopy Zeeman effect and MSE Spread spectrum FTS Imaging systems.

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MOSS Spectroscopy Applications in Plasma Physics

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  1. MOSS Spectroscopy Applications in Plasma Physics John Howard Plasma Research LaboratoryAustralian National University

  2. Outline • MOSS spectrometer • Principle • Doppler measurements on H-1 • Polarization Spectroscopy • Zeeman effect and MSE • Spread spectrum FTS • Imaging systems

  3. Fourier Transform Spectroscopy

  4. MOSS Spectrometer Concept Instrument

  5. Advantages of MOSS High light throughput High time resolution Compact, robust MOSS is optimum in the sense that all photons contribute to three independent pieces of information - intensity, shift and contrast. Light intensity DC atan(odd,even) Flow velocity (shift) sqrt(odd2+even2) Temperature (contrast)

  6. MOSS Hardware

  7. MOSS spectroscopy on H-1 Lines of sight Central ring conductor Plasma cross section Fringe contrast versus time delayArII 488nm, Ti=10, (10), 100 eV Nominal delay for LiNbO3 ( 25mm)

  8. L-H Confinement Transitions

  9. Heat Modulation Experiments

  10. Fluctuation Measurements

  11. Polarization Spectroscopy Zeeman Effect. The Zeeman components are spectrally shifted and circularly polarized when viewed parallel to B. The nett circular polarization is a measure of the intensity weighted longitudinal component of the B field. Total lineshape Relative intensity RHCP LHCP Normalized wavelength

  12. Polarization Spectroscopy By filtering/modulating the polarization state of the plasma light using a spherical quadrature polarimeter, either the coherence (bandwidth) or centre of mass of the spectral line can be varied. The MOSS spectrometer senses these modulations as contrast or phase variations of the interferometer fringes. Spherical quadrature polarimeter

  13. Polarization Spectroscopy Motional Stark Effect. H or D atoms in a heating beam experience an induced electric field E= v x B that generates a complex spectrum. Viewed transverse to E the Stark split s and p components are polarized respectively perpendicular and parallel to E. Combined polarimeter/MOSS system for MSE measurements

  14. Spread Spectrum FTS Spread Spectrum FTS

  15. Imaging systems Multiple spatial channels can be multiplexed through an imaging MOSS spectrometer while maintaining high light throughput and low instrument temperature.Multiple-crystal modulators can be employed for truly 2-D spectral imaging: the spectrum at each spatial position is encoded in the temporal frequency domain.

  16. Spread spectrum data at 587nm HeI Plasma light Calibrationlaser pulse Laser interferogram time (ms) Power spectrum of interferogram

  17. Conclusion • MOSS spectroscopy is a high throughput alternative to traditional grating spectrometers • Well suited to plasma Doppler and polarization spectroscopy • Fully 2-D spectral imaging is possible. • Facilitates tomography of scalar (intensity) and vector (velocity) fields in H-1NF for force balance, fluctuation and particle/heat modulation studies

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