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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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Moss spectroscopy applications in plasma physics

MOSS Spectroscopy Applications in Plasma Physics

John Howard

Plasma Research LaboratoryAustralian National University



  • MOSS spectrometer

  • Principle

  • Doppler measurements on H-1

  • Polarization Spectroscopy

  • Zeeman effect and MSE

  • Spread spectrum FTS

  • Imaging systems

Fourier transform spectroscopy

Fourier Transform Spectroscopy

Moss spectrometer

MOSS Spectrometer



Advantages of moss

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



Flow velocity (shift)


Temperature (contrast)

Moss hardware

MOSS Hardware

Moss spectroscopy on h 1

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)

L h confinement transitions

L-H Confinement Transitions

Heat modulation experiments

Heat Modulation Experiments

Fluctuation measurements

Fluctuation Measurements

Polarization spectroscopy

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



Normalized wavelength

Polarization spectroscopy1

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

Polarization spectroscopy2

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

Spread spectrum fts

Spread Spectrum FTS

Spread Spectrum FTS

Imaging systems

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.

Spread spectrum data at 587nm hei

Spread spectrum data at 587nm HeI

Plasma light

Calibrationlaser pulse

Laser interferogram

time (ms)

Power spectrum of interferogram



  • 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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